Tuesday, November 24, 2009

The Saga of the Torque Wrench, etc.

Having skeletonized the front of the spar box, it seemed that the next step would be to add the ribs to the back side. I thought that would be a simple matter, and I had reason to believe so: the front ribs were easy. It took very little time to learn that I had been overly optimistic. So little time, in fact, that it was the very first rivet that demonstrated the flaw in my thinking. The problem was that the rivet puller wouldn't fit inside the rib because the raised part of the lightening hole punched through the web of the rib was in the way.

I knew what needed to be done: the very first step of the RV-12 construction, which I had skipped. I figured I'd do it when I needed it, and now I needed it. That step involved taking a little wedge shaped piece of aluminum, grinding off some extraneous material (which is why I didn't do it - I didn't have the Scotch-Brite wheel yet), and cutting it into 1/2" lengths. Each of these lengths would then have a #40 hole drilled through it 1/4" from the fat part of the wedge.

All of that work was intended to create a little wedge that could be put over a blind rivet in a tight spot and provide an angled flat surface for the rivet puller to work against. If the nail part of the blind rivet was appropriately bent, the rivet puller would be angled out away from the obstruction but the rivet itself would still be flush against the surface. I think one of the videos linked over in the right sidebar demonstrates this technique.

It's a simple matter to bend the rivet:

Here's the whole contraption in place and ready to be pulled:

It results in nice, flush rivets. For all I know, that might have been the result anyway if I had simple pushed the rib over to the side out of the way, but even if it was just a feel-good technique it worked pretty well:

It was slow going compared to "normal" riveting, but an hour or so of riveting resulted in a fully skeletonized horizontal stab:

I still had to finish the fabrication of the little aluminum tubes that I had let sit over night while I hoped for a flash of brilliance (or, at least, a brief moment of lucidity) to strike me. I was still worried about getting the ends of the tubes flush across without getting them too short. I finally decided to just lightly brush them across a file. If I had it to do over, I'd just cut them 1/32" too long in the first place. They would already be in tolerance at that length, and I'd have a little buffer to allow me to clean them up if needed.

I was forced to tackle that job because the next step was to bolt on the hinge supports and install the metal tubes. It turns out that they are not used as hinges as I had originally thought; they actually act as 'stops' to limit the travel of the stabilator. I installed everything finger tight to see how it all fit:

At that point I needed a torque wrench to tighten them correctly. Van's provides a chart that indicates that the appropriate torque value for bolts this size is 25 inch-pounds. They caution against over torquing and quite definitively state that 25 inch-pounds will not feel like much torque at all. They also are very clear about their feelings regarding torque wrenches that measure in foot-pounds: throw them away, they have no utility in this job. As you can imagine, my torque wrench is measured in foot-pounds.

None of this was a surprise; I had started the process of acquiring the correct type of wrench weeks ago. Harbor Freight even had a 1/4" drive, inch-pounds torque wrench on sale! Now I know at least half of you just rolled your eyes in disgust at the idea of using a Harbor Freight torque wrench on anything more complex than the assembly of an Ikea footstool, but I had done a little research on this. Or, more accurately, read a second or third hand account of a little research done by someone else. What they allegedly founds was that the Harbor Freight torque wrench was accurate enough, but much like a pet hamster, you wouldn't want to get too emotionally attached to it. In other words, good enough to warrant spending $20 instead of the $150+ that it would cost at Sears.

Thinking myself clever, I came up with a scheme whereby I would take the CFO to dinner at a local sub shop which purely by coincidence was right next store to Harbor Freight. And, what with it being right next door, I'd pop in and buy a torque wrench while she went to the sub shop and placed our dinner order. The perfect crime, except for one little thing: Harbor Freight was completely out of the $20 torque wrenches. Not all was lost, though, since I still needed a set of 1/4" drive sockets to go with it, so I'd go ahead and get those while I was there. That too would have been an at least adequate crime, except for one little thing: two registers were open, and both had long lines of impatient customers waiting. It seems that the connection to the credit card verification service was on the fritz. No worries, I thought, I'll just pop back in after dinner.

All thoughts of clever machinations thrown to the wayside, I had my dinner and confessed that I needed to go back to Harbor Freight when we were done. If not the perfect crime, at least still an efficient trip, right? Well, when I got back to Harbor Freight the long lines were gone. In fact, there was only one register open and just a single customer in line. Ha! My patience paid off! Well, it would have, except for one little thing: we waited ten minutes behind that guy as he argued with the cashier over what a $3 discount that he believed he qualified for, while she steadfastly held that it was $1. When she decided that she had to find a manager to resolve the conflict and he was nowhere to be found, I put the sockets back on the shelf (again!) and left.

I simply gave up on the torque wrench and looked for an alternative that was better than the Harbor Freight tool but not as expensive as Sears. I found one on Amazon.com for $48. Chances are that it's the exact same tool as the $20 tool at Harbor Freight, but the extra $28 dollars makes me feel that it's surely both more accurate and more robust. Consider it $28 worth of piece of mind.

But I still needed sockets. Having been fooled once, I know it would take a much more elaborate scheme to trick the CFO into trying again. This time I used the argument that we should try the new chinese buffet that had opened conveniently close to Harbor Freight for lunch, the compelling argument being one of sound economics: if the food is horrible, let's find that out at lunchtime prices. So, off we went.

It was a pretty good lunch and we were soon on the road to Harbor Freight. Then an inspiration of the two-birds-one-stone variety struck me: we could forgo the inevitable Harbor Freight hassle by simply continuing down the road a bit to Sears, where we could also shop for a new Xmas tree. The former tree, which we liked because it had lights already installed and we didn't have to mess around with untangling and stringing lights every year, had gone dark last year. Sure, a $4 string of lights would have kept it on hospice for a few years, but I needed sockets and I had a 100% confirmed report that Sears had Xmas trees. Easy sell, that. On we went to Sears.

Reports of the availability of LED lit (LEDs are supposed to last a long, long time and I'd really like for this to be the last time I have to buy an Xmas tree) trees were proven accurate and we selected an attractive 7.5 foot model with multi-colored lights. Decision made, I went through the formality of walking back out to the car to see if it would fit. It would not. Not even close. Someone would have to hoof it back to the house and return with a more capable vehicle. I nominated the CFO as I still needed to shop for sockets. That took awhile because I didn't want $30 worth of sockets. If you look long enough, you will eventually find the cheaper stuff Sears sells hidden back in a dark, musty corner.

That took long enough that I was starting to get worried that I wouldn't have the tree bought and ready for pick-up by the time the larger car arrived to pick us up. There was no line at the register, though, nor was there anyone else waiting at merchandise pick-up. This was going to be easy! Well, except for one little thing: when the merchandise pick-up guy went to pick-up the merchandise, he found that I had cleverly purchased an empty box. The tree that had ostensibly habitated the box that I bought had been promoted to floor model.


A group of employees gathered to determine what could be done to rectify this situation. I had a suggestion: "Box the floor model back up and sell it to me for $50 off."

That idea was immediately shot down: "We need that tree as the display model."

"Oh yes," I replied, "You definitely want to keep a model of a tree that you don't have any of on display. That's bound to work out well."

There was a counter proposal: "Just pick out a more expensive tree and we'll sell it to you at the same price."

The perfect solution! Well, except for one little thing: I had already bought the most expensive tree.

We finally settled on the expedient of nullifying the transaction and us buying a cheaper tree at 10% off.

Finally, I had my sockets!

And used them:

Van's was right: 25 inch-pounds feels almost finger tight. It's not very much torque at all and I can see how it would be easy to over tighten them without the appropriate wrench.

With that finally done, I went on to the next step which was to retrieve the trim tab hinges that I had cut to length on page 08-03. That would have been quite simple had it not been for one little thing: I hadn't done it. Figured it could wait. It's pretty easy, after all. And it would have been, except for one little thing: the piece of hinge that I hadn't cut to length on page 08-03 had come with a piece of duct tape on the end of it. That duct tape left a sticky residue on the hinge pin (the wire that holds the pieces of hinge together to make it, well, a hinge) and it was buggeringly hard to get that damn wire out. Once done, however, it really was easy to get the hinge cut:

Certain spots on the hinge apparently don't get drilled until a later step. Van's has us mark them to make sure we don't mistakenly drill them:

Drilling the holes was pretty routine work, especially since I remembered that the drill guide fits better if you lightly file the inside edges of the tabs.

With the hinge pieces ready to go, they need to be matched to the horizontal stab skins. Those skins are, unfortunately, still clad in the blue vinyl coating that I hate hate hate removing. It will wait for tomorrow, I suppose.

It should be pretty easy. Well, except for one little thing....

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