Is this bronze?

[Twinsquirrel]

Picked up this 180mm (6") ring of what I thought was brass at a local steam fair, it was pretty grubby. Anyway it doesn't cut very freely and produces short swirls of swarf when cut. In fact it grabs the tool very easily and makes it blunt in no time but this could be the way I have ground the profiles on my tools, to be honest I don't think I can work this material at all with my current level of experience.

Brass round bar is for colour reference.

 

[Bogstandard]

David,
I think you have hit the nail square on.

Welcome to the club of blunt tools and hard knocks.

When doing large pieces such as this, you must remember the peripheral speed of the job. Turn your speed down to very low and come in with a razor sharp HSS tool. No heavy cutting pressures, just a steady feed. Get it right and it will cut like butter, get it wrong and you will start at the beginning again.

John

 

[rake60]

From the picture it does appear to possibly be bronze.

If those swirls of swarf break rather than bend I'd be more sure of that.

On John's note of speed, I cut at 300 FPM with carbide and 150 FPM with HSS.

There's a very simple formula to find those speeds.

SFM/(Diameter of stock) X 3.82

I know that's NOT a perfect formula but it WORKS!

To obtain 150 FPM on a .75" part:

150/.75 X 3.82 = 764 RPM

On a 6" part those numbers change dramatically!

150/6 X 3.82 = 95.5 RPM

Rick

 

[Powder keg]

Usually 660 bearing bronze chips really good. I don't think iv'e ever had it get stringy? But Aluminum bronze will get stringy or short curls. If I remember it is pretty hard on tools also0

Have fun, Wes

 

[Twinsquirrel]

Thanks guys, as I suspected, I think that this lump will sit on the shelf until I feel confident enough not to break anything while cutting.

It must be aluminium bronze as the swarf swirls for about 1/2" then breaks.

I like the simplicity of that formula Rick, the way I have been working things out is much more complicated and comes up with results within 5-10% of yours, do you have a link to a reliable table showing cutting speeds for various stock? I must get myself a Zeus book.

Cheers

David

 

[DickDastardly40]

I must get myself a Zeus book.

David,

The Zeus tables do not have cutting speeds within unfortunately. I can heartily recommend 'the engineer's black book', available from J&L which is rather pricier at about £17 + postage but has loads more in than Zeus.

If you ring 'em and ask they'll send you a 1300+ page catalogue full of machinist goodies to keep in the downstairs loo for those occasional idle moments and also send a mailshot every couple of weeks with special offers. I think I bought my book from the mailshot and it cost £12 IMS. If you buy several things you only pay one postage charge and it's next day delivery if ordered by a certain time.

http://www.jlindustrial.co.uk/BOK-57117J/SEARCH:KEYWORD/product.html

Al

 

[Twinsquirrel]

Thanks Al, catalogue ordered, so many goodies!!!!

 

[DickDastardly40]

First time at seeing the picture of the offending metal this evening (no photobucket pictures alowed at work) and I was wondering if it could be gunmetal. This needs negative rake IMS, though it must be 20 years since I cut any in anger, I do remember the chips flew like cartridges from a belt fed machine gun.

 

[rake60]

David the carbide manufactures have perfect formulas for calculating the perfect surface
speeds for all materials.

They are very impressive with the accuracy but there's a problem there.
Bar stock metals are generally formed in continuous lengths that are cut to 20 foot lengths
for easier shipping.

If you take 4" off the front of that bar, 4" from the middle of the bar and 4" from the end
of the bar and do a precise Brinell hardness test on the 3 pieces they most likely will not
match.

Calculated surface speeds are a guide as to where to start.
The correct speed for the material that is actually in front of you will differ.

Rick