[rwskinner]

I was doing a long machining op @ 6500 RPM this morning when my spindle motor started surging some. I reached up and felt the bottom of the spindle and now have some blisters. It was pretty darn warm is all I can say. Kubler grease was dripping out so....

When I did the pulley conversion I also changed out the bearings for some Timken high speed "cone" bearings and they have been running 100 to 105F during a run but they suddenly started getting very hot, so either the preload is too high or they are coming apart. I doubt they would run for this long with the preload to tight and not show signs of heat.

Anyways, I know Gary, Pete, and Jid I believe went with AC Bearings in their spindles. Hopefully, maybe one of them, or someone else will chime in and let me know how many and what size I need so I can get them ordered. I take it all the AC bearings are still running good?

Any help would be most appreciated. ATC still running like a champ.

Richard

[rwskinner]

Ah, I finally found it. Hopefully I have this right.

1 Lower Bearing - 7207 AC
1 Upper Bearing - 7206 AC

Richard

[LUCKY13]

I have not done this mod yet, but don't you need two A/C bearings in the bottom and one roller bearing at the top of the spindle?


If I am thinking right the two A/C bearings will be preloaded together at the bottom of the spindle, and the upper roller will have some way to allow for heat growth of the spindle (either springs to allow movement, and/or a slip fit to spindle or housing).


I think this is the problem with running two tapered roller bearings. The preload changes with heat and if its not allowed for it will kill the bearings. Just using two A/C bearings in the same way would have the same problems.


Here is one thread I feel gets into the workings of this type setup pretty good.


http://www.cnczone.com/forums/bencht..._bearings.html


Hope this helps.
Jess

[jid2]

These are the ABEC 7's I screwed up on install.

Kit10853 - 7207CYP4 Nachi Angular Contact Bearing 35x72x17 Abec-7
Kit10852 - 7206CYP4 Nachi Angular Contact Bearing 30x62x16 Abec-7

So I'm actually running my backup's which are ABEC 3. But They provided .0002" runout.

Kit10017 7207 Nachi Angular Contact Bearing :Steel Cage:C3:Japan 35x72x17
Kit10016 7206 Nachi Angular Contact Bearing 30x62x16:Steel Cage:C3:Japan

[rwskinner]

Thank you sir. That happen to be what I ordered. Lower bearing was burned up. No grease on it but it got hot enough the grease ran out. Top TRB looked fine.

Richard

These are the ABEC 7's I screwed up on install.

Kit10853 - 7207CYP4 Nachi Angular Contact Bearing 35x72x17 Abec-7
Kit10852 - 7206CYP4 Nachi Angular Contact Bearing 30x62x16 Abec-7

So I'm actually running my backup's which are ABEC 3. But They provided .0002" runout.

Kit10017 7207 Nachi Angular Contact Bearing :Steel Cage:C3:Japan 35x72x17
Kit10016 7206 Nachi Angular Contact Bearing 30x62x16:Steel Cage:C3:Japan

[SCzEngrgGroup]

Personally, I would not run open bearings in a spindle on one of these machines. Use shielded bearings, so the grease *can't* run out. That's what's been in every real machine spindle I've taken apart. The uber-expensive grease isn't going to make a bit of difference to performance - how you setup the bearings will be pretty much the sole determiner of life.

Regards,
Ray L.

[DonKes]

Maybe I don't understand shielded bearings, but I thought they had a metal shield that kept the big trash out (or in) but were not a real seal.

Don

[johnedward]

I'm curious as to what qualifies as a "real machine spindle"?

[arizonavideo]

Standard A/C bearings are fine as long as they are not China. The A/C's are a bit shorter so when you change both you often need a shim under the nut to take up space. If you leave the top bearing you might be fine. I think the top was rated up around 9000 RPM for a TRB.

It is a good idea to make a seal to fit under the dust cap to keep out crud. It is important to not have it fit tight or it will make way too much heat and melt.

You ran out of grease so you might want to check to make sure the grease is the thicker NLGI-3 and not NLGI-2. 2 will run out way too fast.

[rwskinner]

I had about an hour available today so I drove the old bearings and races out and cleaned everything up.

I put the new AC bearings and spindle in the freezer and used my heat gun to warm up the quill. I started by dropping the lower bearing into the quill, then the top bearing. Both were drop in fits with them frozen.

Then I took the heat gun and heated the inner races for a few minutes and set the spindle home.

Very quick and easy. I have to make a spacer to go under the spindle nut and lube the bearings then set the preload. Maybe I can do that tomorrow. I'll probably make a new aluminum cover for the bottom and I may make it where I can install a seal. I'm not sure yet.

Also, my spindle nuts are very sloppy. I remember I had a hard time setting preload because of it last time. I may make some new nuts as well and not worry about the spacer.


Richard

[rwskinner]

I tried to break in the bearings the other day and they did fne until I hit 6500 rpm then the temp climbed to 145F and was rising. I let it cool and tried again with the same results so I torn it down and backed the preload off a little. I intentionally over packed with grease and ran it enough to push the unwanted stuff out. (Syringe broke).

Today, I set up my thermocouples and ran the break in again with the newly adjusted preload. I ended up at 6500 RPM for an hour and there never was anymore than a 20 degree rise max and most of the time it was a 16 degree F rise over ambient. So I saw a total of 112F on the outside of the spindle.

My DTI is in increments of 1/2 Thou and the run out was about 1 needle width which I estimate less than 0.00025".

I'm going to try and run it there and see what happens.

Richard

[Uguessedit]

There are so many options for the 7206 and 7207 including 7006 and 7007 depending on brands. They don’t need shimming as they should be the same width most have in their machines. It seems that angular contact don’t provide enough axial load for our small applications and some of the bearings have a minimum of 8,000rpm up to 20-30,000rpm so if the incorrect bearings are chosen our machines may not even drive enough rpm to benefit the upgrade. Ideally it seems one would want a 20-25 degree contact point with a maximum of 11,000 to 13,000rpm. The extra contact angle provides axial loads similar to that of a taper roller as these were originally designed for. Unless you plan to take light cuts and run small end mills. Now finding a good abec 7 or 9 bearing with the correct contact angle can be challenging. Most the bearings on flea bay are 15 degree and carry very light axial ratings so even in a high precision p4 or p2 you end up with excessive run out at our lower than rated spindle speeds so u install a $300 set and wonder why they are not up to par. I sneer at bearing hunting it always absorbs excessive time and usually results in calling the manufacturer to get a part number that nobody sells unless you custom order the set to specifications desired. Now if someone did us all the favor in finding the appropriate bearings for high speed bench mills using belts or gear boxes and readily inventoried that may provoke many of us to swap them out knowing we don’t need to choose but simply for the price. We’re doing some tests between 3 mills here with 3 different specifications to compare which work better for specific applications and machines. Will post when testing is complete.