Cutting costs on the Seedling [Now with cost data on McWire, G2 Electronics, and Bootstrap Extruder]

Hello again! I'm about to start working on my Seedling, and, looking over the estimated subtotals... it's a bit distressing. The entire thing, with the basic costs will be around $450-$500, before making the extruder. This would be okay if it was the Darwin, but for a RepStrap that I'm building mainly to allow me to build a RepRap... I think maybe it's a bit much.

So I'm going to try to cut corners and stuff to reduce the cost, and I'd appreciate help with ideas (and no this is not whining; I'm willing to chunk out thousands or more if I need to, it's just more efficient if I don't).

The basic McWire price I've come up with is about $340. Here's the breakdown (combined subtotals using prices from Lowes, McMaster, and the RRRF store):
Fasteners: $38.94 (It's a lot of zinc/steel; I guess it just adds up.)
Misc: $70.46 (u-clamp, skate bearings, PTFE bearings, aluminum angle/channel, and springs; most of the cost is concentrated in the aluminum)
Plumbing: $27.97 (the structure, using all black iron pipe fittings from Lowes, except the flange which I can only find in galvanized steel)
Threaded Rod: $2.97 (the leadscrews for driving each stage; from Lowes)
Stepper Motors: $75 (The ones at RRRF are $25 each...)
Acrylic Pieces: $125 (the lasercut parts from RRRF, with the +$25 countersunk option)
Subtotal: $340.34 (sales tax and shipping costs aren't included)

Looking at this, and the "for under $250" comment on the doc page, I figured something was wrong. I'm guessing there are a bunch of places where I'm paying a bit too much, and Hoeken (et al.) found better priced sources.

In any case, the first thing I decided on was switching out the acrylic for plywood. For $ 17.87 (before tax) I can get two 2' x 4' plywood boards, one of each 1/4" and 1/2" thick, at Lowes (I should probably just go with 2'x2' for the 1/2" thick, because I only need 8"x11" or less out of it; in fact, I could take all the wood I need from the single 2' x 4' of 1/4", by stacking two cut out pieces to get the 1/2" thickness necessary for the vertical base).
[Note also that this is Birch plywood - it looked good to me and wasn't as expensive as the Oak, and that's all the choice was based on. I'm a programmer, not a craftsman. If this is a bad choice, feel free to chime in.]
Adding in the countersink from McMaster for $31.20 (before shipping), this gives $49.07. That's a savings of approximately $75.93 over the RRRF lasercut, pre-countersunk acrylic.

The next thing I tried to tackle was the $31.20 countersink. I measured the countersink circles on the stickers that are available from the documentation, and it seems that they are all 1.5cm in diameter, except the ones on the vertical base, which seem to be 2.0cm in diameter.
A 3/4" countersink (1.905cm) would work for the 1.5cm ones, and then I suppose I might try using it for the 2.0cm ones. I would make the countersink top as big as I could (1.905cm), and when I insert the screw, I would sand/file off the very top 0.95mm that sticks out.
The advantage is that a 3/4" countersink is more commonly available; I can pick one up at Lowes for around $11. This would save me about $20; it's not much, but every little bit counts. Is this feasible? Or is it perhaps just not worth it?

The next thing I noticed was that the Stepper Motors were not discussed in the McWire documentation; it only described the motor mounts and the mounting of the motors to the motor mounts (say that 1 time fast). So I figured I'd just use the stepper motors suggested for the Darwin, which I assume are the KL23H251-24-8B motors sold at the RRRF store. These are $25 a piece, and add up to $75.
At this point, they now make up the most expensive part of my system. Are there any cheaper alternatives that would still work (depending on cost differences, I may be willing to step down to either a slower set of motors or a set of motors that may/does not work with Darwin, if such motors are available)?

I'm doubting I can reduce the prices for the miscellaneous items by much. I suppose I could cut $22 off by using 1/16" thick aluminum angles and channels, but I don't know how this would affect the system and the docs suggest against it.

The fasteners just seem to add up. I could probably get them cheaper in bulk quantities, but I don't know what I would do with them, as I'm only building one RepStrap (I'll leave the exponential replication to the mad scientists, or maybe to my Mendel).


Then there's the G2 circuitry, which I'll post about some other time (maybe later on in this thread).
The extruder I've already discussed bootstrapping in another thread. At this point, I'm considering using the McWire to cut the extruder parts, but it's not the only option (and may not be the best option).

So, any ideas on reducing the Seedling cost? Feel free to discuss the circuitry and extruder costs too, if you feel like it; I just don't have the time right now to go into detail on these.

Edited 2 time(s). Last edit at 07/30/2008 01:05AM by Joshua Merchant.

Ok Price reduction starts as follows:

1. Plan on reusing the electronics and stepper motors on the darwin after completing the parts for it. (save $75.00 + elecronics from above)

2. Use the Plywood and see if you can find some 1/4 inch plastic from some friends ( save $75.00+ as listed from above).

3. The extruder can be used on both the Seedling and Darwin units (no cost reduction but you can get by with just one).

Total savings are about $77.00 that you found but also look at this this way.

What is the cost of 1 Seedling and 1 Darwin that you will have built.

With the investment of $262.00 (plus 2nd electronics set) you will have 2 RepStrap/RepRap units that can generate anything that you want to build.

---

Bob Teeter
"What Box?"

So I'll take that as a "No, you've already listed all the significant cost-cutting options."

You could always borrow a countersink bit from someone rather than purchase one eliminating the cost of that entirely.

As for the fasteners, you could always put a post up asking whether other people in your area want to go in with a bulk buy. The only disadvantage with this would be that you're then committed to despatching the parts to others when you receive them.

Alright, I'm now looking over the costs for the G2 electronics.
If you don't want to read the ginormous post (that's in the dictionary now, btw), then I'll tell you now: the final reduced G2 (Arduino-based) cost is $56.42. Just kidding. It's $136.16.

I'll give a few price totals and comment on how to cheapen certain parts. The list at the top is the most expensive but simplest to purchase, and as the post continues, the lists get cheaper but require more time to obtain and put together (though I think the differences in time are insignificant or at most nearly insignificant). As before, I don't cover shipping costs or tax, for simplicity (though I do limit the number of places to ship from to reduce shipping costs). Note that my optimizations are US-specific, as they relate to ordering from Mouser; however, most still work for other locations because they can just be ported to different suppliers - the specific cost differences would vary, of course. Oh, and no MasterCard jokes.

First, I could just buy the full kit from RRRF [store.rrrf.org]. With the Arduino and without the USB cable, this is $185. Order it, throw it together, and poof (and no, I'm not describing your circuits' smoking habits).

