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Shop Made Router Jigs #1: #1: Router Table Jig for Box and Dovetail Joints

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Blog entry by Warren posted 11-28-2018 09:31 PM 683 reads 0 times favorited 2 comments Add to Favorites Watch
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Intro
I started woodworking about 25 years ago when my boys were in grade school and got interested in aquariums. We bought some used 50-gal aquarium tanks but did not have stands. At that time, my tool inventory included a radial arm saw, router, and a circular saw. I wanted to ensure that the aquarium stands were sturdy enough to support the ~400 lb. weight, so I settled on a frame with box joints. I had no way of cutting box joints, so I came up with an idea that had a screw driven carriage with an attached fence that moved along the edge of my home build router table. It worked well enough to make several tank stands, but mostly it sat in the corner of my garage collecting dust.

Fast forward to ~2015. I was retired and had finished building my airplane and needed a new outlet. I gradually started doing more woodworking and collecting more tools. I had an old table saw, then a new table saw, several routers, planer, drum sander, dust collector, etc. I had been making things like cutting boards, pizza peels, serving trays and the like.

The trays I had made had simple miter/spline joints, but I really wanted to make through dovetail joints. The problem was that I did not want to spend the $$ on a fancy dovetail jig, and, as I relearned once again, I can neither draw or cut a straight line so hand cut dovetails never worked for me.

I reviewed Sandor Nagyszalanczy’s description for a table saw jig for dovetails (http://www.woodworkersjournal.com/table-saw-dovetail-jig/), and I built this jig. I was not happy with the results though – too much eyeballing for my tastes. I then looked at Matthias Wandel’s jig (http://woodgears.ca/dovetail/jig.html) and James Hamilton’s router table jig at http://www.stumpynubs.com/dovetail-jigs.html.
I decided to take a little bit from each of these designs and create my own precision jig that was capable of cutting box and dovetail joints. My oldest son just happened to buy a Grizzly G0836 which is what really made it possible for me to build this jig the way it is. I have no doubt, though, that a most of this jig could be made from wood components without the need for machining.

Box and Dovetail Joint Jig

I realize that this approach to box and dovetail joints will not be everyone’s cup of tea, but here goes.

The jig is shown in Fig. 1-3 and its key features include
• Box frame of ½” MDT: approximately 6” X 6” X 18” overall
• ¼” Aluminum screw driven (3/8” X 16) carriage plate
• 1/8” X 2” steel angle clamping mechanism
• V-groove bearings that support the carriage on V-rails
• 12” Digital read-out
• 1/8” X 2” guide bar with a pivot hole and three holes to align the guide bar at 90⁰ for box joints and dovetail slots, and 90⁰+-8⁰ for cutting dovetail pins

The box frame provides for a rigid frame for V-rails and associated V-bearings (4 for $14 on eBay). The ½” MDF frame is assembled with ½” Al angle and machine screws; the screw holes are drilled a little oversized so the fit and alignment of the carriage plate and V-bearing can be adjusted resulting in the carriage plate being square with the bottom of the frame, and no wobble of the carriage as it moves along the rails.

The carriage plate was cut and machined from ¼” Aluminum. A hole pattern was drilled and tapped into the carriage plate for all the components attached to the carriage including the V-bearings, sacrificial backing board, angle brackets for the 3//8”X16” carriage screw, the 1/8”X2” side plates for the workpiece clamp, and the DRO. The V-rails were milled from ½ X ½ 1/8 Al angle.

I used a 1/8” X 2” steel bar for the center guide bar rather than T-track. I already had a couple of T-tracks in my router table, and I did not want to cut slots for another one. Additionally, I needed a wider guide than a T-track to accommodate the hole pattern in the guide bar, so the jig could pivot +&-8⁰ for cutting dovetail pins.
You can see the guide bar in Fig. 2 and 3; it can pivot around a bolt near the carriage plate. The other bolt shown in Fig. 2 is used to set the guide bar at either the 90⁰ position, or the 90⁰+8⁰ or 90⁰-8⁰ position. The hole pattern in the guide bar can be seen in the left photo in Fig. 3. In use, the whole fixture slides fore and aft with the fixture guide bar between the two fixed yellow guides.

The jig is fitted with a 12” iGAGING DRO that purchased on Amazon ($32). With the brackets attached, it is ~17” long. The sensor module is attached to the carriage plate. The DRO seems to be good to ~+.002” or so. Also, I used a lock type washer on the left end of the 3/8X16 screw where it protrudes from the frame to minimize screw backlash, thought a few thou of backlash remains.

