Brass bearings/bushings for Andra & Zwingenberger lathe

[rafau]

Hi!

I was wondering if it is possible to find replacement brass bearings/bushings for my A&Z lathe? I'm afraid the front one has got worn off a bit and will need replacing soon.

I took the headstock apart and put back together a bit more stiff and it should be fine for a while.

Do you know if these elements are available to get anywhere?

 

 

 

 

[oldhippy]

You could get the part made. 

[AndyHull]

If you can't find the part, you may be able to fix the existing one, but that might also open up a can of machining worms.

https://www.practicalmachinist.com/vb/general/lapping-phosphor-bronze-bushing-164839/

 

 

 

 

[measuretwice]

whats the shaft look like?   Is it the typical double taper bearing?  Sorry to be a downer, but I don't know that there is much you can do past the bearing take up which you're tried.  The shaft is likely worn so even if a part was available it likely won't mate properly.  The horse is already out of the barn, but that bearing is really dirty so its not a surprise its in trouble.  Those oil hole should be covered/capped to keep crude out.  A hydrodynamic bearing is essentially a non contact bearing, but only if clean and oiled. 

Lapping a taper requires you to carefully make and properly charge a lap - no loose abrasive!  Reason is that unlike lapping a cylinder where the laps moves back and forth through or over the work,  with a taper, the same place on the lap is always on the same place on the taper so loose abrasive will create rings and basically mess up the geometry.  With the lap as a charged cutting tool it can be done.

I've an abused Schaublin 70 hiding under the bench awaiting bearing work (same style double taper as a watchmakers lathe).  There is no more difficult thing to machine imo than two tapers perfectly mating to a small tolerance and high finish with everything perfectly concentric.  My plan is grind the shaft, lap the shaft (custom made laps) scrape the bearing (by hand) mount the bearing on the shaft and grind the bearing OD.  A big job.

 

Edited February 6, 2019 by measuretwice

[rafau]

Ahh.. Thanks for your responses. Yes, it's a typical one. I think I will give up messing about that bearing. The lathe looks nasty and abused without a doubt but I'm still able to turn balance staffs for pocket watches an winding stems for both pocket and wrist watches. I bought it two weeks ago since it was a real bargain for this machine and a chest of equipment. It will get cleaned soon and greased with proper oil. Unfortunately, the oil holes caps are missing. The bed, the headstock are solid mounted on the base and it all feels like a monolith :) The thing I'm worried about is that bearing, but as long as it works, it's ok if I can't replace it. If it gets out of use, I still have two other lathes :)

[measuretwice]

well if it works, that's something.   i'm usually the charge in and make parts and fix it sort, but doing these bearing arrangements properly presents challenges.   Many companies figured it out and 10's of thousands of lathes were made so its not exactly a moon launch, but still, the trick to it alludes me.  I suspect its something like a series of very precise custom laps, male and female.  A lap btw should never wear out - that is the properly charged variety vs the loose abrasive type.  So its conceivable that this is how its done, making the laps would be very challenging, but they laps would be an investment used to make 100's of lathes.  It would prohibitive to make a series of super precise male and female laps for one lathe.  I'd to love get to meet and discuss this with someone who knew how the lathe makers went about this.

Edited February 8, 2019 by measuretwice

[AndyHull]

Would it be possible to replace with a different bearing type?

I presume there is a reason why this type of bearing was used originally, but is there no modern alternative that could be used to substitute, even if it means sleeving up or skimming down the existing shaft, or packing the replacement bearing in some manner.

When all is said and done, we are simply trying to ensure a shaft rotates in a controlled manner and doesn't wander around, within certain lateral and longitudinal tolerances.

[measuretwice]

I'm all ears if you have suggestions, but I can't think of anything. 

Saying its just a shaft rotating is easy enough, but do get it to do so to the tolerances required and take both axial and radial load is far from trivial.  the double taper design is used so extensively because its just such a perfect solution.  Without a cylindrical grinder, you can't just skim the shaft down as its hardened (or it should be).  You could however stone out minor damage but you're not changing its overall form factor without a grinder.   The real change though is what to put in there for a bearing if not the double taper?   I don't know of another plain bearing arrangement that takes the thrust and radial force.  No rolling element bearings are remotely going have a small enough profile and even if they did, a $500 P4 set of angular contact bearings may not still have the low runout as a watchmakers lathe (and of course wouldn't fit anyway).

The only way I can see coming at  is as I'm thinking of doing for the Schaublin:  clean up the shaft and hand scrape a bearing to it.  It will be accurate, if done in the sequence I envision, buts its a fair bit work.  That I haven't thought of them hardly means there aren't other ways, but I haven't seen them yet and I've asking and questioning for awhile trying to come up with a plan for the sad Schuablin.  The OP says he has other lathes so perhaps that is a possibility.

This is also predicated on the objective being performance such s TIR that is good as typical watch lathe in good repair, which imo is a requirement. 

 

 

 

Edited February 8, 2019 by measuretwice

[nickelsilver]

On a bronze bearing machine like this the spindle probably has some scoring but a light stoning should be enough to get it serviceable. Then like measure says, its a scraping job. Doesn't even have to be perfect, just pretty good and it'll be running true as new, maybe a reduced service life, like 10,000 hours instead of 25-30,000.