M42 x 2 thread, first thread is sharp!

Hey guys,

I'm threading some parts here and I'm under the gun to get this done today.

I've never layed down a thread like this and don't like the way its coming out.

So its a 42mm thread with 2mm pitch. All the complete threads look great, expect the first one.

Because it doesn't have complete material to form the full thread, its coming out sharp and there are burrs. I can't figure out how to overcome this.

Currently, where the thread starts, I put a 60 deg angle on the front wall that the thread enters on, hoping that the 60 deg thread will match up with that angle and leave less of a burr. Its helped a little, but still not great.

The thread op starts beyond the front of the part, then moves in.

Any tricks you guys know to get that first (partial) thread to come out nice and not too sharp?

FYI, the material is Nitronic 60, kinda like stainless 316. Using a single point lay down threading bar. SFPM = 360

Help!! :confused:

Here is what I would do. Put a 45 deg. chamfer in front and than use a file to sort of flatten the sharp section of the first thread. Only takes a few seconds to do it. Juergenwt.

Thanks... thats what we ended up doing after all... :)

Hmmm... we filed by hand after the part was off the machine, but now I wonder if it wouldn't have been better to do it on the machine when the parts turning...

Is that what you meant? Have you ever tried that?

It can be done by a skilled person. You did the right thing.

The trick I use to get a burr free part in stainless is to rough and finish diameter with 45 degree angle on the start then thread part to finish depth. Then run finish turn pass again and run thread pass at finish depth or .0005 above. Use G92 for thread for complete control of thread depth. Takes a little longer but produces a real clean part and can be used on all material.
If you are really serious after threading add a grooving tool in thread cycle and start thread 1/2 pitch further out.If 6mm start on 2mm thread start at 7mm with same lead and end at -1mm pull out makes a pretty higbee at thread start. When I was younger and had real fast reaction speed I used to do this on a manual lathe I still dont know if I was just showing off or was just too lazy to file the start thread. Laziness is the mother of innovation.