Turning Brass

[BeerFizz]

Hi,

I am trying to turn a small brass shaft out of .5" stock brass bar.

Every time I take a a few thou off, the surface left is like sand paper.

I have tried an oil lube, and various speeds.

What am I doing wrong? Also, I would appreciate a quick 5 min tutorial on how to turn brass.

Thanks in advance
Phil

[CNCRim]

positive insert, kick RPM all the way up..... leave more material.

[Mcgyver]

two words. zero rake.

turn & drill brass dry with tools ground for zero rake. milling use sharp cutters. brass needs a sharp cutter, even a file, once used on steel, works poorly on brass. once you start with a zero rake tool it cuts like butter, a pleasure to machine with a smooth bright finish

[Geof]

Originally Posted by Mcgyver two words. zero rake. turn & drill brass dry with tools ground for zero rake. milling use sharp cutters. brass needs a sharp cutter, even a file, once used on steel, works poorly on brass. once you start with a zero rake tool it cuts like butter, a pleasure to machine with a smooth bright finish

Just to add a slight comment...zero rake means that the top surface of the tool is flat and positioned so that it is on a radial line drawn from the center.

I have drawn a couple of pictures.

[ZipSnipe]

Yeah what those guys said but with top speed

[Boots]

I turned brass for years. Solid as well as tubing for the Churches. They use a lot of brass because it looks like Gold when it's high polished. I have also found that if you Hollow grind the top of your tool the chips take an abrupt turn and snap off and won't get all stringy on ya. This works with forming tools also. I used an old SouthBend lathe at top rpm and fed the tool straight in to do the profile. But be carefull cause brass is soft and tries to climb up on top of your tool and it also pushes away. 1/2 in. dia. cannot be hung out too far. Book says no more than 2.5 X the dia. should be hanging out of the Chuck so you have to work as close to the Chuck as you can. Otherwise you may need support from the tailstock.

[BeerFizz]

Thanks for the responses everybody.

Last night I tried to make some more cuts and with great success...

I dug out a 1/4" tool with a right hand indexable HSS insert. This tool had zero rake.

Running the mini lathe at max speed, I was able to make some very nice clean cuts. Of course the point of the tool does leave a slight rib... I think I would need so sort of automated slow feed to remove this, or use a tool with a more rounded cutting edge???

Thanks for all the suggestions.
Phil

[Geof]

Originally Posted by BeerFizz .... Of course the point of the tool does leave a slight rib... I think I would need so sort of automated slow feed to remove this, or use a tool with a more rounded cutting edge??? Thanks for all the suggestions. Phil

You can control the finish a little with the tool position and your own operation of the saddle travel.

If you rotate the tool in the holder slightly so the trailing edge forms a very small angle with the work it will provied a smoother finish; if you go too far the area of contact becomes too large and the work will chatter. You need to find a good midpoint.

For travelling the saddle along for the feed use both hands for the smoothest operation. Don't try turning the handle on the wheel grip the rim and rotate it constantly by using your hands alternately.

[Mcgyver]

Originally Posted by BeerFizz I dug out a 1/4" tool with a right hand indexable HSS insert.

now thats going full circle! get yourself some hss blanks, then you can grind what you need when you need it

i don't 100% understand the 'full speed' recommendations, as always speed is surface speed and depends on dia. brass likes somewhere between steel and AL, maybe 200 sfm using hss

stoning a slight radius on the tool and slow feed will help with finish.

[Geof]

Originally Posted by Mcgyver ...i don't 100% understand the 'full speed' recommendations, as always speed is surface speed and depends on dia. brass likes somewhere between steel and AL, maybe 200 sfm using hss stoning a slight radius on the tool and slow feed will help with finish.

With a diameter of .5" even 200 sfm needs 1500rpm, carbide can be three times that so in this case 'full speed' is probably too slow.

[Mcgyver]

ahhhh you are right, missed the .500

[BeerFizz]

Thanks for all the comments everyone.

Just a quick follow up question:

Where should the tip of the tool be positioned with respect to the center line of the work. Dead on center, a little below or a little above.

thanks again
Phil