Single Point Threading Issue on Lathe

The HLV - H should be able to cut that thread all day long. Most threading on a manual lathe is too slow for carbide to work properly. That is why high speed steel was recommended. Use a tail stock live center. I know they can be in the way. The one I have been using makes it much easier. Don’t know the make. I know it looks like a dead center , but it is a live center EC7A6A0E-5DFC-49CC-B36B-E1318B4A3AC8.jpeg
 
1018 is fairly gummy steel and I see a lot of tearing out on your piece. Unless you can shave pieces off your thumbnail with your carbide insert, it isn't sharp enough and will put too much pressure on your part - as you found out. I agree with the rest of the "use a sharp HSS bit" people.
 
silly question but did you tighten all three adjusters?
I've had work loosen when I've only used one adjuster
 
Thread cutting can put a strong "levering" force on the workpiece so I'm not surprised you could turn the piece without problems
but not thread without it pulling out of the chuck
3/8" grip is not enough without tail support for a piece that long
Now you know :)
It's like running out of gas- you don't know what you can get away with until you can't
 
so you can make your own simple dead center. take a piece of O1 or W1 turn it to 60 degree point, then harden the tip. Then temper it back a little. Leave it long and put it in your tail stock with a drill chuck. Use some moly grease.
 
If you hadn't pulled the part out of the chuck, I would be surprised if, given the diameter and length, the thread didn't end up tapered (larger at the outboard end) and with heavy chatter.
 
if you can't make a makeshift dead center to get you the length you need, the other options are to either bolt the work to a faceplate or use a steady rest on one of those larger diameter steps. Cutting forces go up the closer to full thread depth you get, which is why the DOC goes down, but you still had a lot of force on a smallish diameter a long way out of the chuck.
 
I think I was on pass 4 of the 8 pass schedule when it caught. Below are the incremental depths (orthogonal to workpiece long axis) of the schedule. Again, I had taken a couple of spring passes after each scheduled pass.

Pass 1: 0.010
Pass 2: 0.009
Pass 3: 0.007
Pass 4: 0.006
Pass 5: 0.005
Pass 6: 0.005
Pass 7: 0.003
Pass 8: 0.002
 
Agree that the issue was workpiece clamping. I should have used a steady rest and will do so next attempt.
 
r2784c said:
Agree that the issue was workpiece clamping. I should have used a steady rest and will do so next attempt.
Click to expand...
As far as carbide vs HSS, agree HSS is more suited for the small manual lathe I have. With that said, I ran a test piece first of similar dimensions in length, but with 1" round bar that I had lying around. Used the collet for work holding and didn't have any issues with taper along similar length of threads. No chatter observed in the test piece.
 
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