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

117280

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?

[Steve Rozmiarek]

Something is moving Mike. Either the bit is crawling out of the collet, or the board is coming off the table as the housing is cut. You are right to assume that the settings should be the same.

[Dan Friedrichs]

Steve is right. The depth setting should be the same for both. Try re-seating the bit in the collet and tightening it down good.

[Ken Fitzgerald]

Mike,

I fighting the exact same thing on legs for a cherry candle stand I'm making.

In my case the router bit is walking up out of the collet. I'm a fairly good sized lad and relatively strong for my age. I've got that collet tightened down so tight, a little more I'm afraid I'll break it or the router. I'm going to try roughing the shaft of the bit with a little emory cloth to see if that will eliminate it's creeping.

Thankfully I milled some "test" pieces when I was milling the legs for the table so I haven't ruined any expensive wood yet!

[pat warner]

Lots of surprises making dovetails (http://www.dewalt.com/us/articles/article.asp?Site=woodworking&ID=511)on the router table.
Work has to be free of defects, flat and unform in thickness.
Fixturing, like most, should be rock solid, flat and hold the work firmly.
Hand feeding stock will be willy nilly. Whilst hand routing (router in hand)the things requires a lot more jigging; but you'll have some control.

[David DeCristoforo]

"Lots of surprises...on the router table...."

Whoever said that using power tools takes the uncertainty out of woodworking or reduces the need for skill and understanding should read threads like this one!

[Howard Acheson]

I was taught to first make the groove but to to do it in two steps. The first step is to rout out most of the waste using a straight bit. Then mount the dado bit and go back and cut the rest of the dado groove.

Next I always expect to have to adjust the bit height based on some preliminary cuts in some scrap I prepare identical to the thickness of the actual "keeper" piece if will be routing. Having to fiddle with both the height and the distance from the fence is a given.

[Edwood Ferrari]

Your tail cut as indicated on our drawing is 3/8" just as you planed. The pin cut is 7/16" so likely your bit rode up after the tail cut. You might notice the depth changing on that grove if you check it out with a caliper.

Btw using a straight bit to route out some bulk material is a good idea but a couple of things to keep in mind. be very careful with your depth setting when you change over the bits especially if you are making dovetails wider than your bit. Secondly be aware of the direction of your cut. Again not a problem with a single bit width cut but I have been shocked a couple times routing the edge closest to the fence with the dovetail bit and forgetting the bit was now rotating with my direction. The piece just flew off the table. Thank goodness I was using a push block. I make a lot of sliding dovetail joints using my Incra Jig. I also often overcut the width a tad if the joint is long and a bit too tight.

I also agree your boards need to sit square with the table to get consistant depths and you need to use feather boards to keep things tight.

Also a simple rule for dovetails. Heighten to tighen, lower to loosen the joint.


Ed