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VTC Spindle Work

No Fun

Aluminum
Joined
Jun 2, 2007
Location
Austin
I have an old, noisy spindle that I removed from my machine and took apart. I bought a new set of bearings to install. I've been careful to keep everything clean, and I'm inspecting the various parts for wear. Have any of you replaced your own spindle bearings? What is the technique for removing the bearings from their shaft? I expect reassembly will be difficult given the precise fit of things. Is it beneficial to cool shafts in the freezer to shrink them a little?

As far as the tool change mechanism, it worked well before removal. Should I replace the retention fingers for good measure? How about the springs? I don't think yanking the spindle out and doing those items when they eventually do wear out is such a big deal, especially since the new parts are bound to be expensive and the existing ones aren't necessarily bad.

The tool taper seems to be smooth, not grooved or obviously worn.

This is an old machine and we are a young and poor shop. I recognize that a professional job would be better. We are making do. Thanks for reading. I appreciate your comments.
 
never been where you are but
I've "thumped" more than one spindle bearing off tube by just dropping spindle tube on a piece of oak like it was a post hole driver
bearings will just slip off from there own inertia "hopefully"
freezing the tube may help on install but you need to come back to room temp before locking stuff down
mazak tends to precision grind a labyrinth collar to set the preload on a tapered tube
maybe one of the mazak techs will pop up
if not chances are it will be similar to the old numbers if you bought a like quality bearing
not sure about lube on your mill but when grease is used tendency is to use to much
10 or 20% pack is probly about right with a very slow deliberate break in to put out any excess
1 hr per 200 rpm up to 1000
1 hr per 500 from there to top end

prelode is about end play
to much play is bad but none is not good either
as little as you can get without over tightening
its been a long time but it seems like mazak wants about half a thou. but you need to check that with someone.

as stated, its been a long time so
by all means look for more info than this to reassemble your spindle

good luck
 
I rebuilt many Mazak spindles including old and new VTC's.

I wanted to talk about the spindle in general and the Belleville washer assembly(spings).

Spindles are balanced at the factory so make sure you mark the orientation of every part for reassembly (Very qritical for HI RPM spindles).

A new Belleville washer assembly will pull the Tool into the Taper with a pull force of 2000-2500 1bs. We use a pull force tool to give us a read out of our spindles health.

Visual inspection also can tell you if it is time.

Replace all the washers if any of them are cracked. They must go back in the same order. (two in - one out etc.) $$

If the hardened outer collet sleeve is cracked replaced it. $$$$$$$$

If the inner collet fingers are in bad shape replace them.$$$

If you have through hole coolant replace the O-rings and seal.$

I can help you come up with some simple home made tools to take the assembly apart.

Even if decide the assembly is OK you will need to do the following after you put the spindle in.

Check and adjust spindle knock out.
Check and adjust the spindle orientation position
Check and adjust Z axis tool change position

Let me know if you need help. You can do all this at a fraction of the cost of a new spindle.



Jim
 
I am always amazed by the knowledgeable and helpful people in PM. I appreciate the help. I thought i would be helpful to post a few pics of what we are talking about.

I made the bone-headed mistake of taking it all apart without marking the orientation of the components. I expect that it will not be perfectly balanced then when it is reassembled. It is a 7000RPM max.

My observations:

I did not see any cracks on the belleville washers.

The fingers have a little wear around the edges, I'm not sure what they look like new, so it's hard to say how worn they are.

I thought the tool taper was not bad.

Some questions:

I have been reading some heated posts about bearing preload issues here on PM. It seems that the tapered collar (i think it's tapered) that holds the tube/bearing assembly into the housing is sized to contact the inner race of the top-most bearing. Does this collar take up the slack and set preload when the whole thing is assembled?

What is the technique for bearing removal and replacement? Not easy to move. Special tool?
 

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You may have already gotten there but just in case I will reply.

Preload on the inner and outer races of the spindle bearings are usaually set by the factory via ground surfaces.

You need to accurately measure the width difference between the original and replacement bearings if any and make some alterations where necessary.

Please take a snap shot of the spindle in the parts manual and send here so we can look at the best way to get it apart.

Everything looks good on your tool clamp/unclamp assembly.
 
spindle diagram pics

some diagrams of the spindle
 

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The first thing I suggest you do is remove part number 11 (Probably a spring pin or dowel) cause it will stop the inner races from coming off.

We have a large hydraulic press and if it was me, I would make a sleeve or cup and push down on the ring that you say has .050" play. You need to be real square with the spindle cartridge and press. Whippen boy has some good advice to offer. You can try thumping it as well.

Make sure you put the replacement bearings on the correct way. They often come in sets and are maked with arrows. Look at the directions and parts manual. Probably arrow in from both ends.

Don't worry about the bearing width variance in this case , you can adjust your z axis tool change height if necessary. The outer race preload is preset by the assembly and the inner race is set by the adjustable collar.

Note: Absolutely replace the four 85 mm bolts that hold down the clamp unclamp assembly. They are under a lot of stress and are prone to shear off.

Good Luck
 
complication

The job continues. While pressing off the bearings, I bent the collar, Mazak quote: $375. Nice work. Judging from my pictures is it possible to keep pressing on this collar to get the remaining two bearings off? there is a sleeve that touches the inner race of the upper set, and the inner race of the lower set. This would need to slide off the enable the top set(bearings on the tool taper side of the spindle) to come off. I kinda got the willies from bending the collar, and am a little nervous of going whole hog on it.
 

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The inner and outer collars form a kind of labyrinth seal to keep dirt and liquids out. Since you have already killed the outer collar, I would parallel the spindle on the collar and press the spindle out through the bottom. A box with packing peanuts or styrofoam under the press will catch it. Maybe wrap your vee block parallels around the spindle flange. Maybe the inner bearing races have gaulded up on the spindle bearing race and that is why they are comming off hard. Do a hardness test on the collars and you will find that they are not hard. Measure them out and turn your own. I have also used a clamshell bearing puller to get them off. Remember, it's no good like it is! You gotta get it apart. Me, I get the willies when I 'm hanging on a cheater pipe I got on the press handle and I'm laying down on it with all I got. That'll up the pucker factor.
Lee
 
As a matter of fact I am wrong on your machine having an inner and outer collar. Looking at the mechanicals, the spindle flange actually laps over the one collar. That collar doesn't have enough meat on it to press the inner races off if they are friction welded to the spindle. A clamshell will dig in between the races and you can pull them one at a time. I have had to take a whizz wheel cut off tool and cut the races on two sides and take a chisel and knock them off in two pieces. If you knick the spindle a little, no worries, just dress the hicky up with the grinder or a file. There is plenty of contact surface area left to center the new bearings. Are we havin' fun yet?
Lee
P.S. Another thing that is scary is the collar in the photo has an O ring but the collar in the parts list doesn't show one!
 
disassembly complete

Leelund, thanks for the tips. I carefully thumped the sleeve off (thanks WB) then I was able to wack the gap a few times with a chisel and separate the two inner races. One pressed off ok, the other fought harder and needed to be cut. As it stands, the spindle is totally disassembled and the next step is a thorough cleaning, and reassembly. Well the next step is ordering another ring from Mazak, then reassembly. Pictures coming soon. I am loving the progress.
 
I don't know if I missed it or not. What model vtc do you have? I have the vtc-41. I hope I don't have to deal with this, but if I do, I'm going to save this thread for future reference.
Thanks
Rosie
 
thanks WB

no
thanks norbert (wish i could remember his last name), chicago region service mgr circa 1990
taught me half everything i know about mazaks over the phone sayin' "don't be a puss kevin, it ain't workin' now so what's the problem with divin' in up to your ears"
 
new bearing questions

Here's my thinking, tell me where I'm off track:

I'm ready to begin putting this thing back together. My new bearings are here. The old set was a quad setup with tapered markings on the outer race to show proper positioning one to the next. My new bearings are univers0al type meaning (i guess) that it isn't important where in the stack they go. Obviously, the thrust direction (upside down and right side up) is still important. So I take it that the new ones are identical? Also, these new ones don't have any grease in them just a coating of oil. the old bearings had a generous helping of yellow grease in them. Should i be adding some of the special spindle bearing grease that i read about on other PM posts? thanks for reading.
 
reassembly

I am finally putting this thing back together. I carefully and lightly greased the bearings with some NBU 15 and slid them on in the correct orientation with the spacers, etc. and inserted the little spring pin to keep it all together. After I slid the whole assembly into the housing, I stood it upright. The next thing is the tapered collar. I put it on and lined up the sping pin gap with the spring pin as closely as I could by eyeball. I put a sleeve over the top of the collar and, using the press, slowly slid the tapered collar down. This is when a slew of questions and attendant anxiety started flowing through my nervous system. I could see as it was sliding down that the pressure gauge on the press would flutter, hovering around maybe 10 tons (1953 press, questionable accuracy). I kept pressing until the gauge began to steadily rise, stopping at about 20 tons. When I took my pressing sleeve off, I saw that I had skinned a little bit of metal off the spindle while sliding the tapered collar down. I few wisps of metal were crowded around the top of the tapered collar. I'm not sure how much of a problem that is. My gut says it's unfortunate, but maybe not a big deal.

According to the diagram, any force pressing on the tapered collar is directed through the inner races of the upper bearings, the inner spacer, inner race of the lower bearings, to the base of the spindle. It seems like a "hard stop". So now my questions:

Question 1:
How do you know you've properly seated the tapered collar?

Question 2:
when spinning the housing around (while the center of the spindle is stationary) I can occasionally hear a slight noise. I'm thinking that's the slightly loose fitting outer spacer spinning around. I'm pretty sure there isn't much to keep it from moving around a little bit.

