Threading on a lathe when you cannot set up 29.5 degree compound

[koenbro]

As a home gamer with next to no experience I do not expect high material removal rates off exotic metals. So will remove the pins and try again; not worried about tool rotation under load but who knows.

I would pull those pins.
Personally I can't imagine not being able to swivel my toolpost.

For most other operations, having the compound parallel with axis z works very well, so to me swiveling the TP seems like the exception. Will see as I am learning more.

 

[mksj]

Try threading directly in with the cross slide, using the compound feeding in at an angle is primarily for lighter less rigid lathes. I have the same size QCTP, but I do not use the pins. You do not need to make a new T-nut, you have the option to use the pins or not. In lathes that are taking heavier cuts, there is more twisting force on the QCTP then the pins are an added level of security to keep the QCTP from turning. Also by feeding the thread cutting insert directly in, it is easier to keep track of the actual depth. When I start out cutting a thread, I touch the outer diameter of the rod and then zero the cross slide dial, I then use that as a reference point to back out the cutter on returning to take another pass and then advancing. I typically take 0.01" depth passes until about 80% of target depth, then 0.005", a final pass and then only one cleaning pass. I also recommend knocking down the threads peaks with a file before cutting the final thread dimensions. In some cases, I might cut 90-95% of the thread on the lathe and then use a thread cutting die to form the final threading dimensions. I also use a wire brush on the threads to clean the chips, and use a brush with cutting oil when cutting the threads. The laydown inserts should perform very well in this arrangement.

 

[koenbro]

@mksj Very nice, clean looking thread!

 

[SLK001]

Personally, I'm at a loss as to why the pins are even there. They defeat the purpose of a compound. Yes, you can feed in using only the cross-slide, but some materials will produce cleaner threads using 29.5º compound angles. That's because every advance of the compound "scrapes" the flank of the previous pass, removing any turned up burs. There are some metals that will produce a good looking thread no mater how you advance your tool.

 

[piper184]

Also, there are a lot of times you don't want the tool completely perpendicular to the work. I find that the QCTP lets me use the left and back side mounts to do a lot of things, but there still are lots of times I need to angle the cutter just a bit to get what I want. I run a variety of hand ground HSS, brazed carbide and insert carbide tools. Rotation of the tool post lets me do that.

 

[Huub Buis]

I can do threading only in CNC mode. Than I can choose between 0, 29.5 or 30° infeed angle. In general, I use the 0° infeed angle. For coarse threading I some times switch to 30° threading because than threads are almost fully cut using 1 cutting edge. That 1 cutting edge reduces the cutting edge length and a shorter cutting edge length reduces the cutting forces. For my not so rigid lathe, lowering the cutting forces is a must for successful coarse threading.

 

[verbotenwhisky]

Remove the two pins? Worth a try if you want to use the 29.5 angle. Sometimes the pins are spring loaded, so they may go down. Just remove the tee nut and press the pins out - you really don't need them.

You could simply go straight in, as well, if your lathe is rigid enough. Plenty of folks do that with no ill effect. Really don't need the z offset, save to reduce cutting force. Just take less deep cuts. Try both ways and see which you prefer.

I agree, those pins are stopping him from using the tool post properly.

 

[mksj]

I previously had a PM-1340GT which is pretty much the same as the Eisen 1340 GHE, started out with the compound at 29.5 degrees, but eventually switched to just using the cross slide when I switched to carbide laydown inserts. They have increased rigidity and seem to cut well on both sides. Part of the equation is depth of cut and speed one is using. I have threaded all kinds of material and metal down to 8 TPI and over 0.1" depth w/o any issues. I thread at higher RPM's which improves the finish of the cut, have yet to have any finish issues if you start out with the correct OD and do not exceed the limits of the cutter/insert you are using. I have run the same Carmex threading insert for over 5 years, done 100's of threads in different metals with no issues. I would start out with using the compound set to the proper angle, then try the cross slide. A lot is technique and finding what works best for your machine setup and what your are comfortable with. So try both ways and see what works best for you. It takes time to become more proficient and figure out what works for your particular setup. You have a nice lathe, should be a lot of fun learning on it.

This was a threaded O1 steel tool post with a metric M16-2.0 thread on the base. I have an automatic threading stop system so my relief can be just the final thread position and I over cut it 0.01" from the target minor thread diameter. Since the stop position is driven off of the carriage, the end thread stop position will not change when advancing the cross slide. This was one of the reasons for not using the compound at an angle, and on my lathes there was no noticeable difference in the thread with the lay down insert I am using.


Stainless Steel, a slightly wider relief because there is a small step where they thread into.

 

[verbotenwhisky]

Try threading directly in with the cross slide, using the compound feeding in at an angle is primarily for lighter less rigid lathes. I have the same size QCTP, but I do not use the pins. You do not need to make a new T-nut, you have the option to use the pins or not. In lathes that are taking heavier cuts, there is more twisting force on the QCTP then the pins are an added level of security to keep the QCTP from turning. Also by feeding the thread cutting insert directly in, it is easier to keep track of the actual depth. When I start out cutting a thread, I touch the outer diameter of the rod and then zero the cross slide dial, I then use that as a reference point to back out the cutter on returning to take another pass and then advancing. I typically take 0.01" depth passes until about 80% of target depth, then 0.005", a final pass and then only one cleaning pass. I also recommend knocking down the threads peaks with a file before cutting the final thread dimensions. In some cases, I might cut 90-95% of the thread on the lathe and then use a thread cutting die to form the final threading dimensions. I also use a wire brush on the threads to clean the chips, and use a brush with cutting oil when cutting the threads. The laydown inserts should perform very well in this arrangement.

View attachment 496371

I do not have pins in mine and have never had an issue with it twisting.

 

[MrWhoopee]

There is an old trick of using a thin, fine, metal mesh between the TP and the compound slide to aid in stopping rotation if you are worried about it. Think I saw a reference to metal screen door mesh somewhere once?

Winky just solved this problem using drywall sanding mesh. Good grip.