A new kind of digital Finger Joint Jig

[Christophe Mineau]

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