CNC Precise Hole Drilling Jig

I was beset with a tough problem in how to drill a precise hold in parts I'm making for a project. It's fairly easy to position a part within 1/32nd of an inch but if the tolerances are less, and especially if they are a lot less, it is very difficult if not impossible to repeatably register a part manually with greater precision than 1/32".

The precision I needed was on the order of 1/100" or less. In order to be able to repeatably machine a hole .215"in diameter in a plastic part that measures 1.25"x1.25"x.35" I came up with a method of building and using a jig in my CNC machine made from the same .375" acrylic material the parts were made from.
Small acrylic part after boring hole (left side, near top).
The trick was to first mount the jig blank in the CNC machine, then make the jig itself with the CNC. Once made, it wasn't moved and that guaranteed that registration wasn't going to be an issue.

The part needed to be quite steady as boring out acrylic takes a considerable punch. Any movement of the part or the jig would ruin both. The jig was mounted to the clamp table portion of the CNC machine, then the jig was cut.
Jig mounted on Clamp Table portion of CNC Machine.
By cutting a line into the acrylic to make the jig flexible, and using a press clamp, I could lock the part into the jig easily and securely. It worked as expected. I have several hundred parts to cut and bore so it needed to work without a lot of fuss.
Precise jig in action.


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