[Newbie] Lathe Speed Turning Aluminum

MLDJR said:
I all run them at 750 RPM and not getting a nice surface finish with HSS tooling. Tried with Aluma Tap and WD40 lube. Maybe my tooling is the problem. I am doing a Side Relief 12 deg, End Relief 8 deg. and side rake 15 deg.
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I would suggest 15-18 degrees for both side and end relief, 18 degrees side rake and 35-40 degrees of back rake with a 1/64" nose radius that is nicely blended into the side cutting edge. Be sure to hone it sharp. Aluminum needs a lot of back rake to reduce cutting temps. The increased back rake will also focus the cutting forces at the very tip of the tool and if you use as much lead angle as you can get (without producing chatter) you will be cutting with the intersection between the nose radius and the side cutting edge in almost a backwards cut. This reduces surface irregularities and produces a better finish. Speed counts with aluminum but you have what you have so run at max speed and keep your feed rate low.

WD-40 is fine but for the best finish, try A-9.
 
Wow lots of good info here guys. Sorry I didn't get back sooner. I had a little time in the shop this afternoon and already tried a few things. Haven't tried changing angles on the cutter yet, (HSS by the way) but I did do a little honing and sharpened them up a bit and I could already see the difference. Ran a piece of 6061 bar with amazing improvement over the stuff I was turning out last night. Then after all that I threw in a standard Harbor Frieght carbide cutter and tried it pretty flat to the work and wow much better results. I will keep experimenting. Love the response's though. All good info that I will experiment with. I'll keep you posted. Thanks
 
I am not sure by what "flat to the work" means. Explain,please.
 
Ok, I have not been at this long either, but I have purchase some of the HF carbides to do roughing work with. so if you are getting a better finish on ALU with that, then work on the HSS, as you should be able to get a better finish with it than a slow run on the carbide. I had to do a lot of playing around with the HSS to get it to cut the way I wanted it on the ALU. I also found that if you do not get the cutting edge polished real smooth, and use a good amount of cutting fluid for ALU (rather it be WD40 or whatever) it will build up on the edge and have to be cleaned real well or it just keeps building back up. Oh by the way I am still not very good at grinding HSS. It takes a bunch of tries to get one to work good, no mater what material I am working with.
 
My personal preference is to use inserts. I only grind HSS for specialty shapes.

These are my go-to inserts for aluminum. http://latheinserts.com/CCGT-3251-INSERT-FOR-ALUMINUM-1-03-000329.htm

These were cut at 600 rpm, 0.003" feed rate. Material is 2" 6061 reduced to 1".

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This is 7075 at 700 rpm, 0.005" feed rate. 3/8" rod turned to 3/16".

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Cutting fluid is a 50-50 mix of WD40 & kerosene.
 
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There's no exact law on your cutter design. You do need relief on the cutters edge. I've even used round or slight angles turning metals. Sometimes conventional tools do or don't work. Try your own look at it and the material. I USE rounded toolkit on brass. See what works.
 
Hertel makes, or used to make, a special tool and insert for alum. It was practically chatter free on a job I used to run that was either 6061 or 2024, depending on the part number. But the part was 1 5/8" x ~50" long. Turned beautifully. And at a reasonable speed. I'll see if I can still read the part number on the holder and post it. It has a really odd shaped rhomboid insert, with a very, very high positive rake. Love that tool though. I need some inserts for it anyway, so I'll get it out.
 
Also consider that .30 diameter aluminum has a lot of flex and if you have much extension from the chuck, you probably will get chatter. Turning (but not cutting off) using a tailstock center may help. HSS tooling with a cut angle steeper than that for steel and enough clearance with cut a nice fine chip if you don't try to cut too deeply or too far from the chuck.
 
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