My homemade linear bearings: yes or no?

[tybrenis]

Hey guys,

I am building my first CNC router and I was thinking about inexpensive ways to make myself some linear bearings. So, I drew up this lousy representation first.

The second image is my idea. Basically, you have a square steel tube for the bearings to roll on. Then, you have four bearings bolted onto a piece of L-Angle using nuts and washers to space them out over the top and side of the tube. I was originally going to use L angle for both pieces, but then Irealized that if I used a steel tube, I could easy support it using something like torsion boxes underneath it.

The picture will explain it well.

My machine will have leadscrews of 36" x 36" x 4". Do you think I'll need to support the tubing? I don't care so much about accuracy - even 1/31 or 1/16 of an inch is fine with me since this is my first CNC.

Also, how do I line up my bearings with the tubing? I imagine that being hard, havint to get the hole drilled perfectly. I'm not even completely sure how big my bearigns are, I can't find the specs on them.

Thanks again for the help guys, this community is the best! The second picture is what I have so far, it's only the top or side of one of the bearings.

[tybrenis]

Hey again guys,

This idea might be a bit more expensive (more steel needed) but tell me what you think. The gantry, router, or whatever will mount on top of the T angel steel.

I know this is a really crappy drawing, it looks like the two bolts holding the bearings are touching. They won't be, they'll be offset. If you looked at this same drawing from a view directly above it, one bolt would be higher and one would be lower.

Check it out, attached.

[Brunow]

A while ago i also thougt of diffrent home made stuff. I think it's good for the x and y axis ... not so sure for the z axis.

[svenakela]

There are many different home made design circulating here, browse or search in the forum and you will find.

Regards,
Sven

[tybrenis]

Thanks guys.

What type of bearings do you recomend that I build for the Z axis?

[Brunow]

Hmm use track ball bearings http://img.alibaba.com/photo/1123184...r_Bearings.jpg ?

[beone]

tybrenis, why dont you reinvent the wheel while you are at it?

[Mat-C]

tybrenis: good work on having gotten this far. I've seen the idea of using angle-iron and skate bearings before, sorry to say you didn't invent it
A lot depends on what you intend to do... for instance, you cannot tolerate much in the way of side or upward forces if you rest the gantry on wheels - you'd need to find ways to get at least three bearings around the rail.

Look at linear slides and rails on ebay, there are some bargains to be had and that can be the fastest way forward. Get some reasonable rails and press on, you can always redesign the bearings later and it will be a tonne easier with a working cnc machine

[tybrenis]

Originally Posted by beone tybrenis, why dont you reinvent the wheel while you are at it?

I can't tell if thats a compliment or not...

Originally Posted by Mat-C tybrenis: good work on having gotten this far. I've seen the idea of using angle-iron and skate bearings before, sorry to say you didn't invent it A lot depends on what you intend to do... for instance, you cannot tolerate much in the way of side or upward forces if you rest the gantry on wheels - you'd need to find ways to get at least three bearings around the rail. Look at linear slides and rails on ebay, there are some bargains to be had and that can be the fastest way forward. Get some reasonable rails and press on, you can always redesign the bearings later and it will be a tonne easier with a working cnc machine

Darn, thought I had something there. I have looked at tons of stuff on eBay, but I don't really have any more money to spend on this project. Also, this has been a personal goal for me for the last year to do pretty much everything myself - I even designed and built the controller.

[Zumba]

Just go on ebay and buy preowned THKs. THKs are actually the cheapest linear motion guides out there, in the sense that they hold their value can be resold years down the road for the same price you paid.

Most other linear motion systems are worthless after a certain amount of time and totally eat up your time and effort. If your time is worth nothing, then go for a home made approach. Otherwise, get some THKs and consider your linear motion guide problem solved.

In fact, most CNC components can be treated as commodities just like the THKs. Ballscrews, motors, drives, etc. Geckos are a rare find on ebay (they're high quality and nobody wants to get rid of them). When they do hit ebay, they're usually sold for about 90% new price.

[tybrenis]

I looked at THKS but they arent going to cut it. I'm going to have 2 36" axis, and 1 4" axis. That comes out to 80 inches of THK - and btw, my budget is about 40 more dollars. Ha. Yeah, that's not going to work out so well.

[tybrenis]

BTW, I need to know how to mount stuff onto my leadscrew, how do I do that?

I know I need a leadnut for the leadscrew to turn in, but where can I get one for under 10 bucks a piece? I need it to fit a 1/2"-10TPI ACME threaded rod. I don't have a tap. I could probably tap a piece of Delrin if I had one or used some spare acme rod though.

Anyways, anybody have some good pictures of some or no? I need to figure this out soon, I want to start putting together my machine.