If you have bad news for me, break it easy, ok? I've been making parts since 4 this morning and I'm a little fragile.
 
Man.

I wasn’t aware you were so close to assembling this. I don’t get down here often. Damn, it just seemed like this morning, you were in the CNC section asking about grease. I didn’t have the minutes to look here.

You should never attempt to press fit what your calling the tapered collar. That’s not tapered at all. It has a step in the diameters in the inner diameter. That’s a high interference fit, shrink fit collar.

See your centre picture above.
http://www.practicalmachinist.com/vb/attachment.php?attachmentid=15841&d=1253973180

See what looks like a flying lead thread. That’s for oil distribution under what your calling the collar. The collar is actually part of the upper labyrinth assembly, but its primary function is to secure the inners of the top set of bearings, via the inner spacer and through the second set of bearings to the neck of the spindle.

If you look at that collar, it has 2 drilled and tapped ports. These are for hydraulic removal. You plug one, screw an adaptor to the other, connect it to an Enerpac, Pump that up to 700 bar, and it normally blows clean off, with out ever seeing a press.

The oil under pressure can flow along the spindle along what looks like that shallow flying lead thread turned onto the main spindle shaft. That expands the collar, and it will pop off on a film of oil under pressure. That’s represented by the slanted lines, show on the Mazak drawings you posted first.

It’s a really common design on most Japanese spindles. Because it doesn’t have a thread on the spindle for a normal hug nut, speith nut etc. Thread drunkenness isn’t a problem. The face of the collar will go down and contact to bearings with a high degree of accuracy.

Putting it back on, doesn’t require a press either. You heat that collar to 160 – 200 deg C. It will drop straight on. No galling, or stirring up extruded metal as you press it back on.

While it’s hot, it only drops as far as touching the bearings. That’s not enough force to apply the preload across that bearing arrangement. And when it cools and contracts, it will shrink further away from the bearing inner face, leaving them loose on the spindle shaft.

The procedure is to let it cool to room temperature. Then apply a force of about 700kg’s downward thrust onto that collar. We use a hollow enerpac cylinder, under the spindle, with a high tensile rod, up through the guts of the spindle where the drawbar would be.

We clamp the collar, so it cant move up on a fixture, forcing the spindle from underneath, then connect another Enerpac up to the injection ports on that collar. Same way as they come off.

Blow that back up to 700 bar. It expands, and clearance between the face of that collar is taken up by the force pushing on the spindle. The collar will pop, and glide on the oil film, applying that seating force. You can always hear them, and a DTI mounted on the spindle will show it move.

Release the pressure being injected into the collar, so it grabs the shaft solid. Then release the seating force on the spindle. The interference fit of that collar, has to with stand any forces you can throw at it. We mostly see them after a really big hit, that moves that collar, that leaves the bearings loose on the spindle, and the spindle will float. Mute point as the bearings are normally cactus after seeing such a hit.

Pressing that collar on just destroys that fit. A heat shrink fit has about 3 times the axial holding power of a press fit. You should never have pressed it off, nor attempted to press it back on. . Those drilled and tapped holes shown in the drawings are only there for one reason – hydraulic assistance.

I’m really sorry I didn’t see this earlier. But I did ask you a week back, in the grease thread, to measure the thickness of the bearings. That’s absolutely critical on that arrangement. I’ll explain why when I find the minutes.

Sorry dude, but that’s a mess.

Regards Phil.
 
I have to say this is pretty shocking. I am determined not to get too worked up here. I always knew I was out of my depth on this thing, and that's the first I've ever heard about assembly on these. What I need now is a plan for disassembly and inspection. I have another identical spindle from a scrapped machine that can donate parts to replace what I may have ruined. I am going to go back and reread your post more thoroughly. I am reeling here.
 
I was never going to be able to do a proper assembly. Floating the collar on hydraulic pressure while pressing up on the spindle shaft? It doesn't seem like there is any way to approximate this. I may have ruined something the day I took it apart. Holy crap. OK. Let's try to determine what I haven't ruined here. At this point I'm not sure what can be done aside from sending the whole thing somewhere. I wish I had an inkling of a clue about this before I started. wow. that is a lesson.
 
After reading both threads on this I must say there are alot of opinions out there on spindle bearings. Some I agree with others I do not but hey, if it works it works.

One thing I would like to speak up on is freezing the spindle. many spindles including this one have the bearings separated by spacers. Although the bearings will slip right on, as the spindle thaws you will get alot of condensation which will drip into your new bearings. You may get away with it but hey, why take a chance.

I prefer to heat the bearings with a heat gun. Not so hot that you can't handle them with bare hands. You still have to help them on but not as bad as same temp. componants.

Also, no brass punches. Brass flakes and will fall into your new bearings.

Just another opinion.
 








 
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