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Do Some Boring Bars have a Composite Core Construction?

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awemawson:
Tidying up the workshop while still waiting for the replacement boring bar to arrive to sculpt my chuck adaptor I was about to chuck the off cut from the one Ade let me have in the 'come in useful' bin, when I decided to face off the rather rough end that I'd cut previously using an angle grinder. Now this stuf is hard (over 350 brinel) but taking it slowly with carbide tooling it cut OK'ish.

When I looked at the surface that I'd produced, at first I thought that it had been very deeply surface hardened, but now I've come to the conclusion that it is actually of a composite construction.

Being shiny it's not the easiest thing to photograph hence a couple of different angles but I think that it shows what I'm talking about.

So comments please - any one come across this before - anyone got any definite knowledge.

I can see why on such a large bar (32 mm diameter) adjusting the ringing characteristics would be a 'good thing' but IS this what's been done here?

Sea.dog:
Perhaps it's an effect of the reduced surface speed as you get in towards the centre. You could try facing it at a higher speed to see if the effect moves in towards the centre.

awemawson:
You're not often wrong but you're right again Graham  :clap:

First turning was at 570 RPM manual feed. This one at 1030 rpm auto feed. It's a bit cringing for the poor old carbide insert !

However it turns out (google research) that some boring bars are of a composite construction - the ones I found were Sumitomo - and they have a composite structure as an anti vibration measure.

 . . . .but not this Sandvik one I now think  :wave:

Sea.dog:
Praise indeed  :bow:

awemawson:
When it's due . . . give it  :clap:

You can see how much the carbide insert has worn on the last picture by the size of the 'centre pip' no pips on the previous pictures !

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