Sunday, August 24, 2008
RepStrap Build Using Laser Cut Parts Kit - Update
Here's a picture of the main bot so far:
Things haven't been tightened because I don't have the slide bearings yet and 4 of the side diagonals are missing. I just had to see what it was going to look like.
What went wrong:
1. I broke 2 more of the plastic parts even though I have been extremely careful when tightening bolts.
2. I have not been able to locate a US vendor for slide bearings with the exact specifications as the Skiffy ones from the UK.
3. The side diagonals were short on 2 sides of the main assembly. All of the rods are specified at a length of 600mm and I found that 610mm long rods worked for me for 4 of the rods that make up the 2 side diagonal assemblies. I'd be curious to know if anyone else encounters this. I measured all of the dimensions between rods and I come out with a different diagonal spacing for 2 of the four sides.
4. I've seen the thread on the mechanical forum about splicing the Z belt. It looks like any of the suggestions will work but I'm curious to know what Ian had intended. Hopefully he will add his input to the thread or maybe a procedure on the Bits from Bytes web site. I'm guessing that it's probably the same as for the original Darwin as described by Adrian.
I wasn't happy with trying to adjust the corner brackets that clamp onto the 8mm smooth rods so I used 2 70mm smooth rods and inserted them in parallel with the rod being clamped onto. Here's a picture:
I then took up the slack on the M3 nuts so that the plastic bracket pieces were parallel. Not too tight because you won't be able to remove the 70mm rods. When all of the nuts are snug, remove the 70mm rods and tighten the nuts about another 1/2 to 1 1/2 turns. Once again, not too tight or the bracket parts may crack.
I hope this explanation makes sense.
1,40,38 corner pieces by over tightening and them snapping in line with the bar. Oddly I've not broken 2,13,15,39,41 though.
38 One by over tightening the grub screw and another when moving Darwin before I'd added the cross braces.
44 by over tightening the bolt carrying the bearings.
61 trying to seat one of the nuts next to the corner I broke off the corner.
71 I've broken quite a few of these; fortunately there are already 2 spares. When they snap in the wide part they can be glued easily, but I've had some where the plastic above the small hole has broken and I'm not sure how I'd fix them.
88, I broke off one of the small side tabs. I've reattached it, but I don't think it actually does anything.
The parts aren’t particularly weak, but acrylic seems to give very little indication that it is under too much strain before it cracks.
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