Threading with carbide inserts

[mksj]

Made a new tool post today for another forum member that needed a metric M16-2.0 on the bottom and a 5/8-18 thread on the top. I started with 3/4" O1 rod and turned it down to size. Factory thread post is on the left and new post on the right. This is using a Carmex laydown insert and the M16 is a deep thread. Granted I did the M16 at 250 RPM, the 5/8-18 was done at 450 RPM, gives a clean cut with carbide, this is the insert finish.

 

[rwm]

How in the world do you guys thread up to the shoulder like that???? I have to make a relief groove to stop the tool in.
RObert

 

[mksj]

My hand eye coordination is not so good, I use an electronic stop system. If I recall Lonnie is also using the same system. In the past I would cut a 0.1" relief and thread at around 100 RPM, disengaging the half-nut at the end. Was pretty good at it 9 time out of 10, but also broke a lot of carbide inserts until I went to the laydown type. With the electronic stop my relief is the same width as the threading cutter, and I zero the system to stop at that point. It repeats to better than 0.001" so I do not get the anxiety I use to have with threading, let alone internal to the end of a blind cap. What does surprise me is how clean these type of carbide inserts cut, I can easily shave 0.0001-2" of depth with a nice curl. I also attribute this a bit to the lathe which at 2500 lbs, it is quite rigid and very comfortable to use.

So one other trick that I use for sizing threads, in particular small diameter work where you get more flex, is to cut 90-95% of the thread on the lathe and then do the last finishing fit with as adjustable die cutter. I use the old round style dies with an adjustment screw and have a tap/die holder for the tailstock so they run true. You can flip the dies when done and use the other side to carefully cut the thread to a shoulder or edge.

 

[macardoso]

My hand eye coordination is not so good, I use an electronic stop system. If I recall Lonnie is also using the same system. In the past I would cut a 0.1" relief and thread at around 100 RPM, disengaging the half-nut at the end. Was pretty good at it 9 time out of 10, but also broke a lot of carbide inserts until I went to the laydown type. With the electronic stop my relief is the same width as the threading cutter, and I zero the system to stop at that point. It repeats to better than 0.001" so I do not get the anxiety I use to have with threading, let alone internal to the end of a blind cap. What does surprise me is how clean these type of carbide inserts cut, I can easily shave 0.0001-2" of depth with a nice curl. I also attribute this a bit to the lathe which at 2500 lbs, it is quite rigid and very comfortable to use.

So one other trick that I use for sizing threads, in particular small diameter work where you get more flex, is to cut 90-95% of the thread on the lathe and then do the last finishing fit with as adjustable die cutter. I use the old round style dies with an adjustment screw and have a tsp/die holder for the tailstock so they run true. You can flip the dies when done and use the other side to carefully cut the thread to a shoulder or edge.

I’d be interested in the details of your electronic stop. I too thread to a relief groove, or thread away from the chuck.

 

[mksj]

I have been building VFD control systems for lathes that incorporate a proximity stop system, the sensor is integrated into the micrometer stop and triggers when the carriage when it comes within 12 mm of the sensor. This works in conjunction with the VFD braking system which gives a predictable stopping distance. There is redundancy in the system, so beyond the electronic sensor there is a mechanical limit switch that will also engage. There is also a proximity bypass switch which allows one to press it and back up the carriage without disengaging the half nut. One key factor is that the carriage is traveling at a fairly fast speed at say 450 RPM on a 11 pitch thread, so the machine continues for about 1 second after the it triggers.

It may be possible to rig up some form of mechanical switch that would act like an E-Stop, but without VFD braking the travel would be too long and probably less repeatable.

 

[Lonnie]

I made a short video of the stop in action a few years ago. It's not a great video but it shows how it works and how super accurate it is. There is absolutely no fear of crashing with it. I never used it when making the threads I posted above because there really wasn't a shoulder to worry about but I do use it quite often when there is a shoulder.

 

[mikey]

Gotta' admit that the electronic stop is slicker than owl do-do! Unfortunately, you need a VFD with braking resistors so us poor guys with non-VFD set ups are left in the dust. Mark, you are the man!

 

[Aukai]

Full depth, or step cuts?

 

[Bamban]

Gotta' admit that the electronic stop is slicker than owl do-do! Unfortunately, you need a VFD with braking resistors so us poor guys with non-VFD set ups are left in the dust. Mark, you are the man!

If one thinks the V way mounted prox is slick, here is Mark's one up to his traditional design. The modernized Baby Jet rocks.

The lathe does not have enough space between the gear box and the apron for the V way mounted sensor. On the 1024 the sensor mount rides on a linear bearing rail system and the metal plate that triggers the sensor is attached to the bottom of the apron by a couple of strong magnets.

I thread all the time with the proximity sensor. Don't remember now when we did the VFD conversion, must have been 2015 or 2016. Have chambered around 70 barrels or so on this system . Threads were cut with carbide inserts, and turned with carbide inserts as well.

 

[mikey]

Small wonder you like that lathe so much!