Author Topic: Do Some Boring Bars have a Composite Core Construction?  (Read 442 times)

Offline awemawson

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Do Some Boring Bars have a Composite Core Construction?
« on: June 29, 2021, 05:06:58 AM »
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?
Andrew Mawson
East Sussex

Offline Sea.dog

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #1 on: June 29, 2021, 05:46:32 AM »
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.

Offline awemawson

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #2 on: June 29, 2021, 08:06:24 AM »
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:
Andrew Mawson
East Sussex

Offline Sea.dog

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #3 on: June 29, 2021, 08:12:18 AM »
Praise indeed  :bow:

Offline awemawson

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #4 on: June 29, 2021, 08:17:51 AM »
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 !
Andrew Mawson
East Sussex

Offline jb3cx

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #5 on: June 29, 2021, 10:44:05 AM »
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 .

Offline awemawson

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #6 on: June 29, 2021, 11:01:35 AM »
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:
Andrew Mawson
East Sussex

Offline Muzzerboy

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #7 on: June 29, 2021, 01:51:44 PM »
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!!

Offline awemawson

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #8 on: June 29, 2021, 02:56:24 PM »
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 !
Andrew Mawson
East Sussex

Offline WeldingRod

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Re: Do Some Boring Bars have a Composite Core Construction?
« Reply #9 on: June 30, 2021, 01:49:21 PM »
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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