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Thread: Magnetic Zero Clearance Insert Tutorial

  1. #1

    Magnetic Zero Clearance Insert Tutorial

    One of the more handsome members asked me to share how I make ZCI's. First, I'm using materials that I have on hand. I don't think the material is critical as long as it stays flat and doesn't have too much friction.

    My ZCI's are made of 1/4" Baltic birch plywood and 1/4" HDPE plastic bonded together with epoxy. I score the HDPE to give the epoxy some bite. I removed the adjustment screws from the factory insert and I use some short screws to attach it to the ZCI. A pattern bit in the router table gets me to the right shape and the holes left by the screws tell me where my adjuster screws need to go. Don't forget to mark and drill the finger hole. (I always do)

    Next I drill holes for magnet cups in two of the holes. Do not drill into the plastic.

    Then drill out the holes in the cups to allow the adjustment screw to pass through (I'm using 10-32x3/8" allen head set screws.

    Now I drill and tap all four holes for my set screws. The two with magnets will pass thru the cups and push the magnets down. The other two work like stock adjusment screws.

    To prevent leaving the magnet/cup behind when removing the ZCI, I installed narrow strips of aluminum flashing. It stretches as you tighten the screw.

    Bob Ross
    Ideas, Products & Accessories for Serious Safety-Minded Woodworkers

    Please Pray for Our Troops
    Semper Fi!!

  2. #2
    Join Date
    Nov 2006
    Delton, Michigan
    Do you use any pin for the frnt to hold it in place ?
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

  3. #3
    Join Date
    Jan 2009
    I live in Denton, Texas and ranched at Schulenburg, Texas.

    zero clearance insert

    thanx for tutorial. Your note about epoxy is welcome for my to TRY list with the HDPE & UHMW plastics.

    I am in the process of making several inserts and I'll try the magnets.

    Do U use thin epoxy or the stiff; and do U clamp the two halves together.......

    I see with the Al stripe a slight projection; does this hit the rim of the tabletop?

    Thanx again Ray Gerdes

  4. #4

    No pin front or back. That's what the magnets are for. Two 3/8" rare earth magnets in cups exert a considerable pull.


    I haven't tried epoxy with UMHW; I read that it doesn't work very well.

    I usually use 5 minute set and I guess it's thin because I trowel it on with a tongue depressor. I did try the epoxy for plastics and it didn't seem any better. I don't think I'm actually sticking to the HDPE; I think it's a more of a mechanical bond.

    Yes, I do clamp the two halves. FWIW, I use those Vice Grip 11" clamps with pads. I can lay the insert on the edge of my bench and the clamps will reach the back edge.

    The aluminum strips are inside the perimeter of the insert. What you see is about 1/16" projection of the magnet. The insert is about 1/2" thick and the opening on my Grizzly saw is about 9/16" deep.
    Bob Ross
    Ideas, Products & Accessories for Serious Safety-Minded Woodworkers

    Please Pray for Our Troops
    Semper Fi!!

  5. #5
    Join Date
    Jun 2008
    GTA Ontario Canada
    Bob, there is something in your method that does not sit right with me. I presume the top layer of HDPE plastic is level with the table saw table. You admit that the epoxy is not glueing to the HDPE and the magnets are in the 1/4 ply section. Then there is no pin in the front.

    What happens if the blade binds with the side of the HDPE plastic and flings the plastic out. With the vibration and constant pressure that is going to be exerted on the insert from wood and push blocks going overhead, that "mechanical bond" formed by the epoxy that does not adhere is going to crack loose leaving a piece of HDPE free to fling back at the user if there is the slightest binding on the blade.

    Or do I have something completely wrong in my understanding of your build. We are still a month away from April fools day so I must have a misunderstanding somewhere.

    Please clarify for the sake of safety.

  6. #6

    Good point. I have made four of them for my own use, a thin kerf, a full kerf, a box joint set and a 45* full kerf bevel. None have shown any signs of separating. Maybe the two set screws that pass thru both layers exert some sort of mojo.

    As stated, I used what was at hand. The same technique would work with 1/2" plywood, phenolic, UMHW, MDF, or EIEIO.
    Bob Ross
    Ideas, Products & Accessories for Serious Safety-Minded Woodworkers

    Please Pray for Our Troops
    Semper Fi!!

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