Then, there's buying the separate kits from RRRF and buying a cheap arduino kit. Break it down now:
Arduino kit [www.adafruit.com] with FTDI TTL232 Cable (+$17.50): $35 [Edited because I left out the cable before. Now it's the same price as the RRRF Arduino that comes with the full kit, actually.]
3 Stepper Motor Drivers [store.rrrf.org]: $84 ($28 each)
DC Motor Driver [store.rrrf.org]: $12
PWM Driver [store.rrrf.org]: $11
6 Opto Endstops [store.rrrf.org]: $18 ($3 each)
Temperature Sensor [store.rrrf.org]: $4

Total: $164.00
The primary reason for the cost difference is the reduced cost for the Arduino and that I ommitted the breakout shield [store.rrrf.org]. As far as I can tell, it's really not necessary, and for $20 I'd rather omit it.

Next, you can build the Arduino yourself [itp.nyu.edu] and buy the parts for the rest from Mouser, and the PCBs from RRRF. This is probably the best balanced approach (though I probably won't use it, because it's still not the cheapest). The part numbers for most of these components can be found at [parts.reprap.org].

-----------------------------------------------------------------------------------
Desc.					QtyReq	Mouser	Sparkfn	RRRF	Subtotal
-----------------------------------------------------------------------------------
Arduino (kit $17.50 +$17.50 for usb-serial ):	-------------------------------------$21.57 (with $4.49 stripboard)
 ATMEGA168 Chip	(556-ATMEGA168-20PU)	1	4.11
 Arduino Breadboard/circuitboard		1		
 22 AWG wire				1	
 7805 Voltage regulator (78L05?)		1	0.18
 LED					2	0.24
 220 Ohm resistors				2	0.20
 10 k Ohm resistor				1	0.10
 10 uF capacitor				1	0.06
 1 uF capacitor			      	2	0.12
 16 MHz clock crystal (ECS-2100AX-16.0MHZ)	1	2.11
 22 pF capacitors				2	0.06
 small momentary normally open ("off") button	1	0.75
 FT232RL [www.sparkfun.com]			1		3.95
 28Pin SSOP-DIP Adapter [www.sparkfun.com]	1		3.95
 USB Fem. Type B Connector [www.sparkfun.com]	1		1.25
3 Stepper Motor Drivers (kits $84 total):	-----------------------------------$90.25
 .100 breakaway header			18	2.19
 .100 shunt				6	0.90
 .156" 4 position housing			3	0.75
 .156" crimp-on connector			12	0.96
 .156" header				12	2.02
 0.5 ohm 2 watt resistor			6	0.84
 1 nF ceramic capacitor			6	1.08
 100 nF ceramic capacitor			9	1.44
 100 uF electrolytic capacitor		6	0.54
 100K ohm resistor				3	0.30
 2.7K ohm resistor				3	0.30
 20 pin DIP socket				3	0.66
 22K ohm resistor				3	0.30
 2K trimpot				3	2.25
 3 pin header				6	1.98
 3 pin housing				6	1.32
 3.3 nF ceramic capacitor			3	0.24
 4 pin molex connector			3	2.52
 4.7K ohm resistor				6	0.60
 560 ohm resistor				9	0.90
 5mm green LED				3	0.36
 Bicolor LED				6	2.04
 big heat sink				3	1.14
 crimp-on terminals			18	1.98	
 L297					3	27.09
 L298N					3	9.75
 SB360					24	10.8
 Stepper Motor Driver v1.1 PCB		3			15.00
 Cat 6 cable Wire 				6 feet	
DC Motor Driver (kit $12):			-----------------------------------$11.38
 100 nF ceramic capacitor			6	0.96
 100 uF electrolytic capacitor		2	0.18
 100K ohm resistor				4	0.40
 14 pin DIP socket				1	0.19
 16 pin DIP socket				1	0.19
 4 pin .200" terminal block			1	1.10
 4 pin molex connector			1	0.84
 560 ohm resistor				3	0.30
 5mm green LED				5	0.60
 74HC00N					1	0.39
 78L05					1	0.18	
 L293D (b/o; L293NE substituted)		1	3.05	
 DC Motor Driver v1.1 PCB			1			3.00
 Cat 6 cable Wire				2 feet	
PWM Driver (kit $11):			-----------------------------------$ 9.21
 100 nF ceramic capacitor			1	0.16
 100 uF electrolytic capacitor		1	0.09
 1K ohm resistor				3	0.30
 1N4005					3	0.18
 2 pin .200" connector			3	1.44
 4 pin molex connector			1	0.84
 560 ohm resistor				4	0.40
 5mm green LED				4	0.48
 TIP120					3	1.32
 PWM Driver v1.1 PCB			1			4.00
 Cat 6 cable Wire				2 feet			
6 Opto Endstops (kits $18 total):		-----------------------------------$13.74
 10K ohm resistor				6	0.60
 220 ohm resistor				6	0.60
 3 pin housing				6	1.32
 crimp-on terminals			18	1.98
 H21LOI	(b/o; H21LOB substituted)		6	6.24	
 Opto Endstop v1.0 PCB			6			3.00
Temperature Sensor (kit $4):		-----------------------------------$ 2.72
 .100 breakaway header			3 	(w/Stepper motor's header)
 10 uF electrolytic capacitor		1 	0.06
 100K thermistor				1 	1.58 
 2 pin .200" connector			1 	0.48
 4.7K ohm resistor				1 	0.10
 zip tie					1	See last zip tie comment.
 Temperature Sensor v1.1 PCB		1			0.50

The total is $142.62 ($21.38 savings).

Note that with the suggested parts, the cost of the stepper motor drivers is $90.25, $6.25 more than the kits from RRRF. The total of $142.62 considers using the RRRF kits for the stepper motors, and then buying components for everything else. If I buy all the components, even for the stepper drivers, it's $148.87 ($15.13 less than buying all the kits).

Also note that, while with this method I would suggest using L293NE for L293D and H21LOB for H21LOI because the latter of both are backordered for a while, the prices are the same (because they are different options on the same components; see [forums.reprap.org]) and so this doesn't affect the cost.

[Oh, and also note that I don't write prices for wires; I plan to get most of my wiring from old parts, and I happen to have a ton of ethernet cable lying around. The cost of the entire wiring, if you have to purchase it, should be under $10 (you may have to spend more due to minimum purchase sizes, but you can use the remaining wire for other stuff). Thus, the cost is too insignificant to justify the complexity of factoring in the wiring.]

The fact that I can substitute those components got me thinking. I figure that I can substitute other components, and if I do it right I may be able to realize significant savings.

I'll address each component substitution in order, and then list the final breakdown at the end.
Note that the suggested substitutions are based on the availability of components as of 7/24/2008 from Mouser, and are largely time-dependent. Mouser is getting a bunch of shipments in at the start of September, so if you wait until September, you could probably reduce the price a bit further.
It is also important to realize that because the availability will inevitably change with time, you should do some searching yourself for alternatives, as I have, if you want to get the best pricing. All I did was mess around with Mouser's search, which has nice features that allow quick narrowing and comparison.

