Mazak QT-20 spindle bearing replacement
Anyone have any experience changing out the spindle bearings on a QT-20?
Have you tried calling MAZAK? The HQ is in Lexington. The techs are pretty knowledgeable and at the very least they could fax you some maintenance diagrams. I'd be willing to bet if you got one of their techs on the phone, he could talk you through the procedure.
mazak lathe spindle bearings are doable on sight
i would first call mazak for instructions but they may be slow to give them as they recomend they do them as would be expected.
they come out the front and are assembled on the tube on the bench
there is a criticle laberanth collar grind that sets the preload.
i do not have a blow by blow for any machine except a t2 qt8 and qt20 (the old long beds).
but if you just keep asking eventualy one of the guys who has seen your machine may pop up.
Try Florance Y'all.
Think Snow Eh!
Originally Posted by mavmike72
That blows. Things can sure change in a decade or so.
I'm sure your schedule for this is ASAP and I can't promise a quick answer, but I'll make some calls (naturally, it's the weekend, right?) and see what I can find out.
Do you have the maintenance and parts manuals? The drawings alone are a big help when it comes to jobs like this.
whats the vintage of this machine?
basicaly you pull everything off the back end and push spindle tube out the front
bearing set assembles on bench and is then pushed back in
the only trick is the preload collar.
i don't have the math for that but maybe machtool does
but it may take some diggin' to find them
vintage and serial is a must at this point
Ping; Wippin Boy
All I have is the attached file. The illiustration is not that of a QT20, but the preload spacer thickness for the Tapered Roller is determined using the same formula. I'm like you, keep pulling crap out of the way til the darned thing falls out and hits you on the foot. Angular Contacts are standard, grind a retainer cap til .0008"~.002" preload is achieved. Good luck Mike!
PM me your email addy and I'll email it to you.The server says it's exceded the upload limit?
Last edited by Leelund; 03-14-2010 at 09:29 AM.
I might have seen this done once or twice. This is the spindle with a set of high contact angle angular contacts hidden behind a double row roller bearing at the chuck end. And another double row roller at the drive end.
Those angular contact normally have a part number like 120 BAR or BER and the roller bearings will start with NN30xx K
Itís all possible in the field, probably help if your reasonably familiar with working with spindle bearings, it a fair amount of work to measure the residual clearance in the bearings, then calculate and adjust the control spacers to adjust the clearance out and get into preload.
You need some gear also, granite plate and tenth indicators. And a decent surface and universal cylindrical grinder. A real clean place to work, solvents, synthetic grease, etc
It would be really helpful if you could scan your drawing and parts list.
Any chance Iíd could take a look at that? Iíll P.M you my email addy.
All I have is the attached file.
Leelund was kind enough to email me though a scan of the head, and the procedure. It looks petty stock standard for any Japanese machine of that vintage. I see the same arrangement on Moriís, Okumaís. I even had a Taiwanese Goodway head stock in here 2 weeks back, Looked identical to that.
Iíd assume you have those procedures as well? Is any one showing the real bearing numbers for those bearings? The two rollers details 13 & 27, and the angular set detail 16. Brace yourself, they wont be cheap.
I can probably look those up tomorrow
Front Roller- NN3024KMBCC9-P4 Mazak # F04NP000080
Angular-120BA10XDB-P4 Mazak# F02NP001020
Rear Roller- NN3020KCC9-P5 Mazak# F04NP000060
Originally Posted by Leelund
Man, thatís good work.
Both those roller bearings should be very easy to find. Assuming you were doing this on a budget and didnít want to go to the firm.
That angular is what I was worried about. You would get that from Mazak still, but it almost redundant from NSK. Itís a mongrel size, 120 I.D 180mm O.D, same diameter dimensions as an ISO 70 series, in this case a 7024. But the thickness of a pair is 54mm. A 7024 is 28 mm wide or 56mm for the pair, so they wonít fit with out making the housing bore deeper. They have to be a 70 series, as thatís the same diameter as the NN30 series.
Its also a very high contact angle (30 deg), which it has to be, it has no need for radial capacity sitting right beside that double row roller. Its brother was the xxxBT10X, being a 40 degree.
