[GLCarlson]

The pin inside my 1100 spindle has always been a bit short, barely but adequately engaging the R8 collet. Last week, my PDB was acting funny- it wasn't releasing far enough. Tools that were an easy in/out earlier were almost press fits on the open collet. A little checking showed that the pin was still present, but had been worn to a dished shape and no longer engaged the collet.

Tormach was helpful as usual, but the answer wasn't much fun: the only way to change the pin is to completely disassemble the spindle, as the pin is located under the bottom pair of bearings. This is a summary of learnings from that adventure.

Removing the cartridge is straightforward.Remove PDB. Position the head about 2/3 up from the table. Remove the jam nut from the pulley, remove the pulley from the spindle. Pulley can't be completely removed without taking the motor out; don't bother. Remove 6 bolts holding the cartridge in place and remove it from underneath; it'll clear the pulley.

Mark the position of the spindle nut carefully (needed to restore the preload at reassembly). If possible, measure the height of the nut from the bottom of the spindle (it's about 10 inches up), opposite the screw on the jam nut, as a second check on preload position for the nut.

Remove the nut.

At this point, one has a couple of options. Tormach recommends that one press out the spindle, bracing the cartridge housing via the bolt flange. That worked, but while the top bearings remained in the cartridge, the bottom bearings came out with the spindle. The bottom spindle spacer is designed to be used to remove the bottom bearings; it bears on the inner race of the bearings. The problem with the Tormach procedure is that the bottom bearings are very likely to come out of the cartridge housing with the spindle; the advantage is that there is less pressure on the bottom spacer, and the flange is very strong.

However, one must still remove the bottom bearings. The pin is roughly at the center of the bearing pair.

I was concerned that the spacer (part #90 in my drawing) was fairly thin and might break; Tormach assured me that it was designed to be used to press the bearings off. I made a 4" diameter ring 2" high with a 2.05 hole (which will pass the spindle nose freely) and used that to bear on the spacer. I also obtained some dry ice, and filled the spindle with that -a piece of packing tape held the ice in place- just prior to pressing the bottom bearings off. A minute or so was enough to cool the spindle while the bearings stayed relatively warm. They came off easily. Be careful to maintain and mark the orientation of the bearings; these are deep groove angular bearings and fit only one way. I maintained the order, too.

In retrospect, I think a better approach to removing the spindle would be to pack the entire spindle with dry ice and press against the spacer in the first place, with a ring as described above bearing on the bottom spacer. I suspect the spindle would easily pop out leaving all 4 bearings in the cartridge housing. Life would be much simpler in that case, as long as the spindle reinstallation didn't require too much pressure.

With the spindle free of bearings, one can (barely) locate the pressed in locating pin. Mine was ground very smoothly level with the bearing surface, and was rather hard to see. The pin is 0.140 diameter; mine was 0.326 long, and should have been about 0.375. A drift punch will remove the pin, which isn't long enough to get caught in the spindle bore.

The remaining problem is what to use as a replacement. Tormach does not stock pins, and the pin is not a standard dowel size (either metric or inch). My solution was to use a piece of a #28 drill (0.1405), ground to length. The original pin was easily filed, despite Tormach's comment that it was a hardened dowel (I think that was speculation, not fact). I installed the pin with the collet in the spindle, using a 0.006 shim in the collet groove to make sure the pin didn't bottom on the groove. Tormach recommends using Loctite 609 or similar (eg, 648) on the pin; I did not, as it seemed to be a tight press fit with no wear on the hole.

Reassembly is straightforward. Reinstall the lower bearings (watch the orientation) if they came out with the spindle, using dry ice or a cold soak to get the spindle as small as possible, pressing the bearings on by pushing on the inner race. Put spindle in cartridge housing, reinstall the preload nut. Tormach recommends tightening the nut to 1 full turn less than the original installation (in my case, that was with two threads showing above the nut at the point where the jam screw is located), Correct preload is obtained when the nut is "tight" and the bearings don't exceed 155F. See Tormach bulletin SB0024_Spindle_Bearings_0914B for the detailed procedure. My original bearings ran at 70F even after hours of running; I plan to recheck the reinstallation a few times over the next week or so.

Reinstall cartridge, pulley, PDB, etc. Hope the new pin lasts a bit longer.

Thanks to Tormach for helpful advice through the entire process.

[BIGBLOCK1965]

Sounds like they tried to put the pin as close to the point of torque as possible which is under the bearing. An engineers decision in which a very minor gain in operation results in a major headache for servicing. The Shopmaster cartridge locates the pin just above the lower bearing which is about mid way on the collet. This allows them to use a threaded pin secured by a jam nut which is easily accessible by a hole in the casting. The pin can be adjusted or changed without disturbing any of the bearings.
Attachment 342066

[GLCarlson]

The locating pin is about 1.7" up from the face of the R8 collet, about a third of the way up the locating groove, in the 1100 spindle design. Putting it above the bearings with a threaded pin/jam nut would have it very close to or into the upper bearing surface of the collet. The grove is still there, of course, but there'd be a chance of marring the upper ground portion of the collet, or the mating surface. That design would also guarantee that the pin would hit the inner bearing race and push on it assymetrically during disassembly for any reason, and any adjustment would require disassembly. Or a hole in the cartridge housing, which would still have to be demounted (and Murphy being everpresent, I can just see a jam nut going adrift inside the cartridge).

