A new kind of digital Finger Joint Jig

**Christophe Mineau** · Sep 27, 2017, 05:24 PM

Hi folks,

Here is my new invention.
I wanted a finger joint jig for my table saw, but something more compact and not as big as the usual sled style we can see.
I really have no more room to store contraptions of all kinds in my shop, so here is what I came up with.

It's a narrow cross sliding fixture that is screwed directly to the guide of the sliding carriage on my my table saw.
But the real originality is the indexing system.
I wanted something that did not cumulate errors, like does the often seen method which cuts one finger taking reference on the previous one.
As I am a musician, I imagined to make something similar to a guitar tuner.
I made a video to explain how it works :

I made a couple of animations to show the LED display when cutting fingers the same width as the blade width (8 mm in my case):

and for cutting fingers that are wider than the blade width (ex: 12 mm):

I am preparing an article on my Website to explain the details of the build, but here is a summary :

- For the mechanical and wooden part, I think that the video is straight forward and self-explicative.
- For the digital part, here are some details :

The base part is the digital encoder, which is entirely home-made.
It is made of a wooden wheel, with a number of holes chosen accordingly with the screw pitch, in order to get the resolution I wanted.
The encoder is made of two Infra Red emitters/receivers, spaced so that there is a PI/2 phase shift between both signals, this permits to detect the direction of rotation.
The encoder signal is handled by an Arduino (Nano) which pilots an array of 11 LEDs.
There is a rotary selector which permits to select the finger width. It is a stepped array of resistors that generates a stepped tension, directed to an analog input pin of the Arduino.

Here is the frizting sketch :

The software part includes a software de-bouncing algorithm in order to cleanup the encoder signal (actually the most difficult part), and a quite funny algorithm for displaying the blade position through the 11 LEDS.

And here are some pictures of the build.

==========================
Edit 2018 / 11 / 25 :
Small edition just to say I have released this project on GitHub, with source code and explanations :
https://github.com/ChristopheMineau/...FingerJointJig

Have fun !
Christophe

**wb8nbs** · Sep 27, 2017, 09:16 PM

I made an automated box joint jig a few years ago.
https://wb8nbs.wordpress.com/2014/11...ig-lead-screw/

**rossbotics** · Sep 28, 2017, 12:59 AM

Very well done Chris, very precisely positioning, using a tuning devise was very clever

**Christophe Mineau** · Sep 28, 2017, 02:05 AM

Originally Posted by wb8nbs

I made an automated box joint jig a few years ago.
https://wb8nbs.wordpress.com/2014/11...ig-lead-screw/

Hi,
Yes your project has lots of similarities, I see it is based on Mathias Wandel's jig.
His design is probably one of the best, but I never launched this build because it's simply too big ! And I already have a very good sliding carriage on my table saw,
so I wanted to take advantage of it and make something with lower foot print.
I also see that you powered up the lead screw with a car seat motor. This is certainly something that I would have also done if I used this kind of jig more often.
Actually, the motor (I think I would put a stepper, avoiding the need for the rotating encoder) needs power, so a cord, and it adds weight on the mobile part, so for me this is a big drawback.
In my case, a simple 9V battery is enough, and there is no wire, it keeps light weight.
I also deliberately didn't put any LCD display, in order to save power. In average, I only have ~one(+) LED lighted at a time.

As you say in preamble, the only annoying thing with the lead screw is to keep the count of rotations, even with a gear box like in Mathias's design.
This is the only point I addressed with my "tuner" box, I have no particular issue with turning the lead screw by hand, ( I am not that lazy :o) )

I take good notice about the Hall effect sensor that you used, causing no bouncing. This is a good point, because bouncing was my major problem with the IR optical sensors. I had to setup a software debouncing (polling), and could not use the interrupt mode.
On the other hand I have probably a higher resolution, but this is not really necessary.

On your side, do you detect the direction of rotation ?

Good build, wb8nbs. Keep on posting !

**DIYer** · Sep 28, 2017, 06:20 AM

Thanks Christophe Mineau! We've added your Digital Finger Joint Jig to our Woodworking category,
as well as to your builder page: Christophe Mineau's Homemade Tools. Your receipt:

Digital Finger Joint Jig by Christophe Mineau

tags: jig, electronics, finger joint

**wormil** · Sep 29, 2017, 11:16 AM

Interesting. I will take a second look this evening on my PC.

**Jon** · Sep 29, 2017, 11:41 AM

Congratulations Christophe Mineau, your Digital Finger Joint Jig is the Homemade Tool of the Week!

Tough week to win! We had an excellent Harbor Freight 9"x20" Lathe Tool Post by rossbotics, a Sanding Saw by Mikhandmaker, a Drill Press Chuck Extension by Tuomas, a Micro Waste Oil Forge by Turboconqueringmegaeagle, Machine Guards by MeJasonT, Spline Weights by Captainleeward, Hand Screw Clamps by Guy Gadois, and a Lathe Refurbishing by Y-geo.

You'll be receiving a $25 online gift card, in your choice of Amazon, PayPal, or bitcoin. Please PM me your current email address and gift card choice and I'll get it sent over right away.

And that makes 9 Homemade Tool of the Week wins for Christophe Mineau.

One more and he'll join rossbotics and mklotz as a 10-time winner.

Here are all 9 winning tools: