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"square" Drilling jig for MDF pieces

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  • "square" Drilling jig for MDF pieces

    I am making my bending form for the nose rib. On the first try I just drilled my pin holes using the steel bushings in the working master wing form.
    That " sort-of" worked but the holes were off perpendicular just enough I didnt like it. :-( ( I had used the hand drill through the 1/2 inch long steel bushings so there was a little
    angular slack) I like my stuff square - especially when its a tool for making what are supposed to be exact copies.

    So i cut that one up and tossed it.... made a new one and drilled it in the Milling machine with it clamped down to the table. (thats the best I can do...)
    But thats a bit of a pain to have to clamp all that down for every hole just to ensure that its straight........

    I am considering (probably making) a drilling jig. Something like a square base maybe 4 to 6 inches square-- maybe 3/16 thick steel..... attach a piece of thick
    wall tubing in the center which has a 3/16 center hole. (airparts has CrMo tubing that 3/8 outside and .185 inside) Im thinking I could just hold this down either
    by hand or light clamp--- then thread the bit through the tubing to keep the bit square to the work. ( the 3/4 MDF pieces ) I think i could make the base as wide as I wanted...
    to make it easier to hold down.....
    This would maybe save the setup time for each hole that would have been done in the mill...
    Anyone tried this ?


  • #2
    I don't have any photos to share of my pattern creation, or at least none that would adequately display the process. I had a long story in mind, but I'll try to keep it short

    For the longer story, refer to this post:

    I used my master form (made with the Mylar) to make my bending form. My bending form is made from solid oak, and is full-sized, meaning that I didn't make one for each rib type. They're all bent on the same form, just placed on the bending block depending on what kind of rib they are.

    I transferred the drawing to the piece of oak, punch a couple of pilot holes with a 3/16" clevis pin fed through the 3/16" jig holes in my master form, and then I drilled it square on my bench press. I bolted the set together, and used a router table with a laminate bit to match the bending board to the master.

    After that, I separated them, and used the oak piece as a template to route out a matching backing board. I relieved the edges for bend radius on the side of the bending form I planned to form metal against, and then I routed in and edge-relieved the fluting locations (my fluting technique may be different than yours).

    That's the short story. Using the drill press is what kept everything square. And using the master form is what kept all the holes lined up. Out of all the ribs I drilled, routed, and formed, all the holes lined up, and there was never a problem.

    Remember, we're building an airplane, not a watch. We're allowed a couple thousandths here and there


    ​Christopher Owens, EAA #808438
    Project "Expedition"
    Bearhawk 4-Place Scratch Built, Plans #991
    Bearhawk Patrol Scratch Built, Plans #P313
    Germantown, Wisconsin, USA


    • #3
      Like Chris inferred, if it is at all possible, make use of your drill press. It's a good habit to get in to.

      I used my mill to make a block as pictured. It lets you drill square to surface pilot holes on flat surfaces and also square to surface pilot holes centered on tubing when you get to the fuselage.


      • #4
        I was thinking of a steel flat base with a steel snout about 2 or 3 inches long for the bit to slide in (fitted about .001-.002 bigger than bit)
        I dont actualy have a drill press. Would be handyer than mill if I did !


        • #5
          I don’t have a mill and not that familiar with the options and configurations. Do they have a press-like feature?
          ​Christopher Owens, EAA #808438
          Project "Expedition"
          Bearhawk 4-Place Scratch Built, Plans #991
          Bearhawk Patrol Scratch Built, Plans #P313
          Germantown, Wisconsin, USA


          • #6
            A totally flat base quite often will get chips under it throwing off the alignment. Keeping the contact area smaller helps minimize this issue so the channel helps here..

            Making it on the mill out of a single piece of material will be easier/more accurate than piecing it together out of a base and a separate bushing.

            Put the piece in your vise, locate the Y so the spindle is about centered over the part. and lock the table and leave it there. Position the part in X to where you want the hole and drill. Change from the drill to a mill and traverse the table in X and Z to make the channel. Now unlock the Y and skim mill the surface. Everything is now as parallel/square to each other as your mill.

            You probably only need the length of the guide hole to be about four times the bit diameter to keep things square.

            And you will want a drill press before you go too much further in your build.

            In my experience, a mill is very good for accurate hole placement but is much more unwieldy for typical drilling activities. One gets tired of constantly removing/re-installing/aligning the vise.
            Last edited by BTAZ; 12-08-2017, 10:57 AM.


            • #7
              I made a drill bushing out of a piece of bar stock (I squared it up with a lathe). My suggestion is to use a valve compressor to hold bushing in place. Center bushing with a squared off dowel pin and clamp.

              This is a picture of transferring holes from 032 mylar to master mdf.
              Later, I used the same technique to transfer from mdf into rib blanks.
              I never put a bushing into the mdf. I only used the mdf to center the bushing so that I could clamp.

              With bushing clamped. I could drill safely
              Last edited by sjt; 12-08-2017, 02:32 PM.
              Austin Tx


              • #8
                My mill is one of those "in between" ones thats half drill press and half mill. I am holding the work down with those bolt down gizmos. Works fine but takes a few mins.
                each time. The table has T-slots like a milling table that the hold downs go into. I think I will watch for a cheap used drill press.

                Fascinating (as spock used to say-) how many ways there are to do the same job---
                I think it just depends on what you skill set is and what tools you have and are comfortable with. Thats the way it is with me anyway.

                This is the mill table with the fly cutter making the centeral holes in the nose rib bending form.