How to RepStrap the RepStrap

Since it is still very difficult to obtain the needed RP parts to build a Mendel many (including myself it would seem) are forced to build a RepStrap machine in order to be able to make the RP parts.

My question is how do you build an extruder without the RP part?

It looks like the McWire robot is the easiest route to go but how do I build the extruder? The insulator, nozzel, nichrome wire, kapton tape is no problem but the mechanical part required for the pinch extruder is much tougher...

I really don't want to have to buy the MakerBot extruder kit.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

My question is how do you build an extruder without the RP part?

Try building a tiny CNC mill out of pipe, and machine it.

Then document the process in the wiki.

Edited 1 time(s). Last edit at 02/15/2010 04:56AM by SebastienBailard.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

The Plan
The Result

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Wooden Mendel
Teacup Firmware

I just got some "shapelock" plastic and sqoushed it into aproximately the right shape. It doesn't need to be precise, after all.

I admit, it doesn't work yet, but I'm sure it will just as soon as I get the electronics straightened out...

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I'm building it with Baling Wire

As we're nearing the point of putting together an extruder ourselves, I've been heavily leaning on this design:
Binary Construct
So far it seems the easiest. Really all you need for your extruder is a mount of for the motor, something to grip with, and a way to mount your barrel. Take a sheet of acrylic, or MDF, do some measurements, and attach it to some angled aluminum. Naturally the RP part is nicer, but in a bind such a mount will serve you until you can print out an extruder mount.

sircastor Wrote:
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> As we're nearing the point of putting together an
> extruder ourselves, I've been heavily leaning on
> this design:
> Binary Construct

Yes, that does look pretty simple!

I have several hp LaserJet IIIP printers that I bought for a couple of Euros plus the cost of shipping and handling. I have disassembled one and removed the stepper motor and fan. According to the specifications that I have found it should work fine in a McWire (although I am thinking of using M8 threaded rod instead of the M6 threaded rod specified). The stepper from the printer is pretty hefty and is listed as 7.5 degree, 12 volt, 0.6 amp and 4.3 mN/m. This should work fine to drive the McWire X, Y and Z axis.

Edited 1 time(s). Last edit at 02/15/2010 02:54PM by rhmorrison.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Triffid_Hunter, is your work at a stage where you'd be happy to put up on the wiki? Or is it still too early to check into the Library?

Also, does anyone know who the binaryconstruct fellow is?

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

I asked a similar question in this thread. In particular the post by jeffpark_ where he links to this extruder made from mdf, again from binary construct.

Also, Sebastien I believe this same person is the binaryconstruct fellow.

The currently fatal problem with the mcwire is that there isn't really an extruder design that can extrude SLOWLY enough for the very slowly moving threaded rod driven planes. This pushes printing time through the roof (to perhaps 200-400 hours for the mendel depending on how good you get, not only printing time but time to take the stl's, tweak skeinforge and print all the mendel parts) because you have to babysit pretty much every part the whole time and do a lot of tweaking on each individual part. I have come to the conclusion that doing so isn't worth it...

I have given up on reprap/repstrap entirely and am in the process of just building a standalone device using 80/20 aluminum parts. Something like that is readily available, does not require you to spend a month tweaking settings and printing parts for a whole additional device to build and gets you setup to just start printing what you actually want right away with potentially better performance characteristics (there are a lot of design tradeoffs with printed parts). If you are thinking about going mcwire I would suggest either buying a cupcake (known quantity works well), waiting until an 80/20 device gets worked out (<60 days) or start experimenting with 80/20 yourself (8020.net). In theory you could build an 8020 repstrap device but that just seems silly to me, seems more sensible to make the 8020 device stand alone , you can probably get a 2'x2'x2' size device for the cost of a repstrap + mendel. Based on my calculations realize that the printed parts of the mendel are about 3 lbs of abs (anyone care to confirm?) not including rafts or mistakes. So realistically that is $50-$100 of abs.

