INTERLOCKING FROG TUTORIAL
In creating User Manuals for Streamline Automation’s entire FROG3D system, I had to conceive of many small, fast projects that would engage users while conveying important information that would enable them to independently complete projects of their own.
It’s a daunting task, particularly for the FROG3D system’s core component: the 4-axis CNC panel router. If an operator overlooks a key detail, or fails to foresee a potential tool crash on a CNC wirecutter, operating at 45 inches/minute, the worst case scenario involves a wasted foam blank, and 10 minutes to replace $3 worth of cutting wire. An inexperienced mill operator on the other hand, running a $100,000 machine at 400 inches/minute could easily cause several thousand dollars worth of damage, or worse yet, serious injury or death.
Among the most basic toolpaths you can run on a CNC panel router are simple 2D contour cuts. They are a relatively low-risk introduction to the world of CNC machining.
While I was at the University of Alberta, I enlarged a number of toy interlocking puzzles and milled them from flat stock:
Yours truly, circa 2005
The designs weren’t my own; I copied them from those little machine-stamped children’s toys, and enlarged them. It’s more work than it sounds like, as the slots must be precisely sized at this scale.
I did modify the chicken into a turkey one Thanksgiving…
Interlocking puzzles such as these are excellent learning projects in a number of ways:
From the perspective of design, it’s difficult to visualize how to make slotted forms from simple flat stock such as plywood or MDF that aren’t restrictively rectilinear. Models like these can be used to demonstrate how all manner of 3D geometries can be realized, even out of flat stock, even with a simple 3-axis router that cannot cut slots at an angle.
To ensure a proper fit, the slots must be toleranced tightly enough to hold, but not so tightly that the pieces can’t slide into one another. This takes a surprising amount of finesse. Sometimes, the difference between a sloppy joint and one that is too tight to work is only 0.01”.
One might assume that 1/2” plywood is 1/2” thick. As often as not, it is actually 12mm (0.472”) thick. Even if the plywood is sized to be 1/2”, it may end up being 0.49” or 0.51” thick. The easiest way to adjust the width of the slots in the model is to simply offset the toolpath slightly, either toward the curve, or away from it, in the toolpathing software. It’s important to practice this.Small parts such as these can have a tendency to break away as they are cut out by the spinning tool. Damage to the part is the best case scenario in this instance; tool breakage, or even personal injury could also result. Pieces must therefore be “tabbed” to the overall workpiece. These make an excellent exercise, as tabbing curvilinear forms such as these requires some extra foresight.
With the help of a co-worker, I designed a slot-together frog model for a 2D contour milling tutorial project, as a play on the FROG3D system.
The Frog Tutorial was designed as the first project a new user would complete on the FROGMill.
The tutorial took new users through important safety protocols before introducing best practices in setting up milling projects, from securing workpieces and installing tooling, to setting Program Zero co-ordinates.
Prior to toolpathing the frog parts themselves, new users would toolpath three pairs of test slots. One pair of slots would be run directly along the curve, one toolpath would be offset slightly inside the curve (making for a larger slot), and one pair would be offset slightly outside the curve (making for a smaller slot).
Once the correct offset was determined to make the ideal slot width, the frog parts themselves could be toolpathed and milled.
Note the tabs holding the parts to the overall workpiece.
As with many of the project tutorials I made for the FROG3D User Manuals, this tutorial was accompanied by a short timelapse further illuminating the process.
