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Using a dish carving bit (from LV #16J26.70), I have to route 1/16" recesses in perfect circles.

If the photo upload cooperates, you can see my prototype (done with Forstner bit). But maybe I need more posts first.

I plan to use guide bushings inside a template that I can cut with a fly cutter on a drill press. So, I can make the template any size I need. (There could be some trial and error involved!)

Do you think I can use a guide bushing smaller than the outside diameter of my router bit (1.25")....IF I size the template accordingly?

Thanks.... Greg
Welcome to the forum Greg, unfortunately it isn't possible for the template guide to be SMALLER than the cutter, the latter having to pass through the former with some clearance. The method for calculating the size of hole in the template is:
decide on the size of template guide, the bigger the better, also the size of cutter, the simple formula then is: O/S diameter of guide minus diameter of cutter plus the size of the hole that you want. If you want to use a 1.25" cutter you will need a guide at least 1.5" diameter and supposing that you want to rout a 4" hole, then, 1.5"-1.25"+4"=4.25" hole in the template. If perhaps your largest template guide is 1.25", then use a 1" cutter and we now have: 1.25"-1"+4"=4.25"! No magic here Greg, the DIFFERENCE between cutter and guide in both cases is the same, 0.25", if we divide this by two, we refer to the OFFSET being 1/8". I do hope that this makes sense to you, if not, keep asking.
 

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Premium Member
Retired since June 2000
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15,065 Posts
Greg, I personally use a 40mm guide wherever possible but I'm led to believe by Bobj3 that they aren't generally available in the US and Canada. On many occasions on this forum I've suggested that members DEMAND 40mm guides from suppliers /manufacturers, the 40mm being 1 37/64" but 1.5" would be fine so why not push suppliers/manufacturers for the 1.5". It puzzles me that a/the leading country like America haven't yet realised the benefits of a guide as large as 1.5" or 40mm, some of which are: a bigger variety of cutters can be used, it's possible to SEE what the cutter is doing, the dust doesn't build up, compress and cause extra heat build up on the cutter, projects started with a large cutter like patterns on a box lid, can then have identical concentric/parallel patterns routed going down in size two three of four times if the cutter is small.
 
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