Monday, May 07, 2007


RepStrap 'Acorn' Plans

Now that the boards have been pushed out the door to production, its time to start looking forward to the actual mechanics. I dont have access to printed parts, but I do like the simplicity of Darwin's design. Unfortunately, using smooth rods for structure seems to be pretty hard if you dont have the printed parts. Others have successfully made them out of 4x4 studs, but it seemed to be pretty precise work.

Instead, I've opted to make essentially an open faced cube out of MDF. Hopefully I can use the straight, factory cut edges of the MDF to get a very nicely aligned machine. I will be using the same drive system as darwin for both X, Y, and Z axes... however they have been slightly modified for my setup. I will attempt to skip the smooth rods for the Z axis (i'm designing it so they be added in afterwards, if needed) , and just have the build platform mounted normally. For the Y assembly, like in darwin, there will be two threaded rods attached to the sides of the box in parallel. I will lay and attach two smooth rods perpendicular to those for the bearings. The Y stage will be a plank of 1x3 or something similar. I will make bearings out of CAPA and mold them to the smooth rods while its still warm.

The Y stage will hold the X axis. It will have two smooth rods in parallel, also held down with CAPA or some other means. Just like darwin, There will be a motor on one end and a pulley on the other. The X stage will then be another, shorter plank with the same CAPA bearings as the Y stage. All of these stages will be belt-driven.

As for the rotational bearings (these are the pyramid stacks on each of the threaded rods: Z axis / Y axis / X pulley) These are cheap, easy skate bearings. It goes: washer on bottom, skate bearing in middle, nut on top. The nuts on both ends of the rod, hold it tight, while the washer spreads the strain out, and makes sure the bearing can rotate freely. This makes the tolerance on the wood hole not very important, and should allow for easy adjustments.

Anyway, thats my plan. I'll be in the shop with a friend on Tues or Thurs attempting to construct it. He's a woodworker by trade so I have great confidence in him. Please let me know of any comments / suggestions.

More photos on Flickr

this looks cool, good luck!!!!
Brilliant! And to think I was going to pay someone to CNC my parts. Thank you for saving me money that can go to niceer steppers. Good luck in the woodshop.
thanks guys. i'll make sure to heavily document the construction process. About a year ago when I was in Iowa, I started a RepStrap machine that used belts + smooth rods + CAPA bearings and it slid REALLY well, which is why i'm confident in this design.

if you dig through the archives, you can see posts on it somewhere.
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