[philbur]

Hi Ian, Do you have a reference for preloaded double row angular contact bearings. I am struggling to find any sources. Here is SKF online details regarding their DRAC bearings. They make many references to internal clearance but no reference to preload?

Double row angular contact ball bearings - SKF.com / Products / Interactive Engineering Catalogue/Rolling bearings

Phil

Looking at the bearing maufacturers catalogue and the sealed double row A/C bearing package set-up with manufacturer preload set at the factory

[handlewanker]

Hi Phil, the preload as required is assumed according to the SKF cat specs, the double row A/C with split inner ring (preload predetermined to work with the designed load carrying capacity) does not specify the preload figures as they would be meaningless, (to all but the SKF design team)...IE you can't measure them, but you can design using the preset preload that will satisfy the design characteristics as laid down in the table for load carrying and speed capabilities.....more you do not need...as in...what would you use the figures for if'n the factory specs indicated a preload figure....and more important still, as the preload is not variable, you must apply the figures for loading according to the needs of the spindle design, that is....don't design a pet theory for a spindle requirement with speed needs of 20,000 rpm when the bearing arrangement is only capable of 10,000 max.

In the majority of cases, the speed is the most important factor that will decide if'n the spindle design will fail or survive.

In the majority of cases the load carrying capacity of an A/C bearing set-up of even the most basic of designs will never be exceeded by the loads a CNC situation would impose to the spindle in the radial plane, and to a much lesser degree in the axial plane...unless you intended using the spindle for heavy drilling, in which case you would not be rotating at extremely high speed, and the aspect of preload for heavy one way drilling is not important......horses for courses etc.

The most the DIY design "expert" can achieve is to apply the bearing layout to a conventional bearing configuration, for when all things are equal the simplest solution is always the best.....KISS......unless the situation warrants it...why be different just for difference sake?

The difference between the double row A/C with split and solid inner race is that the split inner race type allows you to assemble them to the shaft after the outer race, balls and cages are assembled, for whatever reason you need that design, but both when finally assembled have a preload that is factory determined.

So, my view is...do not go looking for specifications that will not be of any practical use.

In the design by Cris in post #1, the bearing layout is specified (by him) to be the double row A/C type with solid inner race....built in sealing would be necessary to simplify lube requirements and maintenance free life, and as no added preload is needed that saves some money too.
Ian.

[arizonavideo]

I have 5 double row AC bearing here and all have around .0015" of end play.

They were not OK for ballscrew supports, preload or zero clearance is necessary.

Preload can be specified for a bearing or liner rail.

This is the preload chart for some liner rails.

Hiwin linear bearing preload classifications

If the double row AC talked about in the first post has some preload and is made for spindle use it would be of great use to many to throw together a nice second spindle or rotary table or the like. That is why I asked for the specifications because I have not seen them before.

The bearing is either pre loaded or it will have slop when in use as a spindle bearing.

If pre loaded it will be stated in the specification.

If not stated it will have slop.

[philbur]

Hi Phil, the preload as required is assumed according to the SKF cat specs, the double row A/C with split inner ring (preload predetermined to work with the designed load carrying capacity) does not specify the preload figures as they would be meaningless, (to all but the SKF design team)...IE you can't measure them, but you can design using the preset preload that will satisfy the design characteristics as laid down in the table for load carrying and speed capabilities.....more you do not need...as in...what would you use the figures for if'n the factory specs indicated a preload figure....and more important still, as the preload is not variable, you must apply the figures for loading according to the needs of the spindle design, that is....don't design a pet theory for a spindle requirement with speed needs of 20,000 rpm when the bearing arrangement is only capable of 10,000 max..

