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How to check if a hole was drilled perpendicular to the spar web

RV-Ogler

Active Member
The original owner of my tail kit did some final drilling of the holes common to the horizontal stab spars and their doublers. The plans say to be sure to drill these holes perpendicular to the web. So I’d like to check the accuracy of these holes.

My idea is to cleco the parts together and insert the blank end of the appropriate size drill bit into the holes then use my machinist square to check for perpendicular. Has anyone tried this or know of a different method?
 
That's what I would do! Straightforward and accurate to slide a measured small known square piece of aluminum to the sides. You may have to make one from a piece of 1/8" stock. Or maybe the end of a machinist scale. Anything handy that is checked against a known standard.
 
Put a rivet in, if it looks square buck it.

Yes, I think the OP might be over-thinking this a bit. I suspect Van's added that additional instruction to make sure the hole was drilled square because that's really the first time in the kit where the builder has to match drill through a thicker assembly where it can be easy to drill an unsquared hole. If the rivet or bolt *looks* like its square then it is square enough. It will be pretty obvious if it is not.
 
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