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Finishing a bearing seats and abutments

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PekkaNF:
On bearing books the requirements for fast speed spindle bearing seats are ridiculous. Way beyond my abilities to measure and tools/skill.

At this phase I'm trying to flatten the "grooved" surface after internal turning. Without making the hole bell mouthed or introducing any additional inaccuracy.

For normal bearing load: bearing seat fit of H7 would be fine for floating bearing. For locating bearings fit has to be a little tighter. Another reason is to flatten the "tops" of the turned surface, because bearing can feel pretty tight to seat even when it is just riding on "tops" of the turned "thread".

If my estimation is correct, I need to lap out just last about 0,01 mm after trying my best on internal turning. That is the starting point. Big idea is just to flatten the "tops" and not get into going under the turned surface completely.

Everybody that has done lapping notices that first progress is pretty fast (when only the hill tops are removed) and past that progress will come much slower. I think that on internal lapping at this first phase it is easy to stay on the same axis with turned hole, but after this it might be easier to introduce errors. I think.


Pekka

charadam:
Would burnishing do the trick?

I visualise a hardened, highly polished rod held as a boring bar and "rubbed" on the surfaces you wish to flattten.

I first saw this process at Parker-Hale in Birmingham in the early 60's where it was used for the final finish of rifled barrels. It removed the machining marks and work-hardened the surface.

When I worked for Partek, I saw the process used at Nummi Oy for finishing the bores of hydraulic cylinders. The transformation of the bore was remarkable.

In both cases, the work was done by pushing hardened steel balls through the bores.

PekkaNF:
That probably would require some special tooling and machines and anyway probably would not work well on recess.

Any hint for abrassive powder? I think about 400 grit would be good starting point. Most likely synthetic diamond.

What do I need to know to buy the right abrassive for lapping?

What to buy and where?

Pekka

charadam:
Pekka,

Would this  work?

http://www.ebay.co.uk/itm/COGSDILL-ROLLER-BURNISHING-TOOL-0-812-DIA-No-2-MORSE-TAPER-0593-/222316941090?hash=item33c31f4f22:g:xtQAAOSwPc9W1Fdl

PekkaNF:
Hmm...I only have seen those, never used. I don't know if they have a "floating" element in it or does it duplicates the alignment problem of the tail stock or cross slide. Anyways, that is for tad over 20,6 mm diameter and I need 28 and 32 mm at this point, next will be one bearing size up. Price looks bargain, but mailing it costs 20 GBP adding up a little.

I'm imagining them being very good for hydraulic cylinders and such where dense/smooth internal surface is way more important that geometrical truth. Incidently one friend was working on spur gear manufacturing and he had a diamond burnishing tool which they tested on seal journals. They became too smooth to hold enough lubricant to prevent the lip seal wear. That rather expensive diamond tool got ditched, maybe he still has it.

I think I have bigger chance of succeeding with lapping. Ordered one small/cheap set of lapping paste on syringes last night and today one guy I know is shutting off his engineering shed said he has some diamond paste. Might get ready by this weekend.

Also I think I found out how to key lap and handle together very easy. Sort of oldhamn coupling or half of it.

Pekka

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