Thursday, September 04, 2008


Repstrap and CNC progress update

First of all, please excuse the quality of the image, it was taken with an OLPC, not a traditional digital camera.

I haven't posted much, but not for lack of work. I've been busy working on a repstrap / CNC router design that's buildable for a low cost (< $200 including all tools and materials) from parts available in your local hardware store, with minimal or no tools.

It's been slow going, but a recent prototype linear bearing assembly has shown promise. It's my first to come close to meeting those criteria - inexpensive, no tools required, and all parts available at the local Home Depot. It's built using 1/2" internal diameter black pipe and fittings, 5/16th allthread rod and nuts, skate bearings, and double-eye-hook contraption I don't know the name of. :) The eye-hooks are used to tension the allthread rods, rotating the black pipe floor-mounting flanges and trapping the guide rail between the sets of skate bearings.

Total parts cost for this assembly at the local hardware store was about $15 US.

Now that I have a linear bearing that works, I hope to quickly move on to an entire repstrap capable of being assembled without so much as a single power tool.

Could you take a few more pics of the assembly? I'm having a hard time understanding quite what you've done here.

No problem. As soon as I get home :)
I think I have about got it.

There are a pair of skate bearings on each bolt.

Two bolts per flange.

The flanges are rotated to force the bearings against the running pipe/rail

The rotated flanges are held in rotated position using what looks like a turn buckle (Wire tensioner)


I never would have thought of that one.

Well Done
Just thought you might want to try adding another pair of flanges on the outside to stop the threaded rods from splaying apart when under load.

If you move your turn buckle to the side of the flange away from the rail/pipe it has no chance then of catching anything.

Don't know whether this is of any use to you. Thought it might help.
That's really great! Man, this has been something that I've been trying to come up with a solution to for larger repstraps. The bigger I get the more rigid the system needs to be and this is a great way to do that for a linear slide system. That thing looks like it would scale well, also. good for larger or smaller systems. Looking forward to future posts on this. Good luck. Demented
aka47: you've got it exactly. Excellent description of how it functions. I'd thought of both those modifications previously, but hadn't gotten around to testing them. Thanks for the reminder :) As far as scaling goes... as long as you could find large enough skate bearings, it should scale up well. Down I'm not sure about.
I like the way you have assembled it, essentially like someone would assemble a toy for kids. Easy steps and something that is pretty tolerant for user error. Good thinking out of the box!
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