[NC Cams]

Ask Greg to tell you how they measure and set preload, while you're at it.Preferrabley in Nm or In-oz of rotating torque. STuff lik snug down and untighten so many turns is just to primitive UNLESS the "snug down" includes a torque value..

10000 rpm bearings may work with grease but will work better with oil or oil air mist. IMagine the balss trying to slog their way thru thick viscous grease at speed. Wouldnt be surprised if they run a lite or ultralight fill of grease.

[keen]

Thanks for your post NC.

We have at least two machines now with all four DT bearings installed << << Have you ever of a situation where that could work ? seems crazy to me.

[NC Cams]

Not unless the bearigns were specially marked for Tormach. You obviously cn't swap bearing positions. So, to simplify the thought process for the shop floor, TOrmach had them all marked so the chevrons point to the work end of the spindle.

IF that is the case, something OTHER than "misassembled bearing" caused the original bearings to experience an accelerated failure. IF that is the case, the whole thread essentially becomes a "much ado about nothing, never mind" situation.

Applying thrust in the WRONG direaction makes the balls roll up into/onto the wrong side of the raceway. NOt only is this area not honed like the rast, the shoulder is lower and the balls are easily cut as they roll up the shoulder.

THe more you think about it, the OD chevrons would HAVE to be special marked. A boxcar laod of spindles could not survive the plethora of use they'd see and not raise worldwide havoc.

[philbur]

I think you guys need to post a diagram, otherwise you could be passing each other in the doorway for weeks.

Phil

PS: For me, if all 4 bearings "face" the same way how can it be possible to adjust preload, also the spindle shaft will be unrestained axially in one direction. Surely for a DT arrangement the top pair have to be open end up and the lower pair have to be open end down, then the adjusting nut applies preload between the top and bottom pair.

Hi 4Z7 - Yes what I was describing was preload between a bearing pair.

What we have with the Tormach is two DT top and two DT bottom.

DT is duplex tandem, both bearings face the same way - doubling the load bearing capacity, but no change to the thrust direction (DB is back to back, and DF is face to face).

Angular contact ball bearings should only bear load in one direction, so a pair must be installed in opposite directions. If they are DT the two pairs must be installed in opposit directions. The only connection between the spindle or arbour and the machine is via bearings. two double sets (DT sets), that must oppose each other.

The adjustment means is to either draw the inner races of top and bottom sets together, while the other races are held by the lip, shoulder or faces in the housing.

Or to close the outer races etc which is not the Tormach layout so I wont expand this.

The fact that there is two bearings top and bottom does not change this.

When I installed new bearings last year I contacted Greg at Tormach and he sent me a service/fact sheet to help me. I have just dug out my printed copy.

Although the scale is small you can just see that both top bearings are 'open end' to the top - and both bottom bearings are 'open end' to the bottom.

I have not yet heard back from Greg about this yet. My guess is he is either contacting the factory to see if he can get information on how widespread the problem is - or he is on holiday etc. I await with interest!

[keen]

I think you guys need to post a diagram, otherwise you could be passing each other in the doorway for weeks.

Phil

PS: For me, if all 4 bearings "face" the same way how can it be possible to adjust preload, also the spindle shaft will be unrestained axially in one direction. Surely for a DT arrangement the top pair have to be open end up and the lower pair have to be open end down, then the adjusting nut applies preload between the top and bottom pair.

Exactly Phil ! I think we are last finally drawing to a conclusion. We have been passing each other in the doorway for days! Too true!
We have agreement with NC that all open one way would would be wrong and not last.

NC suggests that maybe the chevrons are specially marked unusually so that they all point one way to aid assembly - good idea, that would explain it.

Except.........I checked the bearings very carefully as they were removed. I noted it down.

They were all - all 4 - open down.

Also I recieved a replacement set from Tormach from the same bearing manufacturer - and they were marked in the normal way.

Phil it is possible to adjust preload with all bearings facing the same way. they are not unrestrained. There is a small land on the open side that can take some weight - for a few hours of running. Especially if they are open side down. The small land does not take the cutter load, only the spindle weight.

I have found and attached a PDF of the spindle assembly. If you enlarge it enough, you will see the bearings are shown open at each end.

[philbur]

The diagram clearly shows open ends facing out, both top and bottom, as you would expect. So that leaves us with the advice 4Z7 received from the bearing technician - quote:

"My original bearings were installed both sets open end facing down and the technician told me that is how I should also install the new NSK bearings which I did".

I'm also curious about the rebuild quote 4Z7 received.

