Bearings for lathe build

[.RC.]

After seeing Evan's lathe build it has prompted me to start a project I have been thinking about for years....

I have a need for a small portable lathe to be used for repairing pump valves..These are made of brass and weigh no more then 1kg at the most..At the moment I have to bring them home to repair...Which isn't easy when the job might be 100km away...So I carry pre repaired valves and swap them over...If I come across something I don't have then I have to put them back in as it and put up with a reduced pumping rate...

I have the general design thought up but do not not know whether to use two angular contact bearings or two tapered rollers..Or what abec # precision to use...All I will have on the end is a four inch chuck so they do not have to be substantial.. The spindle will not be hollow but will have provision to apply preload to whatever type bearing is most suitable..

Also they have to be cheap as I have to buy them...So maybe something like $40 each would be what I am looking at.. Fully sealed angular contact (if available) would be preferable as then I do not need worry about some exotic lubrication system..

[barts]

Well.... what kind of tolerances are you trying to hold?
Are you going to turn the part, or turn the cutter?

My guess is that a pair of trailer tapered roller wheel bearings will work, though... less than $20 for the pair...

- Bart

[darryl]

I must be crazy to want to jump in here, but oh well. If you have followed the recent discussions about Evan's spindle bearing, you should probably have gotten the idea that a few different bearing types would be good enough, but that for a precision spindle with very low runout and consistent pre-load the proper bearing setup would be a pair of angular contact close together just behind the chuck, painstakingly fitted to a precision made spindle of stress-proof steel, etc, and a well fitted rear bearing that can allow for spindle growth with heat.

The fitting of the bearings in the headstock and on the spinde is every bit as important as the choice of bearings. If you're able to work with this much precision (and require it) then copy a good spindle design and obtain the specified bearings. It won't be cheap from all I've heard.

If your needs are more modest, my personal choice would be a pair of tapered roller bearings back to back at the front, with a means to set pre-load, and still with a rear bearing setup that can compensate for spindle growth. The spindle would be made from 4140 or 4340 so it could be turned to precision and not require heat treating. I would be looking for at least abec 5 bearings, 7 if I could find and afford them. You should be able to find a set of bearings and a suitable piece of steel for the spindle for about a hundred bucks. With a proper build, I would expect to get half-thou accuracy out of this, maybe as good as a few tenths. Not as good as what most 'real' lathes would give you, but consider the rest of the lathe- will it be good enough to repeat to a half thou- then consider how closely the valves need to be machined.

If your work need only be within a thou or so, you can probably get by with tapered roller wheel bearings, especially since you don't require a spindle through hole. I once built a spindle using these, and it was one bearing at each end, with adjustment on one end. I machined the taper in the spindle with it running in its own bearings, and I was able to get a final truing cut of only a few tenths that didn't keep re-cutting with subsequent spring passes. I'd say that's pretty good for cheap bearings, but then again that same bearing might be a piece of crap these days.

There you go- some muddy water for someone to stir-

[.RC.]

So long as it does not chatter and can make it flat enough so that the valves hold water at a few PSI...I was thinking along the lines of something a tiny bit better then just plain jane bearings...

[John Stevenson]

Do some research on what car front wheel bearings are available in your location.
Many of these have single sided seals on angular contacts, two of these back to back just as Darryl has quoted in his first paragraph will do fine.

With decent machining, fitting and adjustment these will get just as good a tolerance as any ABEC spec ones given the job in hand.

I am not going to quote any figures as they are meaninless in the real world and in real world applications.

Second choice would be two tapered rollers but these will need external seals although one each end of the spindle will do for that build up.

Don't believe what I say ?
Take a look here

http://www.miragemachines.com

ALL these machines run on off the shelf taper roller bearings,
Go to the page on line boring and you will see some examples.

One thing no one really mentions is that the back bearing of a preloaded pair has to be a sliding fit on the shaft, not press fit like the front one so that when you apply preload and back off it releases the bearing.

What you want to do isn't hard, it's been done many times before.

.

[.RC.]

Thanks for that Darryl...One of my lathes has a setup identical to what you described...Two opposed tapered rollers at the front and a plain ball bearing at the back...The tapered rollers are precision 3 grade (timken)..

Here is a valve I have done on my lathe at home

[Doc Nickel]

Just out of curiosity, why not buy a compact lathe off the shelf? You might need to make a special set of jaws or adapt a special chuck, but a little 7x10 could do that job handily. They run what, $400? And are light enough to load into a car or back seat with relative ease.

You say the issue is a special/unexpected situation, which sounds like a more general-purpose lathe would suit you better than a specialty homebrew lathe.

Now, that having been said, I once ran an indicator over a a truck spindle, with an eye towards making what was essentially a "speed lathe"- basically just a spindle, maybe with a short bed a single lever-actuated tool could be attached to.