No matter which way you are going you will probably need a set of electronics and my suggestion is to start there, Makerbot is currently out of stock and I am not clear if they will ever have G3 electronics in stock again or are just waiting to jump to G4. Once you have electronics focus on getting a functioning extruder. When that is working then worry about getting the parts for whatever your frame is.

You can make a pinch wheel extruder pretty easily using the makerbot barrel and heater parts, some fender washers and bolts and extra aluminum angle (from the mcwire). If makerbot is still out of the pulley I posted a compatible mcmcaster part number (just search mcmaster pulley). However that extruder suffers from the "extrudes to fast" for the mcwire problem. You can only slow down the DC motor so much before it either does not run or you get a lot of slipping on the filament (which will then ruin prints partway through). It is still sort of an open question as to how well the larger mendel parts can be printed without a heated bed.

If you want you can also buy a professionally printed single piece extruder carriage from protovantage.com for about $60.

I am testing a feed through screw design extruder (similar to what rick posted recently, I think the thread is screw feed extruder). The design includes no laser cut and no printed parts. I will post a detailed document as soon as I confirm it works reliably for some number of prints. There is a firmware issue with stepper driven extruders I am currently working on (I use the makerbot firmware, I have never gotten the reprap host software/firmware to work without crashing for any length of time).

The parts are pretty cheap so feel free to order and start experimenting as well. You need 2, 3 inch pieces of the leftover aluminum angle from mcwire. You match those against each other to form a 3 inch long U.

The stepper mounts through the outside (right upper arm of the U) and drives a 45 degree angle nylon gear. That gear meshes with the other 45 degree angle gear (mounted in the bottom of the U). On that gear you epoxy the threaded spacer through the middle, it sticks out about 1/4 inch on each end, One end goes through the nylon bushing into the bottom of the U. The whole thing mounts to the Z axis plane on the left upper arm of the U.

Filament feeds through the top of the threaded spacer insert (which runs through the middle of the gear and out the bottom of the U into the normal PTFE spacer and extruder barrel, fender washers, long bolts setup.


Parts list from mcmaster:

2x 6126K43 Nylon Snap-in Thrust Bearing for 1/4" Shaft Diameter (again just need 1, get an extra in case)
4x 7297K15 Molded Nylon 20 Deg Pressure Angle Miter Gear, 24 Pitch, 24 Teeth, 1" Pitch Dia, 1/4" Bore (you only need 2 but if you make a mistake you need the extras)
4x 93330A449 Aluminum Threaded Round Standoff 1/4" OD, 1" Length, 6-32 Screw Size (only need 1, some extras just in case or if you accidentally break off filament in the insert and can't get it out)

From makerbot you need:

1x barrel
1x nozzle
1x PTFE spacer
1x ABS filament roll (sold as 3mm though actually 2.8mm, this works well with 6-32 threaded inserts). This is village plastics filament I believe. Other diameter filaments will need different threaded inserts. PLA may work, haven't tested.
1x 10ft nichrome wire (you will need the extra over time)
1x thermisistor (be sure to manually validate temperature with an instant kitchen thermometer or such, there are now 3 or 4 different thermistors coming from makerbot and they need different settings in replicatorG to work correctly)
1x DC motor (you don't need this for the through hole extruder but you may want to experiment with pinchwheel, it is a good thing to have handy)

Leftover:
Aluminum angle from mcwire build or just home depot/lowes equivalent

I already have the complete Generation 3 Electronics from MakerBot as well as barrel, nozzel, PTFE spacer, ABS, nichrome wire, kapton tape, thermister and four NEMA 17 stepper motors.

I NEED THE RP PARTS...

and since it doesn't look like I am going to get them the McWire seems the best choice.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Here is another bootstrap extruder I just stumbled accross.

extruder

Sebastian, I want to get things working before I post on the wiki, so it goes up as a tested, working method rather than a bunch of actualised concepts with undefined potential for success

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Wooden Mendel
Teacup Firmware