Laser Cut Parts (Bits from Bytes)

I received my Laser Cut parts and started assembly yesterday. The excitement is mounting!

I was wondering if anyone has the dimensions, or a manufacturer and part number, of the slide bearings used in step 2 of the X assembly as provided by Bits from Bytes? I have found a part at the McMaster site but the OD of the part is 12mm and the holes are 10mm.

Thanks in advance for any help,

Steve... .. .

The Full Mechanical Kit Laser Cut Parts BOM PDF
[bitsfrombytes.com]

Lists the bearings as p/n 008 7150 114 42, which I believe is for www.skiffy.com

[pdf.directindustry.com]

The vitals are:
8mm inner diameter
10mm outer diameter
7.5mm depth
15mm diameter of flange (brim of top hat)

They are apparently black and made of a mix of Polyamid 66, carbon fibre and PTFE.

Hi spcmicro

How is the reprap build going?

I am guessing from your question you did not get the full kit from Ian.

have you had any problems yet?

regards

Stephen

spcmicro put up an overview of his progress at:
[builders.reprap.org]

I've had a few problems during my build but none of them have been show stoppers. Most of them probably won't occur/be a problem for others but I'll list them here in-case.

Problem: Cracking parts through over tightening.
I've broken a few of the parts, mostly in the corner blocks, through over tightening.
Solutions:
- Learning to judge when to stop tightening by how well the part is held, not by how how hard it is to turn the screw an extra turn. The bars are in contact with the corner blocks for about 40mm and so don't need to be very tight to produce enough friction to keep the bar held tightly.
- Super-glue fixes acrylic very effectively.

Problem: The motors are suitable for the Arduino but their Resistance is too low for the PIC electronics to drive.
Solutions:
- Use the Arduino electronics.
- Use power resistors, for the moment I'm using 5v and a 1 Ohm 2w resistor on each phase, which works for testing the wiring and motors but I'm not sure if it has enough torque to be used in the final Darwin Bot.
- I've nearly finished a chopper add on for the pic motor boards to allow it to drive the same range of steppers as the Arduino boards.

Problem: My Cat stealing parts.
Really unlikely to happen to anyone else; In a fit of jealousy, at the attention I've been giving the machine, my Cat stole one of slides described above to play with and refuses to tell me what she did with it.

I'd suggest sodium-thiopental and she'll sing like a bird

'sid

[edit] oh it's commonly known as sodium pentathol

Edited 1 time(s). Last edit at 08/15/2008 12:16PM by sid.

Assembly from laser cut parts is in progress. I have two minor problems to share with other builders:

The shaft of the Z stepper motor does not reach the grub screw inside parts 34 and 35 of Z_Sub-Assemblies.pdf. Swapping the positions of parts 33 and 35 seems to solve the problem. Part 35 needs a hole drilled in the edge to allow access by an Allen key to make it similar to the drawing.

The X motor assembly in drawing X_Assembly.pdf shows part 42 tight against part 44. In this position there is no space for the nuts holding the motor. I have moved 42 and 44 10mm apart to enable assembly but will this be a problem later?

Jon Wise

>The shaft of the Z stepper motor does not reach the grub screw inside parts 34
>and 35 of Z_Sub-Assemblies.pdf. Swapping the positions of parts 33 and 35
>seems to solve the problem.

I had the same problem. I removed a Part 36 (which seems to be a spacer)
I did not have to drill anything. Everything appears to function well.

>The X motor assembly in drawing X_Assembly.pdf shows part 42 tight against
>part 44. In this position there is no space for the nuts holding the motor. I
>have moved 42 and 44 10mm apart to enable assembly but will this be a problem
>later?

I had the same problem. and came up with the same solution. Unfortunately
the solution puts the optic senser in the wrong place. A solution would
be to reprap another longer optic senser holder. But I don't have a working reprap. yet ..... :-<

Solution 2. There is a gap between the two parts. It's just not wide enough.
So I filled part 42 so it could fit into the gap. This worked.
This obviously weakens the part. but I don't think it will be a problem as it does not move.

