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Thread: Router & Bushing Question

  1. #1
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    Question Router & Bushing Question

    I'm working on installing my Benchcrafted leg vise. Part of the install is a 1-1/4" hole through the wood for the screw, but also on the leg I need a 2-3/4" wide by 1/2" deep mortise for the bushing. I don't have a forstner bit that size and am trying to wrap my brain around how to use my router instead.

    I've got the following rockler bushing set https://www.rockler.com/router-guide-bushing-kit which has a variety of bushing sizes in it. I'm thinking I could use a hole saw to drill a larger hole into a piece of plywood and then use a bushing and bit to route the mortise. But, how the heck to I back into the appropriate sized hole saw and bushing/bit combination? Looks like my largest hole saw bit is currently 3-1/8", but I think I can find additional hole saws easier than a forstner bit larger than 2-1/8.

    Template Guides:
    • 1/4" (inside) x 5/16" (outside)
    • 9/32" (inside) x 3/8" (outside)
    • 11/32" (inside) x 7/16" (outside)
    • 13/32" (inside) x 1/2" (outside)
    • 17/32" (inside) x 5/8" (outside)
    • 21/32" (inside) x 3/4" (outside)
    • 5/8" (inside) x 51/64" (outside)

    If I were to proceed with the 3-1/8" hole saw, my math says that I would need to have a 3/16" spacing from the guide that it would make. That way, the resulting hole/mortise was 2-3/4". How do I know if one of these bushings works? is it the difference between the bit cutter and the outside of the bushing? Using bushings for something like this will be a new skill for me, so any help appreciated. Thank you.

  2. #2
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    (OD of the bushing - Router bit diameter)/2 = the distance to the cutline (of the cutout/mortise). But then for a circle, you'd multiple that gap by 2 and add that to the target diameter of the mortise to get the size of the template hole.

    If you use the 1/2" OD bushing and a 1/4" router bit, that leaves a 1/8" distance from the edge of the bushing to the bit. Which means you need a template hole with a diameter 1/4" larger than the planned mortise. So if you had a 3" holesaw, that should work. If you were using the 3 1/8" holesaw, you'd need bushing OD - bit = 3/8" (giving you the 3/16" offset). So the 5/8" OD bushing and a 1/4" bit should work.

    If you wanted more flexibility than the holesaws you have available, you can make a router circle jig out of some scrap to cut the template hole to the exact size you need.

    Whatever you do, I'd definitely plan on making some test cuts.
    Last edited by Patrick Varley; 05-23-2023 at 9:58 PM.

  3. #3
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    Thank you Patrick. Test cuts are a for certain. Your explanation is what I needed to wrap my brain around this. I'll dig into what bit and guide combo I have that gets me to the write size. Thanks again.

    Quote Originally Posted by Patrick Varley View Post
    (OD of the bushing - Router bit diameter)/2 = the distance to the cutline (of the cutout/mortise). But then for a circle, you'd multiple that gap by 2 and add that to the target diameter of the mortise to get the size of the template hole.

    If you use the 1/2" OD bushing and a 1/4" router bit, that leaves a 1/8" distance from the edge of the bushing to the bit. Which means you need a template hole with a diameter 1/4" larger than the planned mortise. So if you had a 3" holesaw, that should work. If you were using the 3 1/8" holesaw, you'd need bushing OD - bit = 3/8" (giving you the 3/16" offset). So the 5/8" OD bushing and a 1/4" bit should work.

    If you wanted more flexibility than the holesaws you have available, you can make a router circle jig out of some scrap to cut the template hole to the exact size you need.

    Whatever you do, I'd definitely plan on making some test cuts.

  4. #4
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    If you wanted more flexibility than the holesaws you have available, you can make a router circle jig out of some scrap to cut the template hole to the exact size you need.
    That right there is the best/easiest way to do it.
    There are a bunch of Youtube videos showing how to make a trammel to route small circles & work in simple numbers instead of trying to shoehorn something and end up with too much slop or not enough room.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  5. #5
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    Can't you get the forstner bit you need on amazon for ~$20? If you need to make one or two holes, even the super cheap Chinese made ones should be fine...

    https://www.amazon.com/ASNOMY-Forstn...dDbGljaz10cnVl

  6. #6
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    I looked at those and some of the other Chinese versions but the reviews were pretty spotty with lots of complaints about burning and poor cuts in harder wood. I can't find anyone that makes a more traditional style forstner bit in 2-3/4 size. Anyway, I figured a 1/4" router bit and bushing would do the trick.

    I also figured a bit like this would work too if I made my template using a 2-3/4 hole saw: https://a.co/d/1fmGP9J But the more that I look at it, I can't tell if it would plunge straight into surface. Looks like there may be a gap between the two blades and it only plunges to one side of the bit.

    My only other thought with the router approach is that its a skill I wanted to learn anyway and it won't limit me to one sized hole/mortise. That said, I'll be trying it on a scrap piece first and if I make a total mess of it, I may well end up ordering the forstner bit you linked after all. LOL

    Quote Originally Posted by James Jayko View Post
    Can't you get the forstner bit you need on amazon for ~$20? If you need to make one or two holes, even the super cheap Chinese made ones should be fine...

    https://www.amazon.com/ASNOMY-Forstn...dDbGljaz10cnVl
    Last edited by Greg Parrish; 05-24-2023 at 9:10 AM.

  7. #7
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    Would it work to use a pattern bit instead of a bushing? Make a template the exact size of the desired mortise. No math required.

    https://www.mlcswoodworking.com/shop...n_flush_anchor
    about 1/3 of the way down the page.

  8. #8
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    Quote Originally Posted by Curt Harms View Post
    Would it work to use a pattern bit instead of a bushing? Make a template the exact size of the desired mortise. No math required.

    https://www.mlcswoodworking.com/shop...n_flush_anchor
    about 1/3 of the way down the page.
    That's what I was thinking with the Amana bit I linked above, but I'll be in the middle of the wood so I'm not sure it would plunge through the surface properly.

  9. #9
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    Here is the game plan that I think I'll run with.

    Thanks to Patrick for helping me grasp the math, I'm going to use the 1/2" Freud spiral upcut bit that I used for my other mortises. I'll use it with the 3/4" OD bushing. That should give me a 1/8" off set from the guide. For the guide, I'll use a 3" hole saw to create my plywood guide, and the resulting mortise should be my 2-3/4" needed cut out. I think I've got the math correct, but please feel free to correct me if I'm missing something.

    3/4" bushing - 1/2" bit = 1/4" difference / 2 = 1/8" offset
    1/8" offset x 2 = 1/4" total + 2-3/4" needed circle = 3" guide

    Thank you. I'll update the thread later once I've given it a go.
    Last edited by Greg Parrish; 05-24-2023 at 9:55 AM.

  10. #10
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    It worked. Thank you. And the Festool OF1400 couldn't have made bushing use any easier. LOL

    routersetup2.jpg

    template1.jpg

    cutout2.jpg

    cutout1.jpg

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