Hold down fixtures are easy with a 3D printer.

Building things is fun. Especially when you are not quite sure what you are doing. Professional CNC machines provide a variety of ways to hold down material, ranging from vacuum systems to vices to aluminum t-slot rails. My experimental design so far is a grid of holes with 1/4” t-nuts underneath. The holes are spaced 4” by 4.2” in a pattern of five rows and six columns.

So I decided to cut my capacitor plates using a 4” square piece of aluminum sheet. These squares were simply cut using a utility knife and a straight edge guide. A sacrifice board of the same size was cut from a piece of fiberboard. This sacrifice board will sit under the aluminum. In order to get a level surface, I faced this board with the CNC, as shown above on the right.

3D Print hold down fixtures

Holding down this “sandwich” of material required a couple of fixtures. These were designed in CAD and 3D printed. The filament used was ABS. As you can see from the pictures, the fixture contained two holes for bolts, a notch to fit against the edges of the material and a flat section to press down.

I also experimented with plastic bots. These worked, but could not take the stress of being tightened into the T-nut holders. The threads kept breaking as I tightened down. So, it was back to metal bolts.  This means that I have to be very careful with the cutting tool paths to ensure that there are no collisions between the cutting tool and the bolt heads.

Once the bolts are tightened down, the material sandwich is held securely in place. Neither the sacrifice board not the aluminum plate move sideways when cut.

This approach to hold down fixtures would be all I needed if not for the fact that thin materials will bow and lift. So, I would need something else to help with the hold down. That will be double sided tape across the interior faces.