I built a William Ng Box Joint Jig a few years ago. I was not thrilled with the way you had to adjust the pin, just not accurate enough for me and took way too much time even though William made it look easy.

 

The first thing I did was make a better way to hold the back board to the sled. I drilled a couple of 1" holes and in the corresponding place on the back board I counter  bored for 1/4"-20  carriage bolts. I turned some knobs and counter bored for the nut. Now I didn't need to have a clamp in my way when making the box joints and I could adjust the back board very easy.

 

Next I wanted a way to move the back board by a couple of thousands precisely. I took a couple of pieces of 6061 aluminum and countersunk for some deck screws and tapped for a 1/4"-20 set screw. I made sure the screw heads were not past the back board. I used a wing nut and a regular nut to lock the wing nut on the half dog point (flat tip) setscrew. Now I can crack loose the lock knobs and back off one screw a tad and tighten the opposite one and move the back board a couple of thousands. Sure made it easy to dial the pin width to match the dado stack minus glue clearance. I use aluminum but hard wood would work fine but when your a machinist and have a machine shop you can't help using metal.

 

Yes the box joint jig is sitting on my William Ng sled which I use more than I assumed I would.

 

 

A test box joint.

 

The back board is for 3/8" dado stack and all you would need is another back board for other sizes.

 

The first cuts are on the front and back starting at the bottom. The arrow points to the bottom of the drawer side.

 

The first cut on the sides you reverse the front or back and place it over the pin then make the first cut on the side. Arrows point to the bottom of the drawer side on the left and front on the right. This gives you a perfect fit on the side.

 

By cutting this way you don't have an holes in the side of the drawer from the bottom dado cuts. I just happen to have an unfinished drawer to show how that works.

 

It almost seems like this should go in a general woodworking jigs and fixtures sub section...

 

JT

Other than needing to install a dado blade set each time, this jig looks like it does a good job.  

At the university where I teach (taught) we have a jig that mounts on a router table. Uses a piece of 3/8" key stock embedded in a 1/2" (12mm) thick bb plywood.  A 90 degree sled has a slot in the bottom to slide on the keystock. BB plywood and bottom of sled are coated with wax to slide easily.  Jig is clamped down on the router table with the keystock 3/8" away from an onsrud 3/8" spiral upcut endmill. Set the bit height above the jig to the thickness of your boards being used. Stand boards up on the sled to push through the spinning bit. Step over the keystock for successive cuts. 

Similar jigs made from 1/4" keystock  use a 1/4" bit for smaller fingers.  For big projects and 1/2" fingers we've got one with 1/2" keystock and use a 1/2" spiral router bit.   

Of course I often cut finger joints on the CNC as we can clamp boards vertically. On the CNC the spacing can be regimented or morse code or whatever you desire so long as a router bit can fit between and around every finger. 

4D 

Neat jig!

 

I was a little confused about 2 wing nut adjusters until I re-read your description.

Thanks JT. Great write up with supporting pictures. 

Those are some good modifications JT.  Having recently built a box joint sled using Ng's design I can see the improvements.

4D, sure wish you could post up a few pics.  I can see where the router table might be an easier set up process where I might only use the jig a couple times a year.  When I built the Ng jig I had it dialed in for 3/8" dado using 1/2" stock.  On a later project I was using 1/4" stock and there was a good bit of test and tune to get the reset"just right".

I cheat! My jig was made by Incra. 

Does that work on a Shopsmith? Just curious....but they are great jigs!

1 hour ago, Fred W. Hargis Jr said:

Does that work on a Shopsmith? Just curious....but they are great jigs!

I'm guessing that since he Shopsmith arbor is not in a fixed position (i.e., the table slides left and right) it would be difficult to line back up to the slot.

 

If I get a chance later, I'll post some photos of box joint jigs that I made that work with a flush cut router bit.  Dead simple to make and no set ups each time you use it.

