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Approximately how long between backlash adjustments on B axis of HMC's

Edster

Diamond
Joined
Feb 8, 2003
Location
Illinois
Approximately how long between backlash adjustments on a full 4th B axis on a horizontal machining center? Is this something that needs to be checked on a relatively new HMC after things break in a little?

Thanks in advance! :cheers:
 
The machine in question is a 2011 Okuma MB4000H with full 4th. It has a worm gear drive with a rotary encoder mounted directly to the B axis. I've been getting intermittent following errors on the B axis for a while and it just started to get worse with an occasional B axis motor overload. The machine was bought new, never crashed, and has low hours.

I'm not real familiar with the maintenance requirements of the B axis. the worm is tapered and there is a procedure for adjusting the backlash. I'm wondering if this is a good place to start, and how often backlash is checked and adjusted on these types of machines.
 
Just call the dealer and they can tell you. The worm gear is not something you would want to jump into blindly. I'm sure you can handle the adjustment, but you would not want to go too far and damage those gears.

It sounds like you might have a bad servo drive.
 
I'd be calling the manufacturer (and then I'd come back here and post the results/experience so we can all benefit from it).

Matt
 
Older Okumas used a rotary Inductosyne scale for B. Not very well protected from coolant and chips, they didn't last as long as they should have. Where I used to work we had 5 of them and all had gone bad within 5-7 years. I have no idea if the newer machines are the same. IIRC, a following error alarm was one of the symptoms leading up to failure.
 
I had a tech out here yesterday morning and he believes it is backlash in the gears causing the problem. He brought up the screen where the position from the scale was, and the position was fluctuating quite a bit. The load was also high on the B axis when jogging it. He disabled the scale and the load went down to normal levels. You could also see the backlash when jogging the b axis after the scale was disabled.

The tech told me about the older design for the encoder and how it was problematic. We have the newer design so hopefully they improved it.

We also drained the oil looking for any signs of metal, but didn't see anything.

I figured the backlash would have to be adjusted some day but not this soon. The machine has around 2000 cycle start hours on it.
 
It depends on the type of rotary. I have some Toyoda HMC's with Nikken table that were arc second accuracy after the thk rails were all worn out.... depends on how they were built and how used.
 
Must not be many full 4th HMC's out there. :)


From my experience - I have come to the conclusion that a full fourth on an HMC is a liability in more ways than one if you doo not absolutely need it.


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Think Snow Eh!
Ox
 
I recently rebuilt a full b axis on an MB5000 and setting the backlash was pretty simple. There is a procedure for doing this. You shouldn't have to adjust the backlash on a machine with low hours like yours. The pinion was steel and the ring was brass or bronze. The pinion isn't tapered either but is offset so the farther in towards the ring the less backlash you have. The pinion bearing housing is threaded and has 6 bolts IIRC. To adjust you remove the bolts and turn the housing. Clockwise one bolt whole pattern would take out backlash etc. The one I worked on had a DD encoder which is a bitch to set. I installed the b-axis but got pulled off the job for some other grunt knuckle busting low/tech job before we set the encoder. :D
 
I don't think there are. Personally, I'd have to think long and hard before I bought a used machine with a full 4th. That seems like a ticking time bomb.

Weird.. I couldnt see life without the full 4th for what we do... We have 5 mazaks with full 4th... I have seen very few issues with the B on these machines... One I seem to recall having an issue, but it was due to negligent "maintenance"
 
Weird.. I couldnt see life without the full 4th for what we do... We have 5 mazaks with full 4th... I have seen very few issues with the B on these machines... One I seem to recall having an issue, but it was due to negligent "maintenance"


If you doo much heavy machining in steel - big drills especially - clear out at the ends of your X travel - you can start wishing that you had a 1* indexing.


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Think Snow Eh!
Ox
 
I have run into one feature in my career where some asshole made two faces half a degree apart (ie 27.5 degrees). I think we had to fudge the fixture so the parts were "off" 1/4 of a degree at each index so it was in tolerance.

I've never run into a true full 4th app for a HMC. Everything I've seen that was full 4th needed a tailstock.
 
Well, the tech was here again today. He adjusted the backlash, but the servo load was still high. He pulled out the worm and the bearings (tapered roller) were pretty rough looking. After taking out the worm, and unclamping the brake, the table didn't want to move by hand. He's thinking the brake is dragging for some reason. That's it for today, tomorrow more disassembly.

20150616_163731.jpg 20150616_163739.jpg 20150616_163830.jpg
 
If you doo much heavy machining in steel - big drills especially - clear out at the ends of your X travel - you can start wishing that you had a 1* indexing.


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Think Snow Eh!
Ox

Well in that case sure... Luckily I have never had a need to do anything like that... :D

We do "just" aluminum for the most part on our horizontals.. Must be from the way we baby them, that is why we haven't had issues ;)
 
Well, the tech was here again today. He adjusted the backlash, but the servo load was still high. He pulled out the worm and the bearings (tapered roller) were pretty rough looking. After taking out the worm, and unclamping the brake, the table didn't want to move by hand. He's thinking the brake is dragging for some reason. That's it for today, tomorrow more disassembly.

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Good luck and keep us posted with this
 








 
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