[Winnfield]

You could chuck the screw up in a drill by the machined portion and hold the drill in a vise and see if you still have the end of the screw whipping. It's crude, but it will tell you if the screw is the culprit.

[DRock]

I just spun it and it doesn't seem to have a whole lot of wobble, definitely not as much as I have in the video.

I just drew up a quick diagram of how the mounts are supposed to be used. The red rectangle is the thrust bearing and the green is the AC bearing and there is about .75" of space between.

I have no idea what is going on...thanks for your help.

[Winnfield]

The portion of material between the two bearings there could be the issue. Using angular contact bearings in the face to face or back to back configuration eliminates any chance for error. The error could be in the thrust bearing race (I would try flipping it over so the bottom race is on top) or the top bore is not perfectly parallel to the bottom bore. Put your nut on it and don't preload it so much and see if it works. The top bore doesn't seem to be critical here if there is a thrust bearing on top - it would be the face of that bore that is critical.

[Winnfield]

The thrust bearing on top won't help you with alignment of any kind because the bore of that bearing probably isn't snug, and they are intended for axial loads only, so it will support the weight of the head, but won't keep the shaft centered. Maybe take that bearing out of the top and check it with your indicator to make sure the top is parallel to the bottom.

[DRock]

Yeah I can see how that would be the case, if the thrust bearing isn't making sure everything is concentric then that could be a major problem. I measured the flat surfaces of each bore and they were only out .0005"-.001" over their surfaces so they should be parallel to each other.

People seem to be using this kit with great success so I wonder what I am doing wrong. Should I get another AC bearing and use that instead of the thrust bearing?

[Winnfield]

The relationship of those surfaces to the mounting surface could be the problem as well. I would check that. Honestly, I would get a regular deep groove bearing for the bottom instead of the AC bearing, and not preload it very much. The problem with an AC bearing there is that it allows it to float any which way, so unless it is preloaded quite a bit, does nothing for alignment. If there is an alignment issue above it (for whatever reason) it will only allow it to flop about. I'd use the bottom bearing for radial support (alignment) and a small amount of preload, and the top (ball thrust bearing) for the axial load. Or, you could do like Optimum does on the BF20 and buy a double row angular contact bearing and call it good. When I converted my BF20, the Z axis bearing was decent enough to use, so I did. You will need to remake that piece, though, probably.

[Winnfield]

Keep in mind that the thing that keeps an AC bearing aligned is either another AC bearing against it, opposed, or a precision spacer.

[DRock]

So I am probably just going to get another AC bearing unless someone can tell me a good reason why I should use a thrust bearing there.

How much material would I have to remove if I were to put an AC bearing in there?

[Winnfield]

That might work IF the thrust bearing is actually the source of the misalignment. You can check that by taking it out and inspecting it with your indicator.

No change in the bearings will fix an alignment issue that isn't due to a bearing problem, obviously.

The load rating on the AC bearing is likely much less than the thrust bearing, but the thrust bearing may actually be overkill.

Did you spin the screw with the machined portion in the drill chuck to see how much it whipped at the opposite end? That will be what tells you if the machined part of the screw if tilted. If you spin the screw itself and watch the machined end, it may not look like it is out very much, but a tiny bit is a lot by the time you get to the other end of the screw.

[DRock]

Yeah I put the machined end in my drill and put it on a v-block and it spun pretty straight.

I think the thrust bearing isn't centering the screw properly and so it's tightening down at an angle. I took a dial test indicator and ran it along the unthreaded machined part and it came out pretty straight also so I think the screw is OK.

I wonder if anyone else has ran into this issue with these mounts.

[Fastest1]

The thrust bearing shouldn't have anything to do with alignment. The AC would control the centering, the thrust carries the load. Are you using 2 v blocks to measure runout? Measuring at the middle of the screw? Or the machined end? Supported by the machined area during measurement or the unmachined ball track area?

