Monday, December 14, 2009

Here's the problem: I'm doing it wrong

In the ultimate case of barn door closure in a post-equine escape scenario, I decided to do a little more research on the topic of edge breaking as it pertains to making a big, stinking mess out of it. What I found is that, well, I'm doing it wrong. The edge breaking, that is, not the making of a big, stinking mess of it. I'm excelling at that, thank you kindly.

So, here's the right way to do it:

"To use this tool, open up the set screw and close the jaws. Then put the tool on the edge of the piece to be broken with the rollers just barely on the edge. Then tighten the set screw just enough to get the rollers to touch the metal. Then open the jaws and close them with the tool set with the edge guide against the edge of the material. Then just pull the tool along the edge without twisting it down. The tool does the work and only bends about 3/16ths inch of the edge down. If the tool does not pull along easily, you have it too tight. Remember, you are not putting a large bend in the edge, but just a 2 degree tilt on the very edge. The tool does that without twisting the tool at all. If you twist the tool down, you will put a crease about 5/8ths inch in from the edge where the inner edge of the tool is. That is not where the break is supposed to be."

That whole "without twisting it down" thing? Got that covered. I was twisting it up!

But yeah, even though I twisted up rather than twisting in the verboten downward vector, I have that whole "crease about 5/8ths inch in from the edge where the inner edge of the tool is" thing going on. The big question now is what to do about it. It's possible that it will flatten out as I rivet the skins down, but it's possible too that some unforeseen genetic mutation resulting from cutting-edge bacon research will result in us all sharing uncontrolled airports with aviating pork-flavored barnyard livestock. I'm not sure I can, or should, count on that.

At least it's the bottom skins. Even if it ends up ugly, it will be on a location on the airframe that only another RV builder would be rude enough to inspect. Guess I won't ever be flying in to Oshkosh if I can't get this cleared up.


Brent Humphreys said...

A little confused. That description is for a different type of tool than the one you posted the other day.

Looks like you have the Avery round tool, and this is referring to the Cleveland vice grip tool. I have both, but neither is a favorite.

DaveG said...

Yes, I have both now. I bought the Avery tool and borrowed the Cleaveland.

I'm not a big fan of either.

This will sound like whining but I'm actually just curious: Van's does so much complex shaping and cutting of these parts that I don't understand why they don't just put this bend on the skins at the factory.

This kit is an odd mix of incredibly clever design and inexplicable lapses. I still don't understand why, after two revisions to the page, they still don't tell you that you need to use a 120 degree countersink for the flush blind rivets for example. It seems an odd thing to leave for the first-time builder to trip over.

Joshua said...

In the introduction to the builders manual for the RV-9A, they do specifically mention the countersink/dimple issue..."Most commonly available flush head blind rivets have 120* heads rather than the 100* for flush head AN rivets. Thus, special dimple die sets are needed for a perfect fit, although almost all builders we know use regular dimple dies and report acceptable results."

I seem to recall reading mention it somewhere else too, in the context of "yes, it's not perfect, but it's close enough", but I can't find it quickly. I've been fine with the 'wrong' angle so far, though the flush blind rivets are probably more rare on the 9 kit than on the 12.

The Cleaveland edge roller tool seems to work well when properly adjusted, but don't do what I've done and get moving too fast, as it is possible for the flared end of the roller--the part that's supposed to guide the tool along the edge--to jump up on the skin and take off cross-country. Yup, that'll leave a mark...

DaveG said...

I went back through section 5 of the RV-12 manual and was unable to find any reference to when to use the 120 degree countersink, but it's possible that I missed it.

That said, even if there is a one-time passing reference to it, I still think it would be customer-friendly to remind the builder the first time it comes up. I fail to see the harm in doing so, and it seems an odd decision in light of the rest of the design of the manual and kit. For the most part, it is very, very hard to do something wrong with this kit. Because of that, when an opportunity to actually do something wrong because of an omission in the directions does come up, it's somewhat surprising.

And that too having been said, now that I've seen how the parts all went together over the top of that particular set of rivets, I don't think it would have made a huge difference if one were to use the 100 degree bit.

The first practice edges that I did with the Cleaveland tool had all sorts of on- and off-road excursions. With the long edges of the tail cone skins, it's easy to get impatient and try to speed things along. It takes a conscious effort for me to keep the pace slow. That's true in a lot of things I do, as it turns out.

It's also hard to keep a steady, even pace as you have to walk along the lengthy edges of the skins. Take a step at the wrong time and poof!, you have a nice crease there.

On the plus side, it will be very difficult indeed to do a worse job than I did on the first couple of skins. I was able to smooth those out quite a bit, though, just by re-doing them with the tool positioned correctly. I don't think there will be any lasting ill effects, and if there are, you'd really have to be looking for them.

Joshua said...

Agree with you that it should be part of the builder's guide. I suspect Van's was trying to prevent us from feeling the "need" to buy another tool that may or may not make a big difference -- not that I'd be stopped from buying it anyway...tool buying is some sort of manifest destiny.

Enjoying following your -12 build; if that model had been available when I started, I may have gone that road instead, as a first-time builder. As it is, you'll probably beat my -9A to first flight. Best wishes ~ JDW

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