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 up 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.

I have since replaced the knobs that tighten the fixture with cam levers. Quicker to lock or release to adjust the angle. 

Cam Levers VS Twist Knobs

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.

Two CNCs in the small CNC lab where I taught also have larger versions of this jig:

Last CNC

The last CNC was bought specifically to use my jig with.  It adjusts from vertical to horizontal.  When horizontal it covers the entire accessible area the CNC can access. I mounted it on a taller stand to permits tenon cuts on the ends of longer stretchers mounted vertically.

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Comments and questions welcomed and appreciated!

Supporting Assembled Projects Beneath the CNC.

The open frame design of Probotix' CNC machines  proved useful when this challenge came up.  A student of mine had already assembled the body of her cabinet. We needed to cut a circular array of holes at each corner on the bottom board.   The only way to cut this hole array accurately was to use the CNC.

Her design has no back panel.  This permitted using bridging supports I designed that could pass through the body to hang it from the CNC frame. 1/4" dowels were installed along the top of the bridges to position her bottom board square and centered in the frame. C-clamps locked the cabinet to one of the bridging supports.

The bridges are made of 3/4" plywood.  A 6" tall side piece joined to a 2" wide top piece. The vertical piece is an inverted arch, thicker in the middle of the span where the greatest load would be.  The top pieces have holes in the ends so they can be bolted into the side frame members of the CNC.

First test of these bridges worked perfectly. The cabinet was lifted up into the frame, the bridges passed through it then dropped onto the side frame members. We slid the bridges to either end of her cabinet to be right under where the CNC work would happen. The bridge ends were locked into the frame, and the dowels held the cabinet securely in position on the bridges.

The tapered legs in this photo were cut using the rotary axis on another Probotix CNC. The pin arrays on the top end of them were cut using an adjustable angle clamping jig I designed that also fits into this CNC t-slotted frame.

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