Mazak QT10 Spindle rebuild, need help!
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    Default Mazak QT10 Spindle rebuild, need help!

    Hi guys I have a early 80s QT10 that needs work on the spindle and I need some help. The spindle was perfect in this machine, never made a sound. But today it suddenly went downhill. In about 15-20 minutes it went from perfectly quiet to a very noticeable bearing noise. I cant understand how it went downhill so fast? Machine has the 3600 rpm spindle and it was only running around 1500 rpm, and couldnt possibly be doing easier work then todays job which was skimming 1/2" rod down to 12.5mm, only taking off 4 thou all day long?? Anybody have any ideas on what could have happened? Something get past seals maybe?

    Where do I start with this? How does it come apart? Does the whole headstock need to be removed or does the spindle just slide out? Is there a cartridge that slides out of the headstock casting or do the bearing races fit directly into the casting? Does all the sheet metal need to come off? Anybody have a cross section drawing of the spindle?

    I will need to do the work myself with help from you guys to make this worth fixing. Going to be hard to justify the cost of sending the spindle out for repair on this old machine.

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    First confirm it's definitely the bearing(s), and where. Use a mechanic's stethoscope (carefully) around the headstock and in the general area to try to pinpoint where the noise is coming from.

    Does the spindle feel rough when turning it manually? Removing the chuck and drive belts (if not direct drive) will make it easier to feel.

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    If it does turn ot to be bearings there was a very good thread that went through the whole process:

    Mazak QT 10N (1986) Which bearing numbers to use in the spindle?

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    Well I pulled off chuck, actuator and all belts and looks like bearings are shot. Sounds a little rough turning by hand and every now and then it makes a louder noise. Not good. I tried using a stethoscope and not getting a whole lot of noise on the bearing housings, cant seem to hear any more through stethoscope then I can without it. I cant say for sure if its front or back bearings, kinda seems noisy from both ends. Only force on it at the time was from tailstock so im guessing the angular contacts in the rear??

    I think I found drawings of my spindle, see attached. This is from a QT10 maintenance manual. Manual mentions both 2600 rpm spindle and 3600 rpm spindle in places, but does not say which one this drawing is for. Pretty sure the 2600 uses some kind of oil and the 3600 is grease packed so they must be different?? Also looks like this drawing has only 3 bearings, CWToyotas rebuild thread looks to be 4 bearings. Anybody know if this drawing is correct for the 3600rpm spindle I have?

    How do I go about removing this without damaging anything else? Ill take the pulley off tomorrow, whats the next move after that? Does the rear bearing block come out first or do I leave this in place and slide spindle out from the front? Doesnt appear to be any threaded holes in the rear housing to remove it. How tight are the rear bearings on the spindle?

    Link to spindle drawings and part list: Mazak QT10 Spindle.pdf - Google Drive
    Attached Thumbnails Attached Thumbnails spindle.jpg  

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    Never have worked on this sort of lathe, but my quick guess is you have to remove the pulley and key, then the front housing assembly and spindle pulls from the front, with the rear bearing housing staying in place (and can be removed afterwards).

    Again, just a guess, so check out the thread that was already linked above. Mazak QT 10N (1986) Which bearing numbers to use in the spindle?

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    Quote Originally Posted by Milland View Post
    Never have worked on this sort of lathe, but my quick guess is you have to remove the pulley and key, then the front housing assembly and spindle pulls from the front, with the rear bearing housing staying in place (and can be removed afterwards).
    I removed pulley and the bolts on the front housing. Gave the spindle a tap from the back and it did start to slide forward. But the front bearing housing is not moving. The inner race and rollers are sliding out of the outer race. See attached pic, everything below the red line in attached pic is moving. I moved it about 3/8" or so and then stopped when I realized this.
    spindle-2.jpg

    Everything still turns nice and free. The ends of the rollers in the front bearing are visible now and have show no signs of corrosion or overheating, and still have a little grease on them (not much). I would like to try and not damage this bearing. If the rear ones turn out to be the problem I may consider leaving the front alone to avoid the risk that comes with grinding spacers and possibly setting preload wrong for a new bearing.
    20200529_223412.jpg

    How do I get everything out from here? The front bearing housing does have threaded holes to jack it out, but they are blocked by a ring (item 9 in PDF) held between the spindle and bearing housing. The nut for the front bearing will soon hit the front bearing housing and drive it out, but the first set of rollers will be mostly out of the outer race by this point. Will this be a problem? Doesn't seem like a good idea to me. Im considering tapping it back in place a little and making a spacer ring (split in sections) that will go between nut and housing and allow spindle to push housing out with the bearing still inside the race. This spacer im thinking about is drawn in blue in the attached pic. Any thoughts on this idea? Should I just keep pushing as is? Will it harm the bearing to let the rollers extend past outer race? Will I be able to get them back in if I want to reuse that bearing? Thanks.
    spindle3.jpg

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    Also, The rear of the headstock has a fair size stain of dried up oil/grease below the spindle. Could this be the grease from my rear bearings? And maybe they just ran dry and failed?
    20200529_201709.jpg

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    At this point, just keep at it, the spindle will come out the front end.

