View Full Version : Franze Kessler Spindle Motor. Help!!!

05-05-2008, 09:20 PM
Hi all,
We have a Deckel Maho DMC-70V vertical machining centre with a Franze Kessler spindle motor type: 100.AL.4.FOS whose bearings are on the way out.
We are considering rebuilding it ourselves (cost of changeover from DMG is horrendous). We therefore need to get specs for this motor such as preloading values etc. Drawings of the motor would be marvelous if anyone has them. Any other advice would be greatly appreciated. Yes we know these are complex beasties but have some experience in the area but not with Kessler motors.
Any advice from the collected wisdom out there would be very welcome.
Thanks in advance.

05-06-2008, 07:57 PM
Hello Adrenal:

I have rebuilt 3 of these Kessler spindles as of now, and I can tell you I am not a fan of these units. I really hate them. I had to rebuild an 18000 RPM unit in a DMU 50 Evolution, and 2 spindles in Dmu 80P machines with a 8000 RPM ( if I recall the speed) top speed. Anyway they are a overly complicated poorly designed items. If you decide to tackle this job you will see what I mean. Please don't read this as me trying to discourage you. I totally agree that what DMG is asking for a rebuilt is robbery. So with that llittle rant off my chest let me give you what few pointers I can , at least so that you will know what you're up against.
First off I don't know from your post what the maximum RPM is, of your spindle. Usually the higher RPM units used ceramic angular contact bearings. Easy way to tell is to use an electrical OHM meter and test from anywhere on the spindle internal tool taper to machine frame. If you don't get continuity they are ceramic, otherwise they are steel.
As far as getting any type of engineering drawings, or any data on these units, I very much doubt you will find it. Kessler is very tight lipped about this. I have an old mate of mine who is a service manager for DMG here in north america, and even he has no technical info on them. So from my experience, here is what I ran into.

1. Is the spindle overheating, or is it noisy too? If it's just heat, check the spindle cooling unit behind the machine. Is it low on coolant? Another problem is the coolant pump, they tend to shear the drive keyway. Even though the motor and fan are running the pump isn't pumping.

2 Regarding the bearings. With the steel angular bearings in our 80P machines the delivery date for the bearings was 12 to 16 weeks. I did find a supplier in the USA, who had stock ,but he couldn't sell them to me as he had a contract with DMG and Kessler as to not deal with machine customers. I had to call a favour from my mate at DMG, to get them to sell the bearing to me.

3. As far as the ceramic bearings, again the led time to delivery was preposterous. These were a special type of bearing with 2 "O" ring groove on the outer races, and a .030 hole through the outer race, to feed an oil mist lube to the balls. What I ended up doing was to disassemble the bearings. This was a nerve wracking ordeal because the bearings cost upwards of 3000 dollars, and I stood a good chance of destroying them doing this nonsense, but i had to. They where never designed to be disassembled, but I had to do it, because the lads in our machine shop had to grind in the 2 oring grooves, then EDM a .030 hole. After all that and a thorough clean, I reassembled them.

4. Regarding the preload. I just put everything as it was, I found I didn't need any preload re-adjust, It was all taken up by the original spacers. No problems there, thankfully. After installing the bearings on the inner shaft, I do take the assembly across the road to another mates shop who has a balancing machine. It is important to do this step IMO for an 18000 RPM rotating mass.

I hope I didn't frighten you from having a go if your up to it. I'm just relating my experience.

I don't work for DMG now, but I did at one time when Deckel and Maho were seperate entities, so all my posts here are honest, and not biased toward the factory works.
If you need more help, please post here for all to read, and I'll see what I can do.
I just hate when the big boys, with over priced spares , try to gouge the little fella trying to make a living.

good luck

05-07-2008, 08:34 AM
Thans a bunch for your reply bodger.

The machine is a 1997 model and max spindle speed is 8000rpm so I gather from what you have said that the bearings would probably be steel...?

The spindle is noisy and if you turn it by hand you can feel a faint rumbling so we are assuming bearings at this stage. We've just got it assembled after shipmenmt and havn't run the machine long enough to establish whether there is any overheating issues but we will keep your coolant pump observations in mind.

You havn't quite scared us off the idea of doing the job ourselves however we may have difficulties getting replacement bearings going on your experience.

Another option for us is to have someone else service the motor. I think we may have to send it OS. Do you know of anyone who you'd trust to do the job in the US ot UK etc. They are bound to be cheaper than DMG!

What do you reckon?

Once again, thanks for taking the time out to help.

