Planer Choice: 3 or 4 Knife Cutterheads?

According to these pros, buying the 4-knife model and running it with just 2 knives makes sense. December 15, 2005

I am looking to upgrade to a 20" planer and have to make a choice between two different Taiwanese four posters. One has a three knife cutterhead and the other is a four knife. They appear identical in all other respects. These are small diameter cutterheads and I was wondering if four knives is too many. Does the angle of the knives change from three to four? All things being equal, is one preferable over the other?

And yes, I know I should be looking for some old Oliver or Northfield, but lack of space and power prevent that. If I get through this growth phase, that will be next. Thanks a lot.

Forum Responses
(Solid Wood Machining Forum)
From contributor T:
Go with the four knife cutterhead and run with two knives. You'll be running a non-jointed machine, and I don't care how accurate you are with setting the knives, you will get a one knife finish.

We (Terminus) sell many cutterheads for jointers, planers and moulders. We actually recommend to our customers to run with two instead of four. We supply filler knives for the other two knife slots. You would not have that option with the three knife cutterhead. Most people believe that more knives give a better finish. That's true to a point, but they also think that the slower they go, the better the finish. What happens is that knives get extremely hot and dull prematurely. Our rule of thumb is that if your RPMs and number of wings are set, you should run your material as fast as possible to get an acceptable finish.

From contributor D:
Interesting question. I recently upgraded from a Jet 15 inch, 3 knife, to the Powermatic 20”, 4 knife (model 209). I upgraded because I needed a heavier duty machine, but still mobile and 1PH. The finish is neither better nor worse. It does a better job handling the heavy stock. I noticed the General machine is a 3 knife, same price, same exact weight. I bought the PM209 because of the 5 horse motor versus 3 and it has a faster feed rate, but also came with a slower feed kit (different sprocket and chain) to slow it down to the 16 and 20fpm that the General ran at. I have not tried the slow feed rate. I asked the salesperson at the store selling the General (the PM was at another store) about the extra features in the Powermatic. I was shocked when he said the Powermatic “seems like a better deal.”

From contributor R:

Trust what contributor T recommended. I second his recommendation. I've owned one of those 20" Taiwanese with 4 cutters cutter block since 2001. If I knew then what I know now, I would buy some other good European machine, but heck, I bought it without knowing any better, so I will keep it till it dies. Since the beginning, I have it run with only two knifes and it is more than okay. It's as good as when I run 4 knives. Bear in mind I’m a pro woodworker making my living out of this - I can't afford losing time or quality.