Bearing race nomenclature

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BadDog
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Re: Bearing race nomenclature

Post by BadDog »

Looks like my last hopeful lead didn't pan out.

I was doing a bit of reading on 17-4 PH hardening for H-900, and it looks relatively straight forward. 900*F (+/- 10*) for 1 hour with no post treatment required. The surprising thing is that's the hardest it gets. Hotter and/or longer changes other properties, but it gets softer. Looks like the only thing left to figure out is how to get 1 hour of time on a 900* oven.
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Bill Shields
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Re: Bearing race nomenclature

Post by Bill Shields »

Send it to a heat treating service...giggle
Too many things going on to bother listing them.
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Harold_V
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Re: Bearing race nomenclature

Post by Harold_V »

While it's not even remotely related to your project, I used 17-4 for the item shown, below. It's the auger for a wheat grinder. I converted an old foreign made hand grinder so it could be powered by my lathe. You can see how 17-4 looks after heat treat. Discolored rather uniformly, and pretty much non-existent scale.

H
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rrnut-2
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Re: Bearing race nomenclature

Post by rrnut-2 »

We heat treated 17-4 in a vacuum furnace and it came out looking different than Harold's picture. :D
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Harold_V
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Re: Bearing race nomenclature

Post by Harold_V »

Yep! It would. I suspect the color is attributed to the slight oxidation of the chromium contained in the alloy.

Industrial heat treat furnaces often balance the atmosphere by simply introducing excess gas (not electric furnaces, needless to say), which would also most likely yield less color. Probably a gray surface. Dunno.

The beauty of this material, aside from its strength, is the ability to heat treat without fear of distortion and oxidation that alters size and surface finish. It is often looked upon as a replacement for chrome-moly.

H
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BadDog
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Re: Bearing race nomenclature

Post by BadDog »

Very nice. And thanks again.
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Re: Bearing race nomenclature

Post by rrnut-2 »

Industrial electric furnaces will induce a color change as well. The exothermic atmosphere contains methanol, nitrogen and for added carbon, propane.

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BadDog
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Re: Bearing race nomenclature

Post by BadDog »

I now have in my possession a stick of 2" 17-4 annealed.

Now I have to make races out of it. I first was thinking, no problem, I'll just grind a form tool. Then I realized I had overlooked a few things.
  • I've never turned this before. As typical of internet content, I found a few saying machining annealed is miserable, but the general consensus seems to be that it machines very nicely. But I couldn't find any information on form tool geometry, and not having fooled with it before, I thought I would ask here rather than experiment with fiddly form tools and expensive material.
    • Rake?
    • Chip breaker?
    • Being stainless, how bad is work hardening?
    • M2/Cobalt blank?
    • Other?
  • While pondering the making of a 1/4" round form tool, I realized I'm also making a ball race for the first time. And that any deviation on the form tool from near perfect dimensions is going to create substantial localized pressure points when 1/4" bb are rolling along (or sitting still) under load
    • How sensitive will this application be for 17-4 H900?
    • Will it be brittle? Prone to cracks due to imperfect profile?
    • Will it displace slightly to form a good profile, perhaps with a little surface work hardening?
Anything else I haven't considered? Now that I'm focused on the profile problem (obviously a bit late) related to ball point of contact, I'm a bit worried I've bitten off more than I can chew. I know this will cause Harold's blood pressure to spike :D but I was considering getting an insert to hopefully provide a more exact profile than I'm likely to get hand grinding a 1/4" blank. Turns out 1/4" round inserts aren't readily available anyway, so back to HSS.

Regarding profile, I've also considered taking a HSS round 1/4" blank and making a holder somewhat like folks use for "tangential" tools. But presenting it actually tangential to the circumference so that the result is actually round matching the blank. Depending on rake/breaker, the top could be carefully dished a bit with a die grinder ball. Or maybe in the lathe. Rough it with some convenient tool, then bring it to size/finish with the round bit, assuming work hardening characteristics allow light cuts...
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BadDog
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Re: Bearing race nomenclature

Post by BadDog »

I went back and re-read earlier posts more carefully and found the answers to some of my questions (mainly the first point/question). The answers are mostly in Harold's post Apr 15, 2021 1:32 pm. As so often the case, he foresaw what I would be asking and provided the answers preemptively, I just forgot, and managed to miss when I quickly reskimmed for review.

