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Powermatic 66 tablesaw arbor shift???4/3
Went to use my Powermatic 66 table saw today and the blade had shifted to the left, perhaps 3/16", and hangs on the insert - see attached photo. I'm trying to track down potential causes as I'd rather not take the time right now to tear down the whole saw. At first I thought that somehow I must have bumped the table top really, really hard in the last two days since I'd used the saw, somehow without noticing or remembering, but it's tight and I can't make it move. I can't think of anything particularly different I've done in the shop in the past few days that might have caused this. Next, I checked the blade runout and it's only 0.005" out. When I grab the arbor and try to move it side to side, or in and out, there's no detectable movement. It appears that the arbor has shifted to the left so I checked the set screw in the bearing arm, and it seems tight; in any case, I can't move the arbor in or out of the bearing arm.
Anyone have any experience with this kind of issue? At this point I'm at a loss for what it might be. A forensic dismantling wasn't on my agenda, but unless someone here has the right suggestion I guess that's just another speedbump in my project path...
Are you sure the blade is at 90° and not somehow gone several degrees past 90° in the non-tilt direction?
If the blade is actually at 90° I personally wouldn't use the saw until I sorted out the problem. I can think of a number of areas that could be causing this but would first just poke around under the saw to see what I could find.
Nope, it was dead 90°. The geometry of the problem kept leading me to the arbor and the bearing bar. I'd checked the bearing set screw earlier and it seemed tight, but wasn't hard to loosen. I loosened it and pulled the arbor away from the bearing bar, exposing about 3/16" of the one of the bearings. There are two bearings supporting the arbor shaft through the bearing bar, separated by a spacer that is held in place by the set screw. I have the arbor where it should be but am not sure how long it'll stay in place. Also not sure that the bearings and spacer are where they actually should be located within the bearing bar. I can use the saw at the moment, but expect that vibration will eventually cause me some REAL problems if I don't get a better handle on the proper setup.
Arbor shafts usually have a step up to a larger diameter where the bearings seat. The bearings are pressed on until they hit that shoulder. If you can see such a shoulder with a space between it and the bearing then the bearing has slipped on the arbor.
Hope that's helpful.
Bearings are cheap. I’d pull it apart and replace them.
Slide the top off on some 2 X 4's.
While the saw top is off, take some photos and post them at Old Woodworking Machines. People there fix stuff like this as entertainment and personal fulfillment.
I had an old 66 with a snap ring, I re-engineered it with a piece of angle iron and some draw bolts, so that the arbor assembly gets pushed left. This was a weak point in the early 66 design.
Look for the exploded view of the arbor. It clears up what's going on.
I've had this happen twice on two different 66's. There's a square head bolt that indexes on the shaft the trunnion rotates on. That gets loose and allows the trunnion to shift over.
It's a stupid design, but once I tightened it up, I never had the issue again.
You might try checking out Daddy's Workshop of the Carolinas on youtube. He does restorations on table saws all the time. He also has an attached email on his account and is super happy to help. He has resolved several interesting issues for me in the past on my Powermatic 66 and an old delta 20 in bandsaw.