Arduino: (Savings $1.11)
ATMEGA168 Chip - I'd rather not mess with this; it's the central Arduino chip and I like the one I chose (556-ATMEGA168-20PU).
Arduino Breadboard/circuitboard - This is one of those situational things. Personally, I have an old stripboard I can use to reduce this price to $0. Alternately, a new one costs $4.49 at your local radioshack; this is the price I included above, so no savings here.
7805 Voltage regulator - The suggested 78L05 [www.mouser.com] is the cheapest. No savings here.
LEDs (2) - The suggested $0.12 diffused LEDs shouldn't be a problem, but you can cut $0.04 off each by using $0.08 LEDs with smaller angles (both green [www.mouser.com] and red [www.mouser.com] are available at this price). Total savings $0.08.
220 Ohm resistors (2) - These [www.mouser.com] are $0.03 each. Total savings $0.14.
10 k Ohm resistor - This one [www.mouser.com] is $0.08. Savings $0.02.
10 uF capacitor - No savings here.
1 uF capacitor (2) - This one [www.mouser.com] is $0.03. Total savings $0.06.
16 MHz clock crystal (ECS-2100AX-16.0MHZ) - This one [www.mouser.com] is $1.30. I don't think it's a clock crystal, but it has better specs anyway. Savings $0.81.
22 pF capacitors (2*$0.06ea) - No savings here.
small momentary normally open ("off") button - You could save on this, but it's probably better to get a cool button that you like pressing, as long as it's reasonably priced.
SparkFun stuff - I looked up similar parts on Mouser, and they are more expensive (even considering the shipping and handling of ordering from SparkFun). So I'll stick with the SparkFun stuff suggested by [itp.nyu.edu].
3 Stepper Motor Drivers (Savings $9.53):
.100 breakaway header - No savings.
.100 shunt - Could save $0.01 per [www.mouser.com], but it would switch the contacts from gold to tin, and the outside from blue to red. I would do it (red is cooler anyway), but I'm not sure how the increased resistance with the tin would affect the circuit.
.156" connectors and stuff - Couldn't find savings; the prices don't look bad and it's hard to figure out what alternatives are available.
0.5 ohm 2 watt resistor (6) - No savings; the suggested resistor is actually a 1 watt resistor; I don't see any .5 ohm 2 watt resistors at Mouser, so this is probably why.
1 nF ceramic capacitor (6*$0.18ea) - These [www.mouser.com] are $0.07ea. They have worse specs, but it should be fine (more tolerance, higher minimum temp, lower voltage rating etc.) Total savings $0.66.
100 nF ceramic capacitor (9*$0.16) - No savings.
100 uF electrolytic capacitor (6*$0.09) - These [www.mouser.com] are $0.03 each. Same specs (aside from manufacturer and that 108-degree thing [not sure what that is, it might be significant]). Total savings $0.36.
100K ohm resistor (3*$0.10 ) - These [www.mouser.com] are $0.03 each, with different temperature coefficients. Total savings $0.21.
2.7K ohm resistor (3*$0.10 ) - These [www.mouser.com] are $0.03 each, with different temperature coefficients. Total savings $0.21.
20 pin DIP socket (3*$0.22) - I'm sticking with the suggested one. There's an $0.18 one available, but I'm not sure if it's really equivalent (there's not much spec data on Mouser, and it's not worth hunting down).
22K ohm resistor (3*$0.10) - These [www.mouser.com] are $0.03 each with different temperature coefficients. Total savings $0.21.
2K trimpot (3*$0.75) - These [www.mouser.com] are $0.59 each. The suggested trimpot is non-stocked and only available in 50+ quantities, so this switch is almost a necessity. The difference between the two seems to be that the suggested is square, and this one is round. They both are adjustable from the top (if you want one adjustable from side(s), they have that for the same price, too; the suggested one is from the top, though, so I picked a similar replacement). Total savings $0.48.
3 pin header (6*$0.33) - Not messing with this one.
3 pin housing (6*$0.22) - Or this one.
3.3 nF ceramic capacitor (3*$0.08) - No savings.
4 pin molex connector (3*$0.84) - Not messing with this one.
4.7K ohm resistor (6*$0.10) - $0.03 each. [www.mouser.com]. Total savings $0.42.
560 ohm resistor (9*$0.10) - $0.03 each. [www.mouser.com]. Total savings $0.63.
5mm green LED (3*$0.12) - $0.08 LEDs with smaller angles. [www.mouser.com]. Total savings $0.12.
Bicolor LED (6*$0.34) - $0.21 LEDs with smaller angles. [www.mouser.com]. Total savings $0.78.
big heat sink (3*$0.38) - Sticking with the suggested.
crimp-on terminals (18*$0.11) - This [www.mouser.com] seems to be the same exact thing by the same exact manufacturer, except in a reel instead of a bag, for $0.06 each. I hope I'm right. Total savings $0.90.
L297 (3*$9.03) - If I was smarter (or just had more time) I bet I could use this [www.mouser.com]. It's another similar chip for $4.23 each. It has 18 pins instead of 20 pins, and Mouser's current stock is not RoHS compliant (although the ones currently being produced are). It has slightly different functioning, and it takes 25mA operating current instead of 80mA. I don't really know how I could redesign the Stepper Motor Driver circuit to use it, but if I could, it would be a $14.40 savings. It might have reduced functioning, and it might not be RoHS compliant, but I'm one of those stereotypical people that cut costs at almost any risk (or I'd like to be... today... I don't know how I'll feel tomorrow ). In any case, no savings here because it would take more than $14.40 worth of my time to figure it out (because I would have to learn a bunch of stuff as I'm not experienced in this area). If anyone has some advice on this, I'd be glad to hear it.
L298N (3*$3.25) - No savings.
SB360 (24*$0.45) - These [www.mouser.com] are $0.25 each at the 25-unit price break. So if you order 25, you pay $6.25, instead of $10.80 for the suggested ones. (Note that these [www.mouser.com] are identical, the only difference being that they are on a reel tape; if the G suffixed ones aren't available, use these RLG suffixed ones; the G ones come in bags, which I prefer - no price difference.) Total savings $4.55.
Stepper Motor Driver v1.1 PCB (3*$5.00) - I could probably make these myself cheaper, but I don't feel like investigating it right now. So no savings here.
Cat 6 cable Wire (6 feet) - As before, I don't really wanna consider wiring. If you don't have the luxury of having plenty of this ethernet stuff laying around... go to your local library or office etc. Take pliers/wire cutters/sharp scissors, and a long-sleeved jacket . [Note that I'm just kidding. This would be vandalism and theft if you then smuggled the cutters in the sleeve of the jacket and proceeded to kneel, to say, tie your shoe, and whipped out the cutters, cut a small piece, shoved it in your shoe or jacket sleeve/pocket, and then browsed some books calmly. This is bad, and you should not do it. You shouldn't even try to come up with a way to do it. Nor should you read about how to do it. Nor should you make suggestions on how others may do it. If you proceed to do these things, I will not be held liable for your resourcefulness and ultra-sneakiness.]

