Intro: Changing the Cutterhead on Your Jointer
In 1994 I bought a new Powermatic #60 eight inch long-bed jointer. Boy, was it nice. Compared to the little 6" hobby jointer I had before, this thing was massive AND accurate. I could actually joint wood square & flat. The only problem with it was in changing and setting the knives. Like most jointers, referencing the knives to the outfeed table was by trial and error -- mostly error.
Image 2 shows the how the knives set into the cutterhead*. What's difficult about setting the knives is that I have to try to reference the sharp edge of each knife to the top of the outfeed table. I finally bought a magnetic bar that would hold the knives to the level of the table: Image 3.
The gauge works fine, but you have to try to align the high point of the knife's arc to a mark on the gauge. Easy enough after you've determined where the high point is. But then you start to tighten down the gibs and the cutter head begins to move all over the place.
In 2003, I figured I'd had enough and I bought a Terminus® replacement cutterhead. It has knives that are double sided, and are indexed into the cutterhead so there's never a need to use any jigs or gauges to set the knives. It only took me eight years to finally remove the old head & put in the new one. (The original Powermatic head had a bearing going out & the Terminus® comes with bearings already mounted in place so I had to do something!)
* Line drawings taken from Powermatic manuals. ©Powermatic (or whoever owns them now).
Step 1: Take Things Apart
As shown in the line drawings, remove the fence and it's support piece.
Remove the blade guard and the blade guard support piece.
Lower both the infeed & outfeed tables so the cutter head can be removed by lifting straight up. There are two bolts that hold the bearing housings in place ("B" in image-2). One bolt is easy, the other has about 1/2" clearance between it's head & the jointer stand. A socket wrench won't fit, but a box end wrench will. It just takes a little longer to remove -- Oh, and having never been touched for 16 years, it needed a little "persuasion."
Remove the pulley and the two bearing blocks. This is the part I thought would be real difficult. But one block just fell off. the other I took to the autoshop next door to use their gear puller. All it took was a little "tug" to pull it off the bearing.
Put the bearing blocks onto the new cutterhead's bearings. (They slipped on without a problem.)
Step 2: Put Things Together
This next step is critical to getting the jointer to cut square. You'll need a dial indicator with magnetic base and some brass or steel shim stock. (You should be able to buy a pack of assorted thicknesses at your hardware store.)
With the old head you aligned the knives to the outfeed table each time you changed knives. With this head the knives are fixed in place: they align with the cutterhead only. So the cutterhead must be in line with the outfeed table.
- Install the new cutterhead, tightening the bearing blocks firmly.
- Bring the outfeed table up to what looks like the right height and lock it in place. (not critical, yet)
- Bring the dial indicator to the near end of the head. Adjust it's position until you find the high point of the head's arc.
- Set the dial to zero. (I have a metal "arrow" that I adjust to where the pointer is.)
- Move the indicator to the far end of the cutterhead and again find the high point of the head's arc.
- Note how many thousands of an inch difference it reads. This is the amount of shim stock you will need to put under one of the bearing blocks to get it to read the same as the other. (Actually, you won't need that much because as you raise one end of the head, the other end will lift slightly too.)
- Fit shim stock on both sides of the bolt under the low reading bearing block.
- Tighten everything down again and do another reading. I was able to get the head to within .002" of level.
Step 3: Set the Outfeed Table
Now that we've done the hard work, we need to return everything to normal.
Set the height of the outfeed table to be in line with the high point of the knives. Looking at image-1 you can see how close the knives are to the edge -- makes me a bit nervous. Image-4 shows that the knives clear the bed all the way across and look level to the surface.
- Lay a straight stick across the outfeed table and the cutterhead (Image-2)
- Rotate the cutterhead by hand until the knife contacts the stick. If the knife doesn't touch the stick, the table is too high. If it raises the stick off the table, the table is too low.
- Adjust the outfeed table until the knives just graze the bottom of the stick --Image-3.
Step 4: Put the Rest Back Together
Reinstall the belt pulley, making sure it's in line with the motor pulley. You shouldn't have to adjust the tension on the pulley belt unless it was too loose or too tight to begin with. Reinstall the fence support and fence.
Reinstall the blade guard support and guard.
Raise the infeed table to within 1/32" of the height of the outfeed table.
Square the fence to the outfeed table.
Make sure your jointer's power switch is in the off position. Plug in the jointer.
STANDING TO THE SIDE & WITH THE SAFETY GUARD IN PLACE & WITH SAFETY GOGGLES ON, turn on the jointer.
Listen for terrible noises (like knives flying out of the cutter head or knives crashing into cast iron tables).
Hopefully, you just hear the sound of a smoothly running machine (and no squeaky bearings).
Take a straight board and edge joint the first 4 or 5 inches (Image-1). Check for square (image-2). Adjust the fence as needed.
Check the depth of the cut; set the infeed table's depth gauge accordingly.
Now joint the whole length.
Look for snipe* in the first one or two inches of the cut and in the last one or two inches of the cut.
If at the beginning of the cut, the outfeed table is too high and is lifting the board. If at the end of the board, the outfeed table is too low and the board is dropping down onto the knives when it comes off the infeed table.
In the end, you should end up with some nice looking shavings (image-3).
*where the depth of cut is slightly greater than the remainder of the board.