Mazak QT-15 stalling spindle ????

I'm having a problem with my QT-15.

On larger diameter work, around 3" or bigger, my machine wants to stall on facing cuts. The job I'm working on now is A-2 material, about 3.800 diameter. I have the machine limited to 1000 RPM. Using Mazatrol, I programmed an edge face cut. I backed off the Autoset feedrate to about .012 feed, and depth of cut to .05, and kept stalling the spindle on the first cut, wasting my insert and guaranteeing that I have to go through and pick up every tool again..........which is a huge pain in the ass. The Autoset feature has the spindle running at about 250 RPM or so during the first few cuts. Based on my manual lathe experience, the speeds, feeds and depth of cut all seem reasonable to me for the horsepower this machine has.

Now, I wonder............... is it possible that I'm programming my cutpoint too close and the spindle isn't getting up to speed before the tool bites in ???? If my stock measures at 3.800, should I program the cut point another .02 or .03 bigger ???? Or is my cut too aggressive........or possibly a mechanical problem, such as loose belts or something ???

Otherwise, the machine seems fine.




Frank

Those feeds and DOC are right at about what I use for 303/304 (My inserts like less than 30 thou at a time though)

The simple solution for finding out if your trying to start too quick would be to feed hold before the cut starts. The spindle should stay going, and if it's lagging it should give it time to get to speed. Cycle start and see if it stalls.

I never program my cut point larger than material size, and I usually bump it closer using the tool path settings if it's a long run of parts. (especially with groovers, mazatrol likes to give them a mile of air to cut it seems.)

I've never been deep enough inside either of our 15's to give you advice for things to look for mechanically. I'd say you have something bad somewhere though, my experience isn't enough to say what though...

Frank,

Over the last few weeks I've been doing onesies out of A2 and D2 steels on our QT15 similar to yours. I think I capped the RPM @1800, but the SFM for roughing is around 240 and finishing is at 310 ish. I backed waaay off on the feed to .006/rev... (Just because I didnt' want to push it, didn't care if it was slow just wanted parts done) and .050 depth of cut. Works fine.

I usually put my cutting point # a little more than the actual stock, +.02 to .03.... but I don't really think that it would stall because of that. Didn't you already put new belts on that thing? What does the load meter do?

Tom

Yes. the machine has new belts installed. I actually forgot to look at the load meter. It scares the shit right out of me when it stops the spindle. I hit feed hold as fast as I can......but things usually get crunched in the meantime.


Frank

Yea... Feed hold wont do much for ya at that point. Unfortunately there is a real possibility you have a bigger problem. Thinking about it and really the only time we stall out these lathes is on our qt20's when we run these 15+ inch diameter steel plates and rough the outer edge. Very slow rpm and these machines don't have enough torque at that spindle rpm considering they were not built for that size part. So I'd say you would REALLY have to get after something to stall one on a small diameter part... Does it work if you back the feed off to something like .006 to .008 a rev?

I didn't get a chance to back it off on this job.......... but I've decreased the feed and depth of cut on other jobs and it did work. Maybe I'm trying to push the machine too hard at a slow speed. I don't know how much low end torque these machines have, and I'm not sure what I can get away with on the machine.


Frank

There are problems in the spindle controller that act like a car engine with a couple of cylinders not firing. Noticeable at low speeds with skipping and lack of power, and not a problem at higher speeds not needing a lot of power. This is more of a problem on a mill that uses the motor to orient the spindle than on a lathe.

The top 3" high box at the top of the spindle controller is the power supply for the electronics. There are roughly 20 outputs that are used to turn the power transistors on and off that are generating the 3 phase power for the motor. When there are missing outputs, there will be missing half cycles in the 3 phase power. Like the car, there is a loss of power. These problems are frequently intermittant, work fine when cold and bother when warm, or just bother at slow speeds under load some or most of the time. In mills during orient, the spindle will drift from orient during tool a change and break pockets in the tool changer, or drop tools.

The good news is, there is a real easy test. Start the spindle at the lowest speed possible, and watch the pulley on the motor. Does it turn fairly smoothly, or does it seem to "cog" or slow down, even momentairly stop, every 1/2 or 1/4 turn? Try the same test on all your Mazak's both mills and lathes and observe the results.

If you have 2 machines with the same power supply, try swapping them to see if the problem stays with the machine, or moves with the P.S., or just goes away for awhile (probably the most common result).

Bill


P.S. the load meter may not show an overload condition. The on screen speed display should show large changes in RPM for moderate cuts at slow speeds.

