Improving single point thread quality?

LVLAaron

LVLAaron

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New PM1440GT - My first real lathe. My metal working education is 5 years of Abom79 and This Old Tony, and a week long precision rifle course in Gordy Gritters shop.

I am using the following carbide insert https://www.mscdirect.com/product/details/05765631?rItem=05765631 (Recommended by Gordy) and am practicing to thread barrels. I am using (allegedly) 416 stainless bar I got on ebay.

I am confident that my tool height is correct.
Cut is flooded with dark cutting oil.
Speed is slow, 100rpm-ish
Compound @ 29.5

Cuts are shallow, 5 thou max, last cuts 1-2
All passes are done by advancing the compound, except for the last pass, I push the crossslide in a though.

I did lick the top of these threads with a file because they were sharp as a cats claw.

Because I am new at this I don't know what I don't know and am open to questions, feedback, etc etc. Let me have it.
 

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I'll bite. What thread are you trying to cut? What TPI? The inserts show they can cut between 16-48 TPI. Can you show a picture of your lathe showing the compound? Not a super close up, but one where one can see the compound and the chuck.

The close up photos seem to have some distortion due to the lens. I also have found taking good pictures of threads is hard. I do see what appears to be a little chatter, if I understand the picture. 416 should cut well.
 
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16 TPI - Disregard the part in the chuck - I was working on something else, but this is how I'd have it set for threads.
 
LVLAaron said:
View attachment 397649

16 TPI - Disregard the part in the chuck - I was working on something else, but this is how I'd have it set for threads.
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Your compound does not look right. It appears to be set at 60 degrees, not 30. Should be closer to the cross slide. Every new guy gets tripped up on this. Different manufacturers measure the angle different. Angle should be 29.5 degrees towards tailstock, with 0 degrees being perpendicular to the spindle axis.
 
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