The problem is that I'm not sure there is a standard for finished ply. It starts out rough and then it gets sanded smooth. That's why it winds up under size. To make matters worse a lot of what I've seen lately is metric thickness to start with I think. Your best bet is probably to use an smaller bit and go with one of the exact thickness jigs that have been posted.
Undersized ply router bits.
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Charles that is what I was thinking of. The bad part is I spent $52 for the 3 bits and now I don't need them.
Someone got my money tree this winter. I may be wrong but it might be Theo that got it. >
:laugh2:Just kidding Theo.
Sure wasn't me, I'd have been bragging about it if so.Charles that is what I was thinking of. The bad part is I spent $52 for the 3 bits and now I don't need them.
Someone got my money tree this winter. I may be wrong but it might be Theo that got it. >
Just kidding Theo.
I work mainly with 1/2" plywood. The few times I need to cut a slot to fit plywood into it, I usually tack a strip to rout a straight line, then mark how wide I want it to be, tack down a strip, and rout that side. So far that gives me just the widths I want, with a snug fit. Used to do a lot of that when I was making my small figure banks. Best I can come up with, because that's the way I do it, it works for me, and not likely to change. I tack everything down, I don't worry about nail holes, because I make sure they will be hidden when whatever is put together. No need to replace tape when it runs out either, a box of nails should last me forever.
All nice jigs, but the downside to jigs like the first shown is that they're "mated" to a specific router - which may or may not be a problem. Another potential problem is that the axis of the collet may not be on the center of the base - an easy check if you have the time. The cure for that is to mark the router and jig so that the router is always used with a marked point on the base touching the guide surface of the jig - or make a sub-base, either square or round, where the bit is perfectly centered on the base, a fairly simple exercise. IMHO the jig shown last is the better choice as the use of a guide bushing makes it suited for use with any router in the shop - just mark the jig with the diameter of the bit and guide bushing used.
The T-square jig shown has the same drawback if the "notch" on the base leg is used to locate the groove to the layout mark in that the router used, and the orientation of the base in case it's not symmetrical, is important. Additionally, it doesn't address the need for a groove which doesn't match the diameter of the router bit being used. While still having the drawbacks stated above, this tip I saw in a recent copy of "Woodcraft" magazine would allow you to cut an exact-fit dado using a smaller bit and two passes as in the other designs. I built the T-square shown, but haven't had a chance to try it out yet.
The T-square jig shown has the same drawback if the "notch" on the base leg is used to locate the groove to the layout mark in that the router used, and the orientation of the base in case it's not symmetrical, is important. Additionally, it doesn't address the need for a groove which doesn't match the diameter of the router bit being used. While still having the drawbacks stated above, this tip I saw in a recent copy of "Woodcraft" magazine would allow you to cut an exact-fit dado using a smaller bit and two passes as in the other designs. I built the T-square shown, but haven't had a chance to try it out yet.
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No one is going to pry me from my DadoWiz! Exact fit, runs on a straight edge clamp, uses a down cut spiral bit. No longer made, but what a great tool. Stopped dados are a breeze. Clamp the guide down and it delivers a very clean groove. I slide a piece of paper in with the sample piece of wood to give a little room for glue. Learned not to pull the router up when it's still running on this jig; the damage was minimal to the aluminum block of the jig, but the spiral bit was a goner. Other than that, I also like this type exact fit jig with a bearing guided mortising bit:
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