(I also put the screw for the motor in backwards. The idea was that the hexagon
nut took up less space than the circular screw head.)

Solution 3. Put the screws in backwards so that the screw head is at the top and kept there by gravity and don't put a nut on it. Reprap should still work. Just don't turn it upside down. Wait for Ians solution.

Well onto step 5. (and hopefully no more problems)

Regards

Stephen

>The shaft of the Z stepper motor does not reach the grub screw inside parts 34
>and 35 of Z_Sub-Assemblies.pdf. Swapping the positions of parts 33 and 35
>seems to solve the problem.

One of the motors in my kit has a longer shaft that can reach all the way through the part 33->37 stack.

Does anyone have have any notes or drawings to help assemble the Y axis drive?

Jon

I'm also waiting on this, I just finished up to stage nine in Darwin Bot.pdf. Does anyone have a 3D model of a fully assembled one? I could probably just use that to finish the design.

mark

The 'Assembly Info' section of the bitsfrombytes web site has been updated and now includes both the Y assembly and a 3d model.

[bitsfrombytes.com]

There are also some pictures, an updated 'darwin bot.pdf' and a pdf of the top corner blocks.

I have not seen the latest messages in this forum so I apologize for the delayed response. I must not have checked the replies box when I submitted the original post. I am checking it now.

Thank you to all of the people who have posted the problems they have encountered. It really helps when trying to sort out problems.

Build progress update:

I've been making good progress on my build. I have the basic frame assembled and have the Z axis drive working with the host application. I didn't update the blog from last weekends activity but I will be updating after the upcoming weekend. My wife is working two 12 hour shifts so I'll have plenty of play time.

My biggest problem right now is finding some of the parts in the states, such as the 8mm slide bearings. I found some in McMaster but the wall thickness is twice what the spec is. By the way, thanks to peteredworthy for the information on those parts. If anyone cross references the part to one that's available in the US I would greatly appreciate the information.

I have requested a little parts kit of all of the hard to find bits from Ian but haven't heard anything back yet. I know he's really busy so I'm not panicking yet. I'm assuming that I'm not the only one that purchased just the Laser Cut parts kit and not the silver or gold. As people are resolving some of these availability issues it might be handy to have a place where suitable parts from US vendors could be listed. Even just the specifications would be helpful, as with the springs and slide bearings.

This may be a dumb question: Does anyone have a more detailed description of what fire cement is? It looks like it's the same as furnace cement but I'm not sure. Is there a description somewhere of exactly what it is and it's characteristics?

Stay tuned... .. .

I have a few more notes from my assembly attempt which may help others:

For the Y drive, I found the belt was out of alignment if I followed Y_assembly.pdf. I replaced the nut and spacer on the motor drive by a washer.

In the Z belt tensioner (Z sub-assemblies.pdf), I added washers on each side of the bearing to make enough space for the belt.

The slot in the bed frame for the Z flag needed a spacer to line up with edge of the adjustable bed.

Part 24 of of the Extruder Assembly is a 25mm M5 bolt. I found I had to cut 3mm off to get it to fit.

I hope this helps.

I like the idea of adding the washers to the Z belt tensioner to help align the belt. I was fighting with the tensioner this weekend and at this point I'm not winning. I have broken at least 8 of the diagonal tie plates, Item #71 on the Darwin Bot assembly drawings. I am going to make 2 out of aluminum for the diagonal rod that holds the Z belt tensioner. This should help keep the tensioner in place but I still think that it takes way too much fiddling to get the balance between having too little or too much tension on the Z belt.

We hit the same problem, but our solution was a bit different. All that is needed is a vertical support (it just needs to rest on it) and it works a treat and then you do not need to over tighten the diagonal ties.

