# Router Bushing/Template Size



## BassBlaster (Jul 7, 2014)

I know this has to be the simplest thing but I just cant get my brain to work today.

I need to cut 20 holes in 3/4" hardwood ply. The holes need to be 3 3/4". I have no desire to spend the money on a hole saw and arbor for this one project so I plan to use my router and a template. The holes don't have to be perfect as they will be hidden so Ill cut a template with a jigsaw. I cant figure out what bushing size to use and what size the hole in the template needs to be to produce a final hole size of 3 3/4". Ill be using a 1/2" straight bit in a plunge router. I don't have a pattern bit.

Reactions: Like 1


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## Schroedc (Jul 7, 2014)

If you use a 1/2 inch diameter bit, just use a 1/2 inch OD collar if you have one, then if you are following the inside of a 3 3/4 circle cut in your template the holes in the lower material will be the same size.


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## Schroedc (Jul 7, 2014)

Whoops, I said collar, I meant bushing on the router. I am assuming the circles that drop out are waste correct? you aren't needing those as well? If you use a 1/2 inch bit, a 1/2 inch bushing the waste circles that drop out will be one inch smaller in diameter. (3 3/4 hole in template will leave a 3 3/4 hole in your board and a waste circle of 2 3/4)


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## BassBlaster (Jul 7, 2014)

Yes the cut outs will be waste. I guess my question now is how does a 1/2" bit fit through a 1/2" bushing? My bit is a 1/2" shank. I guess I should have mentioned that. Sorry to be so confusing but this whole bushing on a router thing is all new to me.


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## JR Custom Calls (Jul 7, 2014)

Well, whatever size bushing you use... Just take that size minus the size of the bit, and multiply that by two... That's how much bigger you'll need to make the template hole. So... If you use a 3/4" bushing with a 1/2" bit, you end up with 1/4"... Multiplied by two equals a half in, so you'd need to make a 4 1/4" template hole.

Reactions: Thank You! 1


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## Schroedc (Jul 7, 2014)

Gotcha. If you have a 1/2 inch bit with a 1/2 inch shank, use a collar that will be large enough for it slide through. If you are using a 3/4 OD bushing your template hole needs to be 1/4 inch larger than the final hole so you'd have a 4 inch hole in your template, if you used a one inch bushing your hole in the template would need to be 1/2 inch larger than the finished hole so 4 1/4 inches.

Reactions: Thank You! 1


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## Schroedc (Jul 7, 2014)

JR Custom Calls said:


> Well, whatever size bushing you use... Just take that size minus the size of the bit, and multiply that by two... That's how much bigger you'll need to make the template hole. So... If you use a 3/4" bushing with a 1/2" bit, you end up with 1/4"... Multiplied by two equals a half in, so you'd need to make a 4 1/4" template hole.




I don't think you need to multiply by 2, the offset on a 1/2 inch bit with a 3/4 inch bushing is only 1/8 inch on each side so a 1/4 inch total to add to the template hole.


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## BassBlaster (Jul 7, 2014)

Hmmm, you both cant be right!! Lol. See Ive went and confused everyone!!


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## Schroedc (Jul 7, 2014)

BassBlaster said:


> Hmmm, you both cant be right!! Lol. See Ive went and confused everyone!!




That's what a test cut on scrap material is for


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## JR Custom Calls (Jul 7, 2014)

Hmmm... I think he's right. I was thinking the right thought, but only halfway through. haha

Reactions: Funny 1


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## BassBlaster (Jul 7, 2014)

Lol, thanks guys. Ill definitely try it on scrap first. Im cutting these holes in 3/4" cabinet grade ply. I cant afford to screw it up!


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