Linear Motion Solution

Since linear motion is so key to these systems, it important to explore all solutions assuming you aren't tied to printed parts. This provider has some really good looking stuff:

[www.pacific-bearing.com]

I read that t-slots were not great for linear motion with their bearings as there was too much play in them, but that material I read was from 2005, so maybe they have improved in that area.

kevin

Since linear motion is so key to these systems, it important to explore all solutions assuming you aren't tied to printed parts. This provider has some really good looking stuff:

[www.pacific-bearing.com]

Looks good. I'm sure the people building more expensive and [[Spindle]] cnc cutter types RepRaps will find it useful. Along with the [[Surface Deposition Manufacturing]] folk.

And the "that's too expensive for the machine I want" folk may speak up.

I read that t-slots were not great for linear motion with their bearings as there was too much play in them, but that material I read was from 2005, so maybe they have improved in that area.

It would be good to tack up a note here about it:
[objects.reprap.org]

It should be noted that most concerns with the 8020 linear motion bearing pads had to do with binding issues using them in the Z-Axis rather than X and Y.

I have been playing with them and I find them to be pretty good all round, in the Z axis you need to address binding but I believe that can be solved with careful consideration to rigidity and symmetry, for example driving the axis with 2 threaded rods (as in mendel) rather than just one. Pretty much every state has an 8020 distributor and they are extremely friend about letting you visit their example "gurneys" which carry a complete setup of everything they offer (hundreds of different pieces). In fact most of them will drive it out to you, I was able to setup an appointment and view one the next day.

There is still a question of the total bearing carriage cost-effectiveness with 8020 but with that system there are about 100 ways to skin any cat. I think that the single unibearing pads will offer the best tradeoff of performance versus cost but the total unit bearing carriages are extremely simple, zero setup, though in price ranges from $35-$90 depending on size. Also take note of seating the bearing pads with a rubber/sand mallet, this makes a huge difference in performance.

I am also experimenting with PTFE strips and/or skate bearings on the default aluminum channel. Whatever the best/cheapest combination solution I find I will document.

If you are getting the complaints about 8020 bearings from CNC users realize they are typically dealing with weight and inertia of a full sheet of plywood anywhere from 30 - 150 lb, which is a very different case than plastic printing (<0.5 lb).

thanks goinreverse,

As I said, those comments were old and did relate to CNC.

what size t-slot are you using? I downloaded their program to estimate warping based on loads at different points across a span. It was interesting to play with some numbers and see what kind of warping you will see.

I look forward to your design, although I personally favor the X/Y movement to all be done at the tool and z at the base versus the other way around. this gives you larger printing areas for total machine volume, and also supports possible future tooling better like lasers and pick and place. The downside is doing x\y movement is a little more painful because the tool itself is in the way, but this is solvable without much effort.

Kevin

I am currently using the 1010 (1" solid) but have some of the 20-2020 (20mm solid) on order, it is potentially a cheaper option. The 1" works fine and is rock solid but probably overkill. I am shooting for a 2'x2'x2' unit with a build area around 1'x1'x1' .

An optimal design to me is one with X/Y movement of both the tool head and the base if you want to support a variety of operations and the added benefit of two planes traversing at the same time, doubling speed without hitting G limits.

Mcmaster seems to have the best pricing for most of the parts, rail can be gotten through the distributors already milled and cut to your specs which is great. It costs next to nothing ($0.25-$5) to have them cut it to length and put holes wherever you want.