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Match drilling new parts to old - technique?

ScottK

Active Member
So, building my -9's tail, I messed up one of the HS spars, bad enough that I just ordered a new one. I've run into a question when it comes to match-drilling the new spar with the existing skins that were already match-drilled to the old spar. I'm thinking that thicker spar metal is going to guide the drill, and if there's any misalignment it'll oval-out the skin hole, rather than the desired action of milling the spar hole to match the skin.

OTOH, I've been most impressed with the accuracy of the pre-punch holes, and I feel there's a very good chance the holes are adequately aligned as-is. So I'm thinking to final-drill(*) the spar without clecoing the skin on, trusting that things will just work out.

Yea or nay?


[* Or ream rather than drill, I think reaming has less tendency to move the hole center.]
 
No issues

I did something rather stupid with my flaps, which meant I had to get some new skins & other parts to mix in with already match-drilled parts. I just reamed the holes in the new parts, and riveted together with no issues.
 
Match drilled parts

I did something rather stupid with my flaps, which meant I had to get some new skins & other parts to mix in with already match-drilled parts. I just reamed the holes in the new parts, and riveted together with no issues.

Same here. I botched the HS SB and replaced the spar. Other than the new inboard ribs, I just drilled the spar full size and everything fit perfect.
 
Have a scrap strip of aluminum that you can use to make a transfer strip?

Make sure you maintain up from down and right to left (don't ask why I mention this! :D)

Use it to compare skin to new spar.

Don't elongate the holes.

When you locate the strip, don't use cleecos. They do not position accurately.
 
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