$100 to dismantle and inspect.
$300 for the 2 sets of bearings,
$3,000 for the complete rebuild.

That makes it look like $2,600 just to put the thing back together again, sounds odd to me.

Tormach will sell you a complete new spindle cartridge for $564. Of course you (or better still Tormach) may need to check the bearing orientation!!!!!

I would also question trying to squeeze 10,000 rpm out of this set-up. There is a compromise. Preload gives spindle rigidity, which is good. Preload with lots of rpm produces heat, which with this bearing arrangement would reduce the preload. The long "preloaded" length of this spindle design makes the preload sensitive to temperature changes. Finding a single preload setting that is equally good for the spindle grunting away “cold” at 500 rpm and running “hot” at 10,000 rpm might be quite difficult.

Maybe the answer is adjustable preload.

Phil

Exactly Phil ! I think we are last finally drawing to a conclusion. We have been passing each other in the doorway for days! Too true!
We have agreement with NC that all open one way would would be wrong and not last.

NC suggests that maybe the chevrons are specially marked unusually so that they all point one way to aid assembly - good idea, that would explain it.

Except.........I checked the bearings very carefully as they were removed. I noted it down.

They were all - all 4 - open down.

Also I recieved a replacement set from Tormach from the same bearing manufacturer - and they were marked in the normal way.

Phil it is possible to adjust preload with all bearings facing the same way. they are not unrestrained. There is a small land on the open side that can take some weight - for a few hours of running. Especially if they are open side down. The small land does not take the cutter load, only the spindle weight.

I have found and attached a PDF of the spindle assembly. If you enlarge it enough, you will see the bearings are shown open at each end.

[keen]

The diagram clearly shows open ends facing out, both top and bottom, as you would expect. So that leaves us with the advice 4Z7 received from the bearing technician - quote:

"My original bearings were installed both sets open end facing down and the technician told me that is how I should also install the new NSK bearings which I did".

I'm also curious about the rebuild quote 4Z7 received.

$100 to dismantle and inspect.
$300 for the 2 sets of bearings,
$3,000 for the complete rebuild.

That makes it look like $2,600 just to put the thing back together again, sounds odd to me.

Tormach will sell you a complete new spindle cartridge for $564. Of course you (or better still Tormach) may need to check the bearing orientation!!!!!

I would also question trying to squeeze 10,000 rpm out of this set-up. There is a compromise. Preload gives spindle rigidity, which is good. Preload with lots of rpm produces heat, which with this bearing arrangement would reduce the preload. The long "preloaded" length of this spindle design makes the preload sensitive to temperature changes. Finding a single preload setting that is equally good for the spindle grunting away “cold” at 500 rpm and running “hot” at 10,000 rpm might be quite difficult.

Maybe the answer is adjustable preload.

Phil

Hi Phil - I take it you mean some kind of 'sprung' preload. we already have adjustment via the spindle nut.

Actually I think we already have a kind of crude 'Sprung preload' ex the nut itself. You know when you tighten a nut - as it contacts its face, it does not stop suddenly, but rather takes perhaps a quarter of a turn, gradually gaining in resistance, before the desired load is applied. I suppose the washer under the nut is flattening completely, the spindle may be stretching slightly, but probably the main flex is the threads of the nut riding up on each other, distorting slighly, giving a little, and providing a few thou of spring.

When I assembled my spindle I decided to take this a small step further. I lapped the top spindle diameter down until the inner races were a lighter fit, and machined up a short travel 'spring' see the attached pics.

I had to machine up several prototypes until I had what I thought was the best travel and pressure.

My spindle now runs much cooler than it used too. - And does not seem to be any less ridgid.

[Tormach]

Guys,
Boy, lots of discussion here on spindle bearings. Some of the points made in the many postings are correct, but a many of the technical points are not really applicable to the PCNC 1100. More expensive machine tools commonly have 30,000 to 50,000 RPM spindles with accuracy tolerance better than 0.00005". In those applications the balance, temperature fits, and clean room type procedures are essential. A spindle repair on many machine tools will cost 4 or 5 times the price of a PCNC mill.

The PCNC mill design does not push the envelope on bearing technology, running only 70% of the rated speed of our bearing design. The process is done in a clean area, but it's not a controlled clean room. Probably the most important part is that only a few experienced certain people are allowed to do the spindle assembly.

