Finger Joints, revisited

[jTr]

Since a recent thread delved into methods for the finger joint on the 'bot and I had a project that was ideally suited to them, I decided it was time to utilize the dovetail jig I've grown so fond of to get the job done. I'm sharing the results I experienced by simply modifying Gary C's program and adding a few spacers to the dovetail jig to convert to finger joint machining. I've always wanted to learn to write my own routines for the 'bot, and this is a great way to get your feet wet - simply take something that already works, modify to suit. (Be certain to air-cut for testing of course.)

Still a small glitch I'd like to eradicate, otherwise, it worked quite well. I simply converted to a 3/16 spiral bit, modified/deleted appropriate lines of code in the original program, and it essentially operated as predicted.

I'll address one inevitable question- Speed.
This box with 4 joined corners, 16" long consumed 18 minutes, including two for re-positioning. The jig is 34" long, so it was able to cut two pairs in one cycle - that's 32" of cutting, resulting in 170 precise fingers in 8 minutes.
With a soft wood such as this pine, I would be comfortable in doubling from 1 to 2 inches per second move speed.

I'll conclude for now by posting some pics and provide more details if anyone is interested.

Jeff

[MogulTx]

Wow! Nice set up Jeff. You must be pleased. I have often fantasized about an extended length Dove tail jig ( or finger joint jig). I also like disparately sized dove tails.... this is something I am going to have to start playing with, I think!
Good work! Details on your jig decisions and hardware choices would be great. Ideas on programming bugaboos would be great also!

Thanks,

Monty

[scottp55]

Nice Jeff! Thanks for including the excellent pics

[jTr]

"I also like disparately sized dove tails..."

Monty, this will not accommodate that option, though I imagine with some ambition, you could write in a sub-routine that skips one, skips two, skip one, back to normal, etc. to generate more interesting joinery.

The beauty of it as it is designed: a pop up screen asks how thick your stock is, how wide, then auto-calculates the cuts. However, this limits you to a series of identical passes to fit the width - a pre-determined lobe cut to compliment the bit radius, (3/32 for the 3/16 in this instance), and a corresponding slot length. This is repeated until the stock width value is reached, then reversed for the second side if you're cycling in pairs.

An interesting anomaly - if you cut too shallow, you'll leave a skin that ends up on the outside ends of the box faces. This could be used deliberately to generate what you could call a "half blind box joint", as it can only be seen on two sides, just like a dovetail. (see photo). Actually, it could make glue ups easier, as that skin could contain squeeze out on that face. Would likely need to go much thicker for durability, but I thought that veneer thin face in photo looked rather nice...

Anyway, fun to "play" a bit with the machine - it's how you find your own signature methodology. Who wants to push buttons and make stuff exactly like everyone else does with their machines, right?

jeff

[Burkhardt]

.........a pop up screen asks how thick your stock is, how wide, then auto-calculates the cuts. However, this limits you to a series of identical passes to fit the width - a pre-determined lobe cut to compliment the bit radius, (3/32 for the 3/16 in this instance), and a corresponding slot length. This is repeated until the stock width value is reached, then reversed for the second side if you're cycling in pairs.......

Ahem, not wanting to appear pushing my software (just a minor hint....). But I guess it can do what you suggest already. Also, both sides can be machined flat without a special jig. Not sure if you followed the thread in "Projects" but in any case more info is here. For simple joints with up to 4 different finger lengths it is actually free.

[ssflyer]

Hehe - Glad you popped in with that, Gert. I was just getting ready to!
I'm moving my shop from my house to a real shop in Napa shortly, and one of my first purchases after getting it setup is your software.

I'm really impressed with the capabilities and ease of use (after way too long as a software/network engineer/DBA) (Funny how they keep tacking on responsibilities)

Anyway, bottom line is that I can appreciate the time and effort that goes into what you are doing, and the absolutely great value you offer!

BTW - not detracting from Gary's great jig setup and basic ShopBot code, since I use that all the time for my dovetail drawers!

Thanks!

[barrowj]

Ron,

Are you aware that you link in your signature is not coming up?

[Ger21]

I'll also add a shameless plug (I won't do this again here).
I also have a software program for doing dovetails. Both half blind and through dovetails, fully customizable joints, limited only by the size of the dovetail bit.
I'm currently working on adding box joints to the program, and hope to have them working in the next few months. Box joints will also be fully customizable. Here's a sample box joint I cut this weekend.
(Mods, please delete if this is inappropriate).