ChrisBruno
Plastic
- Joined
- Sep 12, 2020
Hi all,
I could use some help diagnosing what I'm doing wrong cutting a M12x1.75 thread on a lathe, on some mild steel rod. The threads passes aren't being cut on top of each other, and seem to be offset by 1/2 pitch.
My process is;
1. Turn the outside diameter down -.030mm (to guarantee concentricity without aligning part every time), zero DRO in X/Y axis
2. Put a gutter in, 1mm deep x 3mm wide, starting 10mm from end of rod
3. Move cutter out approx 20mm from end of rod, change to carbide threading tool, set speed to 300rpm, configure gearing for threading
4. Wait for '1' to come round on thread dial, engage half nut, check a pen mark lines up on dial while it's covering the 20mm of air
5. Wait for it to enter gutter, disengage half nut, retract cutter +.5mm from diameter, move cutter back out to roughly 18-20mm from start of rod. Sometimes I'll double check the pitch (it's correct), generally I won't because I can see it looks reasonable and it's just practice.
6. Move cutter in -0.180mm, wait for 1 to come around on thread dial, engage half nut, check pen mark, repeat with depths -.360, -.460, -.560, -.640, -.720, -.8, .880, .950, -.9, -1 (or until it's obvious I
I'm using a carbide insert, have the tool holder and work piece choked up.
I have a metric leadscrew (roughly 26mm x exactly 3mm pitch), and the numbers on the dial match up with instructions (I can use #1 or #5, but always use #1 for simplicity). I've tried advancing top slide at 29.5*, vs the cross slide, and had the same affect, and just use the cross slide now for simplicity. The lathe is brand new, so minimal chance of a previous owner messing with it.
Normally, the second real pass I put down seems to be offset from the first one, I think it's by 1/2 a pitch, but I haven't measured.
I've been able to produce an acceptable thread keeping the half nut locked, and reversing the chuck.
I also had better luck when I returned the tool to *exactly* 20.000mm according to the DRO, but I understand I shouldn't need to do this with a dial, and even then, on pass #5 it wrecked the thread, same as above.
I'm begininig to wonder if the dial has a half count of teeth on it, I'm really stumped what I could be doing wrong. Any pointers or things I'm obviously doing wrong?
I could use some help diagnosing what I'm doing wrong cutting a M12x1.75 thread on a lathe, on some mild steel rod. The threads passes aren't being cut on top of each other, and seem to be offset by 1/2 pitch.
My process is;
1. Turn the outside diameter down -.030mm (to guarantee concentricity without aligning part every time), zero DRO in X/Y axis
2. Put a gutter in, 1mm deep x 3mm wide, starting 10mm from end of rod
3. Move cutter out approx 20mm from end of rod, change to carbide threading tool, set speed to 300rpm, configure gearing for threading
4. Wait for '1' to come round on thread dial, engage half nut, check a pen mark lines up on dial while it's covering the 20mm of air
5. Wait for it to enter gutter, disengage half nut, retract cutter +.5mm from diameter, move cutter back out to roughly 18-20mm from start of rod. Sometimes I'll double check the pitch (it's correct), generally I won't because I can see it looks reasonable and it's just practice.
6. Move cutter in -0.180mm, wait for 1 to come around on thread dial, engage half nut, check pen mark, repeat with depths -.360, -.460, -.560, -.640, -.720, -.8, .880, .950, -.9, -1 (or until it's obvious I
I'm using a carbide insert, have the tool holder and work piece choked up.
I have a metric leadscrew (roughly 26mm x exactly 3mm pitch), and the numbers on the dial match up with instructions (I can use #1 or #5, but always use #1 for simplicity). I've tried advancing top slide at 29.5*, vs the cross slide, and had the same affect, and just use the cross slide now for simplicity. The lathe is brand new, so minimal chance of a previous owner messing with it.
Normally, the second real pass I put down seems to be offset from the first one, I think it's by 1/2 a pitch, but I haven't measured.
I've been able to produce an acceptable thread keeping the half nut locked, and reversing the chuck.
I also had better luck when I returned the tool to *exactly* 20.000mm according to the DRO, but I understand I shouldn't need to do this with a dial, and even then, on pass #5 it wrecked the thread, same as above.
I'm begininig to wonder if the dial has a half count of teeth on it, I'm really stumped what I could be doing wrong. Any pointers or things I'm obviously doing wrong?