Need Help!- play in V bearings

[neomagik]

Hi

I've nearly finished my build but I'm getting quite a lot of play/slop in my V groove bearings.

If I hold the inner part of the bearing firmly, I can rock the outer (V groove) part from side to side. This is transferred to the machine when assembled.

Are the bearings faulty or is there a way I can take out the slop/play?

Thanks

[Dean448]

Are you using eccentric inner bushings? I'm using v-bearings from IMservice and can tighten them up with these special bushings.
http://www.cadcamcadcam.com/cncmachinecomponents.aspx
I'm also using a 1/4-20 cap screw into one inch of thread engagement. Either on angle iron or v-bearing rails they are very tight.

[ger21]

There should be no play at all in the bearings. Sounds like they are defective. What kind are they?

[neomagik]

Originally Posted by Dean448 Are you using eccentric inner bushings? I'm using v-bearings from IMservice and can tighten them up with these special bushings. http://www.cadcamcadcam.com/cncmachinecomponents.aspx I'm also using a 1/4-20 cap screw into one inch of thread engagement. Either on angle iron or v-bearing rails they are very tight.

I'm not sure what those bushings are going to acheive. The ID of my bearings are 10mm and I have them fixed to M10 bolts with an M10 nut either side. This makes the inner part extremely firm. It's the outer part that rocks about the balls.

Would those bushings eliminate this?

I'm not sure what type they are, I'll have a look for any clues when I get home later.

[ger21]

Would those bushings eliminate this?

No, they'll only hold the center tight, but they will allow you to preload the roller against the rail. But if there's play in them, they're no good.

[Dean448]

I have no idea if the bearing is defective or not when there is angular play between the inner and outer races. I would agree that you shouldn't see radial or axial play. I do know that you need to preload in this system. The rails arn't perfect and where it might be snug in one spot it could have clearance in another. Since you fixed the inner race with an M10, can you shim out the rails to tighten it up?

[neomagik]

I have two 10mm holes for the bearings on one side and two 10mm elongated holes the other side so that I can slide the bearings and tighten them on to the rails. I did this by hand so it's probably time to get the clamps out to squeeze them while I tighten the nuts.

I don't have this problem on the X axis and I think it's due to having 8 bearings (4 each side) rather than four.

[ger21]

Last time I say this, but if the outer "V" portion has slop between the inner race, the bearings are bad. No amount of preload will get rid of all the play.

[Dean448]

My gantry machine has 8 bearings for the Y (long) axis and is real stiff. I don't think that each side by itself is that stiff, it takes both sides and the gantry beam to do the trick. My X (short) axis had too much compliance around the z axis (you would notice it if you tried to lift the router) and I had to add a second rail parallel to the X axis, 6" above it, to stiffen it up. I used just two v-Bearings. So I agree that 4 v-bearings won't be very stiff against rotation around an axis.

Just a side note - Must rounter you see have a very tall horizontal beam to try to prevent rotation around that axis. That works but keep in mind that there may be a weight penelaty in materials other than wood or aluminum.

I'm impressed by how robut these bearings are in use. For simplicity, cost and ease of construction, I really don't think they can be beat.