haha, thank you for the generous compliments!! I'm not an engineer, only play one on the internet, but work with them all day, have an engineering business of sorts, have been machining for 30 years and have pursued and written extensively on reconditioning machine tools. So the subject is near and dear and has had me puzzling over it for some time. Always hoping these muses smoke out the silver bullet to this problem....because I don't have it.... here's why.....
Pooched is a technical term meaning "%$#F%^$, why did I ever think I could fix this" or in other words its scrap.
I'm not adverse to trying the time saver, kind of the of farmer's kill or cure approach to a very sick animal. Can't make it any worse.....however, lapping tapers with a taper is verboten in the mechanical and machine work world. No one would do so because it creates rings and ridges vs nice straight lines to the taper's cross section profile. The lap must travel across the work surface so there is averaging....that doesn't happen with a taper as it can't move in and out. The laps or grinding points used in a taper's manufacture are cylindrical and held at an angle to the the work, so they are played in and out and hence work very well. That is the objection to lapping a taper with a taper. Also, lapping is almost always done with a lap, vs work on work. This gives you control, its a bit shade tree (a bad thing, but this side of pooched) lapping work on work.
In my opinion, the double or biconical taper is the most challenging of machining jobs. It is about impossible to do without special fixturers to machine and measure it. Why? How do you know where a taper is along a shaft? Short of a CMM, you need to put a precision ball in it and measure its distance from the end. That holds it own challenges while the work is mounted in the lathe, now do so with two tapers. Then do so with the mating part also with two tapers, male this time so the ball thing doesn't work, and after it all it has to end up sub thou mating! And the two tapers are so different, a tenth of a thou difference laterally along one = a thou on the other other. Enough to drive a man to drink.
It is an amazing well engineered bearing that easily lasts 100 years or more....until some meat head runs it without oil. Bare bones lathes are cheap enough, if the headstock bearings are "pooched", get another one. There is no way I'm aware of rectify this in workman like manner, i.e. bring it back to its intended performance and life span with committing any sins. Garnet lapping (timesavers) MAY make is usable but all you are doing is rounding off corners and creating a bit of slop. May do so and use a thicker oil? Still, its in the catatory of a dodge than might work vs a way to fix these bearings (and no grief from me for trying).
Here's a fairly detailed account, although only 90% complete, of my spindle reconditioning (and everything else) of a a plane bearing Schaublin 70. It has the distinct advantage that I could use bronze, and that it was big enough to scrape the bearing (no fun at all in non-split beating, let me tell you!). Look in the Headstock chapter.
Reconditioning a Schaublin 70 Return to Projects Intro With our North American approach to things, satisfying the masses is what drives most activity. In business, and in engineering, the expression “good enough, is, good enough” is quite correct. Making it better than it needs to be just...
There, after machining the bearing and regrinding the shaft, I scraped the bearing using this shaft as a pattern. Very difficult, weeks of tedium weakening the resolve. As a final step I did use some of the finest yellow timesaver (for soft material). This worked because it had no effect on the hardned steel shaft and was so fine it just knocked the worst of the high points off the brozne. You don't have the dynamic or possibility of that with a watchmakers lathe where both bearing and steel are the same hardness.
Who wants to go through that or has time, equipment and ablity? I did end up with factory new performance, but I won't do it again. Its not worth it. Yet thats what it took, and that was much easier (for reasons noted above) than a watchmakers lathe.
What would be a lot less work is 1) buy another bare bones lathe or 2) mimic a Levin lathe and simply make a new headstock using P4 AC's, the old spindle shaft and a block of durabar (cast iron). FAR easiler than what I did to the Schaublin. Use the old spindle. loctite some steel in place and grind to fit the AC's. Fit a block of durabar and scrape into alignment with the tailstock. Not a weekend's work, but a far more realistic project than repairing damage double taper hardened steel bearings. Lets you use the hardened spindle and drawbar, which would be the tougher bits to make
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