DC Motor Driver (Savings $0.81):
100 nF ceramic capacitor (6*$0.16) - No savings.
100 uF electrolytic capacitor (2*$0.09) - These [www.mouser.com] are $0.03 each. Same specs (aside from manufacturer and that 108-degree thing [not sure what that is, it might be significant]). Total savings $0.12.
100K ohm resistor (4*$0.10 ) - These [www.mouser.com] are $0.03 each, with different temperature coefficients. Total savings $0.28.
14 pin DIP socket (1*$0.19) - Not messing with this one.
16 pin DIP socket (1*$0.19) - Or this one.
4 pin .200" terminal block (1*$1.10) - Or this one.
4 pin molex connector (1*$0.84) - Or this one.
560 ohm resistor (3*$0.10) - $0.03 each. [www.mouser.com]. Total savings $0.21.
5mm green LED (5*$0.12) - $0.08 LEDs with smaller angles. [www.mouser.com]. Total savings $0.20.
74HC00N (1*$0.39) - $0.01 savings possible with a switch to a different IC; not worth the hassle of making sure everything is the same.
78L05 (1*$0.18) - No savings.
L293D (b/o; L293NE substituted) (1*$3.05) - No savings.
DC Motor Driver v1.1 PCB (1*$3.00) - See previous PCB comment.
Cat 6 cable Wire (2 feet) - See previous wire comment.

PWM Driver (Savings $0.65):
100 nF ceramic capacitor (1*$0.16) - No savings.
100 uF electrolytic capacitor (1*$0.09) - These [www.mouser.com] are $0.03 each. Same specs (aside from manufacturer and that 108-degree thing [not sure what that is, it might be significant]). Total savings $0.06.
1K ohm resistor (3*$0.10) - $0.05 each. [www.mouser.com]. Total savings: $0.15.
1N4005 (3*$0.06) - I could probably switch to a slightly cheaper one, but it's not worth the research time.
2 pin .200" connector (3*$0.48) - Not messing with this one.
4 pin molex connector (1*0.84) - Or this one.
560 ohm resistor (4*$0.10) - $0.03 each. [www.mouser.com]. Total savings $0.28.
5mm green LED (4*$0.12) - $0.08 LEDs with smaller angles. [www.mouser.com]. Total savings $0.16.
TIP120 (3*$0.44) - No savings.
PWM Driver v1.1 PCB (1*$4.00) - See previous PCB comment.
Cat 6 cable Wire (2 feet) - See previous wire comment.

6 Opto Endstops (Savings $0.54):
10K ohm resistor (6*$0.10) - This one [www.mouser.com] is $0.08. Savings $0.12.
220 ohm resistor (6*$0.10) - These [www.mouser.com] are $0.03 each. Total savings $0.42.
3 pin housing (6*$0.22) - Not messing with this one.
crimp-on terminals (18*$0.11) - Or this one.
H21LOI (b/o; H21LOB substituted) (6*$1.04) - No savings.
Opto Endstop v1.0 PCB (6*$0.50) - See previous PCB comment.

Temperature Sensor (Savings $0.07):
.100 breakaway header (3 w/Stepper motor's header) - No savings.
10 uF electrolytic capacitor (1*$0.06) - No savings.
100K thermistor (1*$1.58) - RRRF sells it for $1.50 but is currently out of stock. I could also try a different thermistor, but I'll play with these later.
2 pin .200" connector (1*$0.48) - Not messing with this.
4.7K ohm resistor (1*$0.10) - $0.03 each. [www.mouser.com]. Total savings $0.07.
zip tie - See previous zip tie comment.
Temperature Sensor v1.1 PCB (1*$0.50) - See previous PCB comment.


Note that I'm not sure about the performance of the cheaper resistors I listed, as they do have different temperature coefficients. Similar worries apply to the rest of the component changes. Use this data at your own risk; I will not be held liable (I'll run away before you can catch me anyway, so don't even try to sue me; one of my great-great grandfathers was a gingerbread man [I can't swim though...]).

In any case, the total savings for this section is $12.71.

[Note that I got the stepper motor drivers to be cheaper than the RRRF kits, so with this last design I'll no longer be buying any kits at all.]
The final price is $136.16. Woo. That so wasn't worth 3 hours, but oh well (heuristics aren't my parfait). (I mean forte. See, this is what happens when you spend hours trying to save pennies on electrical components. Don't do it! You're too young to... well... nevermind. This does make me want parfait though.)


In any case...
Combined with my $253.85 Plywood McWire project, the running total (maybe its great-great-grandaddy was a gingerbread man too) is $390.01. I hope my extruder will make it in just under $400 (perhaps using scrap parts from the cartbot construction), but I won't know until I test my cartbot a bit (I wanna know if I can rig it to cut/mill the extruder parts).

So... now I have to move my bank funds around and actually buy all that crap. And then I have to put it together. And then hope it works. And then put the extruder together... and then hope it works. And then.. and then... there's a long road ahead

But I shall not lose heart! For thar be treasure 'neath the ocean, and me and mah submarine will rule the world!

Where's my parfait?


[Edit - Updated the figures after realizing (thanks to d0ubled and Larry Pfeffer) that I did not consider the cost of usb to serial conversion. The final price is $9.15 higher, and I fixed various other figures. I may have fudged a few of them because I quickly went through and changed them, so let me know if you happen to find something that doesn't add up. Also note that it will be a bit more than $9.15 more expensive, as I now have to pay for shipping from SparkFun. The cheapest shipping method (USPS 1st Class) costs $3.34 to ship to me, but I'll probably go for the $6.80 method (USPS Priority). I'm a bit surprised they don't ship UPS (they only ship via USPS and FedEx to me). In any case, it's not a major change. It should also be noted that these components could possibly be extracted from scrap devices you have laying around; I know I can get my USB female B connector from scraps, but I might just buy a new one for the shininess. The SSOP-DIP is an option that can be excluded if you feel like manually surface mounting 28 pins; for $4 it's not worth the time it would take me (as I have little experience, it would take a long time). If you exclude both the SSOP-DIP adapter and the USB connector, then you can get the FT232RL chip for $4.50 from [www.mouser.com]. This would be the cheapest option, as you wouldn't have to pay shipping to SparkFun. Whatever floats your boat (your awsomeness RepRapped plastic boat that floats and sports a cheap DC motor with a RepRapped drive shaft and propeller).]

Edited 5 time(s). Last edit at 07/29/2008 06:47PM by Joshua Merchant.

Joshua wrote:

Then, there's buying the separate kits from RRRF and buying a cheap arduino kit. Break it down now:
Arduino kit [www.adafruit.com]: $17.50

----

Note that the adafruit kit (boarduino) *requires* a USB-to-serial cable to talk to a PC (to program in the reprap firmware and to send it commands from the host software.) This cable costs about $20 from adafruit (or others), so your savings there are less than you might hope. One of these cables can be used for other projects, when not connecting RR host to RR controller. I bought a boarduino and this cable recently, and it went together easily and works fine.

