What's new
What's new

Tapping on Bridgeport with RPC

zr1nsx

Aluminum
Joined
Dec 31, 2007
Location
indianapolis
When using a rotary phase convertor, is it possible to quickly reverse spindle direction? Example, tapping at 850 rpm and reversing without stopping spindle?
 
if the RPC is properly sized to the motor, it should be perfectly possible. I don't tap that way, but the lathe has no problem reversing in a snappy and quick manner running on an RPC.
 
I am running a 1hp motor on a 10L Southbend Lathe, a 3hp motor on a Standard Modern lathe and a 2hp motor on a Chinese BP clone on a 5hp RPC. All three motors will reverse when the switch is turned without issue. I occasionally power tap on the mill and Standard Modern lathe.
 
Thanks for the replies. I too have a Bridgeport clone that is currently being run on a static converter. Has been running for 10+ years this way, but of course if you try to reverse the spindle before it is almost completely stopped it just doesn't like it. I got a as new Phase Craft rotary converter for cheap and was curious what to expect as far as spindle reversing performance is involved for power tapping. Have wanted to do this for a long time even though I don't really do that much machining or tapping at home.
 
I'm sure the price of the RPC may have been the determining factor, but going from a static to a rotary when there are so many VFD's out there semi boggles my mind. Unless the RPC was a large unit that powers multiple machines, a VFD would have been a much better choice...in my opinion anyway.:)

Stuart
 
I'm sure the price of the RPC may have been the determining factor, but going from a static to a rotary when there are so many VFD's out there semi boggles my mind. Unless the RPC was a large unit that powers multiple machines, a VFD would have been a much better choice...in my opinion anyway.:)

Stuart

Can you plug reverse a VFD? I have a 20 HP and a 10HP RPC. Be boggled all you want, I also have 2 VFDs and I won't be getting any more.
 
I'm sure the price of the RPC may have been the determining factor, but going from a static to a rotary when there are so many VFD's out there semi boggles my mind. Unless the RPC was a large unit that powers multiple machines, a VFD would have been a much better choice...in my opinion anyway.:)

Stuart


If he wants quick reversing, for tapping, a matched size VFD may not do that. It depends on how fast it can do a decel without an overcurrent, or perhaps an overvoltage.

If oversized sufficiently, it may do a very quick reverse. But mostly a really fast reverse is about the same level of current as starting across the line.

If the VFD can stop the spindle in a very small number of rotations, then OK, but that takes a good deal of current to do. It is not always possible with a given VFD and motor.
 
When using a rotary phase convertor, is it possible to quickly reverse spindle direction? Example, tapping at 850 rpm and reversing without stopping spindle?

I reverse all the time with my RPC. The big question in my mind is how the hell are you tapping at 850 RPM
without a Tapmatic? Are you superman or what? At 850 RPM you would bury any tap in a fraction of a second, how can you reverse it fast enough? I tap 10-32 in aluminum with a Tapmatic at 800 RPM all the time.
 
Are you superman or what? At 850 RPM you would bury any tap in a fraction of a second, how can you reverse it fast enough? I tap 10-32 in aluminum with a Tapmatic at 800 RPM all the time.

i tap circuit boards at about 600 rpm (.3mm per revolution) and its painfully slow even with a tapping head that extracts the tap at twice the driving rpm. i need to automate myself out of a job and build a machine to tap both holes at the same time at about 3 times the rpm.

i watched a friend's brother speedio tap a 3mm (which i think is similar pitch) at 5000 rpm and its tapping the drilled hole about as fast as i would consider drilling it. his machine can start and stop the spindle in 200 milliseconds at 16K rpm.

and it shoves 70 amps of current back up the 240vac line to slow the spindle that quickly.
 
............
i watched a friend's brother speedio tap a 3mm (which i think is similar pitch) at 5000 rpm and its tapping the drilled hole about as fast as i would consider drilling it. his machine can start and stop the spindle in 200 milliseconds at 16K rpm.

...........


At 5k, the stopping is probably within 2 turns, and maybe under 1 turn. Nice.

With manual reverse, it is probably possible to reverse in a total of a second or so, half a second maybe, between the time to move the control and the time to actually reverse. At 800 rpm, that is about 13 turns in a second, and so 6 or 7 in a half second.

With a little advance on the initiation of reverse, so that the tapping actually completes during the slowdown, one might cut that in half. That looks do-able if you have a longish tap and get in a rhythm.

Might not be too hard to screw up, though.
 








 
Back
Top