Friday, September 05, 2008

I promised Forest some more pictures. Here they are, much improved courtesy of a Canon SD1100 IS. The original bearing assembly is on the left, a freshly assembled one with one of Andy's suggested improvements is on the right.

Moving the turnbuckle onto the inside of the floor mounting flange allowed for the use of one less nut per bolt, and moved the bearings closer to the flange, seemingly improving alignment somewhat. Excellent.

I haven't tried mounting additional flanges on the outside of the bolts yet. At nearly $4 each, they're already the most expensive part of the assembly by far. If I can get away without doubling the number of them needed, it's a big win.

More excellent still.

You may want to give Sebastien Bailard a quick Personal Message on the forums Personal Messaging system.

Sebastien was interested in building a "Full Sheet" cartesian bot for some of his sculpture projects.

What you are doing here looks like a dead ringer for Gantry Mounts and Bearings.

You might also want to take a look at Pipe Clamps. They fit to the same ranges of pipe that you are using but are a slide on with a grub screw fitting.

The sort of things they make safety handrails from etc.
I met Sebastien at last year's Penguicon. I'll give him a ring. I would also like to build a CNC mill that can handle a full 4x8 sheet of plywood, particle board, etc. It may have influenced my design ;)

I looked extensively at the type of pipe clamps you're talking about. They're _perfect_ for this sort of application, but exceedingly expensive. $10 - $20 each. By comparison, the black pipe fittings I'm using cost around a buck a piece. They're not as nice, but MUCH cheaper.

Most of my design could be adapted to use kee clamps, and it would be a better machine for it. More easily adjusted and accurate. But that differers from my goal of building a repstrap that's inexpensive and easy to build by anyone who doesn't have tools.
I have a part built machine using kee clamps that is currently on hold as I work on a PlyRap Darwin.

Yes they are expensive you are right to use the less expensive parts.

Their alignment can be a touch pants too as their is a bunch of play in each fitting to allow for misalignment etc.

There are however some parts in the Kee Clamp range that are not available in the pipe fittings. That you might find complementary later on further down the line. If your aware of them then great your already a step or two ahead.
Oh forgot to mention.

If you get to be concerned about accuracy and keeping the threaded joint tight (tapered threads are a bit like that) beg/borrow or long term loan a cheap stick welder and put tack welds on the pipe/fitting joints once you are happy with them.

Tack welds can be ground off again if you have made a mistake, but in conjunction with the threads fix some of those picky issues like getting a closed loop to align and be tight. (You generally get one or the other)
Once again, under the "no tools" mantra, I've been experimenting with steel-impregnated epoxy putty (namely one called Fasteel). I don't know that I'd trust it over a weld in some life-sustaining technology, but the stuff is ridiculously tough. I bonded a bolt to one of these black pipes with it, and wasn't able to break it off with a claw hammer. I plan on using it to attach fiddly bits like the lead screw nuts, motor mounts, etc. It might also work for securing the pipe fittings in place.
Sorry about that... The last post was me. Girlfriend had herself logged in, and I didn't notice. :)
Okay! Now I can see how it works! Thanks!

Obviously, since you're making it out of pipe fittings, it's going to require some heavier steppers to push the positioning table around.

Have you measured how much frictional load it generates?
Nope. Playing it by ear at the moment. I have some hefty NEMA-23 steppers salvaged from large multifunction laser printer / scanner / copiers I plan on using. I'll definitely report on how well they work (or not).
Have you seen:

He does use lots of flanges and bearings.

And 1" pipe. Heavy and more expensive.
Yup. I've seen it. His bearing design results in smoother motion, but requires a drill press, tap, and tap handle. At least $100 in equipment that my design doesn't require. My goal isn't to produce something of phenominal quality, but to build the least expensive, most accessible repstrap / CNC router possible.
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