[bbergami]

I'm just getting my first machine up and running. I used linear ball bearings on all three axis.

On my x and y axis the bearings will randomly hang up for a moment and make the motors skip some steps. There is no pattern to it. I doesn't repeat at any certain spot on the shaft.

I believe my alignment is pretty close. Do these bearings need perfection to run smoothly? Should I be looking at different bearings or are there any tricks or lubrication tips to get them running smooth?
Thanks

[jimbo]

Try disconnecting the leadscrew and move the platform by hand to feel for smoothness. It should be able to glide easily through the entire travel. If it feels smooth then try reducing acceleration and feed speeds, it may be that the motors are not strong enough or you are sending signals faster than can be performed.

[wjbzone]

Need more info.

Is the force from your ballscrew centered between the bearings? When you disconnect the ballscrew
and push the axis do you feel a drag? Are your stepper motors strong enough?

Could it be a loose electrical connection causing the motors to skip?

Bill

[bbergami]

If I disconnect the leadscrew it will move freely then start doing the same. It will hang very slightly on occaision. I'll run it back and forth by hand fast and it seems to dissapear. Then it will return when I move it slowly.

The motors are 214in/oz. I think they are adequate.

The leadscrew is is centered between the bearings on y. On the x axis it's equidistant but off centered about an inch.

I'll try messing with the feed rate, acceleration and steps per second again tonight. Is there any place to find some guidance on this? I've already spent hours with this.
I appreciate the help.
Thanks Bert

[wjbzone]

If it does the same thing by hand, could your linear ball bearings have picked up some chips?
Bill

[tjstraz]

Do your bearing cars have grease ports?
It sounds like they need to be lubricated.

When you move the bearings along the rails do they make any noise?

[bbergami]

I guess It could have picked up a chip? I haven't done much cutting yet. Mostly just cutting air on test runs.

I made the bearing blocks myself. I didn't put in a grease port. I put a little grease in them to begin with. I don't recall seeing holes in the bearings to allow grease to enter but I'll have to check tonight.

The bearings do make a little noise when they run back and forth.

[wjbzone]

Is grease the right lubricant?
If a chip is in there, grease might make it harder to clean. I would try spraying some wd40 to flush it out. A lighter lubricant might be better.
Bill

[tjstraz]

If these were commercial bearings (thk,etc) than more than likely they would have a grease port and would require grease.

Since these were built by bbergami, it would help us to know how these bearings were constructed. This would help us to determine if this is bearing friction or an alignment/mechanical issue.

[bbergami]

Actually all the bearings are commercial. On the x axis with a 1.25" shaft 2 of the bearings I believe are Thomson which came with the used shafts(ebay). These were pretty smooth running by hand on the shafts. The other two are new Barden bearings bought from a surplus outfit. These were not as free sliding as the used ones but Ihope they would break in.

On the y axis they are new Thomson , 2 are open and 2 are closed.

All the carriers were made out of a solid block of aluminum bored to slightly over the bearing od with a set screw.

[tjstraz]

My mistake, I though you were talking about linear rails and not shafting.

I do not have a lot of experience with shafting, but what you are describing sounds like sticky bearings.

[Beezer]

Do your bearings have seals or rubber wipes on them? If they do
make sure that the bearings are lubed properly with a light oil or very light grease. I have had a similar experience before with a scanning system we built at my work were we used Thomson style rails and bearings that had seals. It seemed that the rubber seals worked so well that they wiped away the thin film of lube that is suppose to be left on the rail. This resulted in the rubber seals trying to move along a dry rail which you can imagine could stick abit. We found it was more noticeable when you moved the bearing, then stopped it, then tried to move it in the opposite direction again. Once the bearing was moving you didn't notice the sticking. Eventually this went away the more the machine was run and the seals broke in.

Now if you don't have seals on the bearings then you might have abit of dirt in one of them.

Hope this helps abit.


Carl