[Sparky_NY]

I'm in the process of retrofitting a DM45 mill, a RF45 clone from penn tool co. I did the head first, all the ususal, new abec 7 angular bearings with kluber grease, vfd, belt drive, power drawbar with tormach tooling. I am very pleased so far EXCEPT with the spindle bearings.

I got the head pretty much complete, did the bearing breakin monitoring temps, and it was time to put a cutter into some metal. I had real bad chatter problems. I concluded it had to be slop in the spindle bearings after exhausting all other possibilities. I tore it back apart and checked things much more carefully this time. One bearing looked and felt very slightly bad. ALSO, the upper bearing always ran much hotter than the lower during the breakin. It is also worth noting that the sound of the spindle changed over the hours of breakin, it had a extremely slight raspy sound at the end that was not there at first. Checking things much closer, I concluded the press fits were too tight and this "possibly" was preventing the spanner nut from pulling the shaft/bearings up together and getting proper preload. I "think" one bearing preloaded and the other had slop. I cannot swear to this because its about impossible to veryify with the spindle assembled. It is worth noting that the press fits were such that I had to heat the housing and freeze the bearings to get them installed.

What I seen on disassembly, that I did not like, was the bearing outer races were far too tight a press fit into the spindle housing. I took carefull measurements but do not have them on hand at the moment. The spindle shaft into the inner races was not nearly as tight. When I say those outer races were very tight I mean the press fit into the spindle housing is such that disassembly is impossible without destroying the bearing. The original factory bearings fit the same way.

At this point, I believe the outer race / housing fit is the problem. I am thinking the spindle bore for the race has to be opened up a bit to lessen the press fit. How to accomplish this easily is another matter! !!! Much reading on the matter has found that the bearing press fit is very important with precision bearings and plays a part in determining the installed internal clearances.

So............... my questions are:

What have you other guys that upgraded spindle bearings experienced in how tight the press fits were?

Did anyone have to rework their spindle housing to loosen up the press fits? How did they do this? I am just about positive this needs to be done but a method for the home shop leaves me scratching my head.


I have not installed the second set of bearings and have the spindle apart yet. I want to take every precaution to get it right this time so I am looking suggestions for the collective knowledge of those that have done it here.

Any help / suggestions would be most appreciated.

[arizonavideo]

How round the bearing race pocket is s vary important. The bearing clearance is set by the pre load nut so the race fit will not change that. One of the common problems is not having the bearing race sit truly flat. If the fit is really tight it will most likely skim some material from the side of the pocket when you install them and it wont be flat.

I would remove the race and sand the pocket lightly with 500 grit until it is shinny, looking for any burs and dents that might stop the race from seating flat. Look really close at the lip the race seats on.

The top bearing need to be able to slide without too much force on the spindle shaft so the preload can be adjusted. Most of the time the fit is a bit too tight. Buff the shaft until it is shinny and perhaps a few tents smaller.

[Sparky_NY]

I recall reading posts where someone mentioned they had taken their spindle out a few times to inspect things. This would be impossible in my case without destroying the bearing due to the outer race/housing fit. This is what lead me to believe there is a problem in that area. Also, I have read countless times that fits are critical on precision angular contact bearings. I am assuming that even though the nut sets preload, the balls would ride higher or lower in the groove depending on the fit. I get the idea my outer race fit is MUCH tighter than the norm which would greatly increase the change of the race not sitting flat when installed like mentioned.

Can you remove your bearings without destroying them?

(both my original and later the grade 7 bearings outer race was impossible to remove it was so tight. I ended up, in both cases, using the old trick of running a weld bead on the race and letting it cool, the race then contracts and pretty much falls out without damage to the housing.) Again, I suspect this is FAR tighter than others are experiencing. I have read every thread I could find over time and don't recall anyone having a lot of trouble removing the bearings like I did.

I am thinking a hone is about the only way to open that bore up a bit with available home-shop equipment.

[arizonavideo]

A hone wont let you get the corner square on the seat.

The metal is fairly soft if you can spin it in a lathe or anything you can make up, hand sanding will do the job if your careful but its needes to spin to get it even. Your talking about .0003" to remove.

I didn't try to save the old bearings so I don't know but I can remove the spindle from the housing fairly easy. The bottom bearing comes out with the spindle but you just leave it on the shaft unless its toast then it doesn't mater what you do to it.

I use regular Japan A/C bearings or a standard grade USA bearing and get less than .0003" runout most of the time for less then $30.00 for the lower.

[arizonavideo]

To remove the lower bearing I made a driver on the lathe from aluminum but a soft steel pipe will let you drive off the bearing without damage. The seats are the problem.

Perhaps rolling it on a bench carefully and sanding the seat to get it clean might work. You could put it in the oven at 250 and freeze the race and it will just drop in.