If you can, I suggest you hold on (only ~ a week, honest!) -- "a little bird told me" that there will shortly be a better arduino work-alike for reprap -- also using this cable, and reasonably close to the boarduino's cost, but much better with respect to #pins and size of memory.
I expect a fellow reprapper will announce a software-compatible Arduino alternative shortly, and there will be "great rejoicing" among reprappers.
Apparently, the current firmware is right on the edge of being too big to fit, and some have reported that slight differences in the avr-gcc toolchain lead to sketch-images that are too big to fit current Arduinos. Help (for that) is on the way.

-- Larry

Quote

Apparently, the current firmware is right on the edge of being too big to fit, and some have reported that slight differences in the avr-gcc toolchain lead to sketch-images that are too big to fit current Arduinos

What makes an arduino(or arduino clone) an arduino (compatible) is ultimately the firmware that runs on the uc. So are you referring to a new firmware that takes up less space? A new board with teh same chip is still going to have the same amount of flash available, and the same amount used up.

Porting the arduino code to a new uc seems like a bit of overkill to me, seeing as the atmega328 is on the horizon, at work has already been done on updating the arduino firmware to run on it.

Okay, you can cut some more money off that if you have a solid work bench up against a solid wall. Drop off all your pipe-frame components except two flanges and a single straight piece. Just bolt your extruder assembly to the wall over a work bench and build your axis on the bench itself. No frame necessary.

Or, for even more cost savings, just dispense with the pipe and all and use 2x4 scrap or some such. You probably have some laying around somewhere.

This will cut $27.97 off your total!

Ru Wrote:
-------------------------------------------------------


So are you referring to a new firmware
> that takes up less space? A new board with teh
> same chip is still going to have the same amount
> of flash available, and the same amount used up.
>
> Porting the arduino code to a new uc seems like a
> bit of overkill to me, seeing as the atmega328 is
> on the horizon, at work has already been done on
> updating the arduino firmware to run on it.

There are a number of avr chips larger than the atmega168; the alternative I've heard about uses the atmega644p. With the right config files added to the Arduino dev. software, it'll look like another board type (decimilla, lillypad.... with more memory and pins available.) So, this should be compatible at the arduino-sketch level, if not bit-for-bit firmware identical.

-- Larry

Quote

There are a number of avr chips larger than the atmega168; the alternative I've heard about uses the atmega644p. With the right config files added to the Arduino dev. software, it'll look like another board type (decimilla, lillypad.... with more memory and pins available.) So, this should be compatible at the arduino-sketch level, if not bit-for-bit firmware identical.

Ahh, yes. I'm sure I looked at the 644 for some reason before... www.chip45.com will be offering some boards with it come the autumn, so I guess it will come out around the same time as the 328?

A quick googling shows that some guy called 'hoeken' is working on porting the arduino firmware. I wonder who that could possibly be.

Too bad I learn of this after I've gotten my arduino, but at least it will still be useful for other projects too

Larry_Pfeffer Wrote:
-------------------------------------------------------

> Note that the adafruit kit (boarduino) *requires*
> a USB-to-serial cable to talk to a PC (to program
> in the reprap firmware and to send it commands
> from the host software.) This cable costs about
> $20 from adafruit (or others), so your savings
> there are less than you might hope. One of these
> cables can be used for other projects, when not
> connecting RR host to RR controller. I bought a
> boarduino and this cable recently, and it went
> together easily and works fine.
Well I wasn't too concerned with specifics on that part, as I intend to build my own Arduino (with the last ~$11.31 price) [itp.nyu.edu]. As far as I know, I don't need any special $20 cable for that, right? Just a standard USB cable (of which I have plenty lying around).


> If you can, I suggest you hold on (only ~ a week,
> honest!) -- "a little bird told me" that there
> will shortly be a better arduino work-alike for
> reprap -- also using this cable, and reasonably
> close to the boarduino's cost, but much better
> with respect to #pins and size of memory.
> I expect a fellow reprapper will announce a
> software-compatible Arduino alternative shortly,
> and there will be "great rejoicing" among
> reprappers.
> Apparently, the current firmware is right on the
> edge of being too big to fit, and some have
> reported that slight differences in the avr-gcc
> toolchain lead to sketch-images that are too big
> to fit current Arduinos. Help (for that) is on
> the way.
>
> -- Larry

Well, seeing as the chip I'll be buying is only $4.11, and the rest of the parts are reusable, I think I'll just stick with the current stuff. As it's my first RepRap, I don't want to try so many new things that the whole thing doesn't work and I'm left wondering which of the many switched parts is to blame.
I'll take a look at it when it comes out though, and perhaps trade up later on.

Demented Chihuahua Wrote:
-------------------------------------------------------
> Okay, you can cut some more money off that if you
> have a solid work bench up against a solid wall.
> Drop off all your pipe-frame components except two
> flanges and a single straight piece. Just bolt
> your extruder assembly to the wall over a work
> bench and build your axis on the bench itself. No
> frame necessary.
Wow, that's a great idea (I'm surprised no one mentioned it before). Unfortunately I don't have a wall nearby that I can bolt into.

> Or, for even more cost savings, just dispense with
> the pipe and all and use 2x4 scrap or some such.
> You probably have some laying around somewhere.
>
> This will cut $27.97 off your total!
The 2x4 scrap makes me think (as I do in fact have a bunch laying around). If I made the entire frame from 2x4 instead of pipe, would it be a problem? I'm not sure how stable the platform would be.

The advantage of the steel/iron pipe is that it's heavy and durable, whereas the wood may move around when the stepper motors turn on, possibly fall over, or warp/deform slightly leading to either the previously stated structural problems or to inaccuracies in printing. Are these worries unfounded?

To use USB you need a USB to serial converter chip either as a piece part integrated into your board or as part of a converter cable. I do not see that in your parts list.

From the [itp.nyu.edu] link:

"Parts for wiring up USB communication with computer

Here you have 2 options, the slightly cheaper build your own breakout board and USB connector option, or a ready made adapter from Spark Fun. We don't have the ready-made adapter yet, but we will follow up with that when we get it"

The part number is FT232RL. Alternatively if you have a computer with a real serial port you can dispense with the USB portion of the link and use native serial. You would need an RS232 level translator for this to work.

[edit] Also check your other thread, the L293D is different than the L293. The D suffix indicates the protection diodes are included. ....Never mind you saw it.

Edited 2 time(s). Last edit at 07/25/2008 02:52PM by d0ubled.

d0ubled Wrote:
-------------------------------------------------------
> To use USB you need a USB to serial converter chip
> either as a piece part integrated into your board
> or as part of a converter cable. I do not see
> that in your parts list.

Fixed. Cost difference is $9.15 before shipping, and about $12-$20 with shipping (from SparkFun). See the edited post for details.