Anyway, as I had a crateful of them, I got out a spindle and hub from the front axle of a mid-70s Chevy 4WD. I planned to bolt the hub rigidly, and attach the chuck to the spindle- backwards from how the truck uses it, but more like how a true lathe does it.

The bearings are fair sized, the smaller of the two being some 3" OD. The pair I tested were well-used, but not spalled/brinelled or otherwise damaged.

I found the spindle could be more than acceptably 'tight', with less than a thou of runout- or rather, motion as one pushed/pulled/wrenched on the spindle. Now, I didn't run it at high speeds- or at all, I never built the thing- so I may have had them too tight and they'd have overheated in use, I don't know.

But I wouldn't doubt that, for a specialty and occasional-use machine (IE, it never got more than an hour or so's work at a time) that sort of automotive opposed-tapered-roller setup would work fine.

Doc.

[Spin Doctor]

After seeing Evan's lathe build it has prompted me to start a project I have been thinking about for years....

I have a need for a small portable lathe to be used for repairing pump valves..These are made of brass and weigh no more then 1kg at the most..At the moment I have to bring them home to repair...Which isn't easy when the job might be 100km away...So I carry pre repaired valves and swap them over...If I come across something I don't have then I have to put them back in as it and put up with a reduced pumping rate...

I have the general design thought up but do not not know whether to use two angular contact bearings or two tapered rollers..Or what abec # precision to use...All I will have on the end is a four inch chuck so they do not have to be substantial.. The spindle will not be hollow but will have provision to apply preload to whatever type bearing is most suitable..

Also they have to be cheap as I have to buy them...So maybe something like $40 each would be what I am looking at.. Fully sealed angular contact (if available) would be preferable as then I do not need worry about some exotic lubrication system..

Fully sealed angular contacts? The only ones I am familiar with a FAGs and they ain't cheap. Tapered rollers(aka Timkens) at each end would be plentygood enough. Even without getting in to a can of worms Double Sealed at each end like the spindle bearing Evan is using would provide you with a means to provide pre-loading and a sealed bearing. Now here's a thought. What about using a small wood lathe as your machine base and come up with some sort of x-y cross slide. I am sure that some sort of pre-loading could be modified into the design, the bearings are already sealed, the lathe bed and "ways" are cast iron, it will have a tailstock and the motor is self contained.

[John Stevenson]

SD,
There are quite a few angular contacts that have a single sided seal, that's why i suggested looking for wheel bearings.

I'm sure the original Austin Morris Mini had these, they were definitely angular contact but I'm hazy about the seal.

There are others as I often get asked to press bearings out and new ones in for a couple of local garages on the press but I don't know for what vehicles.

[speedsport]

Why not just buy a minilathe? I dont see being able to make one cheaper than buying one. The minilathes are cheap portable and perfect for your need.

[miker]

Why so Complicated?

Just bolt the chuck onto one of the four wheel drives hubs, jack it off the ground. Bit of tree stump in front for a toolrest and away you go.

Gee Ringer, I thought you were a Cocky!!

Rgds

[jkilroy]

Why use roller element bearings at all? There have been countless lathes, mills, and all sorts of machines, made with bushings that have produced fantastic work, some for well over a century! You seem to have ready access to the raw materials in the form of those valves.

[topct]

The Taig lathe uses two off the shelf 6203zz bearings for its spindle. They are slightly loaded by using a simple spacer between the inner races. The headstock housing is split. While applying a small amount of pressure to the outside races when tightening the split housing, the bearing can be loaded.

If one where to just scale this system up to whatever size needed. It would work just as well.

One thing to consider is the use of rubber sealed bearings where the seal might be exposed to swarf. It could rip it out. The outside of a zz shielded bearing is steel.

[.RC.]

Thanks for all the advice everyone...Mini lathes down here are not cheap they usually start at around the $1000 mark...And small second hand lathes usually go for a similar amount plus I want to build this myself to get more epenis points on this forum ..

What I make will have to be man portable so I can lift it in and out of the cruiser. First I will see what shielded angular contacts I can find available..Making plain bearings is a bit out of my league...

Miker I did not think of that idea, but since it does not involve fencing wire in any way I am not sure if it will work

[Teenage_Machinist]

+1 on sleeve bearings which I believe to be availabe storebougt...

Though in land across the sea that may not be possible.


I do not see how hard it may be to make them... but I am without wisdom.


You might save weight by making it disassembleable. Maybe have the headstock come off easily and the motor removable. Use cone pulleys, easy and cheap.

Perhaps you could use big bar stock for the bed, and a dovetail bed perhaps. Or linear bearings. Head stock would be 2 blocks I shoud think and the motor should hold 3 or 4 step cones for speeds from 300 RPM or slower, might want one fast speed or a countershaft.