binding?

[bobleecnc]

Hi I got some of this stuff from work it was framework for some saftey fences(1515) it was going to the dumpster so it became mine.I'm planning to build a cnc router with it . I'd like to use the unibearings they offer but I'm concerned with tortional binding and drag . Would these bearing work on a machine 40"x80" used mostly for 2d routing ie: cutting out patterns?,or would there be to much friction and twisting therefore causing lost steps?

[dchan413]

I designed one about half that size and planned on using 1020, but once I did the math, I switched to 1530. What materials are you cutting? 1515 doesn't seem stiff enough for the 80" span. If you can build your carriage light enough, and if your material cuts easily, 1515 might be ok. Check the 80/20 catalog pg 37-39 for the deflection calculations.

[bobleecnc]

Hi thanks for the reply well I intend on cutting 1/8-1/4 luan plywood with it
I was planning on supprting the long x axis in several spots or using 2 pcs. of 1515 bolted together . I guess my main concern would be will it tend to bind under a cutting load with 200 oz. motors and maybe cause lost steps .I'm not sure how slippery that uhmw stuff is ?It looks like it might work in a single axis application but what about multi axis where one axis might be working against another axis ?Or maybe this would only be a consideration in a constant contouring cut ?

Bob

[Evodyne]

I purchased two lengths of 1515 and a pair of slide from the 8020 ebay store. My thought was to bolt the 1515 onto a more substantial underlayment and then use it and the slides as a poor man's (that term defines me) linear bearing.

Well, it's sitting here on my living room floor. Let's see... The slides fit snugly-you do have to push a bit to get them to move. You would not be looking at anything that would coast, for sure. Keep in mind these are new-I don't know how they might break in. And what about lubing the rail? Hmmm.

Also, there is a bit of play, desite the snugness, that would allow for a small amount of torsion-induced error. Sorry, I have no way to give you "numbers". Perhaps two slides per rail separated by a distance and bolted rigidly together would help.

Finally, I don't think binding would be an issue. It appears that you might torque a bit of error into an axis, but I believe it would continue to move.

Don't know if this helps.

[maxxgraphix]

1515 will flex over 36". My frame is all 1515 but it's boxed to add strenght. Should have used 1530. I don't think the slides will work. You need to add a THK rail to the T-Slot. I used hardened rods, but should have gone with rails.