# Bit and Guide Diameters

2052 Views 4 Replies 4 Participants Last post by  Pop_pop1
I am embarrassesed to say that I have trouble figureing out what bit diameter and guide diameter to use when pattern cutting. Does anyone have a quick and easy formula or method to determine exactly where the cut will be when using a guide? My trial and error method is getting old. Thanks in advance for any and all responses.
Happy woodworking,
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Oak Park had a very good guide. I'll see if I can attatch them. I've never tried to include or attach a picture in the forum before.
Take one half the guide diameter and subtract one half of the bit diameter.
That is the distance from the guide bushing to the final cut edge.
Hope this helps

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Draw two circles, a large one with a smaller one inside and a dot in the center. This is your visual reference. As an example call the outside circle 3/4" and the inside circle 1/2". Since all cuts will be made from the center point you would get 1/2 the size of the bit(in this case 1/4") on both sides of the center dot. To figure where you need to mark your guide spacing you subtract the bit cut (again 1/4" from the center point) from 1/2 of the guide size (in this case 3/8" from the center point) and come up with 1/8" on both sides of center. How does this work in making a pattern? Lets say you need to make a pattern for a 2" circle. If you will be using the inside of a pattern you will need a guide hole the size of your circle (2") plus the guide distance (1/8" on both sides of center) or 2-1/4" diameter hole. If you will be using an outside pattern to make a 2" circle you take your hole size (2") minus the guide distance (1/8" on both sides of center) and end up with a pattern 1-3/4" diameter. If you are only using one side of the pattern for an outside or inside cut you will use only the guide distance.(1/8", only on one side of center) Now you can change the numbers for your bit & Guide. I hope this helps.
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Oak Park had a very good guide. I'll see if I can attatch them. I've never tried to include or attach a picture in the forum before.
Take one half the guide diameter and subtract one half of the bit diameter.
That is the distance from the guide bushing to the final cut edge.
Hope this helps
If you want to go to the orginal post of this information check:
http://www.routerforums.com/showpost.php?p=1812&postcount=9

If you use the search function there is a lot more information in the forum. I also posted some of my table in the gallery area if they are of interest to you.

Ed
Thanks guys, your information is exactly what I was hoping for. I've already made copies of the chart and diagrams and will cover them in plastic, and keep them close to my router table for a ready reference.
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