In April of 2008 we conducted an audit of the spindle assembly process. I wasn't there, but our China based employee conducted the audit and send us photos, videos, and a written report of the audit. Our only modification to the process was to require better control of the amount of grease used. They were doing OK with the grease, but it was based on experience and not on any volumetric tools. They now use a couple simple tools to measure the volume of grease used in the upper and lower bearings

Here are some comments on a few of the issues discussed earlier in this thread:

• By our estimate the spindle design is fine for anything up to 7000 RPM. Taking it higher is certainly possible, but will lead to shorter bearing life.
• Preloads should be matched to a speed range. As noted, a preload suitable for 10,000 RPM is going to be loose at 500 RPM.
• We work hard to follow quality issues at Tormach, including tracking issues and frequency. Spindle bearing issues have affected less than 0.5% of all machines and most incidents were associated with much earlier machines. The incident that started this whole thread is one of those documented problems. Nearly every problem we see like this is brought up for discussion with the people at the factory.
• The service bulletin mentioned in msg #79 of this thread had not gotten past draft. This is the same doc attached to msg #85. It's available on demand, but we wanted to improve the document before we published it. A final version of it should be posted pretty soon.
• We now stock the spanner needed to adjust the preload. 42 mm spanner, PN 31038. Nobody ever asked for one, we just thought it would be a good thing to stock.
• The cartridge style spindle is not common on low cost machines, but we designed the machine with a cartridge to make it easy for people to replace. While someone can rebuild their spindle, it's easier just to buy a new one.
• Spindles just have not been much of an issue, but it is a wear item. As years go on we expect spindles to be wearing out, needing repair or replacement. If it ever becomes frequent we'll probably sell rebuilt spindles as part of a trade in service.
• We agree with one of the posts, 180F to 200F is a fine range for the spindle bearings at top speed. If the spindle never gets warm you might have too little preload. If the spindle gets hotter than 200F you might have too much preload.
• If anyone ever does need bearings, we recommend buying them from us. We have been fully satisfied with the quality and you'll generally find that Tormach sells the bearings much cheaper than local over-the-counter sales.

[philbur]

Hi keen, It was really meant as an off the cuff comment. The idea being that you dial in a new preload depending on what rpm you intend to run the next job at. Not something you can practically do via the spindle nut.

I think your inclusion of a spring washer could improve the control of preload at different operating conditions but by definition will reduce the axial rigidity. This may be OK for many machining jobs but soon or later, on more challenging work, will show up in poorer performance with regard to chatter, surface finish and dimensional control.

Just some thoughts
Phil

Hi Phil - I take it you mean some kind of 'sprung' preload. we already have adjustment via the spindle nut.

Actually I think we already have a kind of crude 'Sprung preload' ex the nut itself. You know when you tighten a nut - as it contacts its face, it does not stop suddenly, but rather takes perhaps a quarter of a turn, gradually gaining in resistance, before the desired load is applied. I suppose the washer under the nut is flattening completely, the spindle may be stretching slightly, but probably the main flex is the threads of the nut riding up on each other, distorting slighly, giving a little, and providing a few thou of spring.

When I assembled my spindle I decided to take this a small step further. I lapped the top spindle diameter down until the inner races were a lighter fit, and machined up a short travel 'spring' see the attached pics.

I had to machine up several prototypes until I had what I thought was the best travel and pressure.

My spindle now runs much cooler than it used too. - And does not seem to be any less ridgid.

[keen]

Hi Phil.

Yes I was worried about a reduction in ridgidity also. but I did not like the idea of preload back of as the spindle heated up. I made different spring washers until I had a very thick one that allowed quite a decent pre load force.

The true test came when I did a 'before and after' repeat job. Heavy machining to the limit of the Tormachs horsepower (yes I almost stalled the spindle at one stage) machining P20 with a carbide ball nose cutter to the profile below. There was no noticable difference in the performance of the spindle before or after the mod. Of course I was comparing with top bearings that were previously in upside down. But I doubt that would affect the ridgidity as the fault was with the top bearings and preload was able to be applied. Allbeit that the balls cut out quick!

[keen]

Sorry I should have said P20 tool steel - (which is prehardened and tempered steel -to about 35 deg R/C )- the pics look like aluminium !

[keen]

Oh and I should thank Tormach for taking the time to read (obviously carefully) such a long and winded thread!

Good to hear that spindles have not been much of an issue. It seems like my problem is quite rare and unlikely to be widespread.

I would agree that the Tomach replacement bearings are the best price - (well I found that anyway) -and they seem very good quality. I studied the old and new set carefully and they seem to come from a serious bearing manufacturer.

[philbur]

Well there ya go, proof of the pudding.... as they say. Can't argue with that.

It seems amazing what the spindle achieved with the top bearing set in up the wrong way.

Phil

Hi Phil.

