[mioduz]

I working on threading some rifle barrels. (1/2 X 28) I can not for the life of me get the threads to cut cleanly like I would expect. I am using HSS Alloris cutter, compound set at 29.5, advancing .005 - .003 per pass on the compound. I am turning at 70 RPM. I am using Cutting fluid.
I gave up on my sacrificial steel barrel and turned to some aluminum i had laying around with the same basic results.

Any advice?

[txcncman]

70 sounds too slow to me. Are you absolutely sure your tool is on centerline?

[mioduz]

70 sounds too slow to me. Are you absolutely sure your tool is on centerline?

Ill try speeding it up. Unfortunatly it jumps from 70 to 200.
My cutter is just a touch below the center line of the work peice.
Also I forgot to mention earlier that the stock is not extending more than 1-2" out from the chuck

[dak1]

200 RPM is still only about 25 SFPM. Very slow!!

[txcncman]

I was thinking something in the 500-700 RPM range would be good.

[dak1]

I was thinking something in the 500-700 RPM range would be good.

I agree. I'd go to 1000 if the machine accuracy allows it. That's still only about 120 SFPM.

[mioduz]

allow me to clarify something. I am doing this on a manual lathe

[dak1]

Had a feeling. Go as fast (RPM) as you can get by with. It helps that it's a fine pitch thread.

[Leonelix]

Well, there are different variable that comes into play when making threads. First, you spindle needs to be sync with you feed. The feed of you thread is always equal to the lead (which equal the pitch on single start threads). Use the gearbox diagram to select the correct combinations of spindle and feed. If you have 28 thread per inch, then your feed must be .0357 in/rev.

Second, for alloy steels such as 4140 (many barrels are) you are better of working with a carbide threading tool. However, if you still want to cut with HSS, the the surface footage for 4140 (and similar alloy steels) is around 70 sfm. If the barrel is around .5 in in diameter, then your rpm = 3.82*70/.5 = 535. So try from 500 to 600 RPM to see how you make out. Make sure you cross slide is perpendilar to spindle axis. Use the center gage.

[Leonelix]

Well, there are different variable that comes into play when making threads. First, you spindle needs to be sync with you feed. The feed of you thread is always equal to the lead (which equal the pitch on single start threads). Use the gearbox diagram to select the correct combinations of spindle and feed. If you have 28 thread per inch, then your feed must be .0357 in/rev.

Second, for alloy steels such as 4140 (many barrels are) you are better of working with a carbide threading tool. However, if you still want to cut with HSS, the the surface footage for 4140 (and similar alloy steels) is around 70 sfm. If the barrel is around .5 in in diameter, then your rpm = 3.82*70/.5 = 535. So try from 500 to 600 RPM to see how you make out. Make sure you cross slide is perpendilar to spindle axis. Use the center gage.

I just want correct myself, since I forgot that the spindle speed is set to around 1/4 to that of normal contour turning. So, the sprindle speed should be around 125 to 150 rpm with HSS tool.

[neilw20]

Here is a neat attachment. I can thread at 750 RPM on the manual lathe using this.
Cutting 3-8 UNF 24 thread - YouTube
Cutting oil is important. tool center height is too.
with this I advance some on top slide and most on cross-slide to keep it cutting on the leading face.
This will thread cut right up to a face!! and retract. Sweet.
It is a Swedish device, well before CNC was even used in general work.

I am a little lazy so I leave 5 thou to come off and finish with a button die.

Sorry about the poor focus on $12 webcam.

[ErnieD]

It would have been nice to see how the operating rod was hooked up. Does this device have a name?

Ernie

[neilw20]

It was called a snap tap, but SECO have stolen the name and it used for their threading inserts.
The rod slides at a strong point and when at the end of the cut is restrained by a collar making the tool retract.
When the saddle is moved back to the start a strong spring resets the tool.
Looking at the tool holder assembly, there is a small plunger sticking out.
Behind this is a spring holding a ball in a notch.
The pull rod over comes the force on the ball allowing the holder to slide and retract.
When it resets the ball snaps back into the locking groove.

Slide show of pictures below.
http://s399.photobucket.com/albums/p...view=slideshow

1. The toolholder assembly. Mount on tool post with topslide rotated 30 degrees.
2. End view showing slides
3. This is from the 1970's I believe.
4. Saddle slid to the right forces spring to reset the tool. See the video. http://youtu.be/QYm_CJFJEWs
5. At and of cut. Tool restrained from moving closer to the chuck.
6. The attachment on the bed.
7. Easy to swing retract bar out of the way, then lift it off.

-- I have no idea if you can buy one anywhere --