Uneven cap thickness

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Sri Pens

Sri Pens

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I realise after turning my cap on a mandrel M 13x0.8 , the wall thickness arent even . I do not have problem with section and barrel but the cap is bothering me a lot ? where could be the problem . The mandrel I use for holding the cap is running true in a ER 30 collet chuck .

Any suggestions please .
Regds

Mohan
 
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How uneven is it?

I agree with Charlie, you need to put the mandrel in the collet and check the runout with a dial indicator. It is the only way to really be sure.

Are you sure that the mating surface of the cap is perfectly faced off to perpendicular to the centerline? If it is not and the threads are triple start, then 2 of the three starts may not sit perfectly flush and can introduce wobble that can cause unevenness in the wall thickness.

I hope this makes sense.
 
Last edited:
d_bondi said:
How uneven is it?

I agree with Charlie, you need to put the mandrel in the collet and check the runout with a dial indicator. It is the only way to really be sure.

Are you sure that the mating surface of the cap is perfectly faced off to perpendicular to the centerline? If it is not and the threads are triple start, then 2 of the three starts may not sit perfectly flush and can introduce wobble that can cause unevenness in the wall thickness.

I hope this makes sense.
Click to expand...
I did not measure , but it is visible . The threads Are triple start and I frankly did not pay so much attention to the perpendicularity. I will now and observe the difference .
Thanks for your suggestions.
 
Sri Pens said:
I did not measure , but it is visible . The threads Are triple start and I frankly did not pay so much attention to the perpendicularity. I will now and observe the difference .
Thanks for your suggestions.
Click to expand...
Another thing is how you hold the tap when taping., use a tap ,held in tail stock to keep alignment and not by hand.
 
I went through the above suggestions and was surprised that the mandrel was bent and was not truing. I replaced it with a new mandrel and the problem is sorted . Still I wonder how a mandrel could be bent when I stored them properly
 
What are your mandrels made of? I only use brass now.

I have found that even if my mandrel is running true, the cap may run off a hair, depending on which of the three threads it is tightened on.
 
I used aluminum, but found that it still deformed slightly over time.
So far the brass is working well for me. But I didn't start using that until I got a metal lathe. While I could shape the aluminum on my wood lathe, the brass was to hard.
 
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