Hi Ian. I'm not sure what the significance of an SKF cat spec is, it seems to relate to linear actuators? Bearing manufacturers always provide numbers for bearings that have factory set preload/clearance, for metric the numbers are in µm and are useful, even to the hobby builder of machine tool spindles. Can you show me a link that explains how to order a double row angular contact bearing with preload as opposed to clearance. How would I specify light medium or heavy preload. This SKF link seems only to talk about the designation of clearance:

Double row angular contact ball bearings - SKF.com / Products / Interactive Engineering Catalogue/Rolling bearings

The difference between the double row A/C with split and solid inner race is that the split inner race type allows you to assemble them to the shaft after the outer race, balls and cages are assembled, for whatever reason you need that design, but both when finally assembled have a preload that is factory determined.

SKF says: .... double row angular contact ball bearings are also available with a two-piece inner ring. These bearings incorporate a large number of large balls and have a high load carrying capacity, especially in the axial direction.... This in part seems to be due to the absence of filling slots.

For those interested here is SKF's online information regarding preload:

Preload - SKF.com / Products / Interactive Engineering Catalogue/High-/super-precision bearings

Phil

[RICHARD ZASTROW]

arizonavideo, there are double row angular contact ball bearings of more than one design. Look in the catalogs to define which one your looking at. The 5200 series are not preloaded, they have axial clearance as you describe.

The split race types can be made with preload (normal) or with clearance (not normal and probably not readily available).

Dick Z

[ihavenofish]

I have 5 double row AC bearing here and all have around .0015" of end play.

They were not OK for ballscrew supports, preload or zero clearance is necessary.

Preload can be specified for a bearing or liner rail.

This is the preload chart for some liner rails.

Hiwin linear bearing preload classifications

If the double row AC talked about in the first post has some preload and is made for spindle use it would be of great use to many to throw together a nice second spindle or rotary table or the like. That is why I asked for the specifications because I have not seen them before.

The bearing is either pre loaded or it will have slop when in use as a spindle bearing.

If pre loaded it will be stated in the specification.

If not stated it will have slop.

yeah, you cant just grap any bearing off ebay and hope for the best, you need to order the right one. the double row ac's on my ball screw are from nsk, specifically for the task.

[philbur]

As far as I can see in both SKF and NSK catalogs, double row angular contact bearings with or without a split inner ring come with clearance values only. Nowhere can I find preload as an option. If somebody knows how to order this bearing type with factory set preload could they please post it, because at the moment the manufacturers are doing a very good job of hiding it.

Phil

arizonavideo, there are double row angular contact ball bearings of more than one design. Look in the catalogs to define which one your looking at. The 5200 series are not preloaded, they have axial clearance as you describe.

The split race types can be made with preload (normal) or with clearance (not normal and probably not readily available).

Dick Z

[philbur]

That's as maybe, but it doesn't necessarily mean they have any factory set preload.

Phil

yeah, you cant just grap any bearing off ebay and hope for the best, you need to order the right one. the double row ac's on my ball screw are from nsk, specifically for the task.

[RICHARD ZASTROW]

The whole discussion/problem can be solved easily and relatively inexpensive by simply using a pair of sealed angular contact bearings of whatever contact angle, quality level and preload you want.

This is a proven and commonly utilized arrangement. Why reinvent the wheel? Unless you just like to argue (or be a troll)?

Dick Z

[handlewanker]

Hi Phil, in the SKF cat, specs for the double row A/C bearing with split inner race state that there is a clearance, but do not mention the term "preload"......this could interpret that with a split inner race and clearance (between the faces) when you fit to a spindle and secure the inner races by a screwed collar you will take up this clearance....applying a loading against the two inner races.......unless you are able to gauge the force applied by the screwed collar you will either get a bearing that runs loose or with a fully tightened up collar one that is under a preload condition.......without being able to measure the loading application, but I think it is hit and miss, unless it is left to the assembler to tighten the collar progressively until the bearing runs without getting hot or rattleing.

However, it would also seem that the split inner race is a design purely to allow dismantling the bearing inner races for assembly seperately to the shaft once it is inserted into the bearing outer shell, ball and cage assembly, a purpose I can't see the reason for, and in the illustration of the split inner race bearing the "clearance is shown to be a distance dimension from the inner race face to the outer race face...puzzling.

