Series II NC2BC3P spindle problems

[SCMW]

Hi,

Of course, it always happens at the end of a project with one last series of parts to make. One of my Bridgeport Series II NC's S/N T313 (I have two of them S/N T313 and T1344) was having a problem starting the spindle. Both run Mach 3. This mill was running at about 1200 RPM on the spindle and I started dropping the speed as I was cutting some thin styrene plastic. Unfortunately the spindle slowed down and froze. I tried to restart it but just get the three phase hum for a few seconds before I shut it off.

Originally we suspected that the motor might have given up the ghost. Thankfully it is NOT the motor. We backed up the spindle and worked the speed control knob on the upper right of the head back and forth. Getting it to the slowest setting is a real bear. The speed knob rotates smoothly from 1000 RPM and higher. We rolled it up to 1200 RPM and tried the motor a couple more times. She finally broke loose and started spinning. After playing with this a bit more, we suspected that the brake was binding below 1000 RPM.

Today I ran a quick profile job on some .016" 6061. I'm now getting a thumpa thumpa type of a sound. It made me think that the belt was going. I can see the motor load meter ramp up slowly to meet the thumpa each time. I'm beginning to suspect that it might not be the belt or the brake but the variable speed control as the noise seems to be emanating from the front part of the head. Also the speed dial pushes out a little more now.

Does anyone have any ideas what I might be up against? I'd like to get it back to normal as soon as I can. Also, how quiet should these mills be when the spindle motor is on?

Thanks in advance,
Terry

[cvoissem]

This is off subject, but how are you running Mach3 on the Bridgeports? Did you swap out the EZ-Trak controller entirely? Or just the interface computer? We have a Series II EZ-Trak that we'd like to upgrade the controller computer in, but don't really know where to start.

[machintek]

A S2NC is a stepping motor, box way machine with a 4 HP spindle motor and stepper axis motors. I am curious how they interfaced the spindle wizard! So it is not at all compatible with a EZTRAK control.

George

[machintek]

All the vari speed Bridgeport suffer from the eventual demise of the bushings in the vari drive disks. The speed control pulls a arm down that pulls the front pulley down against the forces of a large spring on the spindle motor vari drive disk.
You will have to pull this apart to see where the bind is. It is quite possible that the key may have wedged in a vari drive and thus it may not want to move (but it should turn). I have seen keys fall out and the spring keeper start to turn on the motor shaft snap ring. Eventually it wears through and goes boing then rubs on the cover. Also seen a bushing get free, spin and then prevent the vari drive from moving as it interfered with the key.
Disassembly may be your only recourse.

George