Replies

1. 
   JohnWW | Mar 21, 2008 07:51pm | #1

   My first thought is that a knife has loosened and slipped a bit higher so that each cut by that knife is deeper. Obviously, a knife that has slipped could also be thrown, so the first thing to do is unplug the machine and not use it until you are sure of what is going on.

   Before you remove the knives, or check their height, look in from the front of the machine, at the side of the head, and note how the knives are sitting in the slots in the head. They should only project slightly above the cylindrical surface of the head. The tool's manual should tell you how to set the correct outfeed table height, which will later determine the knife exposure when you install new knives. If the knives are installed too high there is less blade surface to clamp on which can cause blade slipping, and other possibly dangerous problems. If you installed the blades that are in there now without checking the outfeed table height first, they are probably set wrong.

   Also look at how much of the blade is in the slot. As the blades are resharpened they get narrower. At some point there is no longer enough blade for the entire width of the gib to bear on which can cause a blade to come loose. The only solution to this is to throw the knives away and purchase new ones.

   If you find that a knife has slipped, remove all of the knives and thoroughly clean the knives, the grooves in the head, and the gibs and screws. Use a file to clean off any rust or burrs. If the screw heads are badly chewed up, or the screw threads look damaged, you should get new screws and gibs from Jet, they shouldn't be expensive. It wouldn't be a bad idea to just go ahead and do this in any case, since overtightening by the previous owner could easily have caused hard to detect damage, that will prevent you from properly and safely installing new blades in the future.

   Getting a new set of blades, or two, either from Jet or a local sharpening shop, is also a good idea. You'll need spare blades to install in the machine when the first set gets dull and needs to be resharpened. The new blades will also give you a good sense of how far down the old blades have been sharpened away.

   Let me know what you find after you inspect the blade installation.

   John White

   
   

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   Edited 3/25/2008 12:20 pm ET by JohnWW

2. 
   danmart | Mar 25, 2008 02:50am | #2

   a quick check to see if one blade/knife is cutting is:

   take 3 crayons from a kids coloring box. red, green and black for example. crayon the edges of each of the blade with a color and run the edge of the board over the jointer. The high blade will leave a color. I have used this with good results and it takes the mistery out of the spinning head. give it a try

1. 
   JohnWW | Mar 25, 2008 06:27pm | #3

   Good trick.Thanks, John W.

1. 
   danmart | Mar 26, 2008 12:36am | #4

   Its a funny thing John but this occured to me after years of trimming vibrations out of spinning rotorblades on Sikorsky and Bell helicopters. We used to put crayon markings on the tips of the blades(articulated had 5 blades and semirigid types only had 2). As the rotor was spinning at operating rpm, we used a pole with 2 arms at 90 degrees to the pole about 24" apart and 6" long. We tied a string from the tip of each arm and put good old masking tape on it. The guy outside the helicopter would bring the taped string into the spinning rotor tip slowly to see which blade was flying low and high. The crayon markings on the blades would leave a smudge mark on the tape in the plane(hopefully).

   Those were the early days. Now we have strobes, lasers and computers. The desired result is still the same: get the blades flying in the same plane. Results: smooth.

   After all these years, I still trim all of the ceiling fans in my house this way. Everyone of them can be trimmed with a tiny piece of lead tape in the right place on the fan blade.

   I took the idea and used it to find the high low spots on on the jointer and it seems to work very well. The price is right. Maybe some day when you have one that doesn't cut quite right you can try it. If nothing else, take the wobble out of the ceiling fan at the house and impress your wife.

   dan