Dado jig - 'exact width'

[Henry W]

There's nothing 'original' here, I just thought I'd post in case others had not considered such a jig. I suspect others (Joe Scharle, the jigmeister) have posted something like this back in the archives, but pics haven't necessarily migrated to the new platform.

Anyways, I am working on a sheet good project, something I haven't done very often. I need to dado shelves into the sides of a 3 unit set of built-in bookcase/cabinets. So I needed a consistent method to dado.

Many 'exact width' use the concepts of
1. an undersize bit and two passes to establish the two sides - I do this too
2. using the actual material to set the width of the jig - I also do this.
The few videos I watched (Wood Whisperer and other similar ones) were helpful in establishing the types of pieces needed and general dimensions. However they all seemed to use either a bushing or the router plate edge to establish the position, and quite frankly did not appeal to me. Doing so requires use of the same router/bit combo, or bushing/bit combo, each time.

So I purchased a top bearing 1/2" wide bit from Klingspor's (1/4" shank was the only way it came) and used that. So far it has worked flawlessly.

Hints from videos that I found useful were:
1. Clamping the piece into the jig to establish a tight fit dado.
2. Clamping the jig onto the piece helps maintain position
3. Ensuring the reference surface is straight and flat will help.

Here's a few pics of the jig in action; 2nd one shows the top bearing bit.
Sorry, not the greatest pics for a fully explanation, but if you want that there are more than a few videos to see. I wanted a jig that could lay flat on a bench and so put the slots below and the knobs above. THis will handle a 24" width, so I am cutting the shelf sides, then ripping to width. Should ensure perfect alignment.

 

[Yelverton]

The few videos I watched (Wood Whisperer and other similar ones) were helpful in establishing the types of pieces needed and general dimensions. However they all seemed to use either a bushing or the router plate edge to establish the position, and quite frankly did not appeal to me. Doing so requires use of the same router/bit combo, or bushing/bit combo, each time.

So I purchased a top bearing 1/2" wide bit from Klingspor's (1/4" shank was the only way it came) and used that. So far it has worked flawlessly.

Great idea to use a top bearing bit instead of a bushing. I made one of these with the bushing style and it seems like I can never get the bushing/router plate exactly centered, so my results aren't what I'd like. I may have to modify my jig a little bit to work like yours.

 

[Henry W]

.... I made one of these with the bushing style and it seems like I can never get the bushing/router plate exactly centered, so my results aren't what I'd like. ....

That's exactly what I wanted to avoid. I mark one side of the dado and position the jig where needed, clamp it down, and run the router through (several times) on each side. Remember I am using a 1/2" bit here for what is nominally 3/4" plywood.

I might note that I also used the Wood Whisperer's implementation of hardwood strips for the working edges of the jig, rather than plywood edges. Can't recall if others do that, but that's where I saw it. These are thick or wide enough to be resurfaced (which I have had to do once already - dinged one side by removing the router with a moving bit....).

 

[junquecol]

I go a different route. Having made thousands of feet of cubbies for local "Y's", I have cut more than my share of dados. I use a piece of 1/4" plywood with a fence (3/4 stock) attached. Use the router to trim plywood to exactly where the bit cuts, similar to making a saw guide. Use them in pairs. Have a special router set up to do these cuts. It has never been used for anything else. For bit, I use a reverse helix bit from HerSaf (no longer in business.) It uses a screw on cutter. Still using the first one I bought, even after 20 years of service. They were designed to go on panel routers, cutting melamine panels.

 

[mkepke]

I do the same as Bruce. I don't have a router dedicated to the job, so I simply wrote the router, bit and orientation of the router onto the jig.

Clamp the edge of the guide onto the cut line and go...

-Mark

 

[Henry W]

... I use a piece of 1/4" plywood with a fence (3/4 stock) attached. Use the router to trim plywood to exactly where the bit cuts, similar to making a saw guide. Use them in pairs. Have a special router set up to do these cuts. It has never been used for anything else. For bit, I use a reverse helix bit from HerSaf (no longer in business.) It uses a screw on cutter. Still using the first one I bought, even after 20 years of service. They were designed to go on panel routers, cutting melamine panels.

I do the same as Bruce. I don't have a router dedicated to the job, so I simply wrote the router, bit and orientation of the router onto the jig.

Clamp the edge of the guide onto the cut line and go...

-Mark

And how do you deal with undersized plywood? "Use them in pairs" means you set up and clamp two pieces - one for each side of the dado? That would be tiresome, and for me possibly error producing (non-parallel sides).

I don't have dedicated router either, but this approach does use a top bearing bit. Once set up for the shelf material thickness, I have been able to cut all my dadoes for this project without resetting the width, and I use one clamp to position it. I checked for square a bunch of times, until I was convinced that it would set square when properly positioned - of course particles between the edge piece and the plywood can throw that off, so it's worth checking.

Of course there are many possible paths here - and I highlight one that has worked for me so far. Of course others use different methods, and options are always great to hear about.