Dado thickness question

[Chris Cobb]

I'm new to woodworking. I'm having fun making mistakes and piles for the trash as I play with my new tools and stuff. :)

So, today - I experimented with my dado blade on the TS. I got it set up for 3/4 plywood (23/32, I suppose I should say). I ran some test cuts in some pine I had lying around to ensure the fit was appropriate. Once I got that done, I then cut a dado in some 3/4 plywood for a cabinet I'm trying to make for the shop.

Here is what I found - the dado width that fit great when cut in the pine was too narrow when that same width was cut in plywood.

How does that happen??? The same piece of 3/4 plywood that fit in the pine dado did not fit in the pylwood dado (when cut with the exact same set up).

I'm sure I missed something, but it eludes me. To get the dado correct - I just bumped the fence over a tad until I achieve the good fit, so it was not a probem, but it sure seems strange to me. :confused:

thanks
Chris

[glenn bradley]

Shot in the dark . . . the dado is greater than half the thickness of the pine and it opened up a bit where as the plywood would not(?). OK, like I said, wild guess.

No reason for this to happen if the material is stable. Did the ply cut leave behind fuzzys that need to be cleared? Quick fix; do your test cuts in the same material you plan to use for real. I've gotten bit by this once or twice as materials do behave differently.

[Bob Barkto]

I've had that happen...

when the edge of the piece wasn't straight. You get some "healing" in the cut. Can happen if the fence isn't straight too.
Normally the dado will be wider at some points, like just the ends, or just the middle.

If the dado width is consistent then I'd think the wood moved a bit. Check the board for cupping. Very common for pine lumber to get "lively" when cut!

[Bill Huber]

I was having the same problem when I built my shop cabinets, I don't understand it but I had the same thing. I even had the problem when I cut the dados with the router.

What I started doing was to make my test cuts in the same wood I was going to use and had no more problems.

Like was stated I am sure it has something to do with the way pine heals as opposed to the plywood.

[Greg Funk]

Were you using a miter gauge or the fence? If you cut your pine with the miter gauge then it is quite likely that the wood moved during the cut resulting in a larger dado. Try using the fence only and see what happens.

Greg

[Doug Shepard]

I'm guessing that in addition to some of the other replies that your test cut in pine was over a shorter width than your final cut in ply? All those little variances can let a narrower piece slip on snugly where a wider one wont go. If the ply isnt totally flat that can also compound the problems.