[Joe.B]

Has anyone ever had to cut a thread with a relatively "large" lead? By large I mean your "F" is 2.25 (which is approximately 0.444444 threads per inch).

Just curious, what kind of RPM's were you able to use? What make/model CNC did you use?

Thanks

[fizzissist]

Yeah, but I called it a helical groove.
The faster the lead, the slower the rpm.

[txcncman]

Not sure what the make and model of the CNC has to do with it. As fizz indicated, you will have to run RPM within the limits of keeping the IPM feed rate to that your machine can travel. As far as machine makes? Uhhh...Mazak and Leadwell. Maybe a couple of others. Models? Been 5 or more years ago. I do not recall specific models.

[Joe.B]

Thanks, guys. As usual, I'm just trying to do a little research for a company. The statement I was exploring was this:

"You can't keep a 2.25 lead on a new Doosan Puma TT2500 @ 300 RPM's. In fact, there are NO Doosan/Daewoo, Mori Seiki, Mazak, or anybody else that can do that. It's impossible. It doesn't matter if it's new OR old!"

Well, the Doosan techs & engineers say it's totally possible. They also hired an outside guy to evaluate it. They're so confident about it, they'll refund everything & take the machine back if it doesn't work...

But there are always "class A" machinists out there that like to pretend that they somehow know the equipment better than the people that actually designed & built it.

[txcncman]

It is easy enough to do the math. A 2.25" pitch at 300 RPM comes out to 675 IPM. If your machine can operate in feed mode at 675 inches per minute, then it is totally doable for you. The rub comes in when you have a machine that will say rapid at 800 IPM but will only feed at 400 IPM. I have run into this "halvzies" problem with several machines over the last 17 years. Might just be a parameter setting thing. I do not know. To compensate, as long as you can get the finish required, you can just take your maximum feed rate for your machine and divide it by the pitch and get the maximum RPM that the spindle can turn. If your maximum feed rate is 200 IPM divided by 2.25" is 88.89 RPM, rounded down in this case to 88 RPM.

I think you might find when you combine the surface speed of the diameter and RPM with the IPM of the tool at 300 RPM, you will be beyond the recommended surface speed for your tool and material anyway. Just do the math to see.