I broke several of 71 as well, but in my case I originally had one of the corners 2 mm to high and another 1 mm out. It doesn't sound like much but it of cause made it impossible to adjust the rods to the right length. Part 71 was just the weak point between immovable object and unstoppable force. After a weekend reassembling it with excruciating amounts of measuring/checking/re-checking the diagonals were all within 1 mm of the same length before I started tightening.

For the Y axis I went a slightly different route moving the bearing into the motor plate and then mounting the pulley in the same way as at the other end. I'll try to describe it better / draw a diagram later.

My current problem is the X axis gantry binding if it isn't pulled squarely and I can't seem to get the Y belts to pull it squarely enough to avoid binding. My first thought was that it was too loose, but moving the end plates( part 42) tighter into the rail seems to make it more prone to binding and greatly increases the friction while it is moving.

With the X gantry make sure the bars it runs on are absolutly parallel, use the setting bars and be sure they just drop onto the running bars and have no bend in them.

Next attach the belts to the idler side of the gantry and put the gantry at the Y motor end and then pull the belts evenly by hand to ensure the gantry slides very easily, if not ajust check the slide clamps are not to tight, if it goes tight at one end or the other it probably the running bars not parallel. If it all slides OK then attach the belts going around the drive pulleys. Leave the pulley farthest from the Y motor loose i.e. do not tighten the M8 nuts whent the belts are fitted set the gantry exactly square to the running bars and then tighten the loose pulley. This should nail it

Sorry for any speelling mistokes the spell check seems to be on holiday.

---

Ian
[www.bitsfrombytes.com]

This message is a request to davidgoodenough about the Z tensioner post a few messages ago:

Is the vertical support attached to one of the bottom horizontal base rods? I was thinking about something like this when I was having problems and I though that placing the tensioner in the middle as opposed to being close to one of the Z pulleys would also work better. Is that where you put yours?

I would like to see a picture or diagram if you get a chance to post one. It sounds like you are quite happy with your implementation.

The vertical support just sits on the bench with the unit, its not connected even to the z tensioner - the tensioner just sits on it. Whether it will require fixing is yet to be determined in prolonged use, but in tests is seems to work. As its just a piece of wood it does not really justify a photo - but once we have done some more with it we will probably build a proper support that does connect and use that, and that I will publish (both the design and a photo in use).

I've got the Y axis, the X axis' gantry, moving freely now. In the end it was a combination of factors that were causing the binding.

The bars it runs along weren't perfectly aligned. The spacing testers fit at both ends but one was tighter than the other. I'm not sure how significant this was though as fixing it didn't seem to improve the binding problem. I didn't have a method for quantifying the binding though and it was several hours between the checks.

The edges of part 43 are not quite 90 Deg and this was causing them to sit toed in.
World's worst diagram:

      /  \
----------------- <- rod
     /     \
   ----------- <- Part 42

The diagram is quite exaggerated but they were out of line by enough that sliding the assembly with and with out 42 attached had a noticeable change in friction. I filed the ends to 90 Deg and it now slide's as easily attached to 42 as on it's own.

The holes on Part 42 didn't extend quite far enough; at least one of the mounting slots between 42 and 43 was just slightly to short. Using M8 bolts in place of the rods showed that the binding increased just by having 'rods' through 42, even if they weren't attached to anything. It turned out that although the ends through 42 were touching the rail one of the bolts through 42 to 43 had reached the top of it's slot and the assembly of 43s was twisting to allow both rods to touch. Elongating the holes with a file solved that.

The final problem was of my own making; Adding the other side to the gantry and setting them both to the same position resulted in the carriage binding. What had happened was that in filing part 43 I hadn't kept them exactly the same thickness. This resulted in part 42 not being parallel to the Y rails. Trying to pull it parallel, as I was when setting it's position, resulted in a twisting part 42 against the rail. More filing while testing that the filed ends were parallel to the Y rail solved that.