    Check EBay for new-old-stock replacement bearings. The front roller is the least expensive, not sure if I would reuse it.

    I’ve rebuilt three Mazak spindles without the complex measuring and grinding of spacers, and they have all worked well. I just tighten the big adjusting nut till the roller bearing shows a little drag, then call it good.

    YMMV....

    ToolCat

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    OK guys I have an update... I continued tapping the spindle and the nut/plate did push the front bearing block out. This worked ok, but if anybody else ever has to do this I would recommend removing this nut/washer and simply sliding the front bearing out of the outer race, the whole spindle will slide rough out. The front bearing housing can then be removed from the headstock with bolts in two tapped holes. I bet this was the way it was designed to come apart.

    After removing the spindle I confirmed that my spindle does use only 3 bearings, its just like the attached drawings which is different then CWToyotas spindle. I pulled everything apart and to my surprise all the bearings looked good. Not a trace of rust on them, no signs of overheating and they all had grease left on them. The rear bearings were just like new but the front bearing did have some rough spots in it and I guess this was causing my noise. The inside of the outer race of this bearing looked perfect even though the bearing felt a little rough. So I thought maybe It just picked up a piece of dirt or a chip somehow? This would also explain the sudden failure of what seemed like a perfect spindle.

    So I flushed out all the old grease from the bearings, put a little oil on them and they all seemed fine, even the front one! I considered my options at this point and decided it would be worth a shot to just try reusing the bearings again. I flushed the bearings again, carefully packed them with the proper amount of isoflex NBU 15, and put it all back together. Ran it slow for a while, then gradually increased speed to 1000rpm for a short period of time and everything seems fine. Nice and quiet just like before. So may have dodged a bullet here. Time will tell i guess, but looking good so far.

    How should I run in the spindle now? Anything special need to be done to distribute grease or anything before returning to normal operation?

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    Put 2 thermometers as close to the bearings as possible and dont let them pass 60C (140F)
    Start at 200rpm until temp is stable (at least 1 hour)
    Run at 500rpm until temp is stable or dropping (at least 1 hour)
    Run at 1000rpm until temp is stable or dropping (at least 1 hour)
    Run at 1500rpm until temp is stable or dropping (at least 1 hour)
    Run at 2000rpm until temp is stable or dropping (at least 1 hour)
    Run at 2500rpm until temp is stable or dropping (at least 1 hour)
    Run at 3000rpm until temp is stable or dropping (at least 1 hour)

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    Quote Originally Posted by benganboll View Post
    Put 2 thermometers as close to the bearings as possible and dont let them pass 60C (140F)
    Start at 200rpm until temp is stable (at least 1 hour)
    Run at 500rpm until temp is stable or dropping (at least 1 hour)
    Run at 1000rpm until temp is stable or dropping (at least 1 hour)
    Run at 1500rpm until temp is stable or dropping (at least 1 hour)
    Run at 2000rpm until temp is stable or dropping (at least 1 hour)
    Run at 2500rpm until temp is stable or dropping (at least 1 hour)
    Run at 3000rpm until temp is stable or dropping (at least 1 hour)
    Thank you for posting this! I was getting a pretty good temp rise on the front bearing when I briefly had it up to 1000 rpm last night. This worried me a little. I followed your procedure today and sure enough with each rpm increase I would get a little temp rise on the front bearing (10-12 degrees C over ambient) and after a half hour or so it would peak and then start to drop. I have it running now at 1500 rpm and only 4-5 degrees over ambient. This is as fast as I go on this old machine so Im going to call that good. Everything sounding good. Ill put the sheet metal back on tomorrow and put her back to work.

    Heres a video running at 1200 rpm in low range. It does sound kinda loud in video but most of the noise is from the spindle motor fan. Spindle sounds pretty decent off camera. 20200603_192603.mp4 - Google Drive

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