Thread Inserts

[pipeclay]

I dont really think the safety cutout at the rear of the lathe was originally designed to be used as an auto feed/screw cutting depth/travel stop.
It appears to be more of a safety cutout feature so as to nstop people/students running into the chuck or cross slide.
You really wouldnt want to be stopping a tool under load.

[Anorak Bob]

You can probably find a used 3 phase motor of appropriate appearance easy enough Bob, I think people are swapping them out all the time. Yes I agree, the VFD actually brakes the motor, and it doesn't just coast to a stop. Once you've had the luxury of variable speed drive however you'll wonder why you took so long. I am constantly adjusting my speed on the lathe depending on what I'm doing. There's no way in heck I would be changing belts to do the same thing.

Pete

Pete,

Even I have embraced some of the newer technology available. Both mills run on TECO VFDs. I've changed the 9's belt that often that I don't even think about it.

Bob.

[Pete F]

I dont really think the safety cutout at the rear of the lathe was originally designed to be used as an auto feed/screw cutting depth/travel stop.
It appears to be more of a safety cutout feature so as to nstop people/students running into the chuck or cross slide.
You really wouldnt want to be stopping a tool under load.

The lathes didn't originally have VFD either.

The tool isn't under load Peter, it is in the runout groove as per usual. If you were threading without one for whatever reason, the VFD has a brake program, mine is 2 seconds on that machine IIRC. The 2 seconds as the spindle slows down will give you more time to back the tool out while allowing faster threading speeds. I have seen similar stops fitted to other machines to be used in a similar manner and they didn't seem to have an issue.

Pete

Edit: Here is a video of somebody using this type of thing. In this case he's reversing the lathe which would slow the whole thing down I'd think. Using the half nuts would be faster. However the whole point is to allow higher spindle speeds if it's felt that would assist with the carbide cutting.

Auto Thread Stop Video by Arrak_Thumrs | Photobucket

[Anorak Bob]

Hey Pete,

Arthur has to reverse that 102 because it's nutless.

I haven't fiddled with the braking time on my VFDs. I think some drives have a DC braking feature but I'm out of my depth even thinking about how that might work.

At high speed, let's say 1200 rpm and with the feed set at its slowest rate, the cutting tool is going to traverse a fair distance in a couple of seconds necessitating a wide runout groove or more abrupt braking. It would be reasonable to suggest reducing the spindle speed to a more managable rate but carbide thrives on speed.

Might the answer be an inverted tool and the spindle run in reverse?

Bob.

[morrisman]

Hi

Could one use a thread chaser to get that ' clean neat ' look . Only downside is you need a chaser for each pitch .

Mike

[jack620]

At 1200rpm, cutting a 1mm pitch thread would have the carriage moving at 20mm per second. Spooky.

[Pete F]

Bob, I was doing those dummy runs at quite high speed and the spindle stopped reliably within about 10 degrees of not only the same point of the traverse, but of the same spindle revolution of the same number of turns. I reckon that's accurate enough When I spoke to Arthur about his setup he said he "tweaks" the precise stopping position by varying the rpm.

Pete

[Pete F]

Bob I did a test of threading using the electronic cutout. I discovered a major flaw with using the 260 system in this way, at high speed the inertia of the system and braking time means the flat part of the limit stop hits the casting before the whole lot has come to a stop. It would either require an external switch or perhaps a modification to the existing plunger. I did however cut a 1 mm thread quite successfully at 300 rpm, a complete no-brainer. However since this is roughly what speed I'd be threading anyway there was no advantage. However it certainly did prove the system works as expected for those who may be inclined to go down that path and push the speed higher.

Pete