I don't see (here or on general searches) answers to the other questions, which mostly center around realities/details of making a good ball bearing race.

Any further thoughts on any point are much appreciated.
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Harold_V
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Re: Bearing race nomenclature

Post by Harold_V »

HSS is available in rounds. You'd be best served, assuming the radius is critical, to use one of them as you suggested. I'd pursue that avenue were the project mine.
17-4 is tough. It is NOT hard. That's not to say it is free machining. It is not. However, if you work with sharp tools and reasonable positive rake, it cuts surprisingly well, and offers one thing many materials do not. It leaves a respectable finish. It may or may not respond well to a form tool. I had no issues when I created that 3 pitch auger, though. It responds very best to light cuts, and does not horse well. Even in the H900 condition it can be machined, but it's not fun or easy. In that condition it's very hard on cutting tools, as you might imagine.

One thing to consider. When you create any cut that forces chips towards the center of the tool, as this tool is prone to do, the chip stacking can be a serious problem, and would be with heavy feed. I'd recommend you use a light feed, light enough that the chips aren't rigid enough to stack up on themselves. You'll have to balance the feed with not work hardening, but coarse feed is likely to be quite troublesome. Keep the cut lubed and allow the chips to evacuate well.

When you generate your rake, do keep in mind that any deviation of the cutting edge (in relationship to the centerline) will manifest itself as an irregular radius, albeit not by much. The greater the deviation, the greater the error, although it won't really by significant unless your use demands a 100% contour match.

17-4 is known to shrink about .0006"/inch upon hardening. If your finished diameter is critical, keep that in mind, although you could certainly polish a few tenths if necessary.

Don't know if any of this is helpful. Unless you don't have any material to spare, jump in, using good shop practice. You can do it.

Can't remember if I've talked about the noise this material is prone to make. It often squeals when being machined.

H
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stephenc
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Re: Bearing race nomenclature

Post by stephenc »

I don't always have the best ideas and i tend to aproach things from a different angle then most so I'll ask for some leeway at the start .

So this is for a floor jack the bearing races just need to work and not necessarily be precise down to .0005 .
I'm just gonna throw this out there and wait for the flack storm .....

Have you maybe considered using a mill with a ball mill and rotary table to do the radiused grooves ?

Granted this approach comes to me because I have a cnc mill , and would just mill the races but still would try it with a manual machine if I had some extra material ... flame on
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BadDog
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Re: Bearing race nomenclature

Post by BadDog »

Harold:
Your advice is always helpful, assuming my low experience mind can mentally assimilate it all. :D

Thanks for confirming my guess on using the round bit. I had considered the problem with loosing that critical roundness if I take the cutting edge out of the normal plane. Regarding rake vs that problem, I only need to cut on ~120* of the circumference (only in-feeds on one axis for finish). Assuming I orient that undisturbed portion to the final infeed contact area (feeding at about 10* off rotational axis), I'm free to do what I wish with the rest.

My imagination pictures it as something of a pitcher pour spout oriented directly opposite the finish in-feed. The whole being produced on the end of the rod with a careful application of a carbide ball bur for roughing, and finished with an AO ball. Braced with a steady hand that works in my head. I can easily screw up and re-flat to start over until I succeed.

The problem with my imagination is how to deal with clearance. To keep that round profile, I'll have to present the bit "straight up". Kicking it slightly for clearance (maybe 3-5*?) would hopefully yield acceptable results sufficient for a ball race. Or, I suppose I could use my HSS grinding wheel to carefully relieve under that cutting edge, finishing to the edge with a diamond lap.

Contemplating that whole process makes my neck hurt. That's why I was pondering just biting the bullet and buying a 1/4 round insert/holder (any with suitable positive rake) just to get it done with less neck cramp. But a look at ebay indicates that's not likely. Not many at all, and those that were there are either 3/8 and larger, or metric.
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