Tag: Aluminum

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Brackets in place

What I thought would be an hour’s worth of work this morning turned into 3-1/2 hours, but I’m feeling good about the end result. I went over to tighten up the bolts on the wing root brackets and install the brackets on the outer portion of the wing, for the N struts and landing wires.

Snugging up the bolts at the wing root went fine. They’re not torqued to spec, I’ll torque all of the bolts during the initial assembly and mark them all with Torque-Seal or some other witness marking paint. With those done, I moved on to the other brackets. I found that with the very slight variations in hole locations, some of the brackets needed a hole adjusted slightly to get everything lined up properly. It was also a real bear getting the bushings back into their holes after varnishing. Let’s just say there’s no play there… they’re fitted nice and tight.

In the end, I got all of them installed and everything lines up the way it should. I need to find one more AN4-16A bolt, but I think I may have one at the hangar. Next step, I think, will be to cut and fit the cover plates for the brackets where the fabric will be glued down where the brackets come through.

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Wing fittings and aileron work

I’ve spent a couple hours this week getting bolt length sorted out and getting some of the wing fittings attached.

My strategy for the wing attach fittings was to make one of each type of fitting, pilot drill the holes with a 1/8″ bit, and use those to mark the location of the holes in the wing spars. Those holes got drilled on a drill press using Forstner bits. Then I cut the rest of the fittings, used the first ones as templates for drilling them, and figured all of the holes should line up.

Well – they’re close. I’m not a machinist, nor am I using tools techniques of suitable precision to produce perfect parts. For example, when looking at the CAW2A wing root mounting brackets, the holes are not perfectly aligned – so there’s a top and bottom to those, meaning until I figured that out it took a few tries to get everything lined up right. No big deal.

Then I discovered that one of the holes isn’t drilled perfectly square. It’s only off by maybe .010 total, but just enough that you can’t run a bolt through the forward bracket, the bushing, and the aft bracket without interference. If the bolts were just going through holes drilled in the wood of the spar, it would be fine – but the bushings are a snug fit, I had to do a little adjusting of that hole to get everything to fit properly.

We finally got the bottom of the aileron leading edge routed so that it’s now in its final state. When fitting the aileron and checking travel, I discovered that I’d messed up just a little when up finishing out the aileron bay. On the first wing, I’d positioned the top beveled strip with the aileron in place, and checking clearance per the plans. On this one, I just measured the first wing and matched it. I don’t have enough up travel on this aileron. After a little more investigation, it’s just the ends that interfere, so easily cleaned up with a couple minutes of work with the razor plane. I’ll need to pay closer attention on the next two wings. I’m thinking just use a length of 1/4″ shim stock to set the spacing with the aileron solidly fixed in its final location.

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Catching up

I’ve missed a couple of updates to work done on the plane over the past week or so. I got the second coat of varnish on the wing, including the aileron. I got all of the bushings in place, and started to attach the various attaching brackets… oops! No torque wrench. And, I can only find one CAW9 bracket. I think I ran out of 3/16″ x 1″ 2024 flat bar stock before I got them all made; I need to go hunting and gathering again. Once that’s done I can finish off the aileron (the lower leading edge needs a pass through the router for its radius) and move on to varnishing the other wing.

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Boy, I’m bushed!

Today I took the wing brackets over to the shop, sorted them all out, and re-marked them so I could tell one part from the other. There are seven (I think) different bracket types. The acid etch solution had removed all of the markings, along with other stuff.

I sorted out which brackets are needed for the right lower wing that’s on the bench, and checked all of the bolt sizes for proper fit. All are acceptable, if not perfect. I have AN4-24A bolts (1-15/16″ grip length) for the main spar root attachment brackets; I could have used AN4-23A (1-13/16″ grip length). It’s not a problem; a couple of AN960 washers do the trick and are a perfectly acceptable solution. On the rear spar N-strut (outer end) brackets, the AN4-16A bolts are a tad long; I could have used -15A. Two AN960 and one AN960L are fine. As a mental exercise I calculated the weight savings if I ordered the shorter bolts. The shorter bolts would weigh about half an ounce less (total per wing); the washers would bring that up to just a smidge over half an ounce — .53 ounce, or about 15 grams per wing. I can live with that.

But I digress. I got all the remaining bushings cut. Once I wrapped my head around that fact that the bushings do not need to be cosmetically and dimensionally perfect, but just need to be “flush or slightly below” the face of the wood per the plans, things went a little quicker. I pulled the 24 tooth per inch metal blade from my bandsaw and replaced it with a 10 TPI wood blade, which is fine for thin wall AL tubing like this. I set up the miter gauge and fence for the length I wanted. The tubing cut-off end was snagging the blade teeth; Stew suggested a spacer on the rip fence that extends just shy of the blade. That did the trick! Now the cut-offs roll out of the way. I cut one piece and tested for fit in the hole; once that was verified I was able to set the fence once and cut as many pieces of each diameter tube as I needed. Easy peasy. That will save hours of build time.

Now I need some etching primer for the brackets, and spar urethane for the wood, and I can get everything installed and call this wing done.

Oh, after I cut the bracket for the aileron connecting rod.

And get the bearing block holes drilled.

And… whatever else I’ve forgotten.

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More bracketry

Today I got my bag of bolts, washers, and nuts from Aircraft Spruce. Wanting to make sure I had all the correct lengths and all, I headed over to the shop to try them out. As you might guess — especially if you know me — all of the brackets were at home, so no joy there.

