# Guide Bushing/Bit Table



## GulfcoastGuy (Feb 27, 2012)

I've had the need to to recess a male part into a work piece. Kinda like inlay only less ornamental and more utilitarian like mounting a mounting plate to a router table. I know the math but I thought a table would be helpful. 








[/url] Inlay-Insert xref by pat w1, on Flickr[/IMG]
Theoretical at this time - Check on scrap first

The table is two sections. The top section is for creating a female template from the master part that needs to be recessed. The bottom is for cutting the recess for the master using the female template just created. Various bit diameters are listed across the top and the guide bushing sizes are listed along the left side. (sorry - no millimeter sizes). The object is to use the table to obtain a number (in green) that corresponds to a particular bit-bushing pair and then obtain a matching number in the other table with another bit-bushing pair. The red shaded numbers have no match in the other table and the purple numbers are no fit/too tight bit-bushing pairs.

For example:
Let's say I have a odd sized router mounting plate that I need to install in my brand new router table. I need a female template so I pick a bit-bushing pair from the top table. I'll go with a 1/8" bit and a 3/8" bushing. That crosses to an '8' in the top table. I attach the mounting plate to the template material and cut the template. Then I chose a suitable bit-bushing pair from the bottom table. For '8' I have three choices:
1/8"-5/8"
1/4"-3/4"
1/2"-1"

If I used the last one I could get the recess and hog out enough room to get the 1" bushing into the groove I just cut and then use the edge of the recess to directly cut the opening below leaving a 1/4" mounting lip.

I did this on Excel without having the actual parts in front of me to back check my math for fit so if there are more combo's that fall out please let me know.

Also, if anyone sees that I've hosed this up in any way please sing out - I'd hate to be responsible for someone's trashed project.


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## GulfcoastGuy (Feb 27, 2012)

Since this has received some attention I thought I'd go into a little more detail. The image below is a graphic depiction of the example above.








[/url] Bushing-bit table example by pat w1, on Flickr[/IMG]

The dark brown to the right represents the master part.
The light brown to the left the template material.
The Upper smaller concentric circles represent the 3/8" bushing and the 1/8" bit used to cut the template.
The larger concentric circles represent the 1" bushing and 1/2" bit used to cut the recess for the piece.

Note how in each case the critical offset is 1/4". For the template cut this is the total offset from the contact point between the bushing and the master and the relevant outer cutting surface of the bit. For the recess cut the same offset exists from the contact point between the bushing and the inside edge of the template and the INSIDE cutting edge of the bit.

I placed an image of the original bushing/bit pair at the bottom to show how just reversing the original pair would result in an oversize recess.

{you may have noticed by now the numbers in the body of the table are relevant offsets in 32nds.}


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## jschaben (Jun 21, 2009)

Nice - quite a bit of work there but it looks like it will be handy. 
I try to do that stuff in my head and usually go through a couple of aspirins before I get done. Thanks. :thank_you2:


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## GulfcoastGuy (Feb 27, 2012)

I was winding up with too many 'Doh' moments when the math went foul. Anyway my system and aspirin don't play well together. 

There are some other benefits. If the recess is destined to be flocked or other wise lined or you just need some extra space, you can pick a pair that crosses to a higher number (offset) for the template then drop down a number or two for the recess cut. For each number difference the recess will be oversize by 1/32nd on all sides.


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