The gantry now moves freely end to end when pushed by hand from the middle. Without the belts it still binds when moved by just one end. With the belts it can be pushed off center, but still between the part 42 plates, without binding.

I suspect that my problems were the result of the cumulative effect of having 3 alignments all slightly off, but it would be hard to test. For now this hopefully gives a good list of how you can go wrong ;-}> and some things to check if it isn't moving smoothly.

I made a modification to the Z tensioner that solved problems that I was having. See my entry on the builder's blog on September 7th for the details. In preliminary testing the results are good. I haven't beat on it yet because I'm replacing the acrylic parts that hold the diagonal rods in place. I have a list of the parts that have cracked or broken that I will post soon. I think it's important that Ian and his team, as well as people using the acrylic parts, know which parts may be more susceptible to breakage so that they may be modified or in some cases, made from another material that isn't as brittle.

I have another question for anyone in the States that may be using the Laser Cut parts kit. Has anyone found a source in the US for the slide bearings? I can't find a match and it's really holding me up at this point. In hindsight it would have been better to purchase at least the silver kit. I recommend this for anyone in the US because some of the metric parts are not easy to find and when I did find them I had to pay for larger quantities than I needed, sometimes to get just one part.

We have noted the problems and I'm currently waiting (later this week) for some Hi Impact Acrylic which is much more resistant to cracking and gives some slight stress indication before breaking the only down side it's not quite so shinny but very close.

---

Ian
[www.bitsfrombytes.com]

... i prefer Delrin/POM instead of PMMA or Polycarbonat - the surface isn't so hard, but the material is more rigid in specs of wear, brittleness and such. And i can mill it without coolant ...

The main colours are white and black, but there should be some other colours too - only 'clear' isn't possible.

Viktor

Edited 1 time(s). Last edit at 09/09/2008 06:41AM by Viktor.

In the early 80's I used to work for Zymark Corporation, a manufacturer of laboratory robots, and we used a lot of Delrin. The machinists loved it.

Ian

I have had a number of parts fail on me and I have got pretty good with the super glue. (six at last count)

However I would be interested in "upgrading" my reprap system to a
better material. When you have decided on the "better material" Would it be possible to have an upgrade option at just above cost for existing customers?

Obviously screws, nuts and belts etc would not be needed.

regards

Stephen

I really don't care what colour the material is. Could be pink with yellow spots for all I care.

Yes that's a good idea i will try to get some feed back on the problem parts and do an upgrade of those parts.

---

Ian
[www.bitsfrombytes.com]

I have just broken extruder parts 1 and 5 where the nuts from the motor are located. I can attach the motor section with an aluminium bracket but the option to buy replacements would be appreciated.

Jon

Here's a list of parts that cracked when I was assembling. The first number is the quantity that broke, second number is the item number from the relative print.

1 - #41 - Z-corner bracket
2 - #43 - X axis slide adjuster
1 - #17 - setting bar
1 - #11 - extruder motor mount
7 - #71 - diagonal tie plate
1 - #89 - Z belt tensioner plate

Hope this helps...

After breaking bit 7 I have come to the conclusion that the laser cut material is simply not up to the job. Either the screws are two loose in which case the system
seems to shake itself apart or they are too tight in which case you get a nice crack sound followed by some serious swearing.

Personally I would like to replace ALL the bits with a stronger material.
Cast iron would be good.

regards

Stephen

Steel is a wonderfully versatile and laser cuttable material...
powdercoated?
Aluminium - annodised in cool colours would be good.

How about using reprapped plastic parts ? or has that been thought of??!

I suppose the aim of laser cut parts is to build a repstrap and replace components to create a durable reprap, but it does seem a waste when you could be using the 'replacement' parts to build a whole new machine.

I also assume that steel and particularly aluminium parts in the equivalent thicknesses of the polycarbonate will be much more expensive. A redesign for thinner metal would be required. Weight would be an issue too.

Glass is a possibility - you can even cut glass with the wire mesh re-enforcing.