Simplified Acrylic Box Fixture

After being humbled by my ambition overreaching my skills, I abandoned the idea of an articulated build fixture. To keep tolerance variations under control I wanted to build a simplified version just to make sure I can do at least the simple thing. Also, doing simple fixtures will be an useful skill for times when I want to build a one-off project that needs a fixture but doesn’t justify the investment for a complex fixture.

The simplified fixture is a stack of acrylic plates, made of a mix of designs depending on the task for that layer. The common thread along all the plates are strategic cutouts to keep away from the cement surfaces. This ensures any overflowing cement will not seep into the gaps between the box and the fixture and ruining everything.

The box is built upside-down with the side pieces going into the fixture first. Once they are in place and glued together, the bottom of the box is added last. The bottom-most plate in the stack keeps the box panels aligned vertically. The top-most plate locates the square panel that serves as the bottom of the box.

This fixture tells me the kerf compensation I had been using is a tiny bit on the aggressive side. In the previous fixture, the various errors masked this fact, but in this simplified fixture there is no escaping the truth. The four side pieces of the box inside the fixture have a very tight fit. So tight, in fact, that capillary action was unable to wick enough cement into one of the joints, which promptly fell apart after the box was removed from the fixture.

Fixture5
First run of the stack-of-plates fixture, with the very precise (but one corner not sufficiently bonded) box it built.

Which brings us to the advantage of the simple design: I could make an adjustment, cut replacement pieces, and have a better-fitting fixture in a fraction of the time of building the overly complex articulated version.

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