Posts Tagged ‘replacing a cutter head’

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.


Powermatic® Cutterhead endview

Cutterhead showing knives & gibs. ©Powermatic

This image shows the how the knives set into the cutterhead. What’s not showing are the Jack Screws that support, raise, and lower the knives. 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.


Woodstock® Magna Set guage

Woodstock® Magna Set Gauge holds knives flush to the outfeed table.

(Unfortunately, this Company’s image shows the gauge sitting cross-ways over the knives.)

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.  A simple indexing pin built into the jointerhead and bearing supports would fix all this, but such a design change might cost the jointer makers a couple of bucks.  (My Japanese planer has this feature & I can set those knives in about 10 minutes or less.)

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.


Terminus® Arbor Planer

The Teminus® Cutter head (without bearings)


The switch over wasn’t nearly as bad/difficult as I imagined.  I just gathered up a few things I thought I might need and set them near by:


It’s nice to have a flat surface.

It turns out, I have misplaced my manual, So went online to find a pdf. It turns out that the only manual I could get from PM is for their newer model 60. But they are close enough in construction that it would work.

First step is to remove the blade guard & the fence Then remove the fence support (manual says to swivel it out of the way, but couldn’t see the point in that).


Removing the Jointer fence

Removing the fence (image© Powermatic)

Next step is to 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 below). 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.”


Powermatic® schematic-removing cutter head

In reality, pulling out the cutterhead is easy. (Image ©Powermatic)

To remove the bearings & housings from the cutterhead, I tried using wood wedges but that didn’t do it. So I went to my shop neighbor who’s an auto mechanic. He used a press to push things apart. And to be honest, it didn’t take much effort. (When I put the bearing housings on the new cutterhead’s bearings, they turned out to be a slip fit.)

The final step in all this is to align the new cutterhead to the outfeed table. With the old head, you level the knives to the table, but the Terminus® knives are indexed to the cutterhead so you can’t align them to anything but the head itself.  Aligning/leveling the cutterhead to the outfeed table isn’t too difficult if you have a dial guage and some shim stock.

using a dial guage to set the heigt of the cutter

Using a dial guage, I set the heigt of the cutter head level with the outfeed table by shiming under the bearing housings

I was able to shim the head to within .002″ front to back. It’s important to have the outfeed table raised and locked in place. And to tighten down the cutterhead after placing shims as needed under the bearing housings. Taking dial readings with bolts loose won’t be accurate.


Looking across the head, it's a pretty close fit.


The knife looks pretty close to the table. It makes me a little nervous.

This picture shows a few things: the table is still too low. The knives are barely above the surface of the cutterhead. And you can see how the knives are indexed into the head.

Last step is to set the table height equal to the knives:


here, the outfeed table is too low

Here, the outfeed table is too low because when I rotate the head, the knives lift the stick off the table. If I were to joint a board with the table set like this, I would get a snipe at the trailing end of the board.


Outfeed table set "just right"

Here, the table is set correctly. The knives do not lift the stick. Furthermore, when I rotate the head, the knives just barely skim the underside of the stick. If the knives didn’t touch the stick at all, the table is too high and will create a convex bow in the bottom of the board being joined. (The infeed and outfeed tables not being parallel to each other can also cause convex or concave joints.

After all my setups, I ran a board over the jointer.


Joining the first few inches of a board to check for square, smoothness and depth of cut.

What I noticed first off was that the machine was a little quieter and didn’t vibrate as much as before (probably that bad bearing). I also noticed that the cut wasn’t quite as smooth as the old knives after sharpening and honing. Maybe running these knives over a whetstone will help. I checked the depth of the cut (about 1mm) and reset my infeed “depth of cut guage” (about as accurate as a dull #2 pencil). I checked for square and adjusted the fence (using the fine adjustment capabilities of the heel of my hand against the fence adjustment handle — This handle isn’t shown in the fence picture above. I guess it’s been redesigned out).

Checking for square

Checking for square (the clamp is just to hold the square in place while I take the picture)

Shavings from my first cut

Shavings from my first cut

After using the jointer for a couple of weeks, I am pleased overall. There does seem to be a bit of chatter (knife marks as if one of the knives is too high) so I’ll have to look into the cause of that. It may turn out that I will need to hone the knives while in place to be sure they’re all the same height.


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