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Match Drill Center Section

Capflyer

Capflyer

Well Known Member
I am building a HRII and just started the center section. Trying to figure out the best way to match drill the already drilled spars and W-420 spar splice plates to the center section F-404's. Open to hearing all suggestions.
 
Have seen your post and lack of replies for a few days now. What is the background info as it sounds like your approach is different than most?

Are you not starting with the center section normally supplied with the spar?

If not, the only way I can envision this (based on some assumptions) would be to align the spars on a (surface) plane -> get the dihedral correct -> match from that point. Expect a lot of shimming and clamping. Invest in some quality bushings for your initial drilled pilot holes. That will ensure a plumb and concentric start. If you don't have some quality reamers, get those too. These are a very close tolerance final fit.

Let us know some more details about your current situation. Can only help.
 
What I Did -

Here a couple of pics showing what I did -

Basically a steel channel & angle fixture to hold both the bulkhead pieces (fore/aft), and the spars in their correct absolute positions. Then, removing one bulkhead side at a time, I was able to "back drill" pilot holes (except for the outermost -3 bolts) using drill bushings - so as not to damage the precision holes in the spars. Then I carefully "opened" up those holes (drill bushing removed) until I got as close to the final size as I could, without compromising the spar holes. Then I used reamers to final size the holes - very little cutting "pressure" on the spar holes when finish reaming.

If you want more info, call me @ 1 (559) 816-0433

HFS
HR2 S/N 002

There are certainly more ways to do this - I just chose this one.

Note date on first "Polaroid" - 29+ years ago.
 

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Freemasm

You may not be familiar with the Harmon Rocket II build sequence; but, the F-404 (Rocket) bulkhead is undrilled, and it is your job as builder to (somehow) set the wing spar dihedral & butt joint wrt the forward/aft bulkhead faces, and drill/ream same. A bit more complex than having a match drilled parts set. (Way) old school.

HFS
HR2 S/N 002
 
HFS said:
You may not be familiar with the Harmon Rocket II build sequence; but, the F-404 (Rocket) bulkhead is undrilled, and it is your job as builder to (somehow) set the wing spar dihedral & butt joint wrt the forward/aft bulkhead faces, and drill/ream same. A bit more complex than having a match drilled parts set. (Way) old school.

HFS
HR2 S/N 002
Click to expand...

Obviously I don’t. BUT (that’s a big ol’ butt), would my approach not work?

Establish the spar plane and the dihedral, then clamp/bush/drill/ream?

The HR2:guys were being quiet.


Would definitely have a decent pucker factor. Mistakes would be hard to recover from.
 
Like I said in my original post - there are other ways to do this, I just happened to chose this one.

HFS
 
Thanks guys. For some additional detail, this started as an RV4 with clipped HRII wings and the RV4 center section was completed. After the wings were about half completed along with the tanks I picked up a good deal on a I/O540 and decided to make it into a HRII. I needed something to work on and completed the wings while waiting 10 months for the parts to come from Harmon not realizing this was going to be an issue until the parts arrived with the raw wider center section.

I guess I could build a temporary wing holder plus the full wing holder I have so the wings are at even heights and the spars can be butted up together. I was hoping there would be an easier way. I'm open to all ideas and appreciate all your responses.
 
@Capflyer. PM sent.

Since you have the original Center Section, you should have options; modifying, templating, etc if I’m understanding you correctly.
 
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Since you have clarified your situation, I think you have a much more difficult situation than my build at the spar only (not a completed wing) level. Good luck with such a much larger "process" -

Maybe "cannabilizing" your already drilled -4 center sections, like Freemasm suggested, might be the way to go.

HFS
 
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Capflyer said:
I am building a HRII and just started the center section. Trying to figure out the best way to match drill the already drilled spars and W-420 spar splice plates to the center section F-404's. Open to hearing all suggestions.
Click to expand...


The other suggestions from Scott and David are certainly options. Another one is to NOT drill any of those close tolerance holes, but simply extend the outboard portions of your existing RV-4 parts, i.e. the #3 and #4 bulkheads.

Here's a PDF with photos of how to do this. It's probably the easiest of the options presented here.

Be sure to maintain the fore and aft relationship to the spar, probably by inserting the spar, before drilling the "U" shaped side plates. Same for the bottom plate. Afterall, the spars must fit inside when you're done... and the bolts must go in the holes!

Even if it's not your final choice on how to do this, I think you'll find the info useful.

(Note: #3 is the forward face of the 404 bulkhead.)

(Note also... the HR2 uprights are parallel to each other, while the F1 parts are staggered a bit. IOW, the rear uprights are as bit closer together, L&R. That change was made to help the one piece F1 side skins lay down better.)
 
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Thank you Vince. I actually found this on the DB link you sent me last year which I had forgotten about until reminded. Extending the RV4 pieces seems like the easiest and most accurate way to proceed. They were already assembled but it should be easy enough to drill out a few rivets.
 
Of course, my match marking/template approach for mod'ing the 404 is better.

I truly have no idea if anyone else build theirs that way.
 
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