# dado's with slip cupping



## gmack (Jun 9, 2013)

So I bought this dado set http://www.amazon.com/Forrest-DK06244-6-Inch-32-Inch-8-Inch/dp/B0000223VY

I am building a barrister's bookcase, and this dado is big bucks for me. 

I'm using 12 inch wide mahogany for the sides and at this width the guy at the this high end wood shop said everything will have a mild to severe cup. 

Well I didnt think it through because dadoing cupped wood is a joke. The dado is either too shallow or too deep at the side. I tried using a featherboard attached to the fence to push the piece down but it's still off an 1/8 of an inch in some places. 

As I'm sure your aware if the measurements are perfect the stackable sections are not going to line up if they are exact. I can't hide that. 

Guess I should've bought the router but doing finish carpentry with that scares me. 

Guys have any ideas or should I chalk this up to being a newbie?


----------



## woodnthings (Jan 24, 2009)

*I can think of 3 ways to fix it*

First, would be a rabbet plane or plough plane of 3/4" in width.
Anant Bullnose Rabbet Plane - Amazon.com


Second, would be a router with a small base to ride the over cupped edges. A trim router would be best:
http://www.amazon.com/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3Atrim%20router

Third would be to scribe the ends of the board to follow the cup, then remove the tangents off the board parallel to the scribe lines allowing the board to bottom out in the curve of the dado.

You can either fix the dado or adjust the board sorta thing....

Recutting the dado on either a table saw or radial arm saw would be difficult at best. Messed up at worst.

Hand tools are always an option if you are so inclined....a back saw and mortising chisel ..... 

Lastly rip the boards down the center flatten them out and reglue leaving a barely visible joint. :blink:


----------



## gmack (Jun 9, 2013)

Yea no question a router is the best option for this. 

The planer looks cool and would fix my problem but for 30 more bucks I can get a router. 

Thanks for the help.


----------



## Wood4Brains (Jul 25, 2012)

+1 for the suggestions for hand tools to fix up your dado cuts.

I did not realize that 12 inch boards were SO wide that they would all cup. I guess the solution is to go thicker than you need, let it acclimate to the shop, and then plane them flat??? :confused1:

~~~~~~

As for *NEXT TIME*, I would get a router and then get the Router Joinery book by Gary Rogowski and also check out the the Router Joiney BOOK from your Library (or get it used).

I don't think you will be scared of doing any trim or joinery work after watching the video. He makes it easy to understand what, and what not, to do.


----------



## amckenzie4 (Apr 29, 2010)

Honestly, I'd recommend getting flatter boards. I've worked with cupped lumber before for building shop furniture: You'll come to regret it. Shelves won't fit right unless you cut the ends to match the cup. The cup will likely be visible on the outside, and you'll find it harder to attach a back that goes on straight, since the back side of the case will be two boards that are angled slightly towards each other, not parallel to each other. That will make things a lot harder.

There are three good ways that I know of to flatten a board.

1) Get some decent hand planes.
2) Get a planer: 13" should do for your 12" boards.
3) Get a router, and build a flattening sled.

In any case, flatten the convex side first, then the concave side. That way the side that's down will always be stable where it rests on the bench.

I flattened a badly cupped 2x10 yesterday (about three feet long) with hand tools. It was for rough work, so I didn't really care whether the sides were precisely parallel, but it wound up around 1 1/4 inches thick and reasonably close to having parallel faces. If your boards are less cupped, you should be able to do significantly better.


----------



## FrankC (Aug 24, 2012)

I am still wondering why using cupped boards would be suggested by anybody at a high end wood shop.


----------



## woodnthings (Jan 24, 2009)

*Can we assume the boards are 3/4" thick?*

Any planing on those will reduce the thickness to thinness and they will be unusable in the dados previous made...just sayin'

A single rip down the center of each and jointing the edge, and regluing will not change the thickness, just the width by 1/4" or so. 

A double rip would work even better, dividing the 12" wide board into 3 pieces. I don't think planing away the cup is a permanent fix, in my experience. The grain structure and direction isn't going to change by reducing the thickness, and that's the real issue.

Sometimes I wish I could just say ... "Bring them boards over here and I'll fix 'em up for Ya"... :yes:


----------



## afx (Feb 5, 2010)

I agree with woodnthings, I would first make a shallow pass on the wood just to get a guide then use hand planes to plane it down to the correct depth. Since the rabbet plane runs across the cup it will be a consistent depth.

Either that or you need to buy 100 clamps and clamp the wood flat on a table leaving enough in the middle to run a router down the middle to make a dado.

Is it possible that you could screw a flat piece of wood to the bottom, then cut it and remove the screws and fill the holes?

Can you post a picture of what you're making because I think I'm completely off in my head.


----------



## woodnthings (Jan 24, 2009)

*if you're off in your head, leave me out of this*

:laughing:

Don't agree with me then leave the planet. We're either in this together or you're on your own ..... :blink:

.
.
.
.
.
.

i have no idea what you just said..... :blink: :boat:


----------



## gmack (Jun 9, 2013)

frank C wrote:


> I am still wondering why using cupped boards would be suggested by anybody at a high end wood shop.


I am too and I'm pissed. I asked about the cupping, he said that wood this wide (12 inch) will always cup. The cupping is mild but I still can't get an even pass with a dado blade. Makes me even more frustrated that I go to Home Depot to pick up some lawn stuff and I check out their 12 inch oak and it is straight as an arrow. 

I will add I tried the useless method of wetting the convex side and leaving in 80 degree sun...did nothing. 

Grunkle, thanks again I'll check out those books and get a decent router. I need more practice and to do more research just as simple as that.

Look below at what I was trying to build. the plans calls for a dado for top, bottom, and back


----------



## FrankC (Aug 24, 2012)

Not sure how far into this you are but using ply for the sides and shelves is an option, you will still need solid wood for facing but that will be narrower stock and cupping should not be a problem.


----------

