[inthebay]

Hey folks,

Firstly, I read the stickies in this subforum and it did answer a few questions, but I'm still questioning some of my ideas at the moment.

Here's the situation: I was getting around .0035" backlash in my X axis on my G0704 with C4 ballscrews. After adjusting gibs, and checking everything external, I decided to tear it apart and give it a clean and lap while I was at it.

In the midst of doing this, through my own error, I bent my X axis ballscrew (dont ask). So, I'm looking for a replacement as we speak.

In the meantime, I determined that the stock bearing support setup for the ballscrew was where my backlash was coming from, as such, I have ordered some new bearings for it. Specifically:

3x 5200-2RS Bearing Angular Contact Sealed 10x30x14.3
3x 51200 Thrust Bearing 10x26x11

I'm trying to decide on what the correct arrangement is for both the fixed end and the floating end of my ballscrew. Here's what I'm thinking at the moment for the fixed end

Attachment 313324

This way the axial forces are loaded onto the thrust washer, and the radial forces are supported by the double row bearing.

Is this overkill? Should I only have one double row bearing and call it a day?

As for the floating end, I was thinking just a double row bearing on its own and a nut for preload. Any other advice there?

Thank you!

[louieatienza]

There are a few different configurations, the most common I know of is with two AC bearings, with the "open" ends facing each other, so that they take both thrust and axial load. No thrust bearing is needed. You may need spacers to adjust the preload.

On the free end a single row bearing should be fine, usually held with a circlip, and the bearing allowed to "float" in its housing to allow for expansion of the screw.

[inthebay]

Open ends facing eachother, sandwiched together kinda like (nut) > (endplate) < /-/-/-/-/-/-/-/-/ Ballscrew

Where the > and < are the direction of the angular contact bearings.

When you say float in the housing, do you mean in the axial direction (so the screw would expand and slide on the inner race). Or in the radial direction, so overbore the pocket and let the screw slide around on the outer race. That doesnt make much sense to me but I have to ask.

Thanks for your view!

[mactec54]

Open ends facing eachother, sandwiched together kinda like (nut) > (endplate) < /-/-/-/-/-/-/-/-/ Ballscrew

Where the > and < are the direction of the angular contact bearings.

When you say float in the housing, do you mean in the axial direction (so the screw would expand and slide on the inner race). Or in the radial direction, so overbore the pocket and let the screw slide around on the outer race. That doesnt make much sense to me but I have to ask.

Thanks for your view!

This Bearing arrangement can work, though it is not ideal, They should be Back to Back for the best loading, you can also use just (1 ) Bearing which is a double row Ac bearing, these are non adjustable, and usually have no more the .0005 Backlash

You also need to have the bearing in a housing that has the the correct depth for the bearing to do it's job, Photo is a ( 1 ) piece 2 Row Ac Bearing

[louieatienza]

Open ends facing eachother, sandwiched together kinda like (nut) > (endplate) < /-/-/-/-/-/-/-/-/ Ballscrew

Where the > and < are the direction of the angular contact bearings.

When you say float in the housing, do you mean in the axial direction (so the screw would expand and slide on the inner race). Or in the radial direction, so overbore the pocket and let the screw slide around on the outer race. That doesnt make much sense to me but I have to ask.

Thanks for your view!

Yes it's that contact pressure angle of the ball races that take up both axial and radial play, and determines the load rating of the assembly. Imagine an "X" formed by the opposite angled outer races. The wider the "X", the higher the load rating (this would require spacers to get the proper angle as specd by the bearing set). For light duty work, the open ends re sometimes faced away from each other, which narrows said "X" decreasing it's axial load capacity. In the fixed end bearing housing, a thin spacer may be needed between the two inner races to obtain the preload necessary.

On the "free" end, radial ball bearing inner race is seated against the shoulder of the journal of the ballscrew and kept in place with a circlip (hence the groove at the free end.) The fit in the free end bearing block is more of a slip fit, as to not allow play in the radial direction. This is because the "fixed" end takes all the axial load.

On very light axial loads, sometimes two radial BBs are used, very lightly preloaded/

[louieatienza]

Take a look here at THKs website:

THK Store-BK

And NSK's

NSK_CAT_E3162D_2014_Z-8_SUMT PDF download | NSK Global
NSK_CAT_E3162D_2014_Z-8_SUSMALL PDF download | NSK Global

[mactec54]

Take a look here at THKs website:

Not much point looking at those Ac Thrust Bearings, unless he has a spare $800 Plus per set, most hobby users spend from $6 to $40 for the Bearing sets they need, and they are not matched pairs or precision Like what you have posted in the THK catalog

It's a whole different thing to use cheap Bearings, and how to use them effectively, to get the most out of them, everything that is the right way to do it, get's thrown out the window, when they can only use cheap Bearings

Most that have these machines are using a 2 Row sealed Ac Bearing, a $35 Bearing for the fixed end

[louieatienza]

Not much point looking at those Ac Thrust Bearings, unless he has a spare $800 Plus per set, most hobby users spend from $6 to $40 for the Bearing sets they need, and they are not matched pairs or precision Like what you have posted in the THK catalog

It's a whole different thing to use cheap Bearings, and how to use them effectively, to get the most out of them, everything that is the right way to do it, get's thrown out the window, when they can only use cheap Bearings

Most that have these machines are using a 2 Row sealed Ac Bearing, a $35 Bearing for the fixed end

For God's sake, I posted these to show the orientation of the bearings, not for purchase. Why is it different for less expensive bearings?

[mactec54]

For God's sake, I posted these to show the orientation of the bearings, not for purchase. Why is it different for less expensive bearings?

Because the Bearings are not anywhere near the same that are being used in those illustrations/drawings, these Bearing also so have much higher angle of contact, they just don't compare, to standard Ac Bearing, so you have to be creative to use the cheap Bearings, to make them work, to be of any use, the cheaper Bearings have to be orientated Back to Back, not as they are in the Drawings you posted, the best for these guys is the ( 1 ) piece 2 Row AC Bearing, these are a Back to Back configuration, and they work very well for a machine like this

[mactec54]

inthebay

We did not answer your question

Yes you can use a ( 2 ) 2 Row Ac Bearing one on each end of your screw, you can then add a slight Preload ( 4lbs to10 lbs ) with a Nut and spacer on each end of the screw

The Bearings 10x30 Part # 5200-2NSL,Nachi is one of the better quality Bearings in this type, this is if your shaft is 10mm at each end

[inthebay]

Excellent, thank you all for your comments. I'm glad to see that the double row bearings will not need to be shimmed in order to function correctly. This should make installation a breeze.