Jet vertical mill

[Ulma Doctor]

advise and tid-bit's....
it's not that difficult of a job, but it may be a bit time consuming if you have not done it before.
take pictures or make drawings during the process, it may help if you forget something
the manual drawings are great, but it helps to have many forms of backup
don't force anything, unless you are sure all the retainers or set screws are removed
remove the spindle as a whole unit, don't try to replace the bearings in place
i pulled everything out of the top of the unit, reinstalled from the top

i'm happy to help if you get stuck

 

[R.W. Parker]

By God's grace I got the quill out today, it wasn't difficult at all. And that needed to be done anyway, because mice had apparently nested in that head long before I acquired this machine!

The head casting will require a fair amount of cleaning, but I'll do that prior to reassembly. Now, it's time to remove the spindle from the quill. Ulma Doc, if you're still out there, I'll post my findings on that top bearing when I get that far. Shouldn't be long now...

 

[R.W. Parker]

advise and tid-bit's....
it's not that difficult of a job, but it may be a bit time consuming if you have not done it before.
take pictures or make drawings during the process, it may help if you forget something
the manual drawings are great, but it helps to have many forms of backup
don't force anything, unless you are sure all the retainers or set screws are removed
remove the spindle as a whole unit, don't try to replace the bearings in place
i pulled everything out of the top of the unit, reinstalled from the top

i'm happy to help if you get stuck

Just saw your post Doc, glad you're still out there! Thanks for letting me know that the spindle comes out of the top of the quill, that's a help. And although I've kept good notes during disassembly, I may still need some advice on reassembly. Particularly with the installation of the quill downfeed shaft. I removed it as a unit, and I'd like to get its spring preload right the first time when I reinstall it.

I'm not even close to doing that yet, however!

Best,

Richie

 

[R.W. Parker]

Okay, I got the spindle out of the quill by pressing it out from the top (press ram against the end of the spindle where the drawbar goes in). The top bearing was only sealed on one face, and it was mounted with the sealed face aimed toward the machine table.

OD 55mm
ID 30mm
Height 13mm
Marked "NACHI JAPAN 6006NK"

Now I need to get inside that head casting and do some major cleaning! And my neighbor turned me on to a bearing & drive place that I never knew about, so I'll drive out there tomorrow for that top bearing.

Doc, the open face of that top bearing was facing up. A solid threaded cap screws into the quill on top of it. Should I replace it with a "2RS" type like the bearings I ordered for the bottom? Or should I try to get the same type of bearing and pack the open side with grease, before reinstalling that solid cap on top of it? Or does it matter?

I'm also assuming that the top bearing should be the same "C3" clearance as the bottom bearings. Your thoughts?

Thanks!

Richie

 

[R.W. Parker]

Uh oh...

Richard King, I'm afraid you were right about different model number machines having different bearings. Ulma Doc's Jet HVM-728 appears identical to my Jet JVM-728 in every respect. However, the bottom bearing on my spindle is marked "NACHI 6007 Z". (I didn't take them off the spindle yet.)

The bearings I bought are 6008-2RS1/C3.

Gentlemen, have I ordered the wrong bearings?

Richie

 

[R.W. Parker]

Yes, now that I've pressed the three bottom bearings off the spindle, it's obvious that the 6008's I ordered are definitely the wrong ones.

It also turns out that the bearing & drive place my neighbor told me about is a long, harrowing drive from here.

So here's my question, if you gentlemen would be so kind: The MSC catalog lists both the top and bottom bearings I need by dimension, they're categorized under "ABEC-3". The double-sealed 2RSJEM bearings are rated for 7,000 rpm, and are a bit more expensive than the open-type bearings rated for 15,000 rpm. Both open and double-sealed have the same load ratings, both are SKF manufacture, both are deep-groove ball type.

I'm assuming that I should order the double-sealed bearings rated for 7,000 rpm, unless you deem otherwise. But is the "ABEC-3" classification correct for use in a milling machine spindle?

Thanks guys, I'd be lost without your help!

Richie

 

[Ulma Doctor]

Uh oh...

Richard King, I'm afraid you were right about different model number machines having different bearings. Ulma Doc's Jet HVM-728 appears identical to my Jet JVM-728 in every respect. However, the bottom bearing on my spindle is marked "NACHI 6007 Z". (I didn't take them off the spindle yet.)

The bearings I bought are 6008-2RS1/C3.

Gentlemen, have I ordered the wrong bearings?

Richie

your spindle bearings are 6007 Z
that means they are using a single dust shield (Z)
the 6008-2RS (40x68x15) unfortunately they are not going to work for your application

Yes, now that I've pressed the three bottom bearings off the spindle, it's obvious that the 6008's I ordered are definitely the wrong ones.

It also turns out that the bearing & drive place my neighbor told me about is a long, harrowing drive from here.