5 hours ago, Fred W. Hargis Jr said:

Does that work on a Shopsmith? Just curious....but they are great jigs!

Works like a charm on the standard Shopsmith and equally as well on the FrankenSmith. 

 

3 hours ago, kmealy said:

I'm guessing that since he Shopsmith arbor is not in a fixed position (i.e., the table slides left and right) it would be difficult to line back up to the slot.

 

Yep the table is adjustable up, down and sideways and, blade arbor can be moved right and left, too. Makes set up of the Incra and, many other TS jigs, a snap. 

Edited March 28, 20224 yr by Gene Howe

I cheat, too..

Hand cut....

I got a bit tired of having to adjust and test every time you use one, since the dado set might vary slightly from set up to set up.   So I looked for other ways.

 

Here's a couple of my ad-hoc box joint jigs.   I got a mental idea of this and made them, then saw that someone sells one (with fixed width), and last week saw that Woodsmith has one that they built using T-track and a variety of inserts.  Mine is just a piece ripped to a consistent width, then cut in lengths.  The pieces alternate left and right and are butted up against each other and glued and nailed or screwed.  Sides are done on one side and front and back on the other.  Use a flush cut bit and Bob's your uncle.

 

 

result:

I have another in-process that will run off my router table.  I need to decide on a width, but I'll probably go with 1/4"

 

A few years ago, I used a router table and an Incra jig.  That turned out well, too. I got another Incra Jig as part of an auction lot at the club's annual tool auction.   So I may work on remembering those details for different widths.

 

 

 

More than one way to skin this cat.

On 3/28/2022 at 7:04 AM, Cal said:

4D, sure wish you could post up a few pics.  I can see where the router table might be an easier set up process where I might only use the jig a couple times a year. 

I don't have or need the jig at home as I'm not teaching this semester.  But I mocked up the jig and backboard in Aspire and saved the images.

I use two small c-clamps to clamp opposite corners to the router table bed. 

3/8" square keystock in a 1/8" groove in 12mm BB plywood. Hole for the router bit 3/8" away from the keystock.  Backboard has a slot for the keystock that it slides on. First use let it cut a groove in the backboard.   I set it up with a brass 3/8" square block between the keystock and bit. Tests with a scrap to check the fit.  Adjust by loosening one clamp and bumping a bit, then tighten and check with new test cuts.  Repeat until happy with the fit.  I prefer using Onsrud spiral upcut bits as they prove to be just the dimensions they claim to be. Other brands not so reliable. 

4D

On 3/29/2022 at 7:39 PM, kmealy said:

... and last week saw that Woodsmith has one that they built using T-track and a variety of inserts.

https://c-2pn04.na1.hubspotlinks.com/Ctc/RI+113/c-2pn04/MXdgMwNh77tW2pCFzF5qpCPNW2gkVcw4HjRt3N7bK2_L3lScGV1-WJV7CgCXJN7Kd_TxMrnq4W7_Hlmg6Sjf1TW4PhyhM3WPjPzW55B0TT3Xx1KmW3_vQQb3Hp1g8W2jm_9n57f7y-W4kDqxD4-Mp4QW1d1PZj3F5BZgW5Wx9B_55TVLVW1qm8m52FFBZ7W6wWHqS98yzX5W9l5GM77Qg6qVW2kVKfH3qnZ6QW3yssJp3tmvvCW2w9KnC7gsGPgW26J5WG2F8RtfW2mBtDG5Q12C-W12Jjy14Dqh_cW7hpvBs8XR49sW7pHfyp4jsn5MVZgVxy5VDH8sW9bwNRy809BFLV6KvLD5lY9vXW252jbp3D6FFDW4Jpqky7PgC0fN6LqswgnsS16VD4Glw3mR0ykW4RNjNk1dkNB_3d2D1

Also Matthias Wandel (the PantoRouter & Woodgears guy) has one he made using his wood gears to advance the piece.  A friend of mine made one using a 16 pitch threaded rod.  Same thing, just count the turns.