NCcams, bearings again

[bob1112]

Well, here is the update. We actually got our bearing supplier to comp us another set of AC bearings for our upper drive unit. We installed with more precision than surgeon. We installed the spindle and now have about 1 hour total time with about 5-10 min actual machining. The rest has been bearing breaking and spindle warm up. We have the EXACT SAME NOISE again!

The noise is confirmed to come from the upper drive AC bearings and the spindle but when you spin them by hand, smooooth they are. I am hoping all this is is a lack of preloading the bearings from you scaring me tool much:-) The sound would not be one of FOD, loud bearings because they are quiet but the noise is random tick lick bal bearings lightly tapping each other and it is getting worse. I shut it down tonight and said "hell no", and pulled it apart. We have not even modded the spindle yet for 10k rpm and we sure can't do it with this noise.

My gut is telling me more preload but I looking for someone to confirm that. Two sets of bearings in the upper and the lowers?? Nope, we have an install problem. When I setup taper roller bearings, I use a .500" breakover bar on the nut, These bearings are not even close in tension. Holding this assy is more than tricky to get much torque on it. Now we have done some numbers on thread diameter and pitch to figure our force applied but without making a tool, I can't put my torque wrench on it. You tell me, what tool do you select for pulling down the pinch nut? Have we somehow over tensioned both? Man, this is getting old Thanks for any help you can offer.

Brandon

[NC Cams]

First, are you SURE that the bearings are preloaded when installed????

Simple generic A/C's are not preload. ONLY if they are factory preloaded (usually designated by DUL, DUH or DUM in part number in NSK speak) can you be assured of a true preload. A random pair of 7207 bearings will NOT be preloaded. A factory matched pair of 7207DUL's should be preloaded and the preload is usually certified on a chart provided with the bearings. No cert chart, be wary.

Machined bronze cage bearings can/will rattle the cages, ESPECIALLY if you're using a VFD instead of a DC motor drive. The sinusoidal current of an AC motor rattles the heck out of bearings with metal cages. If it is TRULY cage rattle from VFD, then turn up the radio as this is not going away and it is a PITA but not usually terminal.

IF it is cage rattle due to shaft to housing misalignment, this can lead to cage breakage and it needs to be addressed/fixed.

IF the bearing has a plastic cage, they should be quiet as plastic cages typically won't/can't rattle. HOWEVER, if the housing is distorted and the balls are running into and out of a load zone due to uneven or no preload from distortion, you'll hear the balls howl or rattle about. THis will tear up a riveted cage and can pound out a plastic cage eventually

Regarding preload: generally speaking, low speed grunt spindles can use heavy (DUH) preloads. High speed spindles, conversely, use light (DUL) or ultra light preloads (designated by something totally different). For 10K use, I'd expect DUL.

FOr what should be obvious reasons by now, system squareness is even more critical if DUL and or high speeds are involved.

YOu can have the bearings checked for preload by KAF Mfg in Stamford Ct. They can inspect and reset the preload to whatever you want/need.

If this is an upper bearing, mounted adjacent to the drive belt, it might be that the belt tension is unloading the bearing.

You can NOT compare tapered roller preload to round ball bearing preload. TOTALLY different internal geometries. When you preload a taper, you're actually shoving the edges of the rollers up agains the shoulder of the cone. Thus, you have SLIDING friction. When you have a preloaded A/C ball bearing, you always and only have ROLLING friction. BIG difference that should now be self evident.

If the housing is distorted and the axis of the shaft is skewed with respct to the true C/L of the housing, you'll end up with the balls being unevenly preloaded or perhaps even unloaded for a portion of the ball path. They'll make noise as the balls go into and out of the load zone when this happens.

The spec for shaft and housing squareness needed for a high speed spindle often makes service and/or the machinists cry as it is almost perfectly square with NO room for slop. Reason: keep the balls evenly loaded ALL the time.

There is also a possibilty of grease noise. Some greases sound like popcorn in preloaded A/C's - it is the balls rolling over the thickening agent in the grease. Sometimes grease thickeners actually feel like marbles are in the bearings when you turn them.

HINT: wash out the bearings with Brakeclean and see if the roughness goes away when you spin it by hand (lube it with a few drops of DEXRON). DON'T blow gun spin the bearings or run them w/o lube. If they are quiet and free turning lightly oiled, use different grease and see if there is a difference.

To tighten the bearings under preload, assuming you have a slip fit, we use torque turn method. This loads the spindle nut to a torque and then so many turns more. The torque essentially takes up the slack, the turn sets the preload by compressing the A/C's to the point that the inner rings and outer rings touch - this is when the built in preload is finally established.

This spec is established by the OEM when they set up the spindle as it takes spindle nut torque, spindle stretch and/or bearing preload offset and preload into consideration. Your bearing supplier's application engineers should be able to help you with this spec as they can figure out what the ring offset is and how much you have to turn the nut after making contact to affect the proper preload if you give them enough info. If not, they are simply lame.

I after all this, something is probably still awry that you haven't found/fixed yet. You'd better find out what's going on before you even think of 10K. But by now, you now have more to go on....

[bob1112]

both pairs of bearings are DUL mounted back to back. When you spin the bearings by hand fulling mounted and "preloaded" they make noise right in your hand. The cages in the uppers are phenolic and the spindle bearings use plastic. The cages in both are VERY free for movement. They jiggle all over when you turn the bearings in a back and forth motion. This is either that the bearings are "wrong" from the factory and have no preload ground in, something is out of round causing some balls to load and others not, or it is the cages bouncing everywhere.

I am leaning toward the cages because they are not ridged at all and move in and out like .050. OUr spindle DOES repeat, hold tolerance and surface finish is good. All reasons to think they are loaded up. Now there is no way for the uppers or lowers to spin on the races due to clamping force but the middle idler bearing is getting a strong lookover for spinning in it's race.

I am really leaning on this cage issue but I have no idea how to fix it. I realy think those cages go into a chatter or pop back and forth and that is what I hear. More grease, less grease, different grease, new machine? I just can't believe that Kluber's #1 spindle grease would have an issue like this if it is the grease.

Our old bearing cages are somhow fixed to the inner race so they cannot move. Is this a bearing manufacture issue or am I barking at the wrong tree? It just seems the cages are the one thing that, without a doubt, are loose as hell in the bearings to cause this odd noise. Can this cause ball skidding and or fail the bearings?

[NC Cams]

Re: grease noise. I kid you not, some grease is as noisey as a can of marble shaking. IT all depends on the type and quantity of thickener they mix with oil to make grease. Price of grease has no relevancy to noise.

I can cite some pricey, aircraft grade greases (Mobil 28) that use clay as a thickener and the stuff was HORRIBLE for noise. There is also a water pump bearing grease that some guys use in A/C bearings (Chevron SIRI) that was notorious for grease noise. The noise came and went depending on the batch. I don't recall where Kluber grease registered as my bearing clients at the time didn't use it that much

Re cages: There are ball guided and race guide cages. Some cagers are guided on the outer race shoulders and some are guided on the inners. The higher the speed, the more you do not want ball guided cages because of obvious cage stability issues. Cage rattle per se is not necessarily going to cause performance problems outside of PITA noise.

Re alignment: please reread my prior post CAREFULLY. I SAID and IMPLIED NOTHING about shaft alignment or runout. I indicated that if HOUSING were distorted, is would be possible for the net alignment of the outer ring to be off and thus the raceway would be "cocked" with respect to the axis that is trying to be established by the shaft and the raceways. This causes uneven ball loading.

I don't know who's bearings you got nor do I need to. If they are properly preloaded, the raceways should be parallel to the sides of the inner and outer rings. Thus, when they're clamped together, the raceways should be properly and evenly preloaded. If the raceways are NOT parallel to the sides of the inner and outer rings (a real problem to maintain with some aftermarket preloading methods), the bearings will NOT encounter even ball loading.

You'd be amazed at how little misaligment needs to occur to unevenly load the balls. We're talking minutes of misalignment - maybe 5 or 6 minutes which is NOT much.

Like I said, when the machinists saw the squareness spec recommendation for machine tool spindle housings, pretty much all the guys I talked with when I was a bearing engineer *****ed to high heaven about the tightness of the tolerance that our bearing designers spec'd out.

Again, a distorted housing will NOT show up in spindle shaft runout. But it can/will affect ball loading

Strangely and amazingly, the Japanese spindles were typically made that way (ultra tite squareness tolerance) because honorable bearing expert said to do it that way. The other global machine tool makers, especially some of the the American makers, seemed to be less willing to hold such tight tolerances.

You might want to get your bearing supplier to contact the OEM who made the beargings. They may have some ideas on what to look at or for. I know that when we had a spindle rework inquiry, our machine tool design dept HAD to be contacted to approve/review the bearings we interchanged. You'd be surprised at the incomplete knowledge base that some bearing application engineers rely upon (especially out at the distributor level).

You never know, your particular spindle may have had custom bearings that were tricked up by/for the machine tool maker for just the reason you're citing. A "that's close enough" bearing interchange might be the true source of your problems.

I KNOW for a fact that some Bridgeport spindle bearings were totally custom (I have al of of the OEM drawings). If you try to install a generic bearing (ABEC 7 or even a 9), they WON"T WORK because of screwey, selective fit housing sizing. Put a standard bearing into an o'size housing, on an undersized spindle (they were made that way at the factory!!!) and you'll never get the balls to load evenly.

Unfortunately, selectively sized bearings are all but impossible to obtain anymore. Hence, if you have one of the funky housings or spindles with oddball sizes, you'd better find people who can OD and/or jig grind as well as some people who are damn good at applying chrome so that you can properly resize the housing.

[bob1112]

You are mostly refering to bore squareness and unless I have a shoulder issue on the spindle shaft, that may not be the case. I can hear this problem with the spindle out just rolling the bearings with my hand. As you roll them one way and then quickly back the other, you wil hear a tick or clack. The bearings are loaded up so I would think they would be quite as a mouse. Man do I want to engineer an air/oil mister right now! I honestly think those cages have issues. Am I just supposed to run this until it blows or what? Can I reduce grease amount to help? I think this cages are ball guided as they do not contact the inner or outer race, just the balls.

[NC Cams]

From the last paragraph in post #3, your OEM bearings were clearly fitted with land guided cages. These will not click or clack because they are fully supported and essentially can't move radially.

Again, I don't know who's bearings you're using but it seems that via the use of a ball guided cage, and one that sounds like it is free to move about radially, will encounter cage rattle.

As I believe i said previously, true cage rattle can be solved by turning up the radio - it does not/should not affect the durabity or performance of a bearing used in NORMAL service.

HOWEVER, there is always a caveat.

When/if you're going to run a spindle at 10K, you're NOT looking for NORMAL service. You're pushing the bearing to the extreme limits of its operating window.

For 10K service, you may want to talk with the service engineers at a bearing MAKER (not the local distributor). For such applications, they may want/need to use some higher technology that either a machined phenolic cage (real simple stuff and used for low volume, generic cases where it doesn't pay to tool up a tricked up injection molded plastic cage).

I know that the company I worked for had some tricked up cages that evolved once they figured out how to make glass reinforced nylon cages. There are/were some real neat tricks that you could incorporate into a tricked up cage to stabilize the ball, guide the cage and/or better channel lube within the ball cavity that you couldn't even dream of doing with machined or stamped cages.

If you can literally shake the bearings and hear the cage rattle, you're choices are to either add a bit more grease and hope that this helps - not too much however as too much grease will cause heating and skidding problems. Figure on a 25% to 30% fill.

A call to the bearing OEM might be in order. Perhaps they have a better fix. It would not surprise me if you're a victim of a bearing interchange (machine tool OEM used a tricked up, land guided cage, the bearing distributor found the closest part he had in stock that would fill the hole). Frankly, I know that we had much tricker bearings for some OEM applications and these tricks did NOT get incorporated into our generic, albeit ABEC 7 aftermarket service parts.

Don't waste your time with the oil/air misting. Engineering up an oil air mist will NOT fix the cage rattle issue - only a different design cage will do that.

As far as fixing the cage rattle once and for all, please reread the previous paragraph.

Ultimatley it might be time to have a servious talk with your bearing supplier. Show them what you find objectionable and have them get invovled in the problem resolving process. If they care about you and your business, they'll surely do something. If not, it may be time to find a new bearing vendor and bearing distributor.

[set_apart2001]

hello I am a cabinet builder been doing it for nearly 20 years I am interested in cnc routers however I have no clue how to operate them I am wondering if there are schools that teach how to operate them any respons is appretiated joe

[NC Cams]

Memo to SET APART2001: you might want to start a new thread in the router section of this message board to get a repy to your inquiry. Your inquiry is not pertinent to this particular thread.

[NC Cams]

Bump update

I stumbled across this thead and reread it. I must appologize to VIPER6383 as I wrote this reply shortly before I went into the hospital with was nearly a life ending bout with kidney failure. I was apparently very ill at the time and clearly not thinking well. Again, I appologize for not taking his feedback about bearing noise into account.

If I may do so here, I'd appreciate everyone's indulgence by allowing me to address this issue on the first year anniversary of regaining consciousness form kidney failure.

AC bearings should spin freely and have NO appreciable noise when you spin them. HOWEVER, they can rattle about if the inner rings are touching or the outer rings are not touching or vice versa when munted DB or DF. THe only trick is to make sure you have the balls properly loaded before you try the "sounds funny" diagnosis. BTDT myself and it will drive you crazy.

WHile handling bearings, I've had the occasion of the inner ring coming out of the outer. THis is an easy occurence if you heat the bearings and then shrink them on the shaft. THe inner ring cools faster and the outer can drop off.

No problem, simply pop/shove them back together. WRONG.

IF you "press the inner ring and balls" back into an outer, your force the balls to ROLL up over the retention shoulder or the outer ring. In doing so, you WILL brinnel the balls (usually one spot on each) and likewise the shoulder 9as many places as you have balls). THe damage to the shoulder is essentially harmless as the balls never see the shoulder when properly preloaded The balls however are irrepairably damaged. The brinneled balls WILL feel rough and the pattern can come and go as the balls roll around the raceway.

If you do this and DON'T run the bearings, you can salvage the mess by replacing the balls - measure nominal size, then find some grade 3's of same nominal sixe and you should be good to go. If you run them, the brinnels on the balls will harm the raceways and it just gets worse and worse and worse. Heat the outer ring and the balls /inner race should drop out. INspect with mag glass. Raceways should be UNMARRED, DITTO that for balls. ANY mars, dents or shrapnel marks. the bearing is gonna be noisy and will fail prematurely.

Not to misspeak of Anybody, but many times, the problem that was previously solved consistis of steps A+C+D+E+F+G. IF you leave out item D in your explanation, IE reassembled balls because cages fell apart, some seemingly irelevant detail is left out.

This inner ring reassembldy issue is not that uncommon. We even saw experienced spindle shops run into it. Had it happen to me too. It was/is so prevalent that it was the first thing you looked for when doing failure analysis on an AC.

Right fix: place balls in cage, freeze inner ting to allow cage w/balls to drop into/onto inner ring. ALlow to cool,

Set outer ring with open end up. Chill cage and balls, warm up outer ring with heat lamp or small doses of propane torch heat. Chilled inner ring/cage/balls should DROP into outer with NO force what so ever.

I do hope the problem was fixed/resolved. Again, I do hope that my deficient reply at the time did not overly complicate the resolution of the problem. I was simply and unknowingly too ill at the time to speak as intelligently as I try

I hope a reply is issued so we can find out what solved the problem.

[bob1112]

NC Cams, first, very sorry to hear of your health bouts. Our piddly bearings just don't compare to some of lifes other challenges. Glad you are still with is. You helped more than you know regarding bearings. I think we have a pretty decent grasp on them now from a real engineering standpoint. The problems we experienced with the bearings was nothing more than excessive grease in the bearing. The seemed to tap or knock and we were not quiet sure of the noise we heard but by just removing some of the grease, the noise nearly all went away and we left it. It got better as it warmed up so it all made sense from there.

We have sense found some decent references for grease quantities so this does not happen again. the term (30% fill) does not really mean much to us so we were able to learn the exact number of grams given a bearing size and target fill percentage. Just an rookie error I believe.

I made another booboo in trying to use Kluber spindle grease in a shperical roller bearing. Should have used something different and it killing my bearing. NOT smart on my part. Loaded it will axle grease on the next round and we are all good so far.

Thanks again for all your help. Also, really hope your health holds out and you are able to enjoy more that life has to offer. Take care.

[NC Cams]

Grease noise is someting that is not widely discussed. Grease noise is a product of the thickener, not hte lube oil.

Ig congeals at room tiem and can feel like marbles in the bearings. Noise is horrible until tem prise and the thickenre wither melts or breaks up into smaller particles.

The sodium nitrate they use(d) in CHevron made it one of the noisiest greases I ever heard. Great grease for many applications, THink twice if it is noise sensitive app however.

NOTE this opinion was formed a number of years ago. They may have addressed the issue by now but some leopards do not change their spots.

grease fill. ANyone who's ever driven in wet, deep, slushy snow can imagine what the balls in a bearing have to contend with in an over greased situation. YES< you can over grease a bearing<. BTW, the more grease you use, the lower the max speed you can run at. This is same reason why speed ratings for same bearing are lower with grease vs oil lube

This is why ultra high speed bearings run with oil air mist. AIr does the cooling, oil mist does the lube - sort of like dry sumping a race car engine.