New Machine Build- Cheap LinearBearing

[thething84]

Hi all.

i have the rockcliff plans for a cnc router. looking at making the 12x12x5 overhead gantry.

it is designed using 5/8" ground bar, but i was wondering and hoping there is a cheaper alternative.

Wot am i able to get away with, without making it to slack. I can probably make my own bearings.

Thanks James

[harryn]

I am using the cncrouterparts.com linear carriages. They are reasonably priced and saved me a bunch of time, esp. since I have limited capability.

http://www.cnczone.com/forums/showthread.php?t=48749

[thething84]

ok so browsing on ebay. come across somebody who is selling bright mild steel bar, 15mm Diameter 0.590" for you americans etc. Its 35 though smaller, i don't think this will have any real effect on it. I can make my own linear bearings outta aluminium or summat like that at work. Wot you guys think?????

[harryn]

If you are going to use unsupported rail / rod for your linear motion, then that seems pretty thin. I know it is only 12 inches, but the gantry weight always is more than people think. I would use 1 inch / 25mm if it were me, then you would have some confidence in the stiffness.

Take a look at what widgetmaster did with a similar size system design (his mini router in the wood working area)

[thething84]

ok. its not a probelm going up to bigger size. i suppose as the boggest rail is actually 28.5 inches long, and the plans say to use 5/8" ground bar, but i plan on changing the disign of the runners anyway. Although that will only be holding the bed. I believe.

[thething84]

done some thinking today and come up with an idea for my bed runners. I have attached a pic.

it uses 1" steel bar for the rail, and 3 skateboard bearings for the actual runners. Please scrutinise it and tell me wot you think. The main block will be machined out of ally.

[Gir]

You'll want to design it so that the bearing can be adjustable. The top one can stay put, but the bottom two need to be able to move and then be set in place due to tolerances in the pipe and your block. A slot for the bearings to move toward and away from the rail, plus a set screw to adjust it's depth, and then just a nut and bolt to tighten the bearing down through it's center would be enough. Just a thought, though.

Tyler

[thething84]

yeh i am toying with that idea aswell. Will design it proabbly a bit better. But you think it will be a good design etc.

[thething84]

ok here is the improved design.

[millman52]

I only see need for adjustment on 1 bearing. Tightening any (1) of the 3 bearings will squeeze all 3 to the shaft.

Your idea is sound it will take (2) of these units per rail, or 1 common holder With 2 sets of bearings.

With the amount of work involved to make these pieces, & no longer than the rails need to be. I'd think you could find hardened linear bar & bearing carrages on ebay reasonable enough to fit your budget.

Not to discourage you from making your own slides. There's lots of pride & enjoyment from making your own. There are 20MM kits listed there now for 69.00 US each. They have 55" of shaft 2 support posts & 2 bearing slides. I found that on a quick search.

[thething84]

i need 4 per slide as it will run on two rails per axis. and probelm is i am in the UK. and i don't fancy paying nearly 100 quid from wot i have found for them.

[Gir]

I only see need for adjustment on 1 bearing. Tightening any (1) of the 3 bearings will squeeze all 3 to the shaft.

True, but it could cause misalignments. By allowing both of the bottoms one to move you can help straighten things out a bit, but it probably isn't that big of a deal. So you're probably right in that only one needs to be adjustable. I guess it depends on what the tolerances are.