[Winnfield]

Try switching the bearings and don't preload it very much. Let it sort of "hang" there on the AC bearing on top. Make sure the side with the THIN outer race is on top (exposed). If you get this wrong, you will have a separated bearing and a huge dent in your table (or worse). If you can set it up like this without a problem, simply ditch the thrust bearing and use a regular deep groove bearing in the bottom.

[Winnfield]

The thrust bearing shouldn't have anything to do with alignment. The AC would control the centering, the thrust carries the load. Are you using 2 v blocks to measure runout? Measuring at the middle of the screw? Or the machined end? Supported by the machined area during measurement or the unmachined ball track area?

The problem is that the AC bearing will not tolerate near the load the thrus bearing will, and if you tighten it all up and there is either an error in the bearing or the surface it is sitting on, will (an can) tilt the assembly, despite the AC bearing. The AC bearing will not do what it is supposed to do if either of those conditions are the case. This configuration depends on the thrust bearing to keep it aligned because one AC bearing typically uses the other for this - not the load itself. Otherwise, AC bearings would be used like tapered roller bearings in a spindle - with no spacer at all, but they can't be, AFAIK.

[SCzEngrgGroup]

Otherwise, AC bearings would be used like tapered roller bearings in a spindle - with no spacer at all, but they can't be, AFAIK.

A/C bearings are *frequently* used with no spacer at all, even in spindles. Precision A/C bearings are sold only in pairs, and are ground to provide optimal pre-load when mounted back-to-back. Even the inexpensive ones are often very good used this way. I've built several quill-drives for Bridgeport mills using the inexpensive A/C bearing pairs from VXB, mounted them back-to-back, and they gave zero backlash.

Regards,
Ray L.

[Winnfield]

A/C bearings are *frequently* used with no spacer at all, even in spindles. Precision A/C bearings are sold only in pairs, and are ground to provide optimal pre-load when mounted back-to-back. Even the inexpensive ones are often very good used this way. I've built several quill-drives for Bridgeport mills using the inexpensive A/C bearing pairs from VXB, mounted them back-to-back, and they gave zero backlash.

Regards,
Ray L.

They can be used with nothing between the inner races but open air? Like in the top of a spindle box and in the bottom with nothing spacing the inner races?

I don't see how a predictable, consistent preload could ever be set this way.

[SCzEngrgGroup]

They can be used with nothing between the inner races but open air? Like in the top of a spindle box and in the bottom with nothing spacing the inner races?

I don't see how a predictable, consistent preload could ever be set this way.

No, not at all. A/C bearings would almost never be used at opposite ends of a spindle - that's a recipe for disaster when the spindle heats up. Both A/C bearings would be clamped tightly together at the business end of the spindle, literally back-to-back, with NO space in-between - both inner and outer races in HARD contact. The opposite end of the spindle would have a single, simple radial or deep-groove ball bearing, with a slip-fit on the spindle.

Regards,
Ray L.

[hoss2006]

Drock, dd you contact billy at bdtools? From what I hear he's very supportive of his product and may have some insight for you.
Hoss

[Fastest1]

I can tell you first hand that Billy is very cooperative. He will do everything he can to make sure his products work. Contact him for sure.

Also regarding the AC bearings and alignment. The reason I stated it like I did was because the thrust bearing in this case is installed in a non critical bore, however the AC is centered and fits tightly. I am still suspicious of the runout being in the machined or threaded area.

Drock, dd you contact billy at bdtools? From what I hear he's very supportive of his product and may have some insight for you.
Hoss

[DRock]

Thanks for the replies everyone, I have some more fiddling to do before I make a decision.

I am going to send Billy a message today, hopefully he isn't extremely busy in these next few days.

[DRock]

While waiting for his response I am going to try to finish up the X and Y. I decided to lap the gibs a bit to get them flat and I took off a little too much material because the gib now goes right out the back of the saddle so i need to shim it some. I cut a shim that is the size of the whole gib strip right? I am assuming so because I want it to be thicker while keeping the same angle.