Couple threading questions

[Asm109]

That Lazy Machinist.com has a really nice video/whiteboard talk about cutting threads with the compound at different angles.

With the compound at 90 degrees to the carriage travel, the cutter removes equal amounts of material from each side of the cutter.
As the compound is rotated away from the headstock, the cutter removes more from the left side of the tool and less from the right.
With the compound rotated exactly 30 degrees, all the cutting is on the left side and the right follows the thread perfectly.
With the compound at angles greater than 30 degrees, all hell breaks loose and you no longer cut a V shaped thread.
Since you don't want to create a defective shaped thread, you want to stay some distance away from 30 degrees.
So people set the compound at 29.5 or 29 degrees. You could set it at 25 degrees if you felt like it. The right side would be removing more material but still far less than 0 degrees. The key takeaway is to make sure you are not greater than 30 degrees because that does not cut a V shaped thread.

 

[Richrd]

So you,re saying to feed with the compound not the cross slide?

 

[Chipper5783]

So you,re saying to feed with the compound not the cross slide?

No. There are several ways to set your machine up for threading. Compound in feed is simply one method for that portion of the thread cutting process.

One way is to feed in with the compound, then pull out with the cross slide and reset the cross slide to the same setting for the next pass - doing the advance for depth of cut with the compound.

You can also ignore the compound and just do the pull out and in feed with the cross slide.

If you get (make) a retracting tool holder or cross slide - then you can do the tool pull out with the retractor and infeed with either the compound or cross slide.

You can also position the tool in a front or rear tool post (facing up or down) - running the lathe in the correct rotation to get the lead you are looking for. The reason you may do that is if you wanted to do the threading towards or away from the chuck.

Then again, if you are threading metric on a machine with an imperial lead screw you typically need to leave the half nut in and reverse your spindle.

Single point thread cutting is not a big deal. Sometimes folks just getting into machining avoid this procedure (there being a number of pitfalls). Take the time to learn how and it opens up some useful operations for your projects. How you are going to do the threading usually depends on the actual project, your machine, your preference, . . . . .