[kkaylor]

I'm getting ready to convert my CNC'd PM20 to ball screws. Currently, I'm using all stock thrust bearings and acme screws and pretty happy with it. But, I'd like to step up the speed, and lower maintenance with ball screws.
Some of the conversions are changing thrust bearings to AC bearings. Why would you do that? Is it really worth $75 to upgrade? What benefits would you get? Is there that much axial load to warrant AC bearings?

P.s I plan on using MR Codewiz's conversion plans. So, I want to give a little shout out to him for being so generous. I will post my conversion and modifications (if any) to my PM20MV.

Thanks!

[LongRat]

The main benefit of AC bearings is that if you get a matched pair, you just crank them up together and the preload is automatically set for you. I don't know how many people are actually using these matched pairs, I know I'm not so I carefully set my preload with the nut on the end of my screw. In this case, my opinion is that you really don't have any advantage over plain axial thrust bearings, and indeed I have also used these to equally good effect on ballscrew conversions. So if you don't get a matched pair, I'd go for axial thrust bearings if the cost difference is that big.

[LeeWay]

The ground ball screws I have bought came with AC bearings in them already. If you have the precision of a ground screw, I think the effort is worthwhile.
The rolled ball screw machines I have built though use either just simple pillow blocks or pillow blocks and thrust bearings. I used thrust bearings on my lathe and none on my router. I can tell the difference in accuracy and smoothness. These thrust bearing sets were pretty cheap and well worth adding to a rolled ball screw.
I do not think AC's would have gained any added benefit.

[SCzEngrgGroup]

The primary reason to use angular contact bearings is that they can carry heavy axial AND radial loads, and provide more precise location of the screw. Regular ball bearing have very little axial load capacity, and thrust bearings typically have almost no radial load capacity. And A/Cs do the job with less friction. A ballscrew requires rigid support, precise location, and high load capacity to deliver precise positioning. Every little compromise in the precision of the components used in a build reduces the overall accuracy of the entire machine, often to an ever greater degree. $75, in the overall cost of a CNC conversion, is lost in the noise.

Regards,
Ray L.

[packrat]

If you can get FAG 72xxB.TVP.UO bearings in the size to fit your screws they will work. The are ground with zero clearance and work in both DF and DB positioning. I got some on Ebay for $10 a pair.

[kkaylor]

Thanks for all the input. The conversion plans use A/C bearings, so it would be cheaper to buy the bearings and avoid wasted time modifying the parts. Plus, if it can help reduce backlash and make the table run smoother its well worth it.
Pack rat: What does "DF and DB" positioning mean?

[mactec54]

KKaylor

AC bearings come in many different styles, DF /DB Back to Back or Front to Front

This is another style to look at (photo), a lot are using these for easy set up , A good brand of this type will have around .0002 of clearance, they are one piece A/C bearing but with 2 rows of balls, they come as a Back to Back type makes them worth a look at plus they are sealed

[kkaylor]

Thanks Mactec,
So, If I get a set of back to back AC bearings OR matched pair, do I only need one in a pocket VS an AC bearing on each side. I budgeted buying two bearings for each side the stepper motor is mounted. Thus I only need one match pair?

[kkaylor]

Something like this? LR5200NPPU Track Roller Double Row Bearing Sealed 10x32x14 Track Bearings Track Roller Double Row Bearing, Sealed.

[mactec54]

KKaylor

If you use this type in the photo, that is the same as having (2) A/C matched pair Bearings, you only need (1) Bearing if you used this type of A/C bearing on the drive end, & a regular deep groove bearing on the other end, you could of cause use (2) of this type (1) on each end

[mactec54]

Something like this? LR5200NPPU Track Roller Double Row Bearing Sealed 10x32x14 Track Bearings Track Roller Double Row Bearing, Sealed.

No this is not the right type, but you should look for a better quality as well

This is the type Double Row Angular contact Bearing

[Jason M]

What does "DF and DB" positioning mean?

DB/DF/DT designate Duplex back-to-back, duplex face-to-face, and duplex tandem respectively.

The load bearing configuration of each would be <> (DB) - >< (DF) - >> (DT). As you can see from the ">" symbols you get varying axial and radial load capacities and rigidity. The engineering requirements of the application would dictate the arrangement.

good overview or arrangements here

In my experience the photo of the double row angular contact ball bearing in mactec54's post is meant for applications requiring less precision like electric motors, centrifugal pumps, things of this nature, and are found most commonly with an internal clearance that is looser than you would want for a ball screw application.

Hope that's useful information that does more than just muddle the issue for you.

[packrat]

Another thing to watch in buying angular contact bearings. While all series 7xxx bearings are angular contact, they are not all useable in duplex mounting right out of the box. You need to get the right type. The ones I mentioned are, the suffix "UO" is the key. If the AC bearings you end up buying aren't listed in the catalog as 'suitable for duplex mounting, all position' or 'ground for zero clearance', you will have to figure out the correct shims to use between them to get the zero clearance.

So to save a hassle make sure to look up the part number your buying before spending the money, don't ask how I know Almost all brands have pages online telling the specs of the bearings.

