[htrantx]

Before I write off the use of double-row angular contact (DRAC) bearings in a project, I would like to check with gurus in here first.

A standard DRAC bearing does not have internal pre-load, so an external pre-load will render one row useless with its alpha facing the wrong way. I am correct?

Does "pre-loaded" DRAC bearing exist?

ht

[samco]

I thought most car wheel bearings where like this. (newer than about 1985 - guess)

sam

[HuFlungDung]

I don't see a specification for preload in my FAG book, but that does not mean they are loose, either

I think the idea of the DRAC is a space saving design that is simple to mount (no adjustment nuts needed) and will carry thrust in either direction. However, it may not be the best choice in a precision application, like an accurate spindle or a ballscrew thrust application, where you need to be able to tweak the axial movement to zero.

[samco]

These look the they get pre-loaded when tighted down.

http://www.hiana-bearings.com/automo...l_bearings.htm

[samco]

these say internal preload
http://www.bardenbearings.com/cd_doubl.htm

sam

[RICHARD ZASTROW]

htrantx; Ref. your post #1

SKF series 2344 & BTM-A (30 deg. contact angle) & MTM-B (40 deg. contact angle)

These are intended for axial/thrust applications not radial.

Dick Z

[htrantx]

Sam & Dick Z, thanks, and too bad that they are >20 Deg

I have found pre-loaded DAC bearings specifically designed for spindles and ball screws at:

http://www.ukf.de/english/index.html?&vonhier=0

The bearings also look like were designed for wearing on the neck with a thick gold chains... or at least the prices are (ABEC7 and up).

In the spindle section of their site, they have an example of a spindle design with 4 single row AC bearings arranged as \\ // and pre-loaded from two ends. Even with ABEC7s I would think two out of 4 bearings might be out of the pre-loading at a time. The alphas might be like |\/|,\|/|,|\|/,\||/, or perhaps I didn't understand the real pre-loading in this design.

Was this an example of 4 should be better than 2 design?

ht

[SCzEngrgGroup]

Sam & Dick Z, thanks, and too bad that they are >20 Deg

I have found pre-loaded DAC bearings specifically designed for spindles and ball screws at:

http://www.ukf.de/english/index.html?&vonhier=0

The bearings also look like were designed for wearing on the neck with a thick gold chains... or at least the prices are (ABEC7 and up).

In the spindle section of their site, they have an example of a spindle design with 4 single row AC bearings arranged as \\ // and pre-loaded from two ends. Even with ABEC7s I would think two out of 4 bearings might be out of the pre-loading at a time. The alphas might be like |\/|,\|/|,|\|/,\||/, or perhaps I didn't understand the real pre-loading in this design.

Was this an example of 4 should be better than 2 design?

ht

Precision AC bearings will be sold in pairs, or quads, which are individually custom ground so as to achieve perfect pre-load when rigidly fastened together with their "mates". With a single pair of unmatched bearings, you have to either shim and/or control the pre-load by how tightly you clamp them together. With two pairs of bearing, as you indicated, without the custom grinding, you'd have to shim them to get them all properly pre-loaded.

Regards,
Ray L.

Regards,
Ray L.

[htrantx]

Precision AC bearings will be sold in pairs, or quads, which are individually custom ground so as to achieve perfect pre-load when rigidly fastened together with their "mates". With a single pair of unmatched bearings, you have to either shim and/or control the pre-load by how tightly you clamp them together. With two pairs of bearing, as you indicated, without the custom grinding, you'd have to shim them to get them all properly pre-loaded.

Regards,
Ray L.

Regards,
Ray L.

Good point; I thought match pair should be /\ or \/, but never thought of a // match pair or a \\// match quad. Now I understand the pre-loading of the design.

Thanks,

ht

[RICHARD ZASTROW]

There are also "universal" sets which can be positioned in any direction within the set.

AC bearings must be opposed. They can be back to back duplex (DB), face to face (DF), tandem or a pair in the same direction (DT) usually opposed by another pair.

Then there are also DBT, DBD, DBQ, DBTT, DBTD & DBTQ for triples, quads etc.

This is well explained in the engineering section of the Barden precision bearings catalog (mine is C-20)

If all else fails, read the instructions (book) LOL

Dick Z

Hu, my FAG book only mentions "the contact angle and axial preload ensures good ball control" etc. not whether it's light, medium, heavy, or ????????? I TAKE THAT BACK, THEY ACTUALLY LIST THE PRELOADING FORCE IN NEWTONS

[RICHARD ZASTROW]

htrantx, just a reminder. DRAC bearings are designed as double direction axial thrust bearings. If you include them in a bearing "pack", the other bearings need to be only radial bearings such as roller bearings.

In fact, that's the combo they're designed for.

Dick Z

[handlewanker]

Hi, the DRAC bearings I've worked with had the outer races split and this meant the inner race was fixed to the shaft and the outer races were pressed together by the housing covers, similar to the paired angular contact bearing arrangement in the Bridgeport mill spindle,except the bearing has the shell cups facing inwards towards each other.
Ian.