Lathe tool geometry for turning threads in Aluminum

The only time I have concerned myself with the lead relief angle is when I cut multiple leads, and it becomes significant.
 
mikey said:
Savarin, do you think your threads are better because you have more solid support for the tool or because you're feeding in with the cross slide?
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Considering how flexible the standard 9x20 is in its normal configuration I am convinced its the vastly improved rigidity. I also diamond hone the bit both sides and top for a polished edge. I think this helps as well.
 
I suspect you're right. I also think a "plinth" would make turning better, too, which is why mine is under construction. But my compound is tight and I'll use it to cut threads with.
 
I've always threaded with the compound at 90 deg. Parallel with the work. The trick I have used is to advance the tool ahead slightly with each roughing cut eg. .005 doc and advance .002 that way you can control the chip so it doesn't gum up in the thread and scuff the back side. When you reach the root diameter you can move the tool back a few thousands and clean up the back side of the thread then move the tool ahead until you reach the desired pitch diameter. This method works extremely well for acme, buttress and square threads as well as 60 deg threads. It also allows you to cut some pretty coarse threads on small machines.
 
If you had a 60 deg. included angle before grinding the top rake, it will be great for thread cutting. To avoid staining aluminum, never use Chlorinated hydrocarbon cutting fluids. Use regular cutting oil, or better yet synthetic cutting fluid specifically for aluminum. It's more expensive but works so much better.
 
The bad thing about plunging in straight from the side with small lathes is that you'll tend to chatter. With that technique you effectively have a form tool, and form tools are not friendly to less-than-totally rigid lathes.

Feeding with the compound, most of the cutting is done by the left side of the bit and you have half the force trying to bend the tool and bit.
 
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