Bridgeport Manual to CNC conversion...

[Davek0974]

Thanks, so there is no difference in current draw if a 3ph motor is running on 3ph or on converted single to 3ph via a vfd (apart from the internal vfd usage) ??

[Davek0974]

Just got a reply from my supplier, in a flat-out full-load situation, the draw on the supply will be 22.5A, above that then the inverter will start reducing speed, prolonged load will trigger a shutdown.

Question is - can a small Bridgeport actually USE 3Hp/15Nm at the spindle :)

[m_c]

Thanks, so there is no difference in current draw if a 3ph motor is running on 3ph or on converted single to 3ph via a vfd (apart from the internal vfd usage) ??

That depends on where you're measuring the current, which is why you use the KW rating to work it out.
I was going to mention just how much the VFD will allow the motor to run above it's rated power, but I see the supplier has answered that.
Although the motor is rated at 3HP/2.2Kw, that'll be at 50Hz speed rating. When you increase speed, you can think of AC induction motors just like a steppers, in that the key factor is how much current you're putting through the windings.
So double the speed, and you can double the power, which means your 2.2kw motor running at double the 50Hz speed could produce well over 4kw.
Off course as with steppers, you need to monitor temperature, and if running at low speed a lot, you may want to consider getting a forced induction kit for the motor (aka a cooling fan that bolts onto the motor) to avoid overheating the motor.

[Davek0974]

Thanks, i had it running tonight and it draws about 3A idling.

It has a PTC built in for the temperature and that will be wired in to the VFD in due course.

Looks like i have exactly 10:1 speed ratio from 10 to 100Hz which figures, works out nicely at 300 to 3000rpm.

Stopping in 1s is pretty impressive :)

Now to configure it for cnc control...

[Colin Barron]

Thanks, i had it running tonight and it draws about 3A idling.

It has a PTC built in for the temperature and that will be wired in to the VFD in due course.

Looks like i have exactly 10:1 speed ratio from 10 to 100Hz which figures, works out nicely at 300 to 3000rpm.

Stopping in 1s is pretty impressive :)

Now to configure it for cnc control...

Will the momentum of the spindle and cutting tool not damage the belt if you continually stop quickly?

[John S]

Probably not the belt but it will shag the keys and keyways up in the back gear unit.

That and the varispeed sheaves which Dave has got rid of are the weak points in these heads.
No idea why anyone wants to stop that quickly anyway, it's not like a Bridgy is a production machine and saving 1 second on 15 auto toolchangers is a game changer

[Davek0974]

Yes, its hard on the head and it sounds hard on the head, thats my reason to slow it down a bit, there really is no point in sudden stop on a machine with splined quill and all that other crap up top ;)

The chances are that most of the dog-clutch wear was caused by my using it for running a 12-1/2" dia fly-cutter when cutting the saddles on the traction engine cylinder block and chimney base and perch-bracket - these would take many hours of running in back-gear and really worked the old girl. It was a job for a HBM really but when you have a Bridgeport you can do pretty much anything;)

The tiny splines and those dodgy dogs are certainly a weak spot, rarely fail but wear a lot and get very vocal, you can wreck the dogs by being a jack-the-lad and changing gear while the spindle is running, would never do this but have seen the carnage caused.

The belt i have fitted is good for something like 60-70hp so i doubt that will be bothered ;)

[Davek0974]

Been messing with rigid tapping - looks like it will be good:)

Also have live spindle speed on screen by changing the DRO from 202 to 39

Have set the vfd display to show load in kW - i could mount the display remotely or fit an analogue 0-10v meter which would show 0-150% of motor power. So far i have not made it go over 600W :)

Getting there.