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Thread: Finger/Box Joint Software

  1. #1
    Join Date
    Jun 2013
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    Default Finger/Box Joint Software

    I am working on another piece of custom CAM software. I have not forgotten about finishing the Maze software but I dug out a (currently more fascinating) old project to create tool paths for flat machined void free finger/box joints.

    While I use my dovetail software occasionally, most of my project joints are just cut as plain box joints for simplicity and because I can cut the whole part out of a sheet or board without re-clamping. However, it bothered me that such simple box joints need dogbone fillets for the inner corners to avoid interference with the sharp cut edges.

    The whole idea is to cut the joints with a ball end mill and to allow for some decorative patterns using varying finger lengths, either two sided or half blind. The pattern generation was not too bad but I gave up last year over the calculation of the tool paths. Anyway, after a few sleepless nights I finally figured out how to do it. Getting all the bugs out will take a lot more work but today I made my first successful joint.






  2. #2
    Join Date
    Jun 2011
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    Melbourne, Australia
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    Default

    Excellent concept Gert. Hope you perfect it.
    Buddy BT48 with 6' power stick
    2.2 HSD Spindle
    Aspire 9.5
    6" ShopBot Indexer

  3. #3
    Join Date
    Nov 2008
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    665

    Default

    Excellent as usual What programming language you use
    I left woodwork due to office work.

  4. #4
    Join Date
    Feb 2004
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    Rogers, Arkansas
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    Very Nice!
    Ken Zey
    Lookout Mercantile / Digital Millwork
    Rogers, AR
    www.CedarSlabSigns.com
    www.lookoutmercantile.com
    www.digitalmillwork.com

    6x12 PRS alpha

  5. #5
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    Jun 2013
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    Pasadena, CA
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    Default

    Thanks guys, this is a fun project. And probably more useful than mazes for other wood workers. I am envisioning to expand this with a kind of box/drawer wizard so that you just input the outer dimensions and it cuts everything automatically from a board or a sheet without drawing a single line in CAD.

    On the practical side, I am struggling a bit with the clamping. The boards have to be held down flat better than 20/1000" or the joint will have visible gaps on the inside. That is easy with plywood sheet but boards are usually a bit warped or cupped. A surface skim would help but is not really practical. Any ideas?

    Khalid: I am almost embarrassed to admit but I never got the hang of VB or other more modern visual tools. All my PC code is written in text based Liberty Basic (and compiled with the R.T. Russels' Liberty Basic Booster tool). It makes the GUI a bit more work since it is not as simple as dragging boxes on the screen but I have all the code in one piece. I am just not a professional and old dog refusing new tricks. For microcontroller code I use Forth, an even more arcane programming language.

  6. #6
    Join Date
    Dec 2008
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    Diamond Lake, WA
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    Default

    Quote Originally Posted by Burkhardt View Post
    On the practical side, I am struggling a bit with the clamping. The boards have to be held down flat better than 20/1000" or the joint will have visible gaps on the inside. That is easy with plywood sheet but boards are usually a bit warped or cupped. A surface skim would help but is not really practical. Any ideas?
    Here is the board clamp down method I use. It is comprised of 3/4" MDO with tracks. I made simple hardwood hold down clamps for the tracks. I put the MDO on the CNC table, turn on the vacuum and it sucks the MDO flat as a pancake. I make sure my boards are flat using traditional flattening methods (jointer, planer, etc.) then use a wide drum sander to take any snipe out of the board. Then sand it using an ROS.
    Attached Images Attached Images
    Don
    Diamond Lake Custom Woodworks, LLC
    www.dlwoodworks.com
    ***********************************
    Life is not a journey to the grave with the intention of arriving safely in one pretty and well preserved piece; But to skid in broadside, thoroughly used up, worn out, bank accounts empty, credit cards maxed out, defiantly shouting "Geronimo"!

    If you make something idiot proof, all they do is create a better idiot.

  7. #7
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  8. #8
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    Quote Originally Posted by Greencarvings View Post
    Well, it shows that great minds think alike

    Interesting web based program and it does use the same principle of surface rounding. But if I see it right it can only do full depth finger lengths, even width and apparently no half-blind joints. This was actually the difficult part where I got stuck for a long time.

    So, looks like there may be some additional utility in my program and I will surely continue to work on it. I find it also more convenient having a stand-alone program. I can make a change to the joint definition, check the resulting tool path and look at a cut simulation in less than a minute.

  9. #9
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    Jun 2011
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    Melbourne, Australia
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    Gert - on getting your boards flat the simplest method is to buy a drum sander. Once you have one you will wonder how the heck you existed without it!
    Buddy BT48 with 6' power stick
    2.2 HSD Spindle
    Aspire 9.5
    6" ShopBot Indexer

  10. #10
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    Kennebunkport, Maine
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    Bob and all, How accurate are the drum sanders for thickness? Currently making two products out of 3-4 boards at a time that fill table surface of the Desktop and surfacing at 4IPS as they are all different by .002-.004" and some of the cuts are only .025 deep. Can't have cribbage board lines and countersinks disappearing on me like they do when I don't surface Balking at the price tag if it won't get me close to dead nut thickness.
    scott P.
    2013 Desktop/spindle/VCP 11.5**
    Maine

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