The clamp mechanism made up of two 1/8”X2” steel side bars attached to the edges of the carriage plate; These bars have slots cut into them to accommodate a piece of 1/8” X 2” angle. I trimmed off ~1/2” of one leg of the angle so it can fit into the slots in the side bars. A workpiece is aligned to the side bar and clamped to the carriage with one of the ¼-20 screws in the angle bar. A side clamp is needed sometimes needed to keep the workpiece tight against the right-side bar.

I recall spending about two afternoons machining all metal partsfor the jig, which included the 6”X6” carriage plate, the clamp parts, and angle brackets for the 3/8X16 screw. I thought this was pretty good since I had not touched a milling machine in 30+ years. Also, the only components I had to buy were the V-bearings, and the DRO. Everything else I had in my scrap bins.

Cutting Box Joints

The first step to use this jig, is to clamp the guides for the guide bar to the top of the router table. See Fig. 1. I used a 36” yellow steel yard stick, cut in half. With both guides in place, it is easy to adjust the whole assembly so there is no play between the guide bar and the yellow guides, and the whole thing moves easily and smoothly

Next, choose a router bit, and set the bit height about the table top. In the example here, I used a ¼” straight bit, and set it so it sits a little proud for a 3/8” workpiece.

Next, clamp the workpiece to the carriage plate, and find the position where the router bit just touches the edge of the workpiece, and zero the DRO; consider this the reference point for this set-up. You can find the edge either by and moving the carriage until you see it begin to cut the workpiece, or what I prefer, is to use a feeler gauge with the router turned off. See Fig. 4

The DRO makes getting the correct spacing of the box finger easy. On my first jig built 25 yrs ago, I just counted turns, but it is surprisingly easy to loose count, especially on larger workpieces. On the first part for a box joint, make a cut ¼” into the workpiece, then move the carriage .500”, make a cut, and repeat until all cuts are made; see Fig. 5. On the second part, advance the carriage .500” from the ‘zero’ reference point, make a cut, advance the carriage another .500”, and repeat. See the left photo in Fig. 6.

Fig. 7 also shows the dry hand fit of parts as they came off the jig from outside and inside. No trimming, and no mallet needed to fit them together

Cutting Dovetail Joints

Before cutting the dovetail slots, it is helpful to same some sort of layout diagram. For the slots, I use a diagram like that in Fig. 7. You need to take account of the workpiece width and dovetail cutter diameter. In the example shown, I use 3 5/8” for the workpiece width, and a 5/16” diameter cutter – the smallest I have found. Then layout the dovetail slots the way you want it to look.

Cutting the dovetail slots is similar to cutting the box joint shown in Fig. 6. Just make note of how the dimensions are referenced – in my case, the dimensions are referenced from the center line of the router bit and the edge of the workpiece. In other words, start by aligning the center of the bit with the edge of the workpiece and go from there.

Similarly, I make a diagram for cutting the pins as shown in Fig. 8.

With layout diagram in hand, set the jig by swiveling the fixture to the left 8⁰, clamp the workpiece in the fixture, set the router bit height above the table, and align the router bit with the edge of the workpiece. Aligning the edge of the workpiece with the edge of the router bit is a little different than w when cutting a box joint due to the fixture being angled 8⁰. Thus I use a feeler gauge. See Fig. 9 and 10. [Note: the dimensions in the layout diagrams are from left to right, whereas as shown the photos, I cut the slots and pins from right to left. Somehow my aged brain is just fine with this arrangement.]

Thankfully, you do not need to dust off any trigonometric brain cells to do this—just simple arithmetic will do, and a spreadsheet is helpful for minimizing arithmetic errors. All pins are cut with a straight ¼” diameter bit. The dimensions in the table in Fig. 8 assume the edge (not centerline) of the router bit is aligned with the edge of the workpiece.

Once the edge of the workpiece and router bit are aligned/just touching, move the carriage to the dimension in the table in Fig. 8 using the DRO, and make the left cuts, Fig. 11; when all left cut have been made, swivel the fixture right 8⁰, and make all the right cuts, Fig. 12. You can then remove any remaining waste between the pins. The DRO allows one to make cuts that are acceptably accurate for both box and dovetail joints.
Photos of the pins and the assembled joint are shown in Fig. 1. I am pleased with the results and I have made a number boxes and drawers using this apparatus as shown in Fig. 14.



2 comments so far

View waho6o9's profile

waho6o9

8674 posts in 2997 days


#1 posted 11-29-2018 02:03 PM

Awesome

View Warren's profile

Warren

19 posts in 807 days


#2 posted 12-22-2018 10:23 PM

Here is a video of the jig in action here

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