Sunday, April 17, 2016

Advanced Compound Angle CNC Clamping Fixture.

The need to clamp parts beneath our CNC router at an angle or compound angle has increased each semester as more and more of my students realize the potential of our CNCs.  I had previously designed and built a simple angle clamping jig to fit between the rails of our Meteor CNC.  This worked, but was difficult to install and align.  It also would flex in the middle when heavy boards and clamps were hanging on it.

I came up with this advanced fixture only after seeing the weaknesses of my original design and contemplating how to solve those issues over several months.  Components of the final solution came to me slowly.

My first realization was that bolting the jig into the TOP of the frame members would be far easier than bolting into the inner side of them.  I made a few small prototype angle clamping jigs to prove my assumption, and they are indeed easy and quick to install.

Using the front rail (rather than both side rails) to clamp the fixture to was my second "aha!" moment.  The front rail is always parallel to the gantry, so using it would eliminate any need to "square" this fixture when installing it.

Setting and holding the jig at the desired angle was the third challenge.  Locking the fixture angle needed to be quick and accessible. To measure the fixture angle we use a magnetic digital angle gauge attached to a metal bracket that hangs on the fixture.   Locking bolts hold the bar securely in position once the angle is shown on the gauge.

This version has connection ribs that extend in an arc beneath and behind the jig.  A handle/bolt through this arc into nuts embedded into side plates permit easy locking of the angle.  All photos here are of my personal version.

First cuts using the jig happened this day. A student project needed a slot cut through the two end boards of a wood box.  Slots needed to be at 7.4 (82.6) degrees rather than straight through.   The jig held securely.  The slots turned out great.

The support plate of the fixture has an array of rectangular holes to pass c-clamps through for clamping parts to it.  Other "assist" brackets can be attached to the support plate for unique clamping needs.   I like using c-clamps through the plate, and will borrow this strategy for future CNC bed and fixture configurations.


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