Ok, I Give

[Byron Trantham]

There have been several threads discussing the fact that plywood comes in various thicknesses (undersized) all claiming to be 3/4" or 1/2, etc. I just run into the opposite. I am cutting datoes in 3/4" melamine. Did a test piece (thank God) and found out that the stuff is 1/64" over sized!!!!! :mad: A 3/4" router bit will not cut it wide enough to join two pieces together. Am I forced to make two passes with say a 1/2" bit to get the clearance (width)? These boards are 13" wide by 6 feet long and won't work too well on the TS. Two cuts are 17" from the ends and the middle one is about 34" from the end. I think the table saw approach would be too risky.

What about removing the thin melamine layer using the table saw? "Just skin it". Man why can't the mfrs get their act together.

Very frustrated!

[Mark Mazzo]

Byron,

As I understand it, you used the router to create the dado's (but they are 1/64th undersized). I assume that you used a straight edge guide to position the router when you did this. If so, you could try a layer of masking tape along the guide and re-routing the dado with the same bit. If you need a little more width than one layer of tape gives you, you could try two.

-- Mark

[Tim Sproul]

Byron....


easier method, regardless of what you are working with - solid wood or engineered wood product - is to BUILD TO FIT.

3/4 MCP has always been slightly oversize......the plastic melamine coating takes up some space....they start with 3/4 particleboard...which is fabbed to be darn near close to 3/4 thickness and then add melamine to one or both faces.

[Lars Thomas]

Bryon, not realy sure what Tim means by 'Build to Fit', but . . .I would do exactly as Mark suggested. If you have several dados to cut (sounds like you only have a few), you could cut two spacers. One at 1" and the other at 1-1/64". Make your first pass with the the router up against the 1" piece (which is agaist your choice of straight edges), then take your second pass against the 1-1/64" piece (again, agaist your straight edge). That should take care of it. Let us know how it goes. Lars

[Tyler Howell]

[ try a layer of masking tape along the guide and re-routing the dado with the same bit. If you need a little more width than one layer of tape gives you, you could try two.

Good Answer, Good Answer! Thanks Mark, You made my day. I can use that.:)

[Lars Thomas]

Tyler, masking tape is one of the most used 'tools' in my shop! :) There is almost always a roll on my bench - buried under everthing.

I use it a lot when machining multiples of parts. Try it when you need to miter frames. Tape opposing pieces together and then cut. You'll be guarenteed to have square-er frames.

[Byron Trantham]

You guys with the masking tape have the right idea. My wife gave me a plastic 3 ring binder whose thickness is 1/64"!! :p All I have to do is keep track of which side I made wider so all the slots will align. You guys RULE!

[Tyler Howell]

Tyler, masking tape is one of the most used 'tools' in my shop! :) There is almost always a roll on my bench - buried under everthing.

I use it a lot when machining multiples of parts. Try it when you need to miter frames. Tape opposing pieces together and then cut. You'll be guarenteed to have square-er frames.I use it a lot too! I tape up other peoples work and tools on the wish list:D .
Thanks Lars. Please say more about the mitered cuts. I'm not grasping the big picture.:confused:

[Dean Baumgartner]

Byron,

As I understand it, you used the router to create the dado's (but they are 1/64th undersized). I assume that you used a straight edge guide to position the router when you did this. If so, you could try a layer of masking tape along the guide and re-routing the dado with the same bit. If you need a little more width than one layer of tape gives you, you could try two.

-- Mark

Mark,
That's one of those suggestions that should be in the tips and tricks section of one of the woodworkers magazines. You should submit it and maybe win some new toy.

Dean

[Tim Sproul]

Lars,

Build to fit means exactly that.....I've rarely run across a bit and a piece of plywood that are matched perfectly for the stock I'm grooving.

Are you all unfamiliar with the idea of an adjustable dado jig for the router?

http://taunton.com/finewoodworking/pages/w00040.asp

there also used to be a Pat Warner video freely available on a similar jig.....Use a dollar bill or other thin shim to give enough clearance for glue and to accept the male member of the joint. The amount of clearance is dictated by the stuff you are grooving. I find these types of dado/grooving jigs much more accurate and much more flexible than crossing my fingers that the plywood bit and plywood will match....

[Mark Mazzo]

Mark,
That's one of those suggestions that should be in the tips and tricks section of one of the woodworkers magazines. You should submit it and maybe win some new toy.

Dean

Dean: Thanks, but I'm not sure it would win any awards :D

Tyler: No problem. Just trying to pass along some help, since I've been on the receiving end so many times.

Lars: I think that Tim is suggesting another method that would work whereby you would use "zero clearance" fences. This is a fence made with an oversize a layer of hardboard below that is cut to size with the router. If you make two of these and then sandwich a piece of the shelf in between the two with the edges along your layout marks, the resulting dado will be exactly the thickness of the shelf. You can get away with using a narrower router bit,too. I didn't suggest this to Byron because he had already cut the dados ;).

-- Mark

[Lars Thomas]

Tim, I checked out the Taunton link. I see what you mean. I like that idea too. That's pretty slick.

Tyler, as for the frames, take the two opposing sides and tape them together. Then cut you miters. In doing so, the side will be exactly the same length. IMO, it's different sized sides that cause gaps, more so then missed 45's. Does that make sense? If not, I'll try to draw a picture and post tomorrow.

[Steve Jenkins]

If you need to shim the cut just a smidge like you are talking about instead of putting the tape on the straight edge put a short piece on the router base. Then all you have to do to cut the dado is run the router up the straight edge rotate until your shimmed spot is against it and run back the other way. Bingo dado cut in with one setting. If you do a lot of this kind of work you could even use get or make an extra base plate and build out one area with bondo then file it down until you get that perfect fit. Mark the base for the material it's sized for and just put it on when you need it.Steve

[Byron Trantham]

And the winner is...? Steve Jenkins!!! I have been thinking about the various suggestions and yours makes the most sense. I like it. Thanks.

[Tom Hintz]

Byron,
This is a common thing, and ot just recently. I have a plan for an "Auto-Width Dado Jig" (link below) that is an updated version of the one an old-time woodworker who lived behind me 20 years ago used because he was sick and tired of odd-thickness wood back then.
If I don't have the exact bit or stack setup for a piece of wood, I whip out my jig and cut the dados that way.

http://www.newwoodworker.com/autodadojigpln.html