[mactec54]

[QUOTE=Jason M;
In my experience the photo of the double row angular contact ball bearing in mactec54's post is meant for applications requiring less precision like electric motors, centrifugal pumps, things of this nature, and are found most commonly with an internal clearance that is looser than you would want for a ball screw application.


I don't think you will find these bearings in electric motors, & very few centrifugal pumps have them as well


If you have (1) of this type of bearing on each end of the Ballscrew, they will do a great job & just as good as, 2 expensive precision Bearings on (1) end Which you have to seal

Good brand name Bearings like this have around .0002 clearance, Like SKF Etc, so with (2) one on each end, you can put the Ballscrew in tension/light preload, to take up any clearance, so you get the best of both worlds, Great support & low cost

KKayler wants budget, this is the best for him & very little to do for set up

[Jason M]

I don't think you will find these bearings in electric motors, & very few centrifugal pumps have them as well

I sold these bearing types (5200 and 5300 series ABEC3 standard RIC) to electric motor shops and a refinery for their pumps for 15 years, you'll definitely find them!

I understand the budget concerns and if you can take the slop in your application then you may as well save some dollars, sure.

If budget's not an option and precision is top priority you'll want ABEC 7 angular contact bearings or "ball screw support bearings" which are (usually) ABEC 7 bearings arranged and pre-mounted inside a flanged housing.

[mactec54]

Jason

I agree with the 5300 series ball bearing can be used for electric motors, but not the 5200 angular contact bearing, they are not used in normal electric motors, you may have been selling them to motor repair shops, but they were not being used in electric motors

I used to do RD for SKF, I machined custom prototype bearings, & assembles for them, I know bearings & there limitations plus what can be used were, & these are a great fit for what he wants to do on a budget, If done right, there will be zero backlash plus they will last just as well as ABEC7 bearings, for a fraction of the cost, Plus much easer to setup

The 5300 series Radial self aligning A/C Ball Bearing is a totally different bearing to the double row A/C bearing

[Jason M]

Jason

I agree with the 5300 series ball bearing can be used for electric motors, but not the 5200 angular contact bearing, they are not used in normal electric motors, you may have been selling them to motor repair shops, but they were not being used in electric motors

...

The 5300 series Radial self aligning A/C Ball Bearing is a totally different bearing to the double row A/C bearing

You may be right there, we sent few double rows to the motor shop, as far as I knew they just did rewinding and the like but this was a large refinery market, they may have been doing little sides here and there.

I never considered we were talking about self-aligning ball bearings at all.

I used to do RD for SKF, I machined custom prototype bearings, & assembles for them, I know bearings & there limitations plus what can be used were, & these are a great fit for what he wants to do on a budget, If done right, there will be zero backlash plus they will last just as well as ABEC7 bearings, for a fraction of the cost, Plus much easer to setup

Well that's what the internet's best for right there, appreciate the info. If you know, or could find out, I'd like more info, the full part number or a catalog page that shows the engineering info (specifically related to the internal clearance) on the specific series you're talking about? I'm not sure I was ever exposed to the specific bearing you are talking about and now you've got me curious.

Did you have a sweet white lab coat @ SKF like in all their literature and training materials?!

[wizard]

I sold these bearing types (5200 and 5300 series ABEC3 standard RIC) to electric motor shops and a refinery for their pumps for 15 years, you'll definitely find them!

Could be a special purpose motor repair job. Not every motor out there is a NEMA device.

I understand the budget concerns and if you can take the slop in your application then you may as well save some dollars, sure.

If budget's not an option and precision is top priority you'll want ABEC 7 angular contact bearings or "ball screw support bearings" which are (usually) ABEC 7 bearings arranged and pre-mounted inside a flanged housing.

Interesting because I was under the impression that ball screw support bearings where a whole different series enhanced to handle thrust loads. At least the bearings I've seen marketed as ball screw supports where designed with a different contact angle and hefty races.

[mactec54]

I never considered we were talking about self-aligning ball bearings at all. Did you have a sweet white lab coat @ SKF like in all their literature and training materials?!

We were not talking about self-aligning Bearings, but when you put the 5300 number in there, these come in that series

As for lab coats, many places wear lab type coats, even quality machine shops do, But as for color white & Blue I had

[mactec54]

Interesting because I was under the impression that ball screw support bearings where a whole different series enhanced to handle thrust loads. At least the bearings I've seen marketed as ball screw supports where designed with a different contact angle and hefty races.

You are correct most CNC or any equipment with Ballscrews use very heavy duty thrust bearing, some are custom Made to what machine manufacture requires, they can cost any were from $800 up to thousands of dollars, just for 1 Bearing set

We are talking about a bearing that will do a good job, without the cost of a Custom Industrial Duty Bearing

The Bearings I have suggested are no comparison, but do a great job for what they are being used for

They come in different angles from 15deg to 40deg so can take the loading , the grade of bearing ABEC3 to ABEC5

When you are talking about clearance in a bearing, this is a none issue, with low cost angular contact bearings, Because if assembled correctly you will have zero clearance

This means your housing for the Bearing has to be machined correct & ridgid, Plus the method of preload has to be correct as well