Yes I was worried about a reduction in ridgidity also. but I did not like the idea of preload back of as the spindle heated up. I made different spring washers until I had a very thick one that allowed quite a decent pre load force.

The true test came when I did a 'before and after' repeat job. Heavy machining to the limit of the Tormachs horsepower (yes I almost stalled the spindle at one stage) machining P20 with a carbide ball nose cutter to the profile below. There was no noticable difference in the performance of the spindle before or after the mod. Of course I was comparing with top bearings that were previously in upside down. But I doubt that would affect the ridgidity as the fault was with the top bearings and preload was able to be applied. Allbeit that the balls cut out quick!

[LeeWay]

Yep. But with 4 bearings it is pretty stout anyway.

That's a good looking part. Could you say what it is and used for?

[keen]

Hi Lee. I think the design is generic but in case it is not I had better not identify it.

[keen]

"It seems amazing what the spindle achieved with the top bearing set in up the wrong way."

Hi Phil - I may be wrong, but I think you are being polite, but suspect I got a bit mixed up with which way my top bearings were orientated.

I don't blame you if you do - scepticism is healthy - and you were always polite! The dismantling was done 7 months ago and I even began to wonder myself if I had got muddled up. I'd hate to think I could have caused this long thread based on a blunder! so I spent time last night and checked my notes that I always take when I dismantle important assemblies. I wrote in my notes that I marked the bearings 'T' on the top outer race. I found the old bearings and managed to photograph the scratched 'T' (I expect NC Cams wil say you must NEVER, NEVER, NEVER do that) see pic 0002

More later - hot water tank has burst and the plumber has just arrived.....

[philbur]

I'm always sceptical. But I didn't doubt you, well not after the first few posts at least.

I was, and still am, surprised that the spindle didn't have the smoothness of a bag of rusty nails.

Phil


PS: Naughty of you with the bearing marking. A bit like scratching your initials on the back of a Rolex.

"It seems amazing what the spindle achieved with the top bearing set in up the wrong way."

Hi Phil - I may be wrong, but I think you are being polite, but suspect I got a bit mixed up with which way my top bearings were orientated.

I don't blame you if you do - scepticism is healthy - and you were always polite! The dismantling was done 7 months ago and I even began to wonder myself if I had got muddled up. I'd hate to think I could have caused this long thread based on a blunder! so I spent time last night and checked my notes that I always take when I dismantle important assemblies. I wrote in my notes that I marked the bearings 'T' on the top outer race. I found the old bearings and managed to photograph the scratched 'T' (I expect NC Cams wil say you must NEVER, NEVER, NEVER do that) see pic 0002

More later - hot water tank has burst and the plumber has just arrived.....

[keen]

Cheers. Yes Phil, I was naughty. I hope NC cams does not find out.

Plumbing panic over now.

I have another pic showing the bearing taking load in the wrong direction - and anothe pic with it open showing I did have the bearing that way.

[zephyr9900]

I've had a Tormach mill for about a year now. I replaced my spindle bearings for 10000 rpm and I also had to cut down the arbor to fit a high speed taper-lok pulley and power drawbar which involved a new keyway and grind the shaft to 1 1/8" diameter to fit the new pulley.

Did you make any other modifications to the drivetrain other than the ceramic bearings and new driven pulley, 4Z7? Are you using the original VFD? Tweaked PCNC for the new speed range? Adjusted the VFD for accel/decel/braking etc? Just want to get an idea of what all you did...

[*]By our estimate the spindle design is fine for anything up to 7000 RPM. Taking it higher is certainly possible, but will lead to shorter bearing life.

Could you qualify that statement please, Greg? What do you mean by "spindle design"? Current bearings, dynamic balancing, etc.? Does that mean I can just fit a smaller driven pulley, adjust the preload (in my Sherline days, adjusting the spindle bearing preload from standard to 10krpm was "back off the spindle nut 2 degrees" if the bearings got too hot at 10k) and go for it? Would you recommend the upgraded VFD or is the original good to go? Your statement is a surprise compared to what I've seen you officialy say in the past...

Just wondering,

Randy

[SarcasmOMatic]

The dismantling was done 7 months ago and I even began to wonder myself if I had got muddled up. I'd hate to think I could have caused this long thread based on a blunder! so I spent time last night and checked my notes that I always take when I dismantle important assemblies. I wrote in my notes that I marked the bearings 'T' on the top outer race...

Notes are good but photos are better. Given how "cheap" digital photos are I always take tons of pictures when disassembling anything I am not familiar with. It takes very little time/effort to do and has saved me more times than I can count.