I would assume that the double row A/C with single inner race and having clearance, means that the inner race is able to move axially at a certain rate.....possibly not designed with the intention of preload spindle requirements in mind.

Personally, if this is the case in both designs, ie no preload as a design spec, I would definately not be using this type of bearing set for a mill spindle......which is a pity 'cos it seems such a neat package, especially as it also comes with seals too.

As a matter of interest, it would be no great deal to....and here I am suggesting complete heresy....surface grind .02mm off the face of ONE of the inner races which will bring them together and...voila...we have a preload.....monitored by testing the running temperature of the spindle after assembly.....adding a shim if'n you overdo it.

On a regular pair of A/C bearings, I once added a .02mm thick shim to the outer race faces, (cups facing outwards) as they were a pair of odd unmatched bearings I had acquired, and the bearing ran hot after 5 minutes.....even an unmatched pair were a good match in the unshimmed condition, and in the unshimmed condition have been in service for over 10 years now.

So there you have it....a variable double row A/C bearing with split inner races and seals....what more do you want?

I would assume that if'n the need arose for a preloded A/C bearing set up, SKF et al would suggest a matched pair of regular single row A/C bearings in O or X configuration.....however it wouldn't take much to rub the inner race face on one side down on wet and dry paper in the double row bearing set to make them preload as required......more heresy....it would be simpler to use 2 A/C's.
Ian.

[ihavenofish]

That's as maybe, but it doesn't necessarily mean they have any factory set preload.

Phil

its not a maybe, its a fact. they are preloaded if you ask for them to be, period. now stop being a twat and go harrass another thread.

[philbur]

There have been an awful lot of unsupported claims made in this thread. If challenging some of those claims makes me a Troll then I am happy with that categorisation. I leave others to categorise those that are unable to support their claims with any credible references.

Phil

[philbur]

So tell me the correct designation for a double row angular contact bearing with preload so I can ask for one?

Repeatedly insulting somebody who challenges your unsubstantiated statements adds nothing to the thread.

Phil

its not a maybe, its a fact. they are preloaded if you ask for them to be, period. now stop being a twat and go harrass another thread.

[handlewanker]

Hi, If'n the cat doesn't give a bearing type no. to specify when ordering that's a bit offputting......if'n you find out from SKF et al how to order in the preloaded state, post the results, it's probably in the nature of a special order etc.

When a standard bearing arrangement becomes a special order, it probably means the special order is catered for by their standard range.....IE the double row A/C bearing can be ordered with degrees of clearance, (not sure what for), but that is an "off the shelf" scenario and price will reflect accordingly by mass manufacture techniques, but when the same bearing type becomes a "special" it might be dearer than the paired A/C set that it's supposed to replace.

You could always just order the standard split inner race double row A/C set and "adjust" the arrangement to give a preload etc etc, we are after all a bunch of inquisitive experimenters at heart, and the "nothing ventured nothing gained" scenario would apply.

I have no idea of the price difference of the double row A/C bearing with split inner race compared to a regular normal tolerance pair of single row A/C bearings, so the difference might be minimal and the effort to mess around too much.

You know where you are with a tried and trusted bearing design using matched pairs of A/C's etc, so there's no point in reinventing the wheel just to be different......the problem arises when you want to up the speed without adding to the cost for specials etc.

This thread has reinforced my faith in the spindle design with the matched paired A/C bottom end bearing set, but for the top I'm still laying my money on a single row, (possibly double row) sealed radial bearing for the sheer simplicity and trouble free running, but I am also now looking at a roller bearing for the top so that the races can be secured to spindle and housing respectively, and the movement for expansion can take place within the bearing, and I hope the type is also available with integral seals.
Ian.

