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What causes my saw to do this?

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Forum topic by Jackietreehorn posted 173 days ago 1382 views 0 times favorited 24 replies Add to Favorites Watch
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Jackietreehorn

116 posts in 573 days


173 days ago

Topic tags/keywords: powermatic 66

Here’s a video to help explain what’s happening. It’s a powermatic 66, I think around 10-12 years old. When the saw runs, I think it’s pretty quiet and the bearings don’t howl. When I put in a zero clearance insert, you can hear the blade hit the insert when it’s slowing down during shutdown, kind of like there’s a wobble. Another strange thing I’ve noticed, is if you grab the arbor, there’s no noticeable play, but if I rotate maybe 180 degrees, you can feel a very small amount of slop. Is that a bearing or arbor problem? Maybe something else? Also, the set screw to hold the arbor in place is tight. I have a project to finish up and plan on tearing down and at least replacing the bearings and the belts, didn’t know if there’s a way to tell if the arbor should be replaced too.

http://smg.photobucket.com/user/glassman2k2/media/Mobile%20Uploads/trim730F1E37-C76B-43AB-B0DD-CC827EA366B2_zps29a6c80e.mp4.html

-- www.nobleprojects.blogspot.com


24 replies so far

View bigblockyeti's profile

bigblockyeti

1494 posts in 355 days


#1 posted 173 days ago

While running it does sound like there might be just a hint of bearing noise. If the arbor has play in one area, but not 180 degrees rotated I would suspect a slightly (very slightly) bent arbor. That being said, I would try new bearing first and check your current arbor with a dial indicator after installation so as to remove bearing from possible culprits. While running at speed it’s possible the centrifugal force on the blade is bringing it back into a near perfect plane 90 degrees to the spindle axis allowing it to run true. As the machine slows, this force is diminished and allows the blade to contact the insert. Without being able to lay hands on the saw, this is the best theory I can come up with.

View knotscott's profile

knotscott

5429 posts in 2010 days


#2 posted 173 days ago

Whatever the actual cause, it’s pretty minor. Here are a couple of guesses of possible causes…there’s a small amount of runout with every blade and every saw. When the blades up to speed, it spins true, when slowing the runout shows up a bit more. In time the ZCI should open up enough to no longer hear it.

It could also be due to regeneration of the capacitors when the saw powers down… its very common for them to cause some minor vibration, and is nothing to worry about. Theoretically, the right size shunt resistors across the caps could eliminate that if it’s really the cause, but I couldn’t tell you what size resistors to try.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Rick M.'s profile

Rick M.

3885 posts in 1015 days


#3 posted 173 days ago

My saw used to do that little shudder/vibration when slowing, a link belt fixed that problem.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

View Jimbo4's profile

Jimbo4

1133 posts in 1397 days


#4 posted 173 days ago

I agree with bigblockyeti, as there is a slight chipout of the ZCI.

-- BELT SANDER: Used for making rectangular gouges in wood.

View Jackietreehorn's profile

Jackietreehorn

116 posts in 573 days


#5 posted 173 days ago

Thanks for the replies guys. I think since I’ve never changed the bearings or belts and I can only assume previous owner didn’t as well, that it’s a good place to start there and have the arbor checked while it’s out. A refreshment on the machine is a good idea anyway. If I find anything really strange I’ll report back

-- www.nobleprojects.blogspot.com

View lwllms's profile

lwllms

542 posts in 1916 days


#6 posted 173 days ago

Make sure the pulley on the arbor isn’t worn out of round before going any further. It doesn’t take any wobble there at all to create enough of a problem to eat up bearings. If you have to replace bearings buy the whole arbor assembly; bearings, arbor, spacer and spacer rings ready to install. It’s not real expensive and will make the job a lot easier. There’s an internal snap ring retainer that will give you fits getting apart until you understand the complex assembly process. Getting an arbor assembly apart when it’s been in the saw for years generally results in a bent arbor because the interference fit of the bearings on the arbor is very tight and just a little corrosion makes dis-assembly more than difficult.

