sliding dovetails - what am i doing wrong?

Mike Gager

ive been trying to learn how to make sliding dovetail on the router table and ive run into a problem that im trying to overcome



using 3/4 stock i set the height of the bit at 3/8" and make the groove in the first piece, no problems there



then leaving the bit height the same i cut the tenon on the second piece. i can get the width perfect where it just slides in with hand pressure and is pretty snug but not too snug for glue



the problem is it looks like this



dovetail.jpg



there is about a 1/16" gap between the cheeks of the tenon and the flat of the first piece



i thought leaving the bit height the same is how i was supposed to do this but is that incorrect? is there a set amount i should lower the bit or is it trial and error as well? if i am correct at leaving the bit height the same whats going on here? ive tried putting different pressure on the pieces as i route them with no real change. any ideas?

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bobj3

Hi Mike

Here' a tip from Bob and Rick should help..

"Again, check your fit by clamping two pieces of 3/8" thick material together (make sure the bottoms are flush) and cutting dovetails in one end. To adjust the fit, raise the bit to make it tighter and lower the bit to loosen."

Router Workshop: boxjoints

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Cassandra

Hi Mike:

No answers here, but hopefully some guiding questions.

Given:
On router table? Yes
Same bit height? Yes
Bit height? 3/8"

Per your drawing:
Dado is 3/8", which is same as bit height.
Length of tail: 7/16"

Mike, some questions:
1. Are you sure that the dado is 3/8", not 5/16"?
2. Is it possible that one of the pieces is riding the shoulder of the bit? (The Dado might be shallow.)
3. Have you checked the flatness of your table?
4. Have you tried a test joint, using a shallower cut? Try making a quarter-inch deep sliding dovetail.

Your method sounds sound. So, something has to be causing the bit to either cut a shallower dado or cut an extra-long tail.

Cassandra

Edit: I went the wrong way in suggesting 1/2 deep dovetail. Should have gone 1/4 inch.

jmg1017

Mike, you are correct, the bit height stays the same. I make sliding dovetails all of the time for the backs of all my drawers. The only adjustment made is the fence setting for the tenon width. It sounds like you already have that set properly so I'll have to agree with Casandra, must be an error in depth when you make your passes.
I can't think of any other reason for the difference.

Mike Gager

i believe the problem stems from my using the mlcs/harbor freight router plate. it is not flat so the cut especially on shorter stock, is not going to be flat. pretty disappointed right now

as a workaround i built a jig to hopefully overcome the problem but now im having a similar but different problem. i am going to try to figure the problem out tonight and if i do ill post pics of the jig, otherwise im going to try something else