Need help with creating a tongue to fit in dado

[George Bokros]

Bellow is a picture of what I need to do. It is two pieces of 3/4" ply laminated together to become a vertical divider. I need create a tongue to fit into a dado on the case bottom. How would you do it? First off the ply is 95" long so doing it on the table saw is out of the question. I am thinking rabbeting bit but how would control demenison "A" so I know how wide to make the dado. I am doing this way because we know 3/4" ply is not 3/4,

Thanks


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[Ken Fitzgerald]

First, I'd cut the dado in the bottom. I am assuming the board for the tongue would be milled while horizontal. Use a straight edge to guide the router and the depth adjustment of the router to control the depth of cut on both sides of the board to produce the "width" (dimension A) of the tongue.

Practice on some scrap.

[Prashun Patel]

If you have a bushing and straight bit, you can build a 'plunge router dado jig' which is snugged around your tenon to provide a perfect template for routing the dado.

I use these for shelves all the time and it works perfectly. Alternatively, I can lend you my Domino ;)

[Davis Young]

I agree with Ken. Generally you want to make your dado (or mortise) first as it will be easier to size the tenon to fit the dado. Take care with a bearing bit as you don't want to turn the corner. Or go with a straight edge as Ken suggested but ensure its placement is accurate on both sides or you'll get uneven shoulders. A fence attached square to the straightedge will help with that.

[George Bokros]

First, I'd cut the dado in the bottom. I am assuming the board for the tongue would be milled while horizontal. Use a straight edge to guide the router and the depth adjustment of the router to control the depth of cut on both sides of the board to produce the "width" (dimension A) of the tongue.

Practice on some scrap.

The tongue would be milled while horizontal. I was thinking instead of a using a guide for the router use a bearing guided rabbeting bit. Ken has the right thought on cutting the dado first then I would know the exact width. Cut two dado's, one in the real piece and one in a test fit piece. I can and plan to cut the dado on the table saw so making two identical dado's would be easy.

Making the test piece and sneaking up on the required thickness of the tongue is the only way I can think to do it.

[Robert Engel]

A tongue and groove bit set (http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bit_tongue_groove.html) would make it alot easier.

[glenn bradley]

I'm also with Ken on this. A handheld router will follow the inevitable irregularities of your plywood and get you a controlled depth. I would get close on the first passes leaving a final "shave" to get the fit.

[George Bokros]

I'm also with Ken on this. A handheld router will follow the inevitable irregularities of your plywood and get you a controlled depth. I would get close on the first passes leaving a final "shave" to get the fit.


Only issue I see is that I would need a straight edge guide on both sides and have to get them in the exact same alignment. I do not want to take material off only one side.

[roger wiegand]

the ply is 95" long so doing it on the table saw is out of the question.

Huh? That's how I'd do it. Easier than messing with a router. I'd first make the dado then make the tongue in the the plywood with a dado blade in the TS (before laminating the two pieces of plywood). Final tune the fit with a shoulder plane.

[George Bokros]

Huh? That's how I'd do it. Easier than messing with a router. I'd first make the dado then make the tongue in the the plywood with a dado blade in the TS (before laminating the two pieces of plywood). Final tune the fit with a shoulder plane.


At 95" long I cannot handle it on the table saw. How do you support the piece, my table is only 29" to the left of the blade. How would you support the 66" off the table and push it straight into the blade?