An interesting fact, the outer ring is undersize so it doesnít even locate on the bearing outer. The catalog I have in front of me, specifies that the outer will be -50 / -61 micron under size. Thatís so it doesnít fight that roller for radial load, and just gets locked into the housing for thrust load only. The roller being the one preloaded up until itís at minus 5um.
Even finding catalogs for these on the net is hard, when Iím looking for them, about the only place in the States that even list them is Alpine Bearings in Boston. But they never have stock. Iíve got a line on some out of Singapore.
My bearing guys search those via NSK/RHP. They often come up with 5 or 6 sets kicking around, but they will be held on consignment for the larger machine tool companies, and they wonít let them go. Mazak, arenít the only ones using these. There really common on mid 80ís thru 90ís. Because they are not a true ISO size, due to the thickness, they seem to have phased them out some what. And no one else makes them that thin.
There is a newer NSK equivalent, that number would be 120BAR10S, exact same size and contact angle. Even those can be hard to find, the amount of times NSK have come back to me, with what they think will work, and it ends up being a low contact set, great for high speed, but useless for the thrusts these have to endure.
Conversion catalog showing the old and new numbers here, on page 11 of 38
Have we lost Mike?
Couldn't you use the 7024's and grind 2mm off each side of the inner & outer spacer between the roller and the ac's without touching the housing? This would leave the gauge line and the slinger in the rear at their proper locations without thinning the housing.
Thatís a good observation. You can tell how well I studied the drawing you sent me. Iíve got a bit on at the minute.
No reason you cant do that, they seem to be nice and solid. And thereís plenty of the 120mm spindle journal under them. If you did that with a bit of science involved, you could adjust them so you get your lock up across the outerís that hold them in the housing positively.
That would give us that feature you mentioned a few posts back.
And you wouldnít have to touch the front retainer if its in good order.
grind a retainer cap til .0008"~.002"
Thereís a few more manufacturers doing 30 deg in 70 series. In NSK the prefix is A5
thanks for the help guys
think maybe we lost the op though
Should we just keep chatting between ourselves?
Originally Posted by wippin' boy
I was thinking about this last night, thatís probably not the best spindle for him to cut his teeth on. Just those few tricks in setting them up, and there heavy and hard to assemble clean. And your probably looking at $3 - $4k in bearings there. Thereís a bit of risk in it.
kinda depends on vintage
heavy and hard to assemble clean
i got a t2 thats probly 4 foot and 12 inches in diameter
but my tplus is half that big, the tplus would be doable for a newbie if you paid attention
that is what alot don't realize
if you go with factory spec bearings 3/4's or more of the cost is materials alone
the reduction in risk by spending a grand is substantial
seems fairly common to get a 90 day warrenty
that ain't much
i can remeber when i was hot to do all my own spindles
sweat bulletts for the first few weeks then move on to next crisis
so it's deffinatly 50/50
thats what my mama told me about life
everything's either is or ain't
so flip a coin and move on
the only thing that is for sure is that your burnin' daylight worring
Great thread guys. I did a spindle bearing replace on a Mazak QT10N about 9 years ago. She is still running strong and quiet.
Don't you just love how Mazak uses special size bearings?
Another item "customized" by Mazak is the linear guide trucks. I had to replace the trucks and rails on an '88 QT15, and sure enough, the NSK trucks had a special mounting-hold pattern. Hmmm....what to do?
I laid the cast iron turret "box" upside down on my vmc, and proceeded to slot the holes to allow standard guide trucks to bolt up. Also had to run new, individual lube lines to each truck, as the Mazak oem system pumps lube through the casting into their unique trucks.
I will certainly have to remember this thread when it comes time (if?) to replace the bearings in my big ol' QT20N.
We always have the local supply house rep run by and look at the "trucks" and get the data on them and usually he looks around to try and match them up. Usually though we are told that the series we are using is no longer made so we wind up replacing the rails and trucks with an updated model.
I was once told that the trucks are sized to each individual rail and so are a matched set. The do have etched numbers on them like matched sets of dual angular contacts. A serial number then it's position in the row-A,B, C, and D.
Anyway, it's never a direct bolt on replacement around here. Always modifications to do so you are not alone, CNC.