Adjusting Y axis backlash Boss 6.1

[creep_pea]

The other day my machine missed a load of steps in the Y axis while cutting a slot, it was only doing very light passes as I hadn't got a proper slot drill so I was using a center cutting 4 flute endmill and ramping it down. It probably when out of position by 50mm.

It's never missed steps like this before, it occasionally misses one or two steps when doing heavy cuts.

I'm thinking the problem may be a knocking sound that has developed in the Y axis but I can't find where it's coming from, there is a little end play in the bearings on the end of the Y axis ballscrew, maybe 0.03mm.

Can this end play be taken out by increasing the preload on the bearings?

I'm thinking that the preload may be factory set so can't be changed?

Thanks

Chris

[creep_pea]

I managed to get the two opposing angular contact ball bearings out today, looks like they are a matched pair as there is no shims between them.

I'm thinking I could make a shim to put between the outer races of the bearings to give the bearings a bit of preload when they're tightened back up.

Not sure how big to make the shim? reason being that the end play in the bearings is 0.04mm when measuring it with the saddle at full travel at either end but when the saddle is in the middle of it's travel, I can only get 0.01mm end play showing on the clock, this is as the slides are fairly worn in the middle but not at all at either end, how much end play is acceptable?

Don't want to make the shim to thick and ruin the bearings!

Cheers

Chris

[machintek]

It is possible that your gibs are too tight. The ways are worn and dished. Thus more force is necessary to move the Y axis where the saddle is tight and you measure more backlash as the bearings and associated parts take this additional force.
I do not advise you to shim the bearing. The proper solution is to refurbish the ways.

George

[creep_pea]

I think your probably right but I'm guessing a refurbishment of the ways will be expensive and I don't really want to spend any more money on this machine, prefer to spend the money on a better machine with a tool changer.

I don't suppose it's possible to wear the ends of the ways down cheaply so that the wear is even along the ways, I'm guessing it's not easy with the ways been chromed?

Thanks

Chris

[creep_pea]

Well I've gone against George's good advice and shimmed the bearings to remove some of the end play.

Sorry George I do respect your advice and I know your right but I decided the bearings are worn anyway so if shimming them totally knackers them I've not lost too much!

So far since I've put it back together, there's no longer a clunking / knocking sound when changing direction and it's ran the same program that caused it to miss a load of steps without problems, so fingers crossed the bearings will last a bit longer and not collapse under the increased preload.

Thinking of buying a coarse diamond whetstone to stone the slide down a bit at the ends to remove a bit of the friction in the Y axis at the ends, will this work?
Thinking of these they should get into the dovetail too.
Forge-Steel-Diamond-Sharpening-Pad-6-x-2-3-Pc

Cheers

Chris

[creep_pea]

I bought one of them diamond whetstone and gave it a go, it's hard work but it has slowly removed some material off the slides and in doing so made the table less sticky at either end.
Probably needs a bit more removing to make it even better.