# Difficult access carbide



## JimDawson (Nov 25, 2018)

Carbide parting insert would be my choice.


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## benmychree (Nov 25, 2018)

All but the hardest grade of carbide will not cut 60Rc steel accurately, a part like that should be roughed out in the soft state, heat treated and finish ground.  a CBN (cubic boron nitride) tool might get the job done, but finding a workable shape would be a big problem.  Kennametal K6 will cut material that hard, or its modern designation, K313.


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## dgrev (Nov 25, 2018)

Jim and Benmy. Thanks for the replies. I did a test run on one of the bearings and the carbide struggled but did cut it. I expect that if I do use carbide I will have to stone finish the face.
The real issue is access. I have found that there is a parting tool with a tin coated "MGMN300" insert which is "suitable for steel", whatever that may mean
(mild steel?)?

The problem is that I have around 140 of these to return to use. They are a unique 70 year old part that is no longer made and there are no modern substitutes that will fit due to the weird design.
See photo.
	

		
			
		

		
	




The needles run on the middle area of the RHS object. 
On the outer bearing in the  LHS of the photo you can see where the needles run. That too needs to be turned to restore the surface.

I probably need to remove 40 thou total from the 2 in order to use the next size up needles.

The shiny surface on the RHS is a seal face and I am wondering if it will be much less hassle to just Speedie - Sleeve it, rather than also turning it down.

Thanks
Doug


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## JimDawson (Nov 25, 2018)

If you had mentioned needing to do 140 pieces, my answer would have been (is) grind them.  This would be a perfect job for a surface grinder or even a tool & cutter grinder.  Just need a spin fixture.  Once set up it would go pretty fast.  Also could be done in a lathe with a tool post grinder.

Also you might look at ceramic inserts that are engineered to cut hard materials. 

One other option might be to just make new ones out of the proper material and heat treat them.  Might be faster than trying to repair what you have there. But with nothing to scale against, I can't tell how big they are so this might not be an option.


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## dgrev (Nov 25, 2018)

Jim 
Length 50mm
Needle journal 22mm which originally took 30 x 2.5mm needles 13.8mm long.

I will investigate a tool post grinder. Aren't keen on the idea of all that carborundum getting in my lathe though!

Regards
Doug


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## dgrev (Nov 25, 2018)

Cheapest on ebay is $1351 from India. But I think the problem would be getting  a grinding disk that is only 13.8mm wide?


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## dgrev (Nov 25, 2018)

What about a diamond wheel set up square from the tool post?
Will a diamond wheel work with hard steel?


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## dgrev (Nov 25, 2018)

If I went with the grinding option, what grade of disk would I need in order to get an acceptable finish for needle rollers?


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## Bob Korves (Nov 25, 2018)

CBN (cubic boron nitride) works for hard steel, diamonds are not good on steel at higher temperatures.


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## JimDawson (Nov 25, 2018)

dgrev said:


> Cheapest on ebay is $1351 from India. But I think the problem would be getting  a grinding disk that is only 13.8mm wide?



That's should be no problem, I know they are made 6mm wide.  Should be able to find them from 6mm to about 25mm wide.



dgrev said:


> If I went with the grinding option, what grade of disk would I need in order to get an acceptable finish for needle rollers?



I think a 60 grit silicon oxide wheel would give an acceptable finish.  A medium hard wheel should work well.  Or as Bob suggested CBN.

If that piece is only 50mm long, then it must be about 25mm at the largest diameter and the mating part is maybe 50mm OD?  It might be worth making new parts.


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## dgrev (Nov 26, 2018)

Bob, thanks, I have found some CBN diamond shape inserts which will just barely get into the location. So need to buy them and a suitable holder.

Will I need lubricant?

Jim, also thanks, I am wondering about using a thin oil stone either free hand or clamped in the tool holder to give a final polish after using the CBN inserts?


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## Bob Korves (Nov 26, 2018)

I have little experience with CBN tools, but I would use them dry on hard stuff, which is what they are made for.


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