I don't think the stability is an issue. I've built two repstraps both out of steel--one mcwire and another steel tubed box that weighs about 100 lbs--and neither one benefits form all that added stability. You have to remember that this isn't a machining tool. No lateral loads or jitter of the tool on the work piece. Just a hot glue gun in a gantry frame moving sedately to and fro. I'd go with the 2x4 if I were cutting costs.

Demented

If you end up making your own platforms you can use angle iron/alu instead of channel, should reduce the cost of the rails by about half.

Quote

You have to remember that this isn't a machining tool.

But wouldn't it be nice if it could? One of the potential advantages of the McWire over Darwin was that it was a little more rigid, and hence perhaps a little more amenable to doing light milling.

@Ru

I don't see the need. You are mixing up two types of fabrication, additive and subtractive. They both have their strengths and weaknesses. What you would be doing with trying to use a McWire as an honest-to-goodness milling machine is giving it a shit-ton of weaknesses--backlash, slop, lack of precision--for the ability to route a pcb...sort of.

Better to save money and get a good machine without hassle.

Demented

It just occurred to me that the stepper motors are more expensive than I thought. I don't mean that I miscalculated somewhere, but rather that I failed to mention the fact that these are a prime source for the high cost.
The stepper motors themselves are $25 each, and each one needs a stepper motor driver, which are about $27 each. And you need 3. The total cost of using stepper motors will be $155.72, from the calculations I made previously. This is about half of the cost of the entire cartbot/electronics setup.

It looks like a closed-loop system would be cheaper.
Would it be feasible to replace the cartbot stepper motors with GM3's [store.rrrf.org] monitored by the Magnetic Rotary Encoder [store.rrrf.org] and controlled by the DC Motor Driver [store.rrrf.org]?
The total cost for each motor would be $7+$20+$12=$39, compared to the $25+$27=$52 for each stepper ($13 savings per motor). This is $117 compared to $156, a total savings of $39.
The torque of the GM3 seems to be about 1/2 of the NEMA 23's we're using, so I think you'd have to slow the rotation down by half (doubling the torque) using an extra geartrain to get it to work.

Would this idea work for the McWire Cartbot? What about the Darwin Cartbot?


Provided I also use scrap 2x4 for the frame (instead of the ~$30 iron pipe setup), this would reduce the total cost of the cartbot and electronics to around $320. The extruder is probably going to be $10-$30, so this gets the final cost under $350. I like that figure.

The high cost for the encoders ($60 for all three from RRRF) seems like it could use some chopping too, but as the price for the actual chip the board is based on is $12 (as far as I can tell), I'm not sure how much we can reduce this cost. Any ideas?

Edit: I just checked on Mouser and they sell low resolution encoders, like this one [www.mouser.com] (you can get a better idea of what it looks like here [www.mouser.com]; it's figure C at the bottom, but you can get ones that look like B and D for the same price) for $0.54 each. That one specifically is 12 pulse/24 detent, which I think means it can measure 12 changes in rotational position per revolution.

With the 1/4"-20 threaded rod used by the McWire for moving the build platform, I calculated the following:
20 threads per inch=1/20 inch per thread
1/20 inch/thread = 1.27mm per thread
1.27mm/thread=1.27mm lateral movement per rotation of the rod
12 pulses per rotation (ppr) = 1 rotation per 12 pulses
1.27mm per rotation=1.27mm per 12 pulses
1.27mm/12 pulses=0.10583333... mm per pulse ~= 0.106mm/pulse

Wouldn't this mean that, effectively, we could move the platform in 0.106mm increments using this $0.54 encoder? It beats the $12 10-bit encoder if we don't need such high (1024ppr) resolution, and I don't think we do (this is the main assumption that allows the use of such a cheap encoder, so if this is incorrect, please let me know). I think the higher resolution is more for the precise speed control than for distance control (speed control would be necessary for, say, the extruder's drive motor).
Note that using more threads per inch and/or more pulses per revolution would allow even finer control.

I'm guessing that an encoder circuit for less than $5 (maybe $10) could be rigged up for these cheap $0.54 encoders. It's possible that it could just be integrated into the DC Motor Driver circuit, even if it doesn't directly connect to the components of the DC Motor Driver (to reduce PCB, etc. costs).


[end of edit]


[A random thought that just popped into my mind, after reading about using molds for making plastic pieces [www.reprap.org], is that you could make simple parts for the extruder (and possibly the cartbot) using legos (with tape on the bottoms to make flat surfaces, if necessary) with the plastic poured into them. Holes for screws and stuff can be made using the described coring method, or alternately simply drilling after casting. Using shapes that aren't complex, you can easily make an extruder this way. It would probably be cheaper to just use plywood for the bootstrap extruder, though.]

Edited 1 time(s). Last edit at 07/28/2008 05:46PM by Joshua Merchant.

Joshua Merchant Wrote:
-------------------------------------------------------
> It looks like a closed-loop system would be
> cheaper.
> Would it be feasible to replace the cartbot
> stepper motors with GM3's
> [store.rrrf.org]
> oducts_id=43 monitored by the Magnetic Rotary
> Encoder
> [store.rrrf.org]
> ducts_id=80 and controlled by the DC Motor Driver
> [store.rrrf.org]
> ducts_id=69?
> The total cost for each motor would be
> $7+$20+$12=$39, compared to the $25+$27=$52 for
> each stepper ($13 savings per motor). This is $117
> compared to $156, a total savings of $39.
> The torque of the GM3 seems to be about 1/2 of the
> NEMA 23's we're using, so I think you'd have to
> slow the rotation down by half (doubling the
> torque) using an extra geartrain to get it to
> work.

Perhaps not the GM3 (I get the feeling that it's too slow and weak) but there are many other DC motors you can get for cheap that would work the same way. This is a valid strategy, and one that Forrest has pursued before. Check out his blog archives for more info. Be warned though that in the end he gave it up as too difficult to develop for the savings in cost.

> Edit: I just checked on Mouser and they sell low
> resolution encoders, like this one
> [www.mouser.com]
> =EoBBqhYDMngMlT686o%252bTCQ%3d%3d (you can get a
> better idea of what it looks like here
> [www.mouser.com]; it's
> figure C at the bottom, but you can get ones that
> look like B and D for the same price) for $0.54
> each. That one specifically is 12 pulse/24 detent,
> which I think means it can measure 12 changes in
> rotational position per revolution.

At the RPMs we're looking at (relatively low), you'll want way more resolution than that... 10 bit is actually a good target, and $12 is one of the best deals on an encoder that I've seen. The cheap-o Mouser ones _might_ get you acceptable positional accuracy (though I doubt it), but they will almost certainly not be what you need for acceleration ramping and velocity control.*

*Just my opinion - I've never tried using servos on a cartesian robot, so this is indirect experience.

