# Using template bushings



## Colonel (Jul 16, 2011)

Is there a simple rule-of-thumb to calculate the off-set with guide bushing diameters/router bit combinations?

Colonel


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## Quillman (Aug 16, 2010)

1/2 the diameter of the ring = the distance to the centerline of the cutter, any cutter.


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## jschaben (Jun 21, 2009)

Colonel said:


> Is there a simple rule-of-thumb to calculate the off-set with guide bushing diameters/router bit combinations?
> 
> Colonel


Bushing Diameter - Bit diameter / 2 = offset


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## dutchman 46 (May 23, 2007)

I think John has the good answer. The goal is to have it stand perfect all the way around, If You have achieved that, then there is nothing else to do! The difference in dimensions from bushing to the cut can be calculated for Your different bits, if You are good with math


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## sourdough (Jan 31, 2010)

Several years ago I saw a great chart that, while a bit complicated at first glance, showed a large number of bit/guide combinations and what the offsets were. I thought I had set it aside someplace but of course, my poor brain is so filled with information gathered over more than 70 years that some of it falls out my ears. Alas, I cannot find the chart. It was VERY handy.
I have to keep this stuff VERY simple.
Maybe someone knows the chart I refer to.


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## bobj3 (Jan 17, 2006)

Hi

This one maybe

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sourdough said:


> Several years ago I saw a great chart that, while a bit complicated at first glance, showed a large number of bit/guide combinations and what the offsets were. I thought I had set it aside someplace but of course, my poor brain is so filled with information gathered over more than 70 years that some of it falls out my ears. Alas, I cannot find the chart. It was VERY handy.
> I have to keep this stuff VERY simple.
> Maybe someone knows the chart I refer to.


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## dutchman 46 (May 23, 2007)

:no::nhl_checking:Your going to have to add more memory to the old computer! Anyway, that's what My wife says. I could not take Her telling Me anymore that My hard drive was fried! Ha Ha, You say that so well!:dance3:


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## sourdough (Jan 31, 2010)

That's the one Bob. Mine was full page and laminated and I have no idea where I got it but it IS handy at times.
Thanks. I'm guessing some of the folks will get some use.


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## bobj3 (Jan 17, 2006)

Hi Warren

Your Welcome
So many make so hard and the chart makes it so easy, I have posted it many times but Rebel a member of the forum made the chart back in 2006 I think, just a pass it on thing for me. 


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sourdough said:


> That's the one Bob. Mine was full page and laminated and I have no idea where I got it but it IS handy at times.
> Thanks. I'm guessing some of the folks will get some use.


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## Joe Lyddon (Sep 11, 2004)

jschaben said:


> Bushing Diameter - Bit diameter / 2 = offset


*Just to clarify...*

Bushing Diameter - Bit diameter / 2 = offset

Bushing Diameter (BUD) = 1"
Bit diameter (BIT) = .5"

*This **A*: *OFFSET = (BUD - BIT) / 2*
1 - .5 = .5
.5 / 2 = *.25 ?*

*Or This** B*: *OFFSET = BUD - BIT / 2* same as *OFFSET = BUD - (BIT / 2)*
.5 / 2 = .25 *(Divide is done first... like Computers & Spreadsheets do it)*
1 - .25 = *.75 ?*

*?????*


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## jschaben (Jun 21, 2009)

Joe Lyddon said:


> *Just to clarify...*
> 
> Bushing Diameter - Bit diameter / 2 = offset
> 
> ...


Hi Joe - Would be option A, my bad, should have put parens in.


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## Joe Lyddon (Sep 11, 2004)

jschaben said:


> Hi Joe - Would be option A, my bad, should have put parens in.



John,

Thank you very much... I figured it would be that way... but had to clarify in case some of us wanted to use the formula in a Spreadsheet and would NOT want them banging their heads against the wall trying to get the correct answers... :dance3:


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## harrysin (Jan 15, 2007)

Colonel said:


> Is there a simple rule-of-thumb to calculate the off-set with guide bushing diameters/router bit combinations?
> 
> Colonel


To make a template to rout the inside of a box like this the simple formula is:

Diameter of the chosen template guide minus the diameter of the chosen bit, plus the size of the finished recess.

If we want the recess to measure 6" x 4" and use a 1" guide with a 1/2" bit, then,

1" - 1/2" + 6" = 6 1/2"
1" - 1/2" + 4" = 4 1/2" So an opening in the template measuring 6 1/2" x 4 1/2"

using the above combination of guide and bit will produce a routed recess
measuring 6" x 4"

The off-set for this example is 1/4", calculated by 1" - 1/2" ÷ 2 = 1/4"

I've added a couple of shots showing how easy it is to make accurate templates where curves aren't involved, for ones with curves there are still easy ways as shown in the last shots.


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