Results 1 to 8 of 8

Thread: 3 knife Jet jointer problem

  1. #1
    Join Date
    Jan 2018
    Location
    Vancouver Canada
    Posts
    618

    3 knife Jet jointer problem

    I have a Jet 6" jointer, shorter tables, 3 knives and a "bevel" problem. I'm not at home, so I don't have the exact model number.
    I bought it used 5 years ago with it being stored for the last 2 years, and it runs like a charm, BUT, when jointing edges, I am square; when jointing a flat piece of 2+ inches, after 2-3 light passes, I begin to see a bevel in the wood. I define a bevel at the left side being non equal in height to the right side, as checked against the non-jointed side opposite.

    Here is what I've done.
    1) Removed the fence, checked the out-feed table for flat. Not perfect, but within about .010 mm using my Veritas machined level.
    2) Raised the in-feed to dead level against out-feed side with my feeler gauge and checked from the fence to the front over 3 or 4 places - dead flat.
    3) Checked diagonally, still good.
    4) Set up my magnetic dial micrometer on the out-feed side, checked the head; there is a small variation, about .03 mm at various points, but left to right, it may not be significant - but I don't know (hence the post).
    5) Cleaned the slots after the knives and keepers were removed, with brass brush and where rusted, 220 sandpaper; cleaned the keepers after removing and cleaning the bolts, and cleaned the knives. Upon inspection, they were sharp having been done and honed shortly before storage, but there is a slight dip in the middle of the knives - maybe .010mm.
    6) Reinstalled everything and began the setting. This may be my problem. I've tried it 2 ways; I adjusted the knives against a piece of flat wood, checking each knife as I tightened the bolts, then checked with the dial indicator, thought I was OK, ran some wood through very lightly perhaps 1/32" 4-5 times - got a bevel cut.
    7) I triple checked the fence against the tables many times against both tables, alternately putting the square and the holder (Starrett) against each surface, and made sure it was right. Same result.
    8) Loosened the bolts, re-adjusted the knives to equal the height of the out-feed table again, but this time using a steel ruler set on the table until hey juuuuust touched over 3 places per knife. Set the cut to ~1/64, trying to see if I could just get the fuzz (sorry officer) off. Added a little depth of cut, - after 3 passes, it's starting to bevel closest to the fence.

    So, although I've tried to moderate my pressure on the work piece, I MAY be adding a little more pressure against the fence side. Feasible? I'm asking.
    It could be that cumulative errors in the knife setting and a deficiency in the cutter head alignment/bearings is causing the issue.
    My next step will be to move the fence 2-3" into the head area and see if the error is repeatable over the width of the cut.

    A helical head replacement for this jointer runs about $500.00 with taxes. Am I better off selling this machine and getting a new 8" somewhere with the helical already installed. I'm a real part timer, just trying to have a little fun in a stressful old age.
    Young enough to remember doing it;
    Old enough to wish I could do it again.

  2. #2
    First thing I would try is turning the work around after each pass. A small knife nick elevates one side . Check for nicks.

  3. #3
    Join Date
    Nov 2009
    Location
    Peoria, IL
    Posts
    3,030
    Checking against the face that hasn't been machined is a mistake. You may have some twist in the board and you are trying to make it flat, not parallel to the untouched face. The out feed table has to be a few thousandths under the arc of the cutters. With the machine shut off and a small board on the out feed table and cutter head, the knives should lift the board ever so slightly and move the board about 1/8" when the cutter head is rotated. NOT dead even with the out feed table.

  4. #4
    Join Date
    Feb 2014
    Location
    Lake Gaston, Henrico, NC
    Posts
    6,999
    Is the side you ran flat?

  5. #5
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
    Posts
    61,340
    Quote Originally Posted by Tom M King View Post
    Is the side you ran flat?
    ^^ This is the question that also entered my mind. Face jointing nearly always causes some differences in thickness, side to side and end to end, because it's removing the high spots when done correctly. I do use the "flip it around" method when I'm flattening just as a good practice, however, unless the grain doesn't permit it to avoid tearout. The fence has zero use when flattening a board's face.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
    Join Date
    Mar 2006
    Location
    SoCal
    Posts
    21,816
    Blog Entries
    1
    To Tom's point, you can certainly initially flatten a face without relying on the fence. As soon as I have enough surface flat to allow me to plane the opposite side parallel I do that. I then use that face as a reference to fully flatten the original face. Then I edge joint one edge which allows me to check for square with a pocket square or whatever. I know we are focusing on a stock removal concern but just to be complete, I then rip to width and crosscut to length.

    Even with a jointer setup perfectly your technique can cause anomalous results. Just as one can lean off center with a hand plane uneven pressure in feeding your stock can result in less than perfect results from the jointer. I would offer that a degree of irregularity is always present whether due to technique or wood movement during the milling process.

    Multiple people on multiple forums or in trade rag articles have offered the best advice for determining machine accuracy of operation; it is the question "is the result usable?". It is easy to get lost in fractions of a fraction when aligning machines when you reached usability long ago.
    Take me to the hotel - Baggage gone, oh well . . .

  7. #7
    Join Date
    Jan 2013
    Location
    FINGER LAKES AREA , CENTRAL NEW YORK STATE
    Posts
    59
    What is the possibility the knives are all parallel to each other in the cutter head but not co-planer with the tables? You might not see the variance on the board edge but find it easily on the board face.

    Lower the infeed a bit like 1/8 inch or more. Then bring each knife in turn with cutting edge at 12:00 o-clock and set a straight edge (ruler or such) on a couple of shims like a couple pieces of 1/8 inch plexi glass on the infeed table. Sight under the shimmed straight edge or over the top of the straight edge to view the knife edge kind of like a couple of winding sticks on a twisted board. The idea is just to understand if there is any angular difference, misalignment across the length of the knife to the table surface. Just a thought and one variable to confirm or eliminate as cause.
    mike calabrese

  8. #8
    Join Date
    Jan 2018
    Location
    Vancouver Canada
    Posts
    618
    I apologize for the delay in answering thoughts posted here. We had a family tragedy and Ive been unable to focus on woodworking.
    1) I mentioned the fence because I was trying to joint some 2x4 that I had run through the table saw and so wanted to make the cut face perpendicular to the original side.
    2) I have turned the wood around as suggested, but that brings up grain and tear out issues. I mean its 2x4, but Id rather get it right with construction lumber
    3) The side was nearly flat. If it was perfectly flat, Id have passed on the jointer.
    4) Im going to try various solutions like readjusting the knives and lower the outfield table slightly.
    Im also going to have to learn that perfect is the enemy of good enough.
    Young enough to remember doing it;
    Old enough to wish I could do it again.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •