Compound Delete

[Larry$]

above will not work to simulate a compound set at +-30 degrees.

The question is.... Why would you want to?
You can thread perfectly well going straight in, why complicate it?

 

[npalen]

That is another subject. Some people prefer the angle some straight in.

 

[Ultradog MN]

The question is.... Why would you want to?
You can thread perfectly well going straight in, why complicate it?

Off the top of my head...
If you you use the compound to adjust the depth you can set the cross slide to zero and advance the bit with the compound on each successive cut. Makes it easy to keep track of the depth of your threads that way.
My old lathe has a positive stop on the cross slide I can set specifically for that purpose.
It prevents you from cranking the cross slide past zero when you turn it in.

 

[toprecyler]

I think the main reason for setting the compound at 29 degrees is when threading on a lighter lathe using HSS bits. It can be easier taking most of the cut on the leading edge of the tool bit, and it helps keep the carriage pushed back so it takes the backlash out of the half nut/ feed screw.

 

[Provincial]

I think the main reason for setting the compound at 29 degrees is when threading on a lighter lathe using HSS bits. It can be easier taking most of the cut on the leading edge of the tool bit, and it helps keep the carriage pushed back so it takes the backlash out of the half nut/ feed screw.

That makes sense, but I always plunge cut threads on my Atlas 10- and 12-inch lathes with no problems. I do this with a flat-topped HSS tool bit and get acceptable surface finish.

 

[Ultradog MN]

That makes sense, but I always plunge cut threads on my Atlas 10- and 12-inch lathes with no problems. I do this with a flat-topped HSS tool bit and get acceptable surface finish.

Not arguing but asking...
When you plunge cut how do you know how deep to cut them?

 

[savarin]

I plunge cut till the thread fits the nut or whatever I need it for.
However when I made the 4 start thread for my focusser units I set the compound back to get the 1mm advance for each start but still plunge cut the threads.
https://www.hobby-machinist.com/threads/the-giant-binocular.55688/page-25 from post 248

 

[toprecyler]

Not arguing but asking...
When you plunge cut how do you know how deep to cut them?

As with everything, it will depend on how close the OD tolerance is of raw stock. 75% of the threads I do are 12 TPI. Most are 1-1/4” to 2” diameter. Usually I end up plunging .120” overall (.060 DOC) with two spring passes, and the nut will fit nicely.

95% of the time I thread using the actual nut/ part as a test piece. If I do not have the test piece, then I will break out the thread wires and figure out the Pitch Diameter.

I will take .040 or .050” pass, .070” .090, .110” . And 2 at .120” , or maybe last couple at .010” deep, depending on actual work piece and stickout from the Chuck. Sometimes I will advance the compound (set parallel with spindle) a couple thousands each cut, to help with chatter on the back of the thread.

Using carbide inserts. I should also mention this is on a heavy Summit lathe, 20” swing by 84” long, with a 4” thru bore.

Very seldom I actually disengage the half nuts either. The lever is not very user friendly, and is just easier to reverse the lathe with forward/ reverse lever. This is how I have gotten used to threading on my daily lathe.

I also have a Libby lathe that does not have a compound on the cross slide, so I do have to straight plunge to thread on that one. I tend to avoid that lathe if possible, but can do it. Nice thing about that lathe is it has a 10” thru bore in the spindle.

There are definitely more than one way to thread. The right way will be whatever way you learn to do it and end up with a good useable result.


Sent from my iPhone using Tapatalk

 

[npalen]

Off the top of my head...
If you you use the compound to adjust the depth you can set the cross slide to zero and advance the bit with the compound on each successive cut. Makes it easy to keep track of the depth of your threads that way.
My old lathe has a positive stop on the cross slide I can set specifically for that purpose.
It prevents you from cranking the cross slide past zero when you turn it in.

That is interesting and wondering how it works! I assume that the cross slide can be backed off more than one turn between threading passes?

 

[Ischgl99]

Not arguing but asking...
When you plunge cut how do you know how deep to cut them?

I set my cross Slide dial so that the final depth of the thread is at zero, once I get close to zero, I know to take smaller cuts, and then measure once I get to zero, or close to zero, depending on how accurate the thread needs to be. The disadvantage of this way, sometimes I forget what my last depth was and I do a light or too heavy off a cut, but that hasn't happened to often, or caused an issue when it did.

An advantage of plunge cutting, your depth of cut on the dial is simply your OD minus the minor diameter, no calculating the distance to advance the compound based on what angle it is set to.