SonexBuilders.net

I have just started making the wing attach blocks. I have cut the first one from the bar stock, and now have it the correct length and have the chamfer on it. I have a question about the holes:

The two 3/16" holes that will be for the bolts that hold the block to the angle - what size bit would you start the hole with and what steps are used to upsize it to 3/16".

For the other hole - The angle the block gets bolted to came pre-drilled to 3/16" already (as part of the machined angle upgrade). Do I use the other two holes to bold the block to the angle, then drill through the pre-drilled hole in the angle to create the third hole in the block. I know that third hole gets up-drilled in the wing mounting process.

Thanks,
Kevin

I tend to make things more complicated than necessary, but when I drilled my holes in those thick blocks, used a drill press and drilled 1/8, 5/32, then 3/16. When drilling the 1/8, you need to clear the bit frequently.

If I were trying to match that thick block to an existing 3/16 hole, I personally wouldn't try to do it in one shot...I would still use the 1/8 and 5/32 first (centered as best you can)...then for the 3/16 hole, I would use the existing holes in the angle as my guide.

For matching the existing 3/16" in the pre-made angle, If it is recommended that I start with 1/8, then I think it would be best to use some sort of bushing that I can use as a drill guide - something that has an OD of 3/16 and an ID of 1/8 - rather than try to manually center it.

Question is - is there something like that available?

Yes, there are drill bushings available from most of the suppliers (ATS, AC Spruce, etc) and that is definitely the "right" way to go. Also, I've also created my own drill bushings by using some aluminum or steel tube from Home Depot / Lowes.

On thinner stock, using the approach above has worked well for me...fortunately, I haven't had to redo the thick aluminum blocks so I can't really speak from experience there. But as you mentioned, the critical hole is going to get updrilled ultimately.

Another question on this: The plans call for the holes in the in the assemblies with the wing attach blocks to have AN4 bolts in "tight fit" holes. What drill size (or reamer) would create a tight fit? Seems 1/4" would be too loose.

I used a "D" drill bit for mine...got it from AC Spruce.

My "D" drill bit created a hole that is too tight - requiring to much/many strong hammer blows to force the bolt through. I am guessing I need a reamer - but my knowledge there is lacking ...

I would buy a reamer of the appropriate size since this is what they were made to do and it will give you a perfectly round hole. Win win.:)

Reamer Sizes:

Standard Sizes (typical)
Number sizes #70 through #1
Letter Sizes A through Z
Fractional sizes 1/32" through 1" in 1/64" increments
Fractional sizes 1" through 1.5" in 1/16" increments
Metric sizes 1mm through 25mm in 0.5mm increments
Do not use the reamer to remove more than 0.002" to 0.003" of metal.

So you can buy a "D" size reamer to gently enlarge the hole to achieve your snug fit.Check with the members of your local EAA and probably someone has it in their tool box just getting dusty.
Maybe one quick pass will do it .
Cheers,
Mike

I hope that someone can learn from the mistake i just made, i am embarrassed because i know better. But having never screwed this up before.. i got cocky and thought i could pull it off. It bit me hard.

My wings have been on the fuselage for a few weeks, but with 1/4" bolts as i was waiting until i had the right tools to "properly upsize" them to 3/8". I spent about $100 on nice drill bits in 1/32" increments (9/32", 5/16", 11/32") and reamers in sizes .372", .373" and .374" so that i would have a range to get a nice fit. I took a piece of scrap 1" thick stock and drilled three practice holes, one in each of my final reamer sizes and checked the fit with my bolts. They both would not fit through the .372, could be mallet-ed into the .373, and fit nice and snug through the .374" hole. I had found my winner.

So i went on to step up in 1/32" increments which went relatively smoothly and then was sitting there.. .372" reamer in hand, questioning what i was about to do. A few thou under 1/32 was quite a lot for a reamer to bite off.. but i had done it many times before and been left with a nice hole. But those times had either been using a drill bearing or had something clamped down to the table of a drill press.. never by hand. "Eh.. ill figure it out" i said to myself. To make a long story short, and to spare the reader from the many expletives that were yelled, the hole went eccentric. The reamer could not follow the hole, and drilling those damn spar attach pin holes is awkward enough as it is.. if i had gotten it right it would have been from shear luck. The worst part of the story was that i was so angry at myself and not thinking clearly that i went on to repeat the exact same mistake on the other side.

Maybe it would have gone better if i had made that last 1/32" (shy) step using a jobber bit and then tuned the last two or three thou with the reamer.. but i cant say that i would ever recommend (or repeat) the "step up" method for this job. Drilling through three inches of metal with a hand drill and no good way ensure perpendicularity is a recipe for disaster. Jobber bits will follow the hole better than a reamer, but i think i just as easily could have screwed this up if i hadn't tried using a reamer.

I emailed Kerry and fessed up to my mistake. He told me the way that i should have done it was to use a counterboreing bit, part # 110266817 from McMaster Carr http://www.mcmaster.com/#catalog/118/2452/=jcqn1a and done the upsizing in one step



He also pointed out that they strongly recommend dulling out the 1/4" pilot section.

This solution makes sense to me. The remaining hole at the end may be a tad oversized, but only by .001~.002 or so for most AN bolts. And even though it won't be a perfect, reamed hole, the sonex has plenty of margin in its design (no one's wings are ripping off, and due to the pain in the a$$ nature of this upsizing job, i am sure someone has screwed it up and still flown it without problems). If i could do it all over again.. i would use this method for sure.

The repair that i bought myself into is to remake all four wing attach blocks, the forward wing attach angle in the fuselage (definitely) and maybe the aft wing attach angles. I will have to cairfuly match drill the new wing attach blocks to the now existing .374" holes in my spars, but i will be able to do that off the airplane with a drill press/drill bushing so i am confident that will come out ok. I will then need to match the 3/8" hole that i am left with to the new wing attach angles in the fuselage. Man, that is going to suck.

-nick


Here is an example of what not to do.


Problem hole seen with the spar pin inserted


Repeating the same screw up, twice in a row. One of those classic moments in life where you just have to step back and say "yup, you're a dumbass"




ps. Something that i did right was ream out all of my 1/4" bolts using a .248" reamer. Makes a perfect hole for most AN-4 bolts.

Before you start ripping things apart, call Kerry and see if you can continue drilling to the next bigger size bolt. I seem to recall people doing that without issues...there's enough metal to drill up to the next size.

Just a thought...if the factory gives the okay it could save you some time...


Oh, one more thing...the next time you take the wings off, use that opportunity to drill out the pulled CCP rivets that may interfere with the spar bolts and nuts, and re rivet them from the inside out. Maybe six per side, three in front of the spar and three behind. The wing covers them up and doing that will prevent clearance issues. Also learned that one the hard way.

Good luck!