Linear bearings and steppers problem

[flash319]

So I have my machine working but am not happy with the Y axis movement. To much vibration from the steppers. I think it is the crappy bearings I am using causing to much side to side movement.

When I drive in one direction, the left side motor vibrates bad then when I go the other the right side does it. They are racking the gantry. If I lean on the gantry it smoothes out.

Here is the setup, one on either side.


Here is the whole table.


SO the questions....
These bearings are cheap VBX ones (2 per side about 6 inches apart). Will quality bearings (thomson or SKF or something) take the side to side motion out of the bearings?

Is there another solution to this "clocking" out of the gantry?

I am using Gecko 201X's to drive the 2 steppers. I think they are acting normal.

[ger21]

Isn't this a setscrew to tighten up the bearings?

[flash319]

That screw is to hold it in place. I could crank it but that would deform the bearing and would eventually chew up the plastic races.

[analogman]

Darn, that sucks. I have fully supported Thomson bearings (1" rails on X, 3/4" rail on Y) with no play at all. If you cannot adjust the slop in the bearings, I would be inclined to replace them. Hopefully replacement bearings have the same mount size etc.

[flash319]

I think it is just the cheap bearings. If you look inside them there is a row of balls on one side and nothing on the other. So when you pull on one side the plastic cage colapses a bit.

The only way these bearings would have no side to side slop is if you mount the rail on an angle so that you have a row of balls on each side. Stupid design. I am looking into the Frelon plain bearings from Pacific Bearing. The ball bearings just feel notchy to me......

Where are you located Analogman? I am near Barrie Ontario.

[flash319]

I may have found my problem. When I milled the pockets that the alum tube sites in and the bearings bolt to, the plate warped. So when I tighten the bearing blocks to the plate they tilt in causing the bearings to bind. I will take the plates to work and throw them on the grinder.

There will still be some sideways movement of the bearings but I hope it will take the vibration out of it.......we will see....

[louieatienza]

Originally Posted by flash319 I may have found my problem. When I milled the pockets that the alum tube sites in and the bearings bolt to, the plate warped. So when I tighten the bearing blocks to the plate they tilt in causing the bearings to bind. I will take the plates to work and throw them on the grinder. There will still be some sideways movement of the bearings but I hope it will take the vibration out of it.......we will see....

Good to hear. That's one helluva cool machine! Nice build!

[LeeWay]

Another thing you can try is the cable system under the table that should help eliminate racking by equalizing the force to each side.
There is a thread on here somewhere that shows how this is done. Guys have said it really helps alot.

[flash319]

I was looking at those cable systems. Very igneous idea but I would like to avoid it if possible. I hate making things complex for the sake of an engineering problem. Complexity means that there is a mistake somewhere (in my books). The best machines are the simplest.

If I still have racking I will go to plain bearings instead of balls. The motors have tons of torque (650oz/inch each and the whole gantry only weighs 60 lbs) and can pull a lot. The hard part is getting the same lash in both sides. I hate the spring loaded motor setup that many have used. I am sure it works fine and may have to result to it, but am trying to avoid it.