So here's my question, if you gentlemen would be so kind: The MSC catalog lists both the top and bottom bearings I need by dimension, they're categorized under "ABEC-3". The double-sealed 2RSJEM bearings are rated for 7,000 rpm, and are a bit more expensive than the open-type bearings rated for 15,000 rpm. Both open and double-sealed have the same load ratings, both are SKF manufacture, both are deep-groove ball type.

I'm assuming that I should order the double-sealed bearings rated for 7,000 rpm, unless you deem otherwise. But is the "ABEC-3" classification correct for use in a milling machine spindle?

Thanks guys, I'd be lost without your help!

Richie

your spindle will never see 7000 rpms in normal operating conditions, the double sealed bearings will be just fine
ABEC3 is the clearance, this bearing specification is used in electric motors, they will be fine in your spindle
you can get more precise bearings, but you will pay big for them.
have a look at ABEC5 if you want more precision for very small endmills working at high speed
if you are going to be doing work on a NASA contract , buy the better ABEC7 (or up to ABEC9) bearings

 

[R.W. Parker]

your spindle bearings are 6007 Z
that means they are using a single dust shield (Z)
the 6008-2RS (40x68x15) unfortunately they are not going to work for your application

your spindle will never see 7000 rpms in normal operating conditions, the double sealed bearings will be just fine
ABEC3 is the clearance, this bearing specification is used in electric motors, they will be fine in your spindle
you can get more precise bearings, but you will pay big for them.
have a look at ABEC5 if you want more precision for very small endmills working at high speed
if you are going to be doing work on a NASA contract , buy the better ABEC7 (or up to ABEC9) bearings

Hiya Doc!

Yeah, who would've thought, huh? Your machine seemed IDENTICAL to mine! Oh well, it's water under the bridge now. And it goes without saying that a 6006NK is also the wrong top bearing for that HVM-728 you used to own. The JVM-728 and HVM-728 have entirely different spindles, I would've never believed it!

Anyway, thanks for straightening me out on the ABEC classes. That's what I was beginning to think, that these bearings are primarily intended for electric motors. I just couldn't understand why the bearing rated for higher speed was less expensive than the bearing rated for lower speed. Then it hit me: the lower speed bearing in the MSC catalog is a double-sealed type, while the higher speed bearing is open. I believe I'll order the double-sealed type though.

I primarily wanted to replace these bearings because they started to make a little noise, and the surface finish on side cuts was getting a tad rougher than I liked. Nothing that a spring cut wouldn't clean up, but I knew it was time -- bearings are cheaper than endmills! As far as accuracy is concerned, I've run 1/16th endmills with the old spindle bearings, and the accuracy was equal to any J-head.

Last question, Doc: To establish measurements for the initial pre-load, I placed the nose of the spindle on my surface plate, and measured to the top of the bearing nut with a height gage. For the top bearing, I measured from the top face of the quill to the threaded flange that installs over that bearing. These measurements were taken with the old bearings still in place.

I figure those two numbers will give me a good starting point for pre-load. If the new bearings felt okay by hand, I then planned to install the spindle in the quill, and mount the quill horizontally in a bench vise. Then I'd install the drawbar, and mount a dowel pin in a collet. That way I could chuck the opposite end of the dowel in a drill motor, run the spindle for a few minutes, and check for any heat on the new bearings. Do you think that ought to work?

Thanks, buddy!

Richie

 

[Ulma Doctor]

Generally speaking, ball bearings are not pre-loaded in the same manner as a tapered roller bearing in the sense that you don’t want to place loads axially.
Ball bearings are designed to take radial loads. When axial loads are applied the balls wear at an accelerated rate.
I would be looking at low (.003” ) to zero clearance
You can feel resistance by hand
It should spin with little or no drag

 

[R.W. Parker]

Generally speaking, ball bearings are not pre-loaded in the same manner as a tapered roller bearing in the sense that you don’t want to place loads axially.
Ball bearings are designed to take radial loads. When axial loads are applied the balls wear at an accelerated rate.
I would be looking at low (.003” ) to zero clearance
You can feel resistance by hand
It should spin with little or no drag

Understood Doc, thank you! Much of what I've read likely pertained to tapered roller bearings, but the distinction wasn't made clear. I'll just bring the nuts up nice and easy to remove any axial play. The bearings were ordered today, and should be here this time next week at the latest.

Tomorrow I've gotta see a man about a spring, as the quill return spring in that head was broken. For twenty years, my wife ran the night shift at John Evans Sons in Lansdale, they're America's oldest springmaker. I talked to their head honcho today, and he agreed to wind a new one for me. The wire is 5/32, so that spring would be VERY difficult to wind in either of my South Bend lathes (9 and 10-inch)!

In the meantime, I've been keeping myself busy in the parts washer. I'll report in when I have more news...

Richie