05-07-2008, 10:17 PM

My 'hands on' friend who will be doing the work on the spindle would like to know whether there is any way of removing the bottom spindle bearings with the motor in situ?
We are hoping that the bottom bearings are more likely to be the problem ones since they are the ones that are more likely to have their lube washed out by backspray and seal leaks which we believe to be an issue with these units. Can you shed any light??

05-07-2008, 10:33 PM

You're welcome, just trying to help a fellow in need.

Have you look around down under for a local shop that can do spindlemotors? Melbourne is a fair sized town, there maybe a good shop around. Failing that, I always use the punters across the road from me when needed. They are a small setup in an industrial unit, actually a father and son team, but they have always done a top notch job. The shop maybe small but their attention to detail, precision and cleaniness, is the best. Unfortunately there is no website, but I'll post there company name with the hopes I don't upset the Mods here. They are called "Spindle Canada Bearings Ltd." I can have a word with the owner tommorow, and post back here. As far as a USA site, I spoke to a rep from a firm just outside the Detriot Michigan area, who has experience with DMG spindles. I'll post back here tommorow morning with more info. I don't know the phone numbers or anything as such as I'm at home now, and all my stuff is at work.


05-07-2008, 10:44 PM
I agree. The bottom bearings are more than likely the ones that have failed. Do you have the spindle removed from the machine?

05-07-2008, 11:05 PM
If I can recall, the spindle may or may not have to come out of the machine. Depends on the model, and I must confess I'm not sure what the 70 model has. Perhaps a digital photo might help me. The Top end of the spindle has to be disassembled, in either case. The spindle shaft is also retained from the top. I must stress you mark everthing prior to stripping it, again a digital camera, use it. Depending on the spindle type after all the retaining nuts, top and bottom, are free then the whole shaft should come out, with the bearings. Then it's a matter removing the bearings from the shaft. Please note angular contact bearings can ONLY GO ON THE SAME WAY THEY CAME OFF!!! this is important. Examine them carefuly to see the orientation. If you put them back upside down it won't work, and you will most likely damage them trying to fix a cock-up.

05-12-2008, 06:11 AM
Have the spindle removed now. Will send your comments to my friend who is doing the job. Will get some feedback from him so all can learn.

05-12-2008, 08:39 AM
Hi Bodger,

I'm passing on the email and photos my friend sent me today. He's feeling and learning as he goes and has had a couple false starts as he tries to figure the best sequence to pull things appart so any tips from you would be great and will no doubt save him time..

I didn't take a photo and wasn't able to fully examine the latest stage (Top cover off) as I had to leave in a hurry when they shut the factory.
The top cover with bearing and the balancing sleeve with SIZAG encoder are now removed.
Inside you see the spindle / motor shaft (no photo yet).
I don't think there is another nut on the top end.

You can see a gap to the left of the spindle flange on Front1.jpg.

Hope our friend <on cnczone> finds something familiar.....on these photos.

05-12-2008, 11:03 AM
Remember the runout markings on the bearings as well.

P.S What size are the bearings?

05-12-2008, 11:42 AM
It looks a bit different than the spindle that we had here in our shop, but It's probably similar enough to figure it out. You must remove the 2 rings from the top end (motor end) then the cover that has the 3 motor wires passing through it. Once you have it off you can tell if there are retaining nut(s) holding the upper end of the spindle shaft. If it's is at all similar to ours, then the darker area of the outside housing contains the stator windings, and the lighter coloured area, at the other end houses the acual spindle bearings. If I can recall, as you disassemble it further the housing can be separated along this line, so that the stator and bearing housing is in 2 parts. Be careful not to nick or damage the stator windings.

05-12-2008, 06:25 PM
Thanks gotis and bodger.
We'll report back re bearing sizes.
Bodger: As my friend mentioned, he has already pulled the top and encoder off and there does not seem to be a nut at the upper end of the spindle shaft....

05-13-2008, 04:47 AM
BTW: I left I missed the prefix on the spindle type in my first post. Should be:

05-15-2008, 03:35 PM
Hello Guys,

The Nut is the ring with the four notches in it. A spanner wrench is needed.

This is the older style spindle cartridge. It has been awhile since I have had one of these apart.

A common problem is for the seals to leak coolant into the motor. I recommend replacing all the seals before reassembly.

If you get the bearing numbers I may, could help in tracking them down as I am in the US, I also have some connections in Germany as well.

I service Deckels here in the US, and have 23 years as Deckel service experience and 17 of those on my own.

If I can Help, sentnermts@netscape.com

Best Regards