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Match drill?

dstates

Well Known Member
I am starting on my rudder first since one of the the parts for step 1 of my vertical stabilizer is on back order. I’ve just clecoed the skins to the sub structure. The instructions say to final drill #40. I wasn’t expecting that step since the 14 is a final hole size kit. Do I really need to final drill every hole or were these instructions for when they were not final size?

I’ve also noticed that “match drill” is also mentioned. I would assume that these are holes that are not final size or that only exist in one part. Is that a fair assumption?

Thanks!
 

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I've gotten through the RV-14 tail feathers and most of the wing in the last 10 months. There are a few cases where the plans will say to final drill, but then it turns out it's not necessary. Most of the time if the plans say it, it is necessary.

Tip #1: The best way to tell if it is necessary is to insert an appropriate sized rivet into the hole. If it slides in easily, final-sizing isn't needed. If it goes in with trouble or doesn't go in, and you are sure the parts are well aligned, then you need to final-drill.

In this particular case, the skin holes may be final sized, but the trailing edge holes are not. Note that many of the components are shared between models. I think some of the rudder parts are shared with the RV-9, and the RV-9 parts aren't final sized. The plans tell you to final-size those parts. So, the RV-14 isn't final-sized everywhere.

Tip #2: A final-sized hole still needs to be checked for burrs. One side of the hole is usually terrific, and the other has a burr. Usually such burrs are very slight, and I sand them off if they are on an interior part (will be primed anyway). If the burr is on the exterior of the skin, I use a deburring tool.

Final-drill is used when all the components have a hole, and they just need to be sized up to the correct size. Match-drill is used when you need to use an existing hole to create a new hole in a component (or two) that doesn't have one.

Tip #3: Be a perfectionist about drill alignment when drilling through thick materials. If you drill from even a slight angle through the rudder horn, you will get oblong holes. Ask me how I know.
 
Van's told there ins't a specific document that states it, but generally if it's a 5 digit part number it's final sized, if it's a crossover part like a three digit number, it will need final drilling. But always good to check. There are some of the pieces that are final sized, that I have noticed a little imperfection in the hole, and if not taken care of it can cause a dimple to crack, so I've been double checking all the holes for any issues.
 
Thanks for the info! I did go ahead and check/final drill all of the holes with a #40 reamer and there were just a handful of holes that created any shavings.

Thanks again!
 
Hint on achieving best alignment.

Learned from Vaughn Parker, foreman/supervisor of Lockheed's Vega division prototype shop.

If not final sized hole, drill "locating" holes in the rivet's fractional size then use a rivet instead of a cleeco for alignment.

It will be a push fit with a sharp drill.

YMWV (Your Mileage Won't Vary - tolerance too tight!)
 
Another note that I just learned a lesson on, check everything anyway. On my tail kit, section 10 vertical stab attach point on the tail cone, one of the pieces was laser drilled, and I only deburred and ended up with quite a few dimple cracks. Got another piece, and noticed the pretty rough laser cut, inside the holes rough, and reamed, turned out much better on the second try. Only one dimple had a very small crack I filed out.
 
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