Having been a reader of this forum since inception, this is so far as I know a singular incident. I much prefer that Tormach chose the optimum engineering solution in a low-to-almost never probability event. As I noted, my specific machine's pin always seemed short to me, and that probably let to early failure (if 7 years can be called early). Given that it's no harder than swapping out the bearings, I can't say I feel that this was a major headache, nor do I expect to have to do it again.

[toyshop]

Most people with manual machines take the pin out. (easy on a Bridgeport.)
Thought about it on my 1100. Didn't know it would be a big job.

Dave

[GLCarlson]

Most people with manual machines take the pin out. (easy on a Bridgeport.)
Thought about it on my 1100. Didn't know it would be a big job.

Dave

Interesting. Never heard of that practice or encountered it on any of the manual mills I've operated in other shops.

A missing pin leads to malfunction of the power draw bar, or did in my case. The collet rotated a bit on each actuation -not much, perhaps a fraction of a degree, but it was a consistent direction. That led to the collet eventually not releasing as far, and it got harder and harder to insert or remove tools. Probably a good thing it didn't go the other way; tool pullout can be exciting.

I had a job to finish, so I used the manual drawbar for a day or so. Perhaps it was just me, but even though I tightened the collet down hard, I was surprised how much less tight it felt when I went to change tools. Not to the point of anything falling out, but not as tight as expected, and that seemed to be consistent. I concluded that not having the pin in place was a safety issue that could allow a tool to loosen up. Along with hassle of no PDB, that made it a critical item to repair. I may be overly cautious.

I probably should have included a time estimate for this. Altogether, a couple hours. That was spread over a few days because I chose to replace my lower bearings and needed to get a set in, but actual work time wasn't all that much. And a couple hours more to check bearing preload and adjust per the service bulletin. Call it a morning if everything is on hand.

[popspipes]

Most people with manual machines take the pin out. (easy on a Bridgeport.)
Thought about it on my 1100. Didn't know it would be a big job.

Dave

I know a couple of manual machines that the pin was removed, due to missuse or damage of some sort. In the 1100 I would think that wouldnt be good if one uses a probe as once the probe is aligned to the spindle it shouldnt be rotated as it could alter the alignment.

[SCzEngrgGroup]

A significant percentage of R8 machines have had the locating pin either removed, or sheared off due to inadequate drawbar tightening. Contrary to "conventional wisdom", the pin is absolutely NOT necessary for proper operation, though, as someone pointed out, the Tormach PDB may be different, since even small collet rotations can cause pre-load on the Bellevilles to be gradually reduced, or even increased. This, of course, is not a problem for manual drawbar operation, or operation with a torque-style PDB. But, point is, failure of that pin is extremely common for well-used R8 machines. For every R8 machine I've ever worked on, the pin has been easily accessible through an exposed hole in the side of the spindle nose, and can be removed/replaced in seconds. The Tormach seems unusual in making it very difficult to access.

Regards,
Ray L.

[instructor37]

The locating pin is about 1.7" up from the face of the R8 collet, about a third of the way up the locating groove, in the 1100 spindle design. Putting it above the bearings with a threaded pin/jam nut would have it very close to or into the upper bearing surface of the collet. The grove is still there, of course, but there'd be a chance of marring the upper ground portion of the collet, or the mating surface. That design would also guarantee that the pin would hit the inner bearing race and push on it assymetrically during disassembly for any reason, and any adjustment would require disassembly. Or a hole in the cartridge housing, which would still have to be demounted (and Murphy being everpresent, I can just see a jam nut going adrift inside the cartridge).

Having been a reader of this forum since inception, this is so far as I know a singular incident. I much prefer that Tormach chose the optimum engineering solution in a low-to-almost never probability event. As I noted, my specific machine's pin always seemed short to me, and that probably let to early failure (if 7 years can be called early). Given that it's no harder than swapping out the bearings, I can't say I feel that this was a major headache, nor do I expect to have to do it again.

If that is your personal preference it's one way to do it. However in servicing any sort of mechanical device, the less you disturb, the less chance of errors. If you have a perfectly balanced spindle with proper pre-load etc. and only need to change the pin, the Shopmaster is the far better way to go. Taking the entire spindle apart for this simple operation opens up a whole bunch of potential re-assembly issues and you will never get it 100% back to its original settings.

[GLCarlson]

If that is your personal preference it's one way to do it. However in servicing any sort of mechanical device, the less you disturb, the less chance of errors. If you have a perfectly balanced spindle with proper pre-load etc. and only need to change the pin, the Shopmaster is the far better way to go. Taking the entire spindle apart for this simple operation opens up a whole bunch of potential re-assembly issues and you will never get it 100% back to its original settings.

It's certainly true that the less one must do the better. In this case, repair was straightforward and the spindle went right back together. Neither spindle temperature nor runout differ from original measurements.

Heat/cold is clearly the best way to disassemble and reassemble. Tormach didn't mention that when I initially consulted them, and that advice could have been better. Earlier posts in this forum have clearly identified the use of temperature differential as a best practice; in retrospect, I should have searched the forum before getting on with this.

As Ray noted, the pin seems to be necessary for the Belleville-style power drawbars (which I have). Small collet rotations were absolutely causing PDB problems. Ray's observation that inadequate drawbar tightening can cause pin failure could be a cause for this problem, because I used the machine with the manual drawbar for 5 years. There may well have been times when the drawbar should have been tighter. I continue to think it was mostly that my pin was almost too short from the start, but I may be minimizing the effects of operator error there.

I haven't seen any machines with the pin removed or failed, but clearly that is a well known situation.

Thanks to everyone for comments. As usual, I've learned something from the collective wisdom.