Kyle Corbitt Wrote:
-------------------------------------------------------
> Perhaps not the GM3 (I get the feeling that it's
> too slow and weak) but there are many other DC
> motors you can get for cheap that would work the
> same way. This is a valid strategy, and one that
> Forrest has pursued before. Check out his blog
> archives for more info. Be warned though that in
> the end he gave it up as too difficult to develop
> for the savings in cost.
The GM3 can be retrofitted with the RM2 [www.solarbotics.com], which is intended to fit in the GM3, replacing the standard RM3. It's only $2.25 and has "approximately 3 times the speed, twice the torque and quadruple the power-draw" of the GM3's standard RM3. The torque at 6V would be more than that of the [$25] steppers sold by RRRF, and it looks like you can take it up to 9V or further. As to the speed, it should be fine too (I hope).

> At the RPMs we're looking at (relatively low),
> you'll want way more resolution than that... 10
> bit is actually a good target, and $12 is one of
> the best deals on an encoder that I've seen. The
> cheap-o Mouser ones _might_ get you acceptable
> positional accuracy (though I doubt it), but they
> will almost certainly not be what you need for
> acceleration ramping and velocity control.*
See my post about achieving mechanical advantage for encoders [forums.reprap.org]. If I'm right and that idea will work, then a gear train with a mechanical advantage of 1024/12~=85.33 should allow me to achieve the same resolution as the 10 bit (1024ppr) encoder with the $0.54, 12ppr encoder.


> *Just my opinion - I've never tried using servos
> on a cartesian robot, so this is indirect
> experience.

Yeah, I'm suffering from lack of experience in this area as well. 'sall good though.

Okay now that I've got a clear idea of my components lists for the cartbot and electronics (I hope I'm not forgetting anything in those), I think it's time to make a rough list for the extruder.

Basically, it will use the standard heated barrel, connected to a plywood frame, using the same GM3 as the standard extruder. It will be direct drive, with a bend in the filament.
[A side note (which can be skipped): It did occur to me that with a direct drive extruder, bending the filament is not totally necessary (some people seem to have implied this). A gear with an outer diameter smaller than the screw's can be locked (with glue/welding/whatever) onto a portion of the screw which has been reduced in diameter (by a lathe or whatnot, similar to the portions of the screw that sit in the bearings), such that the gear does not touch the filament. A geared shaft on the side of the screw opposite the filament can contact the gear and thus connect to the motor without having to bend the filament. I'm not entirely sure if this is actually "direct drive"; that is, I don't know whether "direct drive" references the lack of the steel wire or the direct connection between the motor and the screw drive. In any case, this would probably be the optimal setup, provided the components can be efficiently produced.]

Anyway.
The drive screw will either be M6 like the standard drive screw, but it may not work well in the 10mm thick screw/poly holder (there would only be 2mm of plywood on each side, and I'm afraid it might break). I'll try the M6, but, if it doesn't work, I'll use an M3 screw (since I'll be using long lengths of M3 in other places, I guess I figured [when I was designing] it would be easy to get a bunch of M3 screws than a bunch of M3 screws and one M4 or M5 screw. Then again, this is up to experimentation. For now, I'll act as if I'm using the M6 screw.

Note that instead of buying a bunch of different lengths of M3 screws, I'm going to buy threaded M3 rod and cut it to the correct lengths, and then use hex nuts to tighten both ends.
It should also be noted that the M6 studding for the heated barrel and for the drive screw can be cut from the same 1-meter length of steel studding.

Parts
----------------------------------------------------------------------------------
Desc.					QtyReq
----------------------------------------------------------------------------------
Heated Barrel1
 PTFE holder				1
 M6 studding barrel			1
 Nozzle					1
 Nichrome wire				1
 JB Weld					1
Barrel Clamp
 Structure2				1
 M3x5cm screws				4 (20cm)
 M3x10cm screws				4 (40cm)
 M3 nuts					4
Holder Shaft Holder
 Structure2				1
 M3 nuts					4
Screw/Poly Holder
 Holder Structure2				1
 Cover (Spring) Structure2			1
 M6 studding (Drive screw)			1
 Half-bearings				2
 Bearing springs				2
Biplate
 Plates2					2
 GM3 (Gear Motor 3)			1
 M3 nuts					18
 M3x20 screws				2 (4cm)

1The thermistor is not included here, as it is part of the Temperature Sensor section of the G2 Electronics.
2These are made of 1/2" plywood scraps left over after building the cartbot (cost thus included in cartbot cost).


The combined part list for pricing is:

----------------------------------------------------------------------------------
Desc.					QtyReq	Lowes	McMaster	RRRF
----------------------------------------------------------------------------------
 PTFE holder (# 8803K15)			1		5.33	
 Nozzle					1		9.88/50	1.50~
 Nichrome wire				1			0.60
 JB Weld					1		8.34
 M6 studding (barrel and drive screw)	1		1.19	
 M3 threaded rod				64cm		1.43
 M3 nuts					36		1.07		
 Half-bearings (# 94855A115)		2		1.06
 Bearing springs (# 9657K59)		2		6.04
 GM3 (Gear Motor 3)			1			7.00

~ Denotes the supplier to be used.

Note that for the half bearings, I'll be taking 6-32 square nuts, drilling the center with a 4mm bit, then cutting off half (probably using a file). I'll only reduce the drive screw to 4mm diameter where it rests in the half-bearings, instead of 3mm.

So the current price is $33.56 with a lot of parts left over. I'll go to Lowes tomorrow and see if I can get some better prices (probably through purchasing lower quantities, as the 100 packs from McMaster aren't always the best option ).
I'll probably just take the springs from some random device, as I don't think they need to be strong/precise, taking the current price down to $27.52.

Quote

It should also be noted that the M6 studding for the heated barrel and for the drive screw can be cut from the same 1-meter length of steel studding.

Steel is not the best choice for the heater barrel as it is a poor conductor of heat.

Quote

I'll probably just take the springs from some random device, as I don't think they need to be strong/precise.

They don't need to be precise because you adjust the tension with the nuts, but they do need to be very strong, e.g. 1.5mm x 9mm x 25mm.. I only use two at the bottom and space the pump halves at the top with two or three washers. I got them from the lid hinges of an A3 scanner.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> They don't need to be precise because you adjust
> the tension with the nuts, but they do need to be
> very strong, e.g. 1.5mm x 9mm x 25mm.. I only use
> two at the bottom and space the pump halves at the
> top with two or three washers. I got them from the
> lid hinges of an A3 scanner.
In that case I may just go ahead and buy them. McMaster's part # 9657K56 would be my current bet. (3/16" diameter x 1" length, 0.028" wire, 5.72lbs; 0.66" compressed length.) They're only $6.04 for 12 (I only need two for my design).
Anyway, I did rethink the way I'll be using them, though, as I didn't previously plan on using a screw to adjust them (oops). I did manage, however, to get the change in design to use already available components (the M3 nuts and threaded rod, both of which I will have a surplus of).


