Single Point Threading on a PM-1030V?

[Aukai]

Your giving me incentive to give it a try, I'm a bit leery of it.
I bought a thread wire set, and when it came out of the package it was a bunch of Pixel sticks, that came out of the pouch.

 

[erikmannie]

Your giving me incentive to give it a try, I'm a bit leery of it.
I bought a thread wire set, and when it came out of the package it was a bunch of Pixel sticks, that came out of the pouch.

So your thread wires were broken? I bought a pair of Brown & Sharpe on Amazon for about $33, and they are great.

You simply must try single point threading. It is one of the most fun things that I have ever done.

This morning I had two failures. The first one I overshot the pitch diameter, and then when I tried again with new stock, I overshot the major diameter on that.

When I overshot the pitch diameter, I didn’t realize that dialing in a thou on the compound would result in greater than .001” reduction in diameter. This is because I have a diameter machine. Well, now I know.

Another problem that I had this morning is that I took an overly aggressive cut (.003”) and it ruined the workpiece. The insert dug in, I hit the e-stop; I tried to finish the cut by hand and instead of cutting like I wanted, it just tore off the thread. I don’t know why the insert didn’t follow the helix; probably because it was an overly aggressive DOC!

 

[jwmelvin]

I’m confused about 0.003” being an aggressive cut. I haven’t cut threads but my small lathe (G0602 10x22) certainly takes plenty larger cuts turning. Are you advancing the cross slide or the compound? I must be missing something?

 

[stupoty]

I’m confused about 0.003” being an aggressive cut. I haven’t cut threads but my small lathe (G0602 10x22) certainly takes plenty larger cuts turning. Are you advancing the cross slide or the compound? I must be missing something?

I think its todo with the engagement of the tool as it's a form tool the area is quite large, i mostly do a 0.010 or less first pass and back it down at the depth increases, 0.003 per pass sounds not to bad. (I do my threading on a 13 inch lathe btw)

Stu

 

[Nigel123]

I take the first cut .010 to .015 then decrease to .005 over the next 4 cuts
I set the compound to 29.5 degrees and divide the no of threads per inch into .75
that gives me a close measurement on the amount of infeed for the compound
I only use hss bits sharpened with no rake
Have some carbide inserts but as you mentioned depth is a problem also machining with a center
Always use the half nuts when possible (sae) lot quicker and less nerve racking

 

[erikmannie]

I’m confused about 0.003” being an aggressive cut. I haven’t cut threads but my small lathe (G0602 10x22) certainly takes plenty larger cuts turning. Are you advancing the cross slide or the compound? I must be missing something?

I was surprised, too. When I am nearer to the outside of the work, or working on something much smaller than 1" OD, I can easily make a .010" cut; I have a diameter machine, so a .010" cut reduces the OD by .020".

The .003" figure was single point threading on a 1", 8 TPI mild steel stud so a lot of material is coming out even with a .003" DOC when you are near the end of the task. I am advancing on the compound at 30 degrees.

My RPM was about 206, and note that at 8 TPI the carriage is moving pretty quickly.

Summary: dialing in .003" on the compound set at 30 degrees near the end of an 8 TPI thread on a well lubricated 1" mild steel bolt at 206 RPM will bury the carbide insert into the workpiece.

I just finished one of these with zero issues, and my cuts near the end of the task were only .001" on the compound.

 

[erikmannie]

Let's see if I can do a simple trigonometry problem without making a mistake:

I want to detemine how much I need to dial in a compound set at 30 degrees in order to reduce the diameter by .001". I ask this because we know how far we want to go straight in by looking at the difference between the major diameter and the minor diameter listed in a reference table for a given thread pitch.

We have a 30 degree angle where the compound comes in to cut. The compound travel is then the hypotenuse of a triangle where the cross slide travel is the adjacent side.

So the angle is 30 degrees. The length of the hypotenuse is, say, 1 (this is moving in the compound one unit). Cosine is the adjacent divided by the hypotenuse.

The cos(30)= .866, so the ratio of the adjacent side to the hypotenuse is .866.

If I did this right, dialing in .001" of the compound reduces the minor diameter by 86.6% of that, or .00086". But that is not what was asked.

Note that 1 divided by .866 is 1.155 ("the inverse of .866 is 1.155").

If I did this right, you need to dial in the compound 1.155 thou in order to reduce the diameter by 1 thou.

So in practice, if we still need to go in another .0100", we will need to dial in another .01155" on the compound.

Beating a dead horse here, if the entire task requires going in .1000", we will dial in the compound .1155".

 

[Downunder Bob]

Yes, a QCGB is a wonderful thing to have on any lathe, but is certainly not essential, and even on lathes equipped with a QCGB, it is sometimes necessary to use change gears, mostly when changing from imperial threads to metric, but also there are many threads that are outside the range of most QCGB.

The most common QCGB are set up to cut only the more common threads, but this range can be added to by using change gears.

 

[Aukai]

My thread wires came out like the game pick up sticks, I remember it by the other name....

 

[shooter123456]

in order to reduce the radius by .001"

in order to reduce the diameter by 1 thou

Maybe a little bit of the confusion comes from this? If you want to reduce your diameter, you dial in half of what you aim for in reduction. If you are reducing the radius, your math looks correct to me.