View Shawn Masterson's profile

Shawn Masterson

1253 posts in 583 days


#7 posted 173 days ago

I have a mid 70’s PM66 with the exact same condition.

View oldnovice's profile

oldnovice

3716 posts in 2002 days


#8 posted 173 days ago

I doubt it’s the bearings as my TS is over 40 years old and on the same bearings … it’s a Craftsman 10”, and the ”turn off shudder” left after I installed a link belt and turned pulleys about 25 to 30 years ago!

-- "I never met a board I didn't like!"

View upinflames's profile

upinflames

84 posts in 797 days


#9 posted 173 days ago

When you replace the bearings you really need an arbor press to get them off. The first thing you have to contend with is getting the woodruff key out of the arbor, this can be a PITA. New bearings will run around $40, a new arbor can be had for $130. The belts should be a matched set, no link belt on a multi belt system. there should be no vibration what so ever in that saw. I have a ‘73 model, you can hardly hear it run and no vibration at all.

View lwllms's profile

lwllms

542 posts in 1916 days


#10 posted 173 days ago

That $130 for the arbor is for the whole assembly; bearings, spacer, shims, and tension ring. It’s all factory assembled. A three ton arbor press wouldn’t budge anything when I replaced the bearings on mine. A mechanic friend got it apart with a 50 ton hydraulic press but bent the arbor in the process. The repair guy at a Powermatic Service shop told me that was more the rule than the exception. I ended up buying the arbor assembly after first buying bearings. You can’t press new bearings off the arbor without deforming the bearing races because of the way it’s all assembled. There’s no way to get access to the inner races to use as a pressure point. It also turned out that the pulley set screws had worked loose over time and had ever so slightly worn the bore of the pulley which probably caused the bearing problem.

The saw originally had a three belt drive and replacing a three belt pulley would have been very expensive. It was quite a bit less to retrofit to the current two belt system with both pulleys and new belts than to buy just a three belt pulley.

I bought my saw new in 1982 but it’s seen a lot of use professionally. I have no idea how many thousands of board feet of hardwood I’ve used over the years but it’s been a lot of semi loads.

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Jackietreehorn

116 posts in 573 days


#11 posted 171 days ago

I have some friends in the machining business that would have means of getting bearings off and checking the arbor for being true, but buying a complete arbor means I can tear saw down and have it back to running faster so I might go that route. I need to get new belts too, I keep seeing posts here and there about matched belts, any truth to it? If ordering online, I wouldn’t trust anyone to pick matched belts because it was requested.

-- www.nobleprojects.blogspot.com

View Grandpa's profile

Grandpa

3101 posts in 1310 days


#12 posted 171 days ago

Matched belts come in sets of 2, 3 or whatever they should be for your tool. There is something to it. Buy a matched set and it will work better.

View Jackietreehorn's profile

Jackietreehorn

116 posts in 573 days


#13 posted 170 days ago

Where does one go for matched belts? Any must have brands? I’ve read in the internet show the link belts are no good for the powermatic, not sure if true?

-- www.nobleprojects.blogspot.com

View bigblockyeti's profile

bigblockyeti

1494 posts in 355 days


#14 posted 170 days ago

Linked belts don’t do well in a multi-strand setup. The brand is less important than the type of belt. An AX, BX or CX section belt are held to higher specifications than A, B, 3L, 4L or 5L section belt.

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Jackietreehorn

116 posts in 573 days


#15 posted 170 days ago

Cool, so if I order two belts with a ‘x’ I shouldn’t have to worry about them being matched by lot etc. That’s good since ordering matched sets seem hard to find. 6077225 is what I found for part#, powermatic a part store says its 3VX220, does vx fall into same tolerance category as the ax,bx, etc?

-- www.nobleprojects.blogspot.com

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