Some technical VMC spindle questions I have please

The first question is what caused the grinding marks on my spindle taper seen here on the tool holders? The marks on the tool holders are caused by linear high spots in my spindle taper that are about .12" apart. The spindle is a 10k BT30 that had steel bearings in it but was rebuilt using ceramic. It looks like the taper is a little tight at the top too.



Next question, what are the master tapers used to check spindle tapers called? I am trying to find out where to get one and how much it will cost for a dual contact BT-30. No luck so far using my search key words.



My Kitamura's spindle bearings are getting too noisy and I think I have just started seeing a lack of preload in some facing operations so it is time to deal with it. The 3 options I am looking at are ship it to Setco in L.A., I am told this is who does them for Kitamura, have C&M in Portland do it, or if possible do it myself with help from this forum. The taper is in perfect shape so it doesn't have to get ground. If replacing the bearings myself is out I am not sure which way to go so I would like your opinions please. The good and bad of each option:

Setco - I will have to box up my spindle and ship it 1,000 miles, which is not without risks. I will be down an extra week or two for shipping. With shipping, the price will be the same as C&M, just over $6k. I have no experience with Setco, anyone here have any? What did you think of them?

C&M - I can drive my spindle to them so fast risk-free shipping. They have rebuilt one spindle twice for me so I have some experience with them. The downside is they don't have a master taper to grind the spindle to, they ask that you supply a tool holder for them to use. I don't find that acceptable with a spindle as nice as the one on my Kitamura so I will have to buy and supply the master if they do the work. Being Big-Plus will only add to that cost.

Do it myself - Spindle is from a 2001 Kitamura. 15k direct-drive BT-30 with two angular contact bearings in the nose and a roller bearing at the top with through spindle coolant, cartridge. If there are any sorta special tools needed to work on it I will have to get them. I have never done one before but have re-balled ball screws and replaced linear ways and blocks without screwing anything up.

DavidScott said:

.....The marks on the tool holders are caused by linear high spots in my spindle taper that are about .12" apart. .....

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It may not be the spindle taper that is generating the marks. I could be irregularity in the roundness of the toolholder.

Vancbiker said:

It may not be the spindle taper that is generating the marks. I could be irregularity in the roundness of the toolholder.

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Could be, but if he sees a similar pattern in all his holders (of roughly the same time in use) I'd think it's the spindle taper.

If it is the spindle, perhaps the current grind was done with an imperfectly balanced wheel and arbor, or there was a periodic error the same as what's observed in the linear bearing pack and rails of the grinder, or failing bearings in the grinder inducing a "whirl" in the inside taper.

Or, Aliens. When it doubt, blame the Aliens...

For the taper master, talk to Frank at Maritool, he went though this exact issue when he wanted to make dual-contact toolholders. He can (hopefully) advise on procurement, may even offer it himself.

And if you DIY, please run a thread on it if it's not too much effort. Would be interested in your approach, and you could get feedback on technique.

Milland said:

Could be, but if he sees a similar pattern in all his holders (of roughly the same time in use) I'd think it's the spindle taper......

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Yes, that is how I discovered a bad batch of toolholders once. We had a new Makino and all new holders from a couple different manufacturers. After some time in service, all the holders from manufacturers A and C showed no odd wear pattern but some of the holders from manufacturer B had a pattern of "wear" similar to what is shown in DavidScott's picture.

Wasnt there a post on her last year and this Subject came up and it had alot to do with how tight the pull studs where in the tool?
could have been Frank or duelkit (for some reason those 2 names ring a bell on it) that talked about it in depth?

Vancbiker said:

It may not be the spindle taper that is generating the marks. I could be irregularity in the roundness of the toolholder.

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It's the spindle. These same marks are on several other tool holders, all Maritool, to varying degrees of hard use. Holders are 3/8" stub sidelocks so they are pretty solid. Other Maritool holders on my other machine do not have these marks.

My first thought is the preload is off from swapping ceramic for steel, with ceramic balls deforming far less than steel balls.

I can't imagine it would be the pull studs. They are torqued to 15 ft-lbs with a little blue Loctite to seal against coolant egress, which I think shortened the life of the first re-build. Drawbar force is 500 lbs so not exactly high.

Vancbiker said:

Yes, that is how I discovered a bad batch of toolholders once. We had a new Makino and all new holders from a couple different manufacturers. After some time in service, all the holders from manufacturers A and C showed no odd wear pattern but some of the holders from manufacturer B had a pattern of "wear" similar to what is shown in DavidScott's picture.

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Frank will like this thread. I think all the tool holders with these marks are from the same single purchase. I will take a look at some other tool holders on that mill when it stops. These tool holders never leave the machine, part of an ongoing run that this machine is dedicated to.

DavidScott said:

My first thought is the preload is off from swapping ceramic for steel, with ceramic balls deforming far less than steel balls.