> Steel is not the best choice for the heater barrel
> as it is a poor conductor of heat.
Can I still get away with it though? [reprap.org] does list steel as an option, and it would add $13.10 for a pack of 25 suitable aluminum studs (#93225A872) or $8.83 for a pack of 10 suitable brass studs (#93025A963). These two are both packs of ANSI 1/4"-20x2" studs (not metric). The cheapest option (i.e. disregarding per-piece cost) would be the $6.75 1/4"-20x24" brass stud (#98812A029).
If I wanted to stick with the M6 studding, I would have to go with brass (as McMaster only sells aluminum studs in ANSI sizes), and fork out $17.69 for a 1-meter length (the smallest size, #90162A070).

What would be the disadvantage of using steel, exactly? Would it just take longer to heat up (and more energy)? Or is there something else?

For the heater barrel a brass bolt, or cap screw may be cheaper and more available. Hacksawing the head off is very easy with brass and the softer metal should make drilling the centre hole easier as well.

My guess as to a problem with any poor heat conductor is it becomes hard to tell what temperature the plastic is at. The thermometer and heater are on the outside which will change temperature more rapidly than the middle where the plastic is. This is further complicated by pushing cold plastic into the space at varying rates.

0.028" wire is only 0.71mm, so less than half the diameter of my springs. I think spring tension is 4th power so 20 times less strong.

I think the same as Peter on the steel v brass but I haven't tried it.

---

[www.hydraraptor.blogspot.com]

peteredworthy Wrote:
-------------------------------------------------------
> For the heater barrel a brass bolt, or cap screw
> may be cheaper and more available. Hacksawing the
> head off is very easy with brass and the softer
> metal should make drilling the centre hole easier
> as well.
>
> My guess as to a problem with any poor heat
> conductor is it becomes hard to tell what
> temperature the plastic is at. The thermometer and
> heater are on the outside which will change
> temperature more rapidly than the middle where the
> plastic is. This is further complicated by pushing
> cold plastic into the space at varying rates.
nophead Wrote:
-------------------------------------------------------
> I think the same as Peter on the steel v brass but
> I haven't tried it.
Okay, it looks like I'll be using M6x50mm brass hex head cap screws (#93270A460) which come in a 10-pack for $10.22. Since I'll still have the steel studding left over, I might also make a duplicate out of steel and compare the two (probably some time after I get everything working), though I would have to buy a second thermistor and length of nichrome wire (possibly another PTFE rod, depending on how easy/difficult it is to remove the old barrel at that point).


> 0.028" wire is only 0.71mm, so less than half the
> diameter of my springs. I think spring tension is
> 4th power so 20 times less strong.
Not sure about the exact calculations for that, but it is true that the 5.72lb (~25.4N) springs will probably be insufficient, as the docs [www.reprap.org] say that you need 4 springs with 30N compression force each, which is 120N total. Since I'm only using two springs, I need 60N (~13.5lb) or more from each.
The 25.4N springs are thus obviously insufficient (though I really don't know where they got the 30N figure from, probably just experimentation).

McMaster part # 9434K49 (13/16" length, .24" OD, .042" wire, 13.8lb [~61.4N] load) should work okay, for $4.61/5-pack. I chose it for the load, the cost, and the size, in that order.

The spring tension required varies with the type of plastic and is quite critical with the current extruder design. Too little and the screw thread fails to bite into the plastic and propel it. Too strong and the the friction is too high for the motor.

The values in the wiki are for PCL extruded quite slowly. PCL is quite soft compared to the other plastics. ABS is harder but it extrudes very easily. The tough ones are HDPE, which needs a lot of pressure to extrude, and PLA which is very hard to bite into.

---

[www.hydraraptor.blogspot.com]

My biggest problem with McWire, that I cant find pre-made length (3", 6", 9", 12") plumbing pipe.

I have been told in a specialised "plumbing" store, that today everybody is using copper pipes (with "hot soldering"?). And they only have 3/4" pipes in 6meter pieces.

Its a bit overkill to order plumbing pipes from USA to Europe union (McMaster.com). How much would be the shipping cost? (couldnt figure out in mcmaster.com).

I have the same problem with ABS coil. Everybody has only in table format (2mx3m for example), but not in coil.

So for me the biggest problem is availability and not cutting few bucks here and there...

nophead Wrote:
-------------------------------------------------------
> The spring tension required varies with the type
> of plastic and is quite critical with the current
> extruder design. Too little and the screw thread
> fails to bite into the plastic and propel it. Too
> strong and the the friction is too high for the
> motor.
>
> The values in the wiki are for PCL extruded quite
> slowly. PCL is quite soft compared to the other
> plastics. ABS is harder but it extrudes very
> easily. The tough ones are HDPE, which needs a lot
> of pressure to extrude, and PLA which is very hard
> to bite into.
It shouldn't be a problem, though. I plan to use polymorph at first, and if the springs are inadequate when I decide to switch to a harder plastic, then I can switch em out then. I can see it working out (nearly) perfectly.... muhaha.

khiraly Wrote:
-------------------------------------------------------
> My biggest problem with McWire, that I cant find
> pre-made length (3", 6", 9", 12") plumbing pipe.
>
> I have been told in a specialised "plumbing"
> store, that today everybody is using copper pipes
> (with "hot soldering"?). And they only have 3/4"
> pipes in 6meter pieces.
>
> Its a bit overkill to order plumbing pipes from
> USA to Europe union (McMaster.com). How much would
> be the shipping cost? (couldnt figure out in
> mcmaster.com).
I'm building my frame today. It's going to be out of 2x4 (1.5" x 3.5") lumber. I'm going to use some cheap hand-held tools to plane it and get it down to a nice, squared 1" x 3" cross section, and cut it into a few lengths for the structure. I'm a little worried about how much weight the vertical piece will be able to hold (that's the piece that holds the backplate and extruder), but I'll work it out (I might need to add extra supports around it). The biggest piece I'll be using is 1" x 3" x 14", and I'll be attaching the pieces to each other using some wood screws I have laying about. I think this kind of wood is available in the EU, but I'm not sure. If it isn't (or if it's too expensive), almost any other structural material will do.

> I have the same problem with ABS coil. Everybody
> has only in table format (2mx3m for example), but
> not in coil.
Not sure what to say about this part, and I think you'll get better advice from other people, but if it was me, I'd probably just make it myself .

> So for me the biggest problem is availability and
> not cutting few bucks here and there...
Well, availability is part of cutting cost; the whole reason you wouldn't order from McMaster is because it would cost too much.

In any case, good luck, and I hope someone else has more information for you.

I'm trying to build the frame using 3/4" ABS pipes. I seem to be able to get all of the same connections as with the steel. I've put an order in for the laser cut plastic pieces from the rrrf, following that I'll be able to confirm whether the flange I selected will be suitable

I've got a thread lurking around here which I'll add to as I go. You can see a couple of pictures of my test assembly of the frame there.

I already have many of the bolts, fittings etc that I'll need. The most major component I'm missing at the moment are the stepper motors.