[packrat]

This thread has reinforced my faith in the spindle design with the matched paired A/C bottom end bearing set, but for the top I'm still laying my money on a single row, (possibly double row) sealed radial bearing for the sheer simplicity and trouble free running, but I am also now looking at a roller bearing for the top so that the races can be secured to spindle and housing respectively, and the movement for expansion can take place within the bearing, and I hope the type is also available with integral seals.
Ian.

It has worked for BridgePort for a long, long time. Go for it

[handlewanker]

I get a warm glow when something I think and want to do is the way it's been done before....sometimes it doesn't pay to stray too far from your box just to see what's round the corner.....if'n Bridgeport found it to be good, who'm I to argue against that logic.

In Cris's case he is designing for a purpose, not to make a Bridgeport lookalike spindle, but to make something that will apply the same principles of spindle support as a Bridgeport, but tailor it for DIY use with materials off the shelf.

It would appear that the jury is still out on the aspect that the double row A/C bearing package has preload or not, which makes it a "no go" for any spindle design that would be suitable for a milling operation and definately needs to be preloaded.

In actual fact, cost aside, it does not involve any more or less machining to fit two A/C bearings in place of the double row A/C set.

There still needs to be a machined housing with bearing cap to retain the outer race/s and a spindle with a retaining nut behind the inner race, and a seal system to suit.

I would not suscribe to a press fit for the bearing outer race/s in the housing, or a press fit for the inner races on the spindle....this would be counterproductive to assembly and maintenance.....so standard pracice for bearing fits in these areas are already established.

That just leaves the cost of a single double row or twin seperate bearing package to sway the argument.

Where the argument gets thin is when the spindle, being for CNC, would like to be used with a high speed aspect as the prime reason for making it.
Ian.

[Chrisjh]

Hi All,
Sorry to be absent so long. I received the dreaded phone call. Someone wanted me to come back to manage some technology transfer between continents. I am supposed to be retired and I don’t know what they will do when I kick the bucket.

I also had a disaster with my CNC lathe. I broke the Z Axis ball screw. Entirely my fault, I had under designed the section where the bearing retaining nut threaded area is undercut at the driven end. Happily I have recovered and the lathe is working again. It will never break again!!!

Recently I haven’t had time to devote to my spindle design. I actually concluded that, for purists, 2 Angular Bearings back to back with a preload nut is the best way forward and have come up with design to this objective. I actually completed the 3D model for this before the phone call. It took me some effort today to revisit and understand what I had done.

I was trying to avoid cutting an external thread for the preload nut on the spindle but relented.

I have a CNC lathe so I can cut threads, internal and external. See video here: [ame=http://www.youtube.com/watch?v=B63tuYJB44E]Using Mach3 to Cut an Internal Thread - YouTube[/ame]

The good news is that I have found a company in Melbourne who specialize in hardening and received some excellent advice from them. I have now decided to use 4140 steel for the spindle and get the tapered section selectively hardened using a plasma nitriding process. The cost is pleasantly low. They gave me a budgetary quote of $5 AUD per kilo for plasma nitriding but have a minimum charge around $40. I thought that this was very good.

As has been suggested, I think that, for hobbyists who can tolerate a small amount of clearance, a single double row angular bearing would be sufficient. Perhaps I can create a 2nd lower cost design using this approach later on.

Regards
Chrisjh

[philbur]

Have you considered the risk of distortion caused by nitriding.

Phil

[Chrisjh]

My understanding is that plasma nitriding presents a low risk of distortion due to the relatively low temperatures involved. Google "Plasma Nitriding" for more info.

Regards

Chrisjh

[philbur]

You have to consider the context. Distortion related to general engineering or distortion related to precision engineering. Are commercial made precision spindles nitrided, if not why not.

Google for more information.

Phil

My understanding is that plasma nitriding presents a low risk of distortion due to the relatively low temperatures involved. Google "Plasma Nitriding" for more info.

Regards

Chrisjh