[Sparky_NY]

Thanks for the replies. When I made the original post I did not have my measurement data on hand. When I say the fit was tight, the bearing bore in the spindle was .0012 smaller than the bearing od. I researched the recommended fits. NCcams had some excellent posts here and I also looked at data sheets. In short, the bearing bore should be anywhere from zero to a half thou OVER the bearing size. A press fit is asking for real trouble. I was curious what others were experiencing, thus my post. Of course these are chicom machines so variation is probably to be expected. I think I just happened to get a tight one.

At any rate, I have successfully reworked the bearing bore to a acceptable fit. I also checked with the bearing installed and a depth mic to be sure it was fully seated in the bore.

I used grade 7 fafnir bearings because I was able to find them on ebay pretty cheap. Grade 7 is overkill for this application BUT it does not hurt a bit especially if the price is comparable to standard bearings.

So, I believe the fit problem was my original problem, causing the upper bearing to have excessive preload and the lower bearing to be loose and chatter. The fits are now corrected, I have new bearings. I am just being a bit overcautious, I certainly don't want to do this a 3rd time !! I spent far too much time chasing down this problem and am more than ready to get on with the remainder of the retrofit !!

Thanks again
George

[arizonavideo]

Preload had to be the same on both bearing. You have one adjustment so the pressure is equal.

The roundness of the lower bearing pocket will have a huge effect on the runout. The race will form to the roundness of the pocket so a high grade bearing may or may not give better runout over a standard grade bearing.

It sounds like you got the race to fit so you good to go.

[Sparky_NY]

Will find out soon enough if I am good to go ! I will recheck everything carefully, measure the kluber grease in and begin the breakin process. I had 3 temperature meters on the head, upperbrg, lower brg, and motor. The upper bearing always ran much hotter, hopefully that will change this time.

[RotarySMP]

What method did you end up using to resize the bearing seat? Line boring, grinding honing?

[Sparky_NY]

What method did you end up using to resize the bearing seat? Line boring, grinding honing?

All the methods you mention would be preferred to accomplish the task but unfortunately not available in the normal home shop. I tried a brake cylinder hone first. The hose stones wore down very fast without removing any material worth mentioning. I have some specialized "sandpaper" rolls which have a plastic backing and very fine grits. (original use was industrial equipment for polishing stainless shafting). I cut strips of sandpaper sized to just wrap around the bore and drove the paper with the hone against the paper. I used some wd40 for lube and to stop the paper from loading up. Although far from ideal, the hone gave even cutting pressure and taking care worked quite well. Inspecting the bore after test fitting showed a very even contact pattern with the bearing (much better than oem). I used a depth mic to verify that the bearing was fully seating against the shoulder at the bore bottom.

So...... although far from ideal, it worked well with the equipment available in a home shop. Only about a thousandth was removed, I don't think I would try this if it was much more.

George

[RotarySMP]

Glad it worked. Have you run in the new bearing yet?

[Sparky_NY]

Not assembled and run just yet. The break in procedure takes quite a while too. I will get to it in the next few days.

[Sparky_NY]

Ok, its reassembled and I did run the break in procedure about three cycles now. I have temp gauges for the upper and lower bearing and the motor. The temp pickups are as close to the bearings as possible. After just over a half hour at 8000 rpms the upper bearing reaches around 108 degrees and the lower about 8-10 degrees less. This is a order of magnitude better than before, before the upper would hit 130 and still climbing when I would stop.

ALSO, on reassembly I was surprised to see that the spindle itself pulled about a 1/4 inch higher into the quill than before. That confirms that the bearings were not fully seated. I had to recut my tophat for the collet closer as a result. For kicks, I measured runout, inside a tormach TTS ER toolholder taper mounted into a TTS R8 collet. Runout measured .0003 inside the toolholder taper, quite acceptable.

The spindle runs cooler now and sounds better also. Unfortunately, I still have chatter issues but far less than before. The chatter will need investigating but I don't believe its spindle related.

[arizonavideo]

Chatter should be the Z slide fitment.

[Sparky_NY]

Chatter should be the Z slide fitment.

I sure hope its something that simple. I have decided to continue forward with the retrofit and worry about the chatter later if necessary. I figure that the saddle, Z slide, table and such will all be coming off to investigate and install the ballscrews and such which will give me the opportunity to looks those things over at the same time.

Poking around with a indicator and pry bar the other night revealed the only real movement I could get was in the ways. The amounts varied from 3-4 thou roughly under moderately heavy pressure against a tool holder prying from the vise. Measuring from the head casting to the spindle produced no measurable movement on the indicator. So, I am leaning towards (hoping) for slop in the fit on some of the ways. I plan on tightening/checking all the gibs today just for kicks before proceeding with the retrofit.

Did you have issues with your Z slide fitment? If so, how did you address them?