I would half the doc, bring down the feed to. 01, definitely run it much faster if it's a rigid set up. I work with two of the same machines and they can handle massive cuts so I'd check belts and above suggestions.

I paid a guy to install the machine, and he noted that the belts were worn. I ordered the belts and he put them on. I haven't looked at them since. Maybe he doesn't have the proper tension on them ??? How tight should they be ???



Frank

Not sure of the QT-15 in specific but generally speaking belts should have less then ~1/2" deflection in the longest span.

I don't know Mazaks but isn't your problem locking the spindle RPM so low? Take the RPM lock off, try 80-100 SFM, if it works you can always wind up the SF. Assuming your feeding in IPR.
My little Mori's that never saw 20hp on a good day did this cut all day in 410ss at 40hrc

If it was the belts and you arnt getting an audible squal when the spindle stalls you might want to look for oil leakage on the drive groves of the pully ,or a worn pully.

Pull the covers and look

I am not familar with a mazak but if it where a mori it could also be the clutch.

I dunno about Mazaks, but I second the clutch. Does the lathe have a transmission? Could it be stuck in high gear?

There's parameters on the spindle drive that governs the time it takes the spindle to reach the programmed spindle speed and more parameters that governs the length of time it takes to slow down or stop. If these have been backed off a bit, meaning that it takes longer for the spindle to wind up (which is better for the drive) then it could be that you're starting to cut as the spindle is just winding up. We're talking seconds and fractions of seconds here, Greg and Wippin' boy know more about this than I do. If your rappids are at 100% I'd say reduce them to half and prog the tool to rapid to a small bit above the job and start feeding should give the spindle a chance.
I'm only thinking out loud here really.

Is this programmed in IPR, or you did the math and are feeding in IPM?

If it is in fact programmed in IPR, a stalled spindle should NOT blow the tool eh?
(Just ass_u_ming as I most always prog in IPM)


-----------------------------

Think Snow Eh!
Ox

I would check the belts

Just wondering, if the belts slipped wouldn't the machine know the spindle it going Zero and the motor is still going at whatever speed and alarm something, or is that the 1 alarm nobody thought to put on there?

My thoughts are it is belts. If you just have had them replaced then it seems quite likely. It might have been put on a bit loose and belts generally get a bit more loose as they wear in, I would loosen and try adjusting the pulleys to make sure they are reasonably taunt.

rockfish said:

I'm having a problem with my QT-15.

On larger diameter work, around 3" or bigger, my machine wants to stall on facing cuts. The job I'm working on now is A-2 material, about 3.800 diameter. I have the machine limited to 1000 RPM. Using Mazatrol, I programmed an edge face cut. I backed off the Autoset feedrate to about .012 feed, and depth of cut to .05, and kept stalling the spindle on the first cut, wasting my insert and guaranteeing that I have to go through and pick up every tool again..........which is a huge pain in the ass. The Autoset feature has the spindle running at about 250 RPM or so during the first few cuts. Based on my manual lathe experience, the speeds, feeds and depth of cut all seem reasonable to me for the horsepower this machine has.

Now, I wonder............... is it possible that I'm programming my cutpoint too close and the spindle isn't getting up to speed before the tool bites in ???? If my stock measures at 3.800, should I program the cut point another .02 or .03 bigger ???? Or is my cut too aggressive........or possibly a mechanical problem, such as loose belts or something ???

Otherwise, the machine seems fine.




Frank

Click to expand...

The programmed cut you have should barely register on the spindle load meter. I would be surprised if it reads over 10% load.

Problem is the belts slipping BADLY (likely cause) or spindle drive issue (doubt it). Take off the side cover, shine flashlight on motor. If motor stops, spindle drive issue. If motor continues to spin when spindle stalls, tighten up the belts.

With a 1,000 RPM MAX in program, the spindle will have plenty of time to slow down for next facing cut, so that is not the issue.

This machine has no clutch or gearbox--one speed range. The motor is oversized to compensate for a lack of transmission. The belts need to be in good working order and properly tensioned to transmit full torque at low speeds.

SND said:

Just wondering, if the belts slipped wouldn't the machine know the spindle it going Zero and the motor is still going at whatever speed and alarm something, or is that the 1 alarm nobody thought to put on there?

Click to expand...

no you can run the spindle motor with no belts. ie your spindle has spindle noise, take off belts and run motor only to see if it is in the spindle or the motor. You would only get an alarm when trying to thread.

Justin Terry