Tom Veatch
12-18-2008, 4:02 PM
For anyone else out there that might encounter the same problem:
Making some minature chests and using my Jet JPM-13 to plane some boards to about 1/4" thickness. (Yeah, I know, the manual says don't go thinner than 1/2"). Found that one side of the board fit my 1/4" dados perfectly while the other side was either way too loose or way too tight. Using digital calipers, the side thicknesses were as much as .02 different. The planer wasn't cutting parallel to the table.
Owners manual says the blades are out of adjustment - too high on one side. Adjusted the blades, no help. Adjusted the blades over and over until I was convinced the blades were as close to perfectly set as I could get them. Planer still made tapered cuts. This is the first time I've tried to work to this close tolerences with this machine, so this may have been going on since the machine was new. But in any case, the results were simply not acceptable.
So, I made a spacer block and checked the distance between the table and the cutterhead body - not the blades, the body itself. Sure enough, the cutterhead itself was about 1/32" higher on one side than it was on the other - or, looking at it the other way, the table was about 1/32" lower on one side than the other. That induced a taper in the cut that was about .0025 inches per inch. Or about .015" difference across a 6" cut. That was just about what I was seeing. If one side of my work measured right at .25, the other would be between .26 and .27. Just enough to mess up the fit of the piece in one or the other of the matching dadoes.
So, what to do about it? Note that this description is specific to the Jet JPM-13 and may not be applicable to any other planer.
The table height is adjusted by two lead screws, one on each side, coordinated by a chain and sprockets so they both turn the same amount when adjusting the table. The sprockets are not keyed to the lead screws but are held in position by two set screws through each sprocket that bear on the lead screw. Perhaps the sprockets slipped on the lead screws over time or maybe they were maladjusted at the factory. But, loosening the setscrews on one sprocket and turning that lead screw while holding the other stationary, I was able to raise the low side of the table to match the other side. When reinstalling the setscrews, I used a drop or two of blue thread locker in each setscrew hole. Maybe that will make sure the setscrews don't loosen or the sprockets turn on the lead screws.
Now the spacer passes under the body of the cutterhead with about the same resistance at all points along the cutterhead, and the planer cuts the board to the same thickness on both sides. Maybe I can finally finish those Christmas gifts in time for New Year's.
I'm posting this solely for the benefit of anyone else who runs into this problem and can't seem to cure it by properly setting the blades in the cutterhead.
Making some minature chests and using my Jet JPM-13 to plane some boards to about 1/4" thickness. (Yeah, I know, the manual says don't go thinner than 1/2"). Found that one side of the board fit my 1/4" dados perfectly while the other side was either way too loose or way too tight. Using digital calipers, the side thicknesses were as much as .02 different. The planer wasn't cutting parallel to the table.
Owners manual says the blades are out of adjustment - too high on one side. Adjusted the blades, no help. Adjusted the blades over and over until I was convinced the blades were as close to perfectly set as I could get them. Planer still made tapered cuts. This is the first time I've tried to work to this close tolerences with this machine, so this may have been going on since the machine was new. But in any case, the results were simply not acceptable.
So, I made a spacer block and checked the distance between the table and the cutterhead body - not the blades, the body itself. Sure enough, the cutterhead itself was about 1/32" higher on one side than it was on the other - or, looking at it the other way, the table was about 1/32" lower on one side than the other. That induced a taper in the cut that was about .0025 inches per inch. Or about .015" difference across a 6" cut. That was just about what I was seeing. If one side of my work measured right at .25, the other would be between .26 and .27. Just enough to mess up the fit of the piece in one or the other of the matching dadoes.
So, what to do about it? Note that this description is specific to the Jet JPM-13 and may not be applicable to any other planer.
The table height is adjusted by two lead screws, one on each side, coordinated by a chain and sprockets so they both turn the same amount when adjusting the table. The sprockets are not keyed to the lead screws but are held in position by two set screws through each sprocket that bear on the lead screw. Perhaps the sprockets slipped on the lead screws over time or maybe they were maladjusted at the factory. But, loosening the setscrews on one sprocket and turning that lead screw while holding the other stationary, I was able to raise the low side of the table to match the other side. When reinstalling the setscrews, I used a drop or two of blue thread locker in each setscrew hole. Maybe that will make sure the setscrews don't loosen or the sprockets turn on the lead screws.
Now the spacer passes under the body of the cutterhead with about the same resistance at all points along the cutterhead, and the planer cuts the board to the same thickness on both sides. Maybe I can finally finish those Christmas gifts in time for New Year's.
I'm posting this solely for the benefit of anyone else who runs into this problem and can't seem to cure it by properly setting the blades in the cutterhead.