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Thread: Planer Knife Protrusion/Stickout

  1. #1

    Question Planer Knife Protrusion/Stickout

    Hi. I just purchased a circa-1994 Powermatic Model 15 planer that needs a basic tune up. This is my first planer. It didn't come with the knife-setting jig, so I've decided to 3D-print my own. I took some rough measurements today and modeled the cutterhead in CAD. The cutterhead itself is 2.875" in diameter, and I read in several places that having the knives protrude 1/16" beyond the cutterhead is good. 1/16" protrusion makes the overall cutterhead diameter 3", which is what I modeled.

    Looking at my model, which probably isn't super-accurate, but isn't bad either, it looks like the tips of the knives protrude beyond the gibs just .009" (red arrow distance in the attached detail pic). The blue dot distance in the pic is .074", so just a bit over 1/16".

    Does this look right? I'm concerned that .009" isn't "enough tip," and that I'll be constantly adjusting the blades to keep enough edge past the cutterhead. On the other hand, I've read a few posts saying the "less tip" the better.

    I can certainly move the blades out (limited by the amount of lateral clearance to the chipbreaker), but I'm not sure this is the right thing to do, and it changes the cutting angle (although I don't know how sensitive these machines are to changes like that).

    Thoughts? Also, thoughts on the knife-setting jig shown in the overall pic?


    Attached Images Attached Images
    Last edited by Matt Culik; 01-18-2022 at 10:14 PM.

  2. #2
    I put the sharp edge almost an 1/8 th inch past the edge of the gib

  3. #3
    Join Date
    Jan 2009
    Suggest you ask PM. Brian

  4. #4
    Just make sure the gib edge is entirely on flat surface . Not into the grind

  5. #5
    Join Date
    Sep 2016
    Modesto, CA, USA
    Make sure the bottom of the knife is at or below the bottom of the gib. If it is not it is too worn and needs to be replaced as a balanced set.
    Bill D

  6. #6
    Do you have a manual?

    You make the table parallel to the head first. Then you decide your knife projection. Some manuals will tell you. I tried some different numbers and .050 above the head works well on my machines. Its one rotation of my dial so makes it easy.

    You are making a cutting circle. With your bed parallel to the head make all your knife projections the same above the head. On the SCM stuff with the .050 I use ive never had to adjust the rollers and not even checked them as its always works well with the same knife projection used each time.

    You might have to set the rollers and pressure bars and all depending if it was set to some other number a fair bit different than what you are going to use. Most manuals have a sectional side view and give you the heights of all that stuff.

    Not so common but machines with knife grinders they set the knives higher as they expect you to get 5 of 6 hones out of them before pulling the knives up again.
    Last edited by Warren Lake; 01-19-2022 at 12:13 AM.

  7. #7
    Ask the manufacturer/ see if you can find a manual online. If the knives are in the head now and the machine feeds ok it is probably safe to copy the existing knife projection. If they are too far out of spec you may find it impossible to adjust the chipbreaker, feed rollers and pressure bar properly.

  8. #8
    About 1/8" proud of the cutter head.

    I suggest you check the table for parallel before using a jig.

    I adjust mine off the table b/c I've never been able to get the table perfectly parallel. But that's a 20" planer.

    On mine the rollers and pressure bar are set relative to the knives.

    Definitely get the manual!!

  9. #9
    Join Date
    May 2013
    Northern Virginia
    Quote Originally Posted by Robert Engel View Post

    Definitely get the manual!!
    Just download a grizzly/shopfox/jet/delta (any 15" 4 post) manual. They are all identical.

  10. #10
    Thanks, everyone. For those saying get the manual, I've reviewed several, including the Grizzly, the new Powermatic and the correct manual for this machine. They all provide specs for roller and chipbreaker heights relative to the cutterhead, but as far as knife protrusion goes, they all say to use the jig. For whatever it's worth, the Grizzly manual did say the cutterhead diameter is 3". My understanding is all these machines have a cutterhead diameter of 2.875" WITHOUT knife protrusion, so I'll take that as I'm headed in the right direction with my 3" approach.

    I was out in the shop last night looking at it, and it's also possible the gib in my model is wrong. It doesn't appear to extend past the cutterhead nearly as much in real life as it does in the pics above. I re-measured and am not sure where I'm wrong, but maybe...

    Anyway, 3D printing is cheap, fast and easy, so I'm going to print my jigs as designed and see how it goes.

    Again, thanks for the help! Will let you know how it goes.

  11. #11
    You answered your question with your numbers your knife projection is 1/16" .0625 above the head. Id still get the manual for roller, pressure bar etc set up numbers. If you look at 3 or 4 different 24" planers the set up numbers for each are different.
    Last edited by Warren Lake; 01-19-2022 at 12:34 PM.

  12. #12
    A somewhat more sensitive gauge can be made with a button tipped dial indicator held in a wood block that straddles the knife pocket. Here's an excellent primer on adjusting traditional planers with shop made gauges by Bob Vaughan of sainted memory The gauge can be seen in use at around 7:00 in.

  13. #13
    Join Date
    Feb 2011
    New Brunswick, Canada
    Quote Originally Posted by Mel Fulks View Post
    I put the sharp edge almost an 1/8 th inch past the edge of the gib

    I did too Mel. I have a General 130 with the same 3" diameter- 3 knife head. The specs call for 1/16 " protrusion as well. I installed new knives after I bought it. So. I moved it out to the !/8 "+ if anything. Works well.

  14. #14
    Join Date
    Feb 2011
    New Brunswick, Canada
    Matt, on another setting as I just finished adjustments today, the table rollers call for .010 " above the table. I'm probably at .011". Book says that anything over .010 could result in snipe on both ends. No snipe yet. Got to tinker the adjustments is my best advice. Greg

  15. #15
    Join Date
    May 2021
    New Hampster, USA
    That drawing must be inaccurate because the gibs should not protrude as shown in the drawing. The protrusion of the knives beyond the cutterhead is not limited to a single exact distance as far as I know, i.e., it doesn't have to be exactly 1/8, 3/16, or whatever. You can probably just set the back of the knife bevel about even with or slightly above the cutterhead provided the knives don't bottom out. What is critical is that the knives are parallel with the table and that the infeed roller, outfeed roller, chipbreaker, and pressure bar are all set relative to the height of the knives. This may help you with a full tuneup . The 3D printed gauge will not be user friendly. Do yourself a favor and buy magnetic jigs to hold the knives and a precision gauge to set all heights (and remove the springs under the knives if they are there because they will lift the magnetic jigs off the cutterhead).

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