Dado Tips

[Arcrist]

Now that I've done about 20 of these, with a high failure rate, I thought I'd ask you guys for some advice.

Say Im joining two boards. I run one board over the straight bit to get the grove. Usually I can get the grove center. To get the tongue part though, is there an easy way to do that with the straight bit? I find myself shredding a little bit on each side until I get the right fit, but its always off center.

Also one more question, is there a way to not have that lip overhanging? Here's what I mean: http://dreadcraft.com/pic.JPG

 

[Arcrist]

I think I just figured it out. If i cut the tongue part first, I can see how much width is left on each side of the tongue. So then just cut the grove that distance from the edge of the board. Right?

 

[Monty]

Cut the groove first, with a single pass of whatever diameter bit suits your needs (assuming you're using that nice new router table setup!)... then you know how wide to make the tongue so it fits the groove. Just to point out... the tongue does not have to be centered. In fact, you can remove all the material from one side and have the tongue just on one side -- that would make it a rabbet, which looks nice and is much simpler to size!

(sorry for the big pic... )

 

[Steve D]

If you do want to still make it a tongue, you would still want to make your groove first. youwould then route one side the depth you want to control (offset). Once that is established, flip the board over and workon sizing the tongue to fit the joint. Make your second to last cut about 1/32 shallower than you need and then make a final pass that is a very shallow cut.

 

[Arcrist]

Ah ok, ill try that. Im takin a break for a few minutes now cuz my toes are freezing, being out in the garage for a few hours.

Ill use this time to update my site with my new router and project pics.

 

[Mtnman]

Andy, cut your grove where you want it first. Then cut the tongue. Cut each side of the tongue in alternate passes adjusting the fence to get a good fit to the grove. Alternate passes on each side of the tongue will keep it centered automatically, just sneak up on it slowly. Once you get it snug you have it set for more tongues if needed. Just be sure all your stock is the same thickness, and do the setup on a test piece.

 

[DavidF]

Andy; cut the groove first. Make a small short temporary tongue piece that is a snug fit in the groove. Bring this up to the router bit and raise the bit until it just scrapes the tongue; this is the setting for the face side of the real tongue - see my posting on "back to basics" regarding face and edge marks. Put the face mark down on the table with both pieces of wood and they will line up perfectly. Once that cut is done, flip the stock and route the other side of the tongue, creeping up at the end until you get a snug fit. This way you groove does not need to be in the middle.

 

[Arcrist]

Ok im getting confused again. I cut the grove near the edge based on how thick the joining piece is right? Say I am cutting 1/4" grove. I need a piece thats obviously atleast 1/4" thick. So if the tongue board is 1/2" I cut the grove board 1/4" from the edge, leaving the 1/4" tongue in the grove and the remainding half matching up with the edge.

Im a complete visual person, I cant picture things by reading about it. If i see it done, I can do it.

 

[DaveO]

Andy, what exactly are you trying to accomplish. If you are setting a bottom in a box, the groove should be a little above the bottom of the box. If you are setting a top flush in a box the cut a rabett and set the top piece in it. If you are doing a divider or shelf then the dado is the width of the board or you can also do it like Insom illustrated. Some more specifics might help to get you questions answered.
Dave

 

[Arcrist]

Im just trying to understand how to get a flush edge. Using the tongue style in the drawing above, but doing a grove at the bottom. I can get it done if I waste a lot of wood, but whats the right way to do it?

This might help: http://dreadcraft.com/drawing.jpg
the bottom of the grove board and the bottom of the tongue board, how do you make sure they're even?

Because I have to reset the routers fence to do the tongue after the grove. Is shaving a little bit off each time the only way?

 

[Monty]

Like this:

 

[DaveO]

OK that gives a little more insight into you problem, not the application, but it's a start. Say you are working with 3/4" stock. Set your router fence a 1/2" away from the closest edge of a 1/4" straight bit. Set that bit for a 1/4" height. Cut your grooves on all pieces with the stock lying face down on the table (outside up). Then re-set the fence to be a 1/4" away from the farthest edge of the bit. The fence should touch the closest bit edge (split it away from the bit if you don't want to or shouldn't cut into the fence). Set the bit height for 1/4" and run a first pass on the face side of the piece that you want to be flush. Then adjust the bit to be at 1/2" height and run a second pass. That should result in a groove 1/2" from the top of the "sides" and a tongue 1/2" from the face of the "top". Practice each cut on scrap to test your settings once dialed in perfectly cut your good stock. Clear as mud???

Dave

 

[Arcrist]

Thats kind of clear. It also comes down to the ruler built on the table top. That thing throws me off. If its set on 0 (zero) with a 1/4" straight bit, only half of the bit should be cutting right? So when I want to take 1/4" off the end of a board in doing a rabbit cut, I have to account for the blade too right? So I'd set the fence for 1/8"?

Its been a long day, maybe Ill have some dream about this tonight and wake up with new knowledge. I've actually done that before, I was dreaming about diamond-back snakes and somehow woke up knowing that a diamond-back is rattler. I checked online and sure enough I educated myself in my sleep!

 

[DaveO]

I never rely on the measuring tapes on tools unless I know that I have zeroed them out and that they are accurate. Get a small 6" metal rule at the BORG (the kind with the stupid pocket clip) and verify your set-up with it, it measures to the 64th and that is precise enough. Once you have determined that everything is dialed in then you can trust the built in measuring systems. Follow what I previously wrote and measure everything and I bet you'll be dead on.
Dave

 

[Monty]

I think this is how I would do it... same idea, just uses a dado blade to make the rabbet, and results in a dado & rabbet joint like the second picture I posted above...

Use a ¼" bit on the router table, and the only thing you have to worry about is making sure the distance between the edge of the dado (farthest from the fence) and the end of the stock is exactly the same as the thickness of the mating piece (hold the mating piece up over the bit to help set the fence). If you get that step right, then you can make a rabbet in the other piece that lines up at the edge like you want it to.

Bottom line is, I think trying to make a tongue that is centered in the end of the board is really making the problem seem more complex than it needs to be.

 

[DavidF]

Still on this topic! The fence position in step 3 only affects the length of the tongue and therefore does not affect the alignment of your pieces. In fact if the groove was made 1/2" deep in step one the fence position would not need to change for a perfect fit for 1/4" wide groove, 1/2" deep and a 1/2' long tongue set 1/4" from the face.

 

[Arcrist]

I still dont get it, DaveO maybe I can stop by again sometime this weekend and get some help. Again, I can do what we're talking about, I can only do it by trial and error.

 

[DaveO]

Andy, you are always welcome to drop by any time:-D

Dave