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SQT 250MS sub spindle jittering.

Scruffy887

Titanium
Joined
Dec 17, 2012
Location
Se Ma USA
Ran last Friday for about 6 hours straight and threw an overload alarm. Sub spindle rotation was a bit stiffer than normal, and chuck very warm. Motor was very hot. Let it sit all weekend and all seemed fine Monday morning. This Mazatrol program uses the sub just as a bar puller and both spindles are linked at start up. We always need to unlink before running after startup. I could hear the slight singing of the windings like normal. I put some rotational pressure on the sub and it started twitching about 25 degrees back and forth. Bad cable? Guessing that was what caused it to overheat and shut down. 1998 machine I think.
 

RoundHouse M&F

Plastic
Joined
Oct 12, 2020
Location
Speedwell
How many hours total on the sub? We have a 93 SQT18ms that had to have the sub rebuilt, all of a sudden one day it would throw an over-current/over-amp alarm if it revved to fast, and it became guttless, A normal cut in a program that did say 20% load went to 60% which would also cause it to alarm out. It would run and made a electrical whine/groan.

Sent the motor off to be rebuilt and they said the bearings were good (had them done anyway), but the rest of the inside looked like crap but not completely trashed. Also replaced the encoder board on the back of the motor (think it was a PLC board, cant really remember what it was called) and updated the flexible conduit as it was wore out and the metal was showing.
 

madmachinst

Stainless
Joined
Jan 15, 2007
Location
Central FL
How many hours total on the sub? We have a 93 SQT18ms that had to have the sub rebuilt, all of a sudden one day it would throw an over-current/over-amp alarm if it revved to fast, and it became guttless, A normal cut in a program that did say 20% load went to 60% which would also cause it to alarm out. It would run and made a electrical whine/groan.

Sent the motor off to be rebuilt and they said the bearings were good (had them done anyway), but the rest of the inside looked like crap but not completely trashed. Also replaced the encoder board on the back of the motor (think it was a PLC board, cant really remember what it was called) and updated the flexible conduit as it was wore out and the metal was showing.

OMG how much did that cost? Mine sitting 1 year in container just today got a phase converter for it and teh sub spindle seems like it is stuck. Greased it well with PB blaster surface shield, but now stuck. I am praying that some solvent and lots of rags will help. Wasn't stuck before. BTW here video of machine running spindle before I bought it. MAZAK SQT-18MS - YouTube suggestions on how to unstuck it? Deadblow hammer on the jaws? Small fast impacts with a soft anvil?
 

RoundHouse M&F

Plastic
Joined
Oct 12, 2020
Location
Speedwell
Rebuild was around 6-8K. Not including our repair tech putting it back in and re aligning everything or the encoder board. Also it still makes a pulsing sound when the two spindles are synced, might be the spindle drive. Had to have that gone thru not to long before the spindle had to be rebuild.
 

Scruffy887

Titanium
Joined
Dec 17, 2012
Location
Se Ma USA
I spoke with Mitsubishi yesterday and was told the sub may need tuning. Or it could be the drive. They can send a tech to diagnose who will have a spare drive with him if I want.
So I looked at the Mazatrol program and added a M301 at the end to un ling the sub. Machine ignored it. Took it out and looked at the last unit, SUB SPINDLE MOVE. I had a 1 there telling the sub to link with main while traveling home. Sub would stay spinning until it parked, then stop and start the rotary oscillations. Changed it to 0. Running fine now. Sub spins up to 500 rpm for the bar pull, chuck opens and sub stops spinning and goes home.
 

cnctoolcat

Titanium
Joined
Sep 18, 2006
Location
Abingdon, VA
Good to hear you got it sorted out.

Usually, jittering or hunting of a spindle is indicative of a bad/out-of-adjustment PLG, or flakey spindle drive.

The PLG is relatively easy to tune in, an oscilloscope is required for the best results.

The Mitsubishi spindle drives in Mazaks are set for blazing accel/decel from the factory, and after a couple decades that can help explain why the spindle drives are such a common failure point on older Mazaks....

I always slow the accel/decel rates on my Mazak lathes, helps the drives last longer and saves a bit on electricity.

ToolCat
 

Scruffy887

Titanium
Joined
Dec 17, 2012
Location
Se Ma USA
Good to hear you got it sorted out.

Usually, jittering or hunting of a spindle is indicative of a bad/out-of-adjustment PLG, or flakey spindle drive.

The PLG is relatively easy to tune in, an oscilloscope is required for the best results.

The Mitsubishi spindle drives in Mazaks are set for blazing accel/decel from the factory, and after a couple decades that can help explain why the spindle drives are such a common failure point on older Mazaks....

I always slow the accel/decel rates on my Mazak lathes, helps the drives last longer and saves a bit on electricity.

ToolCat

I spoke too soon. Got 12 bars through the machine when it happened 2 weeks ago, 13 today and same thing. Sub motor was so hot I could not keep my hand in it. Sub only spun up for bar pull. Small simple part and we get 87 parts per bar in a 32 min run cycle. Reboot control to clear errors and just powered up the sub to about 5-800 rpms and could hear a lot of noise from the windings as there is some sort of problem.
Tomorrow I will remove any powering up of the sub and just bar pull without spinning.
 

Scruffy887

Titanium
Joined
Dec 17, 2012
Location
Se Ma USA
2 Days straight with no issues, as I removed all rotation of the sub from the program. But I did power up the sub to 10 rpms and the rotation was noisy and jerky. Then I moved the B axis and the spindle stopped and there was this sorta hissing sound. Cable problem.
 








 
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