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Do Some Boring Bars have a Composite Core Construction?

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jb3cx:
Andrew have you seen the price of these anti vibration boring bars ,my mate got one from sandvic  I think it was about 25mm dia £1600 + vat a lot of money for one tool ,but when needs must .

awemawson:
Oddly, when I'm searching eBay for tooling one of the first option check boxes that I tick is 'used' - strange that, anyone would think that I'm a tight fisted Yorkshireman  :lol:

Muzzerboy:
I can't see how a different grade of steel would help with damping vibration. Most of those clever boring bars seem to use damping fluids etc to reduce the Q factor, as they are much lossier than tempered steel, which is presumably what we see here. A spark test would confirm that.

Suspect that may be showing the depth of through hardening due to oil(?) quenching. You need to cool some materials down pretty rapidly to attain the required hardness, yet the material at the core is some distance from the cooled surface and will consequently only see a relatively slow rate of change of temperature. That would leave the core fairly soft and the skin hard. The skin would be a lot thicker than what we could normally call surface hardening which is a diffusion process and generally only microns deep.

If I'm right, you could temper it by heating up and allowing to cool, at which point the hardness would be even throughout and a polished surface would not show that pattern. Obviously you'd want to have checked those 2 regions' hardness beforehand.

This question surely requires experimentation!!

awemawson:
Well it could be a uranium core to give maximum mass :bugeye:

But it isn't as my later turning test inspired by Graham shows that it's the same material throughout, and anyway the core is magnetic !

WeldingRod:
A core with a little wiggle room gives good damping at low cost in stiffness.  Of course, solid carbide is really where you want to go!

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