[ekcourter]

My tool end angular bearings(2) have a catalog preset range but the outboard angular bearing(1) has a smaller preset range. Set with belleviews and spacers. If I use the larger numbers will I wear out the smaller one? Should I just plan on replacing the top one sooner?

7005 and 7002 ceramic balls, steel race. CNC softwood carving at around 15/18K, 1/2 Ball Mill. Would like to keep it light as possible for wear, looks like lowest would be around 14lbs/60N. The published rang is very large.

[RICHARD ZASTROW]

Are all the bearings preloaded with the spring washers? Normal practice is to have a hard location for the tool end and allow the opposite end to "float". This compensates for heat expansion of the spindle shaft. Might be different at the speeds you are running.

Dick Z

[ekcourter]

Its set up as you said, only one spring for the small end which functions as both preload and temperature expansion. The two hard end bearings were set up tandem fashion where the shaft needs a preload upward (to outboard end) to seat the two angular bearings (same orientation) it looks like it came with around 27 lbs but didn't last long. I can pull one of the doubled springs and get about 15 lbs. Both are within the mfgs range but on low end. I just don't know if I'll get any bounce in the shaft with what I'm cutting(see first post), seems light duty? I also wonder if the ceramic balls effect the preload. Thanks Edward

[RICHARD ZASTROW]

Typically the tool (hard) end has the AC bearings back to back. This is provides a more rigid set up.

Dick Z

[ekcourter]

When the bearings arrive I'll see if they will work this way. There not matched but with some careful measure/hone/sort/shim I might get it. If they clamp together with 0 end play and low friction I'm close. Its a cheap spindle so an experiment is possible. The problem is I don't know the dimensional stretch needed for each preload. There is mfg data on changing load but each starts with a matched set. Edward

[RICHARD ZASTROW]

You should learn the nomenclature of you bearings manufacturer. Somewhere in those numbers, letters and symbols is the code that identifies the preload. Typically it's stated as low, medium or high. This is the preload that bearing is designed for. If you change the preload, the life of the bearing and it's speed capacity will change.

Dick Z

[ekcourter]

Thanks, I'll check it out Tuesday when I have all the numbers. All the specs I've seen are for either matched sets installed as shipped all flush. If I ordered a matched set (probably wish I had) set up for mirror installation they would have a pre defined preload. With a parallel pair of angulars it seems it must be set at install, one direction opposite race offset. One learns but never fast enough. Thanks again

[RICHARD ZASTROW]

Angular contact bearings must be opposed by either another bearing or some sort of loading force. I don't quite get "one direction opposite race offset". Do you mean a pair of AC bearings back to back (in opposition), face to face (in opposition) or back to face (not in opposition)?

Without some preload AC bearings would have end play, defeating their purpose. In operation, they actually have some elastic deformation.

BTW, Your steel race/ceramic ball units are usually referred to as hybrid angular contact bearings.

Dick Z

[ekcourter]

The working end of the spindle is back to face(not in opposition). The loading force is a smaller AC bearing on the other end pushed outward by a pair of wave springs. The springs when compressed produce about 27 lbs. If I use one spring its 15 lbs. I am inclined to pull one spring...... Quote from NSK spec sheet:

"As a general rule, an extra light or light preload should
be selected for grinding spindles and the main shafts
of machining centers, while a medium preload should
be adopted for the main shafts of lathes requiring
rigidity."

How would a 2.2 KW VFD CNC spindle cutting wood be defined by the above quotation? Sounds like heavier equipment. From their table for my AC bearings (back to face), the pre load is....extra light 7 lbs. and light 14 lbs.

I did consider in a previous post changing to a face to face big end configuration but I doubt my ability to measure and match my mid-priced (and also not a set) AC7005's. From what I can tell this would be a stiffer setup as you recommended and the spring end can be left to float for heat expansion but......... My best indicator reliably reads to .0005, where preload adjustments steps (spacer grinding) on a 25mm bearing looks to be in the 5um range (.00019). My instincts tell me to keep the builders (China) bearing layout, reduce the preload and buy a better unit when I can.

My research has also revealed the importance initial break in and warm ups. This may have contributed to the early failure. Thanks for your kind attention.

[RICHARD ZASTROW]

You describe a set-up for a grinder. OK for a grinder that doesn't have axial thrust. Maybe OK for a soft wood router as well. If you employ helical router or end mill cutters they will want to pull the tool into the work and further reduce the axial load. However, I don't believe that will be the case for your work description.

If you have access to the original specs for your spindle bearings preload, you might only need to replace the springs to restore them to proper preload. 10,000/18,000 rpm is pretty high rpm.

Believe me, without a really good grinder/operator, it's nearly impossible to produce sufficiently accurate spacers or bearing races. Remember, you're dealing with microns in size and parallelism all magnefied by high rpm.

Dick Z

[mactec54]

ekcourter

Your spindle is designed to have the 2 front bearing facing the same way, you can not change this design, with out making a lot of changes to the spindle, they are made this way for high speed, you don't need the 2 springs at the top, one spring & a thin spacer to take up the gap were the other spring was work just fine, when assembled you should have a pull down of .001 to .003 max at the spindle end, this number can be less, but you have to remember you are running grease, not oil & at those speeds you need some clearance for expansion, the spacer it does not have to be accurate, within .001 is fine as it is only sitting under the spring

[ekcourter]

I'll give it a spin, Thanks all

[RICHARD ZASTROW]

Ref. post #10 I was referring to spacers placed between bearings used to set preload not a washer with a spring. Our spindles cannot tolerate a .0001" out of parallel condition. These are not DIY spindles, these are ABEC7/9 bearings. They don't like much beyond perfect.LOL

Dick Z

[mactec54]

RICHARD ZASTROW

You are talking about a totally different type of spindle, You can not put spacers between the bearings in these spindles as they are, it is just the way they are made, they have (2) bearings in the front, both facing out & the top bearing is in a Back to Back with the front bearings this is were the spring does the preload

These spindles can be modified, to have spacers & Back to Back bearings, in the front, but you are looking at major rework, They are made this way, because of the high RPM up to 24,000 RPM is not easy to do with a grease only spindle, & a price of $150 to $350 for the complete spindle, sometimes with the drive as well

These spindles also run ABEC 7 bearing

[RICHARD ZASTROW]

mactec54, that's why I suggested checking the specs. on the springs. It might just be a case of weak springs. I admit it took me a while to figure out the bearing arrangement, ours aren't that light duty.

That's a pretty good deal on those bearings. We use (4) sealed, greased for life Abec 9's @~$900 a set. Less than .0001" runout, in fact an indicator doesn't hardly register. (we cheat, finish ground spindle on its bearings while installed in housing.)

Dick Z

[ekcourter]

I just got a reply from WD bearings and they thought 47N preload, with the usual disclaimers of course. I set them for about 67N (one spring) they were pretty noisy but I'll see how they break in. I'm having a hard time getting them up to temp with the water cooling and no load.

[RICHARD ZASTROW]

Be sure to follow their break-in routine. Mostly they vary the speed to get the lube where it belongs. Most likely the temp will rise over some point and then back down again and level off. That should be the normal operating temp.

Dick Z

[mactec54]

ekcourter

I would of started with no more then 35n then up to 45n if it was needed, what you are using, is way to much 67n, remember the less preload you can use the better your spindle will be, I have run them at 17n to 20n which in most cases I found was enough

If the bearings are making a noise, something is wrong, the bearings should be very smooth, when you turn it by hand