Author Topic: Finishing a bearing seats and abutments  (Read 2164 times)

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Finishing a bearing seats and abutments
« on: November 06, 2016, 02:34:47 PM »
This is time for a bit more serious small spidle build. Tired of glued ball bearings.

I have an idea, but there are two avenues:
* traditional bored/ground trough hole with bushings
* Bored trough, two different diameters.....

I build today a gauge for 32,00 bearing nominal dimenssion, this is for fixed end and bearings will be abuted against solid outer wall. Gauge min/max diameter portions worked out pretty good. M33x1 thread did seem to come out ok, but banjo kicked out middle of it. I tried to reset gear back and got major/minor diameter right, but when I checked the thread it had too wide groove. Have to make another. And maybe couple of nuts on same go.

Not too happy with my laps yet. Started to make some cast iron laps. However, the abrassive part is harder part. So far I have used loose lapping abrassive.

Now I am trying to charge the lap with abrassive, but which abrassive to use and how to charge?

Progress so far.

Pekka

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #1 on: November 07, 2016, 03:37:58 PM »
Finding a whole lot of traditional loose abrassive lapping, like this:
  Lapping (and honing) - some techniques for discussion
http://www.modelenginemaker.com/index.php/topic,1908.0.html

And some industrial machines, but no much hard laps I'm looking for.

http://www.grstools.com/PDF/LIT-322_CastIron.pdf

Some anekdotal information suggest that it is not very optimal as a method:
http://www.aspe.net/publications/Annual_2001/PDF/POSTERS/PROCESS/POLISH/1291.PDF

Might revert back to bad bad habits.

Pekka

 

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #2 on: November 13, 2016, 01:46:16 PM »
I got pretty good hit to have a look on morse taper collet.

+ near 1:20 taper
+ economical
+ available reamers and collets

- All dimessions all over the places for metric world and even taper is 1:20:ish....

MT2 12 mm collet seems to be close, MT3 16 mm collet would have left only 2-3 mm meat.

Anyway got 28 mm and 32 mm OD dimenssions -0,01....-0,03 mm under nominal OD. Hope they retain the shape after splitting trough.

I'm thinkking to use band saw blade to cut a single slit slightly diagonal. What do you guys think? Doesn't diagonal sound better than straight?

Pekka

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #3 on: November 14, 2016, 03:07:59 PM »
Some progress.

Funny how fast stuff comes together with standard parts.

I need to use key or something to tie up together lap and handle. Any suggestions? Slot trough three parts and key?

Pekka

Offline charadam

  • Jr. Member
  • **
  • Posts: 30
Re: Finishing a bearing seats and abutments
« Reply #4 on: November 14, 2016, 04:56:22 PM »
Pekka,
In the final product, what order of precision are you aiming at?

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #5 on: November 15, 2016, 12:19:28 AM »
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
« Last Edit: November 15, 2016, 05:19:19 AM by PekkaNF »

Offline charadam

  • Jr. Member
  • **
  • Posts: 30
Re: Finishing a bearing seats and abutments
« Reply #6 on: November 15, 2016, 08:56:30 AM »
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.
« Last Edit: November 15, 2016, 11:45:16 AM by charadam »

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #7 on: November 16, 2016, 03:34:04 PM »
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


Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #9 on: November 17, 2016, 02:43:02 AM »
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

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1821
  • Country: fi
Re: Finishing a bearing seats and abutments
« Reply #10 on: November 20, 2016, 01:23:05 PM »
Few more parts nearing finish, before I'll get the actual work. I actually might have all the tools ready before parts arrive.

Pekka