Why Do My Threads Look So Rough?

Brino and Mark,
My compound is set at 29*, and I used a fish tail gauge to get the tool square to the work. I used the cross feed to zero my tool on the work, then advanced the tool with the compound. The one thing that has been brought up more than once is the tool may be dull. My bit sharpening skills need a little practice. I'm on the learning curve. God bless.
Jon In Tucson
 
Built up edge is a likely culprit, inspect the tool after each pass if any material is stuck on the cutting edges you will never get a good finish.
 
Best lube EVER for Aluminum is "Tap Magic Aluminum" - I love this stuff - better than kerosene or WD40.

A very easy way to get your tool height set - find the smallest round stock you have - I use 1/8" but use can use 1/2" if that is the best you can do. The smaller, the more accurate. Chuck up the stock and bring the tool almost up to it - then lightly pinch piece of something flat (I use a long xacto blade) between the tool and the round. If the blade isn't vertical, you're not on center.

I turn a lot of 6061 and thread some - I get better results than you but NOT super smooth. A handheld wire brush on the threads turning in the lathe is often enough to leave a much nicer finish. If not that, the triangular file.
 
29 degrees in the right direction ?...... threads look like narrow and pointy - like mine until it was pointed out that I need to set the 29 from the left hand 45 mark or something like that. Others can clear that up better than I.. It's been a year ago...
 
Jon,
The compound will be set 29 degrees to the right from perpendicular to the work piece.
Kerosene is another good cutting oil for Aluminum.
A light pass or two with a flat file followed by a fine wire brush will often take care of the burrs from "gummy" material.

Some technique questions:
Do you have the right relief angles on your threading tool?
Is the threading tool set to the right height?
How much are you taking off with each cut?
Are you taking "free cuts" (not advancing the compound) to compensate for any spring back of the work?
 
That looks like a real gummy aluminum. How does the stuff turn?

Get aluminum that you know has good machinability and try again using all of the advise above.

When I had my mini lathe I used to buy the hobby metals at Ace hardware to keep on hand. They have a K&S metal bin in every store I've been in with foot long, 1/2" diameter pieces of aluminum, brass, and stainless. All three machine well using sharp HSS bits. If you can't thread that metal, something is wrong.

Chris
 
gheumann said:
Best lube EVER for Aluminum is "Tap Magic Aluminum" - I love this stuff - better than kerosene or WD40.

A very easy way to get your tool height set - find the smallest round stock you have - I use 1/8" but use can use 1/2" if that is the best you can do. The smaller, the more accurate. Chuck up the stock and bring the tool almost up to it - then lightly pinch piece of something flat (I use a long xacto blade) between the tool and the round. If the blade isn't vertical, you're not on center.

I turn a lot of 6061 and thread some - I get better results than you but NOT super smooth. A handheld wire brush on the threads turning in the lathe is often enough to leave a much nicer finish. If not that, the triangular file.
Click to expand...

I use that method for centre hight setting, it works pretty good, i use thin shim sheet off cuts.


Stuart
 
timbertoes said:
29 degrees in the right direction ?...... threads look like narrow and pointy - like mine until it was pointed out that I need to set the 29 from the left hand 45 mark or something like that. Others can clear that up better than I.. It's been a year ago...
Click to expand...

Yes the Protractor on my Grizzly zeros at parallel to the work so the protractor reads 61 deg. when 29 deg. of perpendicular. But it does not look as though the back side of the tread is at to great of an angle.
My bet is it is tool bit related, dull , off center, lacking relief, Or feed to fast/deep. As mentioned before the threads look forced.
Mark
 
I went to visit Jon today. He had a set of bigger threads (8-10tpi?) he had previously cut and did a very good job, especially considering he is learning everything by reading, trial-&-error.

For his 1/2-28 attempt on aluminum I recommended he sharpen his bits a little more. Also try some lighter cutting oils.

We were talking about how to get his speed down when he remembered about being able to engage the backgear on the lathe (I'm not familiar at all with Logan lathes). That dropped the speed down wwaaaayyyy slow. Too slow for aluminum, so Jon bumped it up to 100rpm which looked pretty good for practice...and about 2 1/2 times slower than he had been before.

The lever that engages the backgear doesn't stay put, so that is something that needs to be addressed. I did a search and found that quite a few Logans are missing a detent or have other issues with the lever staying put.

For the amount of time Jon has put in rebuilding his lathe and learning, he is doing very well. He should have some nice, clean threads in the near future.
 
planeflyer21, Awesome. I applaud you taking time to go help Jon. I wish when I started the same way as him I lived in Tucson. But as he did I found my way here. You are the kind of guy that makes this forum great. A big atta boy from me. Thanks
Mark
 
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