Trouble turning brass

T

Topsy

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Hey guys,

I'm about to ask a question very worthy for the beginners section I think!

I've been turning brass mandrels to hold fountain pens.
Those that I did are fine, except for their rough finish and their no so true threads, so I'm doing new ones.
I haven't got much brass left over so I wouldn't mind getting it right. :p


I've recently had my tool sharpened locally and asked for a grind that works well with brass.

I got this here:
WgX2Owcl.jpg


When I tried to turn brass though it "eat" itself into the piece and got pretty jammed. No matter how little I was trying to turn (I believe I took off around 0.15mm), it kept doing that.

It works well for acrylics and absolutely brilliantly for aluminium however.

So my question is: will this angle not work for brass or am I doing something wrong?

If it's the former I'll turn it with the dull tool I turned it last time and if it's the latter I'm willing to learn. ;)


Thanks for your answers!
Topsy
 
Brass requires a negative angle on the tool. Otherwise it will continue to grab and dig in to the work.


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The clearance angles are not as critical as the rake. You could also get away with using a belt sander.


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Try a rounded high speed tool bit. Use a center to support your work, as for threading if it's grabbing I'd use a die to cut the threads use plenty of cutting oil . Hone the tool bit , brass don't like knife edges. Sharpen it with the rake slightly downward.
 
neshkoro said:
Brass requires a negative angle on the tool. Otherwise it will continue to grab and dig in to the work.


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Click to expand...

That would explain it!
To prevent stuff like this I actually asked the local machinist to grind something for it to work with brass... I was hesitant of going there anyways.
My dull tool (which I luckily didn't take along) has a negative angle, so I guess that's why it worked. :)


Bob Korves said:
A neutral rake will also work with brass. Yours is cut to a high positive rake and clearance (relief), and would probable be quite good in aluminum. Why not make your own cutter? It is not too difficult if you have access to a bench grinder. Here is some help:
https://www.littlemachineshop.com/instructions/GrindingToolBits.pdf
Click to expand...

I sadly don't have access (nor space currently) to any grinders.
Well, I do have one an old Metabo hand powered grinder which I should try to use! Will report back tomorrow.


Silverbullet said:
Try a rounded high speed tool bit. Use a center to support your work, as for threading if it's grabbing I'd use a die to cut the threads use plenty of cutting oil . Hone the tool bit , brass don't like knife edges. Sharpen it with the rake slightly downward.
Click to expand...

My lathe is an old Unimat SL, not in the best shape ever anymore but it works. I did use a die to cut the threads, however I noticed too late that the old tailstock which I spring loaded (removed the lead screw and replaced it with a spring, used a 3jaw chuck to hold taps and dies) to help with threading was crooked, about .7mm off center. Not sure if I shall try to find another tailstock or if I can correct it somehow. I know that there's no adjustment possibility, but maybe a file might help.


Thanks for your answers everyone! :)
 
Yikes. I can't believe that there in no adjustment to align the tail stock. Maybe there are some chips between the tailstock and the bed ways. Or is it that worn out.


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Also, make sure the tool height is on center of the stock.


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Like silverBullet said it the tool is to sharp on especially with positive rake it will try to grab. I had the same problem on a sherline. Neg rake and did no try hone or sharpen it and it worked better. Just make sure to get all the ridges out and smooth the edges, but not sharp like you do for steal or AL. Good luck.
 
neshkoro said:
Yikes. I can't believe that there in no adjustment to align the tail stock. Maybe there are some chips between the tailstock and the bed ways. Or is it that worn out.

Also, make sure the tool height is on center of the stock.

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Click to expand...

Sadly the unimat SL is like that. I have two tailstocks, one that is reasonably (but not perfectly..) true and the other one. No chips on the ways, but in. However not as much as to impair the accuracy of the better tailstock.
I read somewhere that during manufacturing the tailstock was drilled whilst mounted on the lathe, and thus only the original tailstock will be a perfect fit.

But I won't complain for the price I paid two years ago, it's paid itself a couple of times already. :)
 
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