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I have read (but perhaps only once) that in hybrid bearings (steel races, ceramic balls) that the curvature of the race "track" is slightly different than that of conventional steel bearings to account for the higher modulus of ceramic balls. Not sure about this, especially with angular contact bearings where you're running at practically a line contact, but it's conceivable.

I take your "preload" as being spacer driven, not drag? If so, then yes, you may be loading the bearings more than anticipated due to the lower deflection of the balls. Also accelerating wear of the races as the balls push a standing wave around the race due to the extra deflection.

Milland said:

I have read (but perhaps only once) that in hybrid bearings (steel races, ceramic balls) that the curvature of the race "track" is slightly different than that of conventional steel bearings to account for the higher modulus of ceramic balls. Not sure about this, especially with angular contact bearings where you're running at practically a line contact, but it's conceivable.

I take your "preload" as being spacer driven, not drag? If so, then yes, you may be loading the bearings more than anticipated due to the lower deflection of the balls. Also accelerating wear of the races as the balls push a standing wave around the race due to the extra deflection.

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This spindle is a direct drive BT-30 with two angular contact bearings in the nose and two at the top, with a spacer setting the preload.

barbter said:

Looks like fretting and i too wonder if the pull stud is distorting the top?
But is your drawbar pulling good?

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Definitly not fretting, other than there is a small spot of fretting on the left tool holder towards the nose.

DavidScott said:

Definitly not fretting, other than there is a small spot of fretting on the left tool holder towards the nose.

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Well, I think technically it is fretting, just not localized the way you'd get with a bellmouth or swollen small end.

DavidScott said:

This spindle is a direct drive BT-30 with two angular contact bearings in the nose and two at the top, with a spacer setting the preload.

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If you kept the races but changed over balls, or even installed new steel races and ceramic balls of your own choosing, but kept the original spacer setup, then there's a good chance you're off somewhere.

Ideally you'd do some careful stack measurements and determine what actual spacer thicknesses were needed to get the designed preload (factoring in ceramic balls), or have a radial drag value (sounds primitive, but a fish scale and string can give good results) for proper setup.

Milland said:

Well, I think technically it is fretting, just not localized the way you'd get with a bellmouth or swollen small end.

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True it is polishing the grinding marks out but not digging holes leaving the bronze film.

Just checked another tool holder, Lyndex, and it too has the lines on it. Also, all my tool tapers are covered in grease and the lines are clearly visible in the grease. It's the light grease used on the linear rails and helps tools release from the spindle when used hard. I have one tool that I use real hard that does this to the tool holders, currently, that tool is held in a stubby sidelock that only Frank sells this short, so that is why this problem is most prominent on his tool holders. I am 100% certain it is the spindle taper.

Well, when the rest of the spindle is healthy you'll want to have the taper reground. Then there's the "do I worry about the old holders in the new taper" question.

barbter said:

But on the left holder, it looks like the holder is snug at the top, and the vertical lines are micro movement where the spindle isn't fully contacting the bottom.
Effectively holder movement back and forth?
Hence my question ref drawbar pressure?

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Drawbar is around 500 lbs so is good, a little more than what it's supposed to be. I think the taper is the spindle was ground using a tool holder for the master and blued up beautifully with no pull stud. This spindle has had the shit beat out of it, spun a tool holder in it on a hard crash, had an extra set of drive dog slots milled into the nose, and chromed to fix the missing steel. The only thing I did was to have the chrome done the last time I had it rebuilt.

Milland said:

If you kept the races but changed over balls, or even installed new steel races and ceramic balls of your own choosing, but kept the original spacer setup, then there's a good chance you're off somewhere.

Ideally you'd do some careful stack measurements and determine what actual spacer thicknesses were needed to get the designed preload (factoring in ceramic balls), or have a radial drag value (sounds primitive, but a fish scale and string can give good results) for proper setup.

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Both rebuilds have been done by C&M in Portland with new bearing sets, standard full price rebuilds.

Milland said:

Well, when the rest of the spindle is healthy you'll want to have the taper reground. Then there's the "do I worry about the old holders in the new taper" question.

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I would bet money the regrind would look the same.

DavidScott said:

I would bet money the regrind would look the same.

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Now I'm confused. If you think it's the spindle taper profile that's causing the marks, why wouldn't a (proper) regrind of the taper on good, new bearing not give a better surface to engage the toolholder tapers?

barbter said:

So when it was rebuilt, it was chromed but not ground after?
This could be your problem then? Uneven build up of chrome thickness along the taper?

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The clearance grind and chrome were done first, then it was assembled/ rebuilt. The grinding job looked flawless when it was new and still looks very nice. Funny though how I could see a shadow in the blue from where the taper needed to be built up when I checked it after the rebuild. I just looked up my invoice. Last rebuilt on 12/2012, estimated .005" thick chrome and 565 lbs drawbar force. It's an Enshu so drawbar force doesn't degrade much over the years.