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Routers, hole saws, and spade bits (oh my)

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  • Routers, hole saws, and spade bits (oh my)

    I’m building up my cutting templates, and am planning to use a router to cut the lightening holes in the templates and in the metal. I’ve ordered a plunge base for my router and the recommended circle cutter jig (thanks!) for the template holes, and will use a laminate bit in my soon-to-be constructed router table when cutting holes in the metal. The question is, what do folks do for the smallest holes? If I scale from the plans, I see a 5/8” hole in the flap ribs, a 1-1/4” hole in both the flap and aileron ribs, and a 1-1/2” hole in the aileron ribs. What’s the smallest practical size to use the router for both the circle jig (template) and laminate bit (metal)? Here’s my current plan of action:

    -Use circle jig to cut holes in templates bigger than 1”
    -Use space bit or hole saw to cut holes in templates 1” or less
    -Use laminate bit to cut all metal down to bit size (practically down to 5/8”)
    -Use unitbit directly in metal for holes less than 5/8”

    (My original plan was to use a fly cutter for the majority of the holes directly in the metal, but my drill press won’t turn slow enough to use it safely... and I really don’t want to buy a new drill press if I can avoid it.)

    I’m just a bit nervous about these smallest holes... how many folks just locate the centers of these holes with the template as a drill jig and use a hole saw or spade bit directly in the metal?


    Edit: after posting, I realize this probably belongs in “building techniques.”
    Last edited by nborer; 03-02-2019, 11:10 AM.
    4-Place Model 'B' Serial 1529B (with many years to go...)

  • #2
    The router table works for all the holes in the flap and aileron ribs. You just need to drill a pilot hole for the router bit to go through. It would have been easier if I had used a unibit....


    • nborer
      nborer commented
      Editing a comment
      So you’re saying use the unibit for the pilot holes prior to the router?
      Last edited by nborer; 03-02-2019, 08:33 PM.

  • #3
    My 2¢ -- I'd rethink the drill press. It will probably be the most used & important machine in your shop. If your drill press is too fast, it may be deficient in other areas as well, like size, precision, or reliability, and you need all of these. They can be had for under $200 if you look long enough. And you're a scratch builder like me, so you have plenty of time to find a good deal. Put feelers out now!

    As for the holes, a hole saw could do it but I used my fly cutter directly in 7/8 MDF to make the cutting form masters and copied them with the router for the mates.
    Scratch building Patrol #275
    Hood River, OR


    • nborer
      nborer commented
      Editing a comment
      Oh, I have feelers out! Been watching craigslist for local deals. Mostly see junk for now. Problem is, to get down to less than 250 rpm, it can’t be a benchtop unit - it needs 3 pulleys to get the speed down. The only ones I can find that get to that speed are floor models, $500+. That will buy a lot of sheet metal!

      My drill press isn’t going to win any competitions, but it’s a benchtop Craftsman unit. It gets the job done. Just doesn’t have 3 pulleys. I’m going to try the circle jig with the router for the templates. If I can’t get the results I want... then I guess the search for a better drill press ramps up.

  • #4
    Unibits do a great job on thin metal. I never used one before this project. The biggest one, #5, is over an inch. It does a beautiful job thin aluminum. The big one is also rather pricey. I don't use it on anything else as I don't want to waste its edge on anything but thin aluminum.


    • #5
      YES !--- good question !
      I just did this thing about 1 month ago. The problem may not be so much what type of bit to use--- but what type of bit will preserve the centration of the jig hole.
      I thought about using a forstner bit ( I talking about .025 and .032 2024) and it cuts great. But the problem with all of them I could find is the they all seem to have a little
      pyramidal centering point which is only 1/8 inch at its base. It rattles around in the 3/16 jig pin hole--- so no accurate centration there.

      So--- for the 1/2 inch hole -- if found a wood bit which had a little tiny auger in the center. I put the shank in the lather and worked on that little auger with the round grindstone
      and ground down the auger from 1/4 to 3/16. That grinding turned it into a smooth cylinder about 3/16. So when I put that through the jig pin hole in the sheet--- the cutter cant
      wobble any. I cut 1/2 way through from each side. (at like 75 RPM)

      For the 1 inch hole for the flap tube--- I found a surplus cutter which is a counterboring cutter that is made with a removable smooth pilot point. The shank on the pilot was all ready 3/16.
      The cutter on the end had a 2 blade cutter like a non spiral endmill. I took my Dremel and trimmed back the 2 cutting surfaces EXCEPT for about 1/16 at the outer edge. That makes
      the cutting area very small-- which exerts little force trying to spin the work. It cuts like a hole saw except it is very accurate. (unlike a holesaw which is always a wobbley mess)---
      also used at about 75 rpm.

      So those 2 cutter worked fine. Happy !

      Considered the unibits--- but I didn't trust them to maintain center after jumping all those steps. And they are expensive too.

      Don't know if that helps.
      Last edited by fairchild; 03-02-2019, 11:36 PM.


      • #6
        Uni bit is the way to go on holes up to about 2 inches.


        • #7
          E102DAB6-6DC8-4B3C-A69D-88394E0D53CD.jpeg Tried my first round with the router circle jig today - pretty slick! I don’t think I’d use it for much less than 1.5” in diameter... the jig goes down to 1”, but it’s best to hold the center disc in place with screws on either side of the hole centerline, and you need to cut with at least a 1/4” bit. Maybe if I held it with nails instead of screws, then I would feel okay about smaller holes. But, for now, my plan is to use a hole saw for the 1.25” holes in the template. I’ll still use a 1/4” trim bit for the actual aluminum in those holes. Plan to just use a unibit for the 5/8” holes in the flap. Thanks for all the advice! Hope to finish the holes in all the templates soon... after 2.5 months, I may even start cutting some metal!
          Last edited by nborer; 03-09-2019, 10:47 PM.
          4-Place Model 'B' Serial 1529B (with many years to go...)


          • #8
            Unibits should work pretty well and they don't tend to wander off center as you might suspect. If you want to spend a bit more you could get some chassis punches which make perfect circle but require a pilot hole as well. I tend to use them a lot because I had them from my electrical career. Here is a link. If you do something in the drill press make sure it is firmly clamped down.