The Barn Find Build

[alexM]

That all looks really nice. A syringe is a game changer but that mixing gun is even better. I'm probably going to break down and buy one for my wing ribs, since I'll have no difficulty using up an entire set of tubes.

Nice save on riveting that push-pull tube. I think I was in a near panic when I mixed my first few batches of Hysol. I've gotten better about making sure everything is absolutely ready before mixing, and I've also learned that I don't need to be in that big of a hurry with it.

[Eric Page]

A syringe is a game changer but that mixing gun is even better. I'm probably going to break down and buy one for my wing ribs, since I'll have no difficulty using up an entire set of tubes.

Amazon has the best price I've found for the 50g dual cartridges of Hysol (when it's in stock...), but it's still far more expensive per gram than the cans. The only reason I'm using them is that my wings are already built and I didn't expect to need very much. I bought two cartridges, and got two more with a couple of the parts kits I bought from Kitfox.

It would be an expensive proposition to build a set of wings at $15.69 per 50g cartridge; I'd be surprised if you could get more than two ribs out of each one. Discounting waste, I probably used ~1/3 of one just gluing the few parts I did yesterday.

If you do buy a mixing gun, you'll find that there are many brands, with plungers for many mixing ratios. Now that I have the gun in front of me, it doesn't appear that it would make any difference which ratio plunger you use, as long as the business end of it fits into the Hysol cartridge. Both plungers are ganged together and move forward in unison, so the followers in both tubes of the cartridge are pushed equally regardless of plunger diameter.

The gun I bought is listed as working for 1:1 or 2:1 ratios and it came with a 2:1 plunger. The "2" side fits the Hysol cartridge tube perfectly and the "1" side is a little more than 1/2 the tube diameter, but since both move forward at the same rate and the cartridge tubes are the same diameter, it works as a 1:1 dispenser. I suspect that 2:1 epoxies must come in cartridges with different diameter tubes. Anyway, it feels nicely made and works well.

[Eric Page]

I started today inspecting the outcome of my gluing work yesterday. The bottom rib in the tail is solid and straight, and the false ribs are back in business. The door trim angle on the right side worked out fine...

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...but the left side, not so much. My clamp slipped off, so the Hysol cured with the gap open. Fortunately, I think I can get a small hacksaw blade in there to remove the Hysol for another try. Some other day...

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Next on the agenda was working on the rib reinforcements for the flaperon hinge brackets. I didn't want to mess with the Series 5 brackets, so I purchased the new ones from Kitfox. I started by making a drill template for the brackets, so I could get them to come out more or less the same.

[Permit me a brief digression: Why in God's name does Kitfox show the hole locations in these brackets to three decimal places? Without a precision machined fixture it's impossible to locate a hole 0.438" x 1.188" from the corner of a part, and in any case, it makes ZERO difference if these holes are accurately located! Thank you; now back to our regularly scheduled programming...]

I taped the template to each part in turn, then used a punch and hammer to mark the hole locations.

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With the locations marked, I first drilled them with a #45 (for no particular reason, other than it was the first small drill bit I grabbed), then up-drilled to #30 and deburred.

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Next I test fit a left and right bracket to rib #9 and had my daily moment of panic. The flange of the brackets sits against an aluminum doubler under the cap strip, but that doubler isn't long enough to reach all the way to the forward end of the bracket. The first photo shows the doubler; the second shows the gap between the bracket and cap strip where the doubler ends.

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I figured I might as well take a step ahead and see how bad the problem really is, so I grabbed a hinge bracket, clamped it to the trailing edge, and voilá! The hinge bracket isn't long enough for the gap to matter; all the rivets will go through the doubler and the reinforcing bracket.

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So, with disaster averted, I match-drilled the holes through to the other side, and repeated for the other four ribs, being careful to mark each pair of brackets for the wing and rib they now matched. There was one tiny problem, which you'll see in a minute...

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With all the holes drilled, I deburred, cleaned, and performed the usual alchemy to turn them into golden airplane parts.

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The sharp eyed among you will have noticed the extra holes in the "R3" brackets. There was just enough space at the trailing edge for the right side bracket to slide a bit further aft than the left side, which I didn't notice, so the forward-most hole ended up with virtually no edge margin. Since I was still feeling righteously indignant about the three-decimal-place hole locations, I just punched another one nearby. I'll rivet all four, and no one will ever see them again!

[rv9ralph]

Permit me a brief digression: Why in God's name does Kitfox show the hole locations in these brackets to three decimal places? Without a precision machined fixture it's impossible to locate a hole 0.438" x 1.188" from the corner of a part, and in any case, it makes ZERO difference if these holes are accurately located! Thank you; now back to our regularly scheduled programming...]

I agree with your reasoning. When I was building an RV I thought a callout for 2 23/64 was odd, seeing that my ability to achieve this accuracy was challenging. I then realized why they had such detailed callouts for holes and cutting dimensions.... it was drawn with CAD and they took the dimensions called out in the drawings.

Ralph

[jiott]

Those 3-place decimals are merely fractional conversions to decimals (7/16=0.438, 3/16=0.188); no need to get your panties in a wad Eric.

[jrevens]

Yeah, what Jim said! I composed a verbose, overly complicated explanation but deleted it now. It’s kinda late and time for bed.

[Eric Page]

Yeah, OK, that's all true, but come on... If they meant 7/16 x 1-3/16, then they should have annotated it that way. Expressing a dimension as 0.438 x 1.188 has meaning, and it doesn't mean, "punch a hole roughly as shown."

Thanks, guys. As usual around here, voices of reason prevail!

[/RANT] [/PANTYWAD]

[jiott]

I don't mean to belabor this discussion, but feel I should point out that the tolerances for measurement in the Kitfox build manual have nothing to do with how many decimal places are shown on the drawings. The tolerances are spelled out in the first section of the manual, I believe its called Builder's Tips, where there is a section on measurement accuracy. If my memory is right I believe it says +or- 1/32" is acceptable, except of course drilled or reamed holes. This is also true in the world of engineering drawings; the general tolerances are spelled out in the title block of the drawing and specific tolerances as a +- number after the dimension. If the title block says 4 place decimals are +or- 0.001 then that is what you do. Our Kitfox project "title block" is the first section of the manual. Sorry for the blather.

You're doing a great job Eric, taking everything seriously, which is much better than the alternate.

[rv9ralph]

Yup, measure with a micrometer, mark with a dull sharpie, cut with a chainsaw.

Ralph

[alexM]

As a guy who has designed thousands of aircraft parts I might be guilty of some pretty screwy numbers. If I'm designing a flange on a sheet metal part I start by sketching lines that give me sufficient edge margin. That takes care of my first and last hole on the flange. If it looks like five holes will be spaced about right, then I space the rest evenly with no regard for what the dimension will be. Once I'm looking at the holes on screen I make sure the spacing is to the design specs of my employer, adjust if necessary and "send it". It's going to be a machine that punches or drills it, and that machine doesn't care.

I'm sympathetic that those numbers you reference look screwy but what jiott said is absolutely correct. I have worked in almost zero machine chops that use fractions (I'm talking with a "/" here), but all read .187 (or .188) and say 3/16" (or read .312 and say 5/16) like it was natural.

Get to where they drill a lot of holes and the phrase "a 1/4 inch hole" could mean a .246 reamer to one guy or a .257 drill to another, and they'll just nod and go do it. Depends on whether you want to press a 1/4 dowel into a hole or be able to bolt something together.