I had a Monarch toolroom lathe with a set thread stop and reverse to the lead screw, and one of my friends has a Pratt & Whitney with the same feature, and they are wonderful! they will thread a coarse thread right into a thread relief, they just stop dead, then you withdraw the tool using the cross feed that has a dead stop, for long threads, the half nuts can be opened to return to the starting point for reengagement, then the lead screw is re engaged, and it's off to the next cut. Short and coarse threads, the lead screw is merely reversed and runs back to the starting point, where it is again kicked off by a set stop.
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Hard threading anyone?
- Thread starter SmokeWalker
- Start date
I do hard turning several times per year using ceramic hard turning inserts, works well when the part is 40-50 RC.
Above that it is a crap shoot, have used the same tools for turning the shanks of HSS taps with decent results. You will likely go through many tools and parts before you get it working. Traditionally thread grinding is the way to go.
Above that it is a crap shoot, have used the same tools for turning the shanks of HSS taps with decent results. You will likely go through many tools and parts before you get it working. Traditionally thread grinding is the way to go.
Okay. I decided not to do it. I spoke to another fellow who's done hard turning and threading, and what he told me is that there is a good chance that without thread grinding, I'll end up in a position where it's really challenging to complete the thread form; a tool sharp enough to complete it might break, and the only tool strong enough to do it will have too much nose radius to form a complete thread. I think I could still make it work for my application, but I'm going to try it out of aluminum (!) and see if I can't get away with it.
I've cut threads in metal at/around the Rockwell 42 range with no problem at all using standard carbide threading inserts. What are the dimensions of the workpiece and most important, precisely how hard is it? If you don't know the actual Rockwell, do you know if it is just store-bought prehard material? If so, it will cut like butter because that's only 28-32 Rc -which is not really hard at all. If you scrape it with a file, does the metal scratch or does it laugh at the file?
We need more details...
Ray
Hey everybody. The project is over, and I didn't end up having to deal with the hard threading. I ended up making a part myself out of aluminum and it worked fine!
FYI, I also use an electronic stopping system, but even though it will stop to 1/10,000" at just about any spindle speed, I still do not thread at high speeds. If you look at the recommended SFM for hardened steel using carbide inserts it is somewhere in the 100-150 SFM range under ideal conditions. With a 2.5" diameter at 400 RPM you would be around 260 SFM. Fine for aluminum and softer materials, but not super alloys and hardened steel (45-60HRC) per the carbide insert manufactures recommendations. There are specific inserts for hardened steel, I am using lay down BMA type. I usually shoot for 50% of the manufactures SFM, based on decreased lathe rigidity and also non optimal coolant (brush).
