I didnot write this, Skeeter did. Hope he doesn't mind me using it.
Sounds like your lip has too much cleareance to start with.
Coley
Skeeter says,
Personally I try to get as tight of a fit that I can. The reason is because as long as the slot is square, then as the epoxy cures it can cause the lip to twist and not be at 90 degrees with the top and bottom of the lure. If you are having a hard time with the blade twisting in the saw while you cut the slot then try tightening the tension of the blade alittle. The rest is practice. Just take your time. I draw the outline of the bait and then draw the slot on the center line. I draw the slot 1/2 inch back from the nose of the bait. For angled lips I use the 1/2 inch mark to draw the bottom line for the slot. In other words let's say you want to draw a slot for a lip that is at 30 deg. Draw your center line through the bait from nose to tail. Make a mark on that line 1/2 inch back from the nose. From that mark draw a 30 deg. line to the bottom edge of the bait where the lip will exit. If you are using 1/16 inch thick material for your lip then measure 1/16 from that bottom line and draw another 30 deg. line. This is the top of the slot. Then make sure that the slot is 1/2 inch deep,even if you draw the end of the slot above the center line. Get a fine toothblade for your band or scroll saw. I use a scroll saw and use blades that are meant to cut PVC pipe. Now, very first thing..... cut the slot for the lip. Then cut out the rest of the bait. Once you have rounded the lure and sanded it to shape, the lip slot will be about 3/8 inch deep. You need this much glue surface for the lip and slot. If you are using a hard wood then you will need to make a channel in the middle of the lower lip of the slot for the wire used in your line tie to slide into. With balsa you can just push the lip and wire in and it will just cut its own slot into the wood. Drill a 1/32 in hole into each corner of the lip and get your epoxy down inside those holes, this is a glue point and will secure the lip like a post once it cures. Hope this helps you.
Skeeter
Skeeter