I did order a 14 TPI bi-metal bandsaw blade, it should arrive tomorrow. The 24 TPI metal blade is just way too fine for cutting this tubing. Stew says the 10 TPI wood blade I have would do fine — but I want something I can use on the 2024 stock without worry.

Once back at home, I treated all of the brackets with Alumiprep (now known as “Bonderite C-IC33 Aero”). It’s a phosphoric acid etching cleaner, does a bang-up job of cleaning up and etching aluminum parts prior to conversion coating or painting. Well, as it turns out, my Alodine is no good any more. No surprise, really. I left a set of brackets in the bath for an hour and could barely see a tinge of tan or gold color, not enough. Too bad, I was really hoping to use that. I’ll need to pick up some good self-etching primer instead, I’m not spending close to $100 for a quart of Alodine that I’ll then have to dispose of later on.

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Bushings

On Wednesday I went over and tried cutting some of the bushings used for the bolts that hold the brackets to the wing.

I’ve cut a couple with a chop saw, but one got away and ruined a saw blade and almost took my thumb off. I think I could fix that problem, but after ruining one nice Freud carbide blade I’m not really inclined to pursue that method again. I’ve been using my small (9″) band saw with a metal cutting blade, and it’s been a bit of a struggle. I’ve had no success getting the miter slot aligned to the blade, so I made a custom miter gauge with a slight angle to get straight cuts. I wrapped masking tape around one end and made test cuts until I got a square cut. After cutting, I typically need to take a few thousandths off with sandpaper before I get the correct length.

Until now I’ve been scribing a line with a micrometer and following that with the blade. I think I’m going to switch to clamping a fence down on the table and using that for repeatability. I have three sizes of tubing — 5/8, 1/2, and 3/8 OD. Bushings are made with one, two, or three pieces of tubing nested together, so I need to cut identical length pieces. The 1/2 and 5/8 tubing is a snug enough fit that I can cut them together, but the 3/8 OD is not a snug fit, so I end up having to cut that separately or it spins and moves out of position. I’m going to just try a different approach, as making these bushings is taking forever.

I’ve been using a 1/2″ wide, 24 TPI metal cutting blade on the saw. I think it’s too fine for the AL tubing; I’m going to try a different blade. Of course I’ll have to order it. I have the 24 TPI, as well as 6 and 10 TPI wood cutting blades. I think I want to try 14 TPI.

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Wing metal parts

Over the past couple of days I’ve been collecting, drilling, and prepping the aluminum wing attachment parts. These are a collection of pieces cut from 6061 and 2024 AL bar stock. They will be used to attach the wing spars to the fuselage, attach flying and landing wires, and attach the N struts, and connect the upper and lower ailerons. Each one must be cut from the raw bar stock, drilled for bolts, and some of the ends rounded. I’ll do some sort of finish to prevent corrosion. I have some Alodine left over from when I was building the RV-12; if it’s still usable I’ll use it. If not, I’ll most likely buy some.

More than once the instructions have caused a little bit of panic. For example: Yesterday I drilled all of the holes in the attachment brackets to their final quarter inch (0.250) size. I remember that I’m short some pieces, but didn’t remember which ones or how many. I’m also unsure of which ends of which brackets need to be cut and sanded round. This morning I looked at the plan revision sheets that show the drawings for the parts… and saw that the drawings call out all of the holes to be 0.1875″. Panic!! Holy moly, did I just ruin all of those parts and waste all of that work? Oh, wait. I’d made little 3D printed pieces to help mark the ends for cutting… and those have 1/4″ bosses to fit the holes, so I planned 1/4″ holes before. And a 3/16 hole would fit an AN3 bolt. I’m pretty sure the plans call for AN4 bolts everywhere, and there’s no way in hell I’d be comfortable with wings held on with AN3 bolts…

Back to the wing spar plans… Yep. AN4 bolts and 1/4″ ID bushings everywhere. The supplemental drawings are incorrect or out of date, no big surprise. Back to work.

I did manage to badly mis-drill one of the CAW9 brackets, so that’s scrap — but it really doesn’t matter in the long run. I came up a little short on the 3/16″ 2024 stock needed for some of the parts, so I’ll need to buy another 12′ length anyway. It’s an odd size that is difficult to find on line, but fortunately my local supplier can get it for me even in single piece quantity. Even they don’t list it in their catalog. Most places only carry 2024 in 1/4″ thickness or more.

After inventorying my parts I need another 60″ or so of 2024 stock, and I only have about 3′ if that. Fortunately the parts I have on hand are enough for the two lower wings, so I can cut the bushings, buy hardware, and attach all the pieces on the two wings I have built and get them finished before moving on to the upper wings.

I got over to the shop to make sure the bolt lengths called out in the plans were OK. I’m glad I did. IN each case I decided to bump the bolt up one number to get the next longer grip length; the exception was the three bolts on each wing that attach the CAW-4 landing wire brackets. Those were specified nearly half an inch short; I had to go from AN4-20A to AN4-24A to get the right grip length. I’m glad I checked. I also ordered a couple dozen standard and half-thickness AN960 washers to get everything done up right. The hardware is ordered, now I just need to get the bracket ends done and get them prepped for installation.

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Scallops and metal work

Today I had Stew help me mark the leading edge for the scallops, and got those cut. After getting home, I spent an hour or so rounding up and drilling all of the aluminum wing brackets I have cut so far, which is most of them — all but a couple, I think. I seem to recall I ran out of 2024 with one or two left to go. Anyway, I figure I should get them all done up. I’ll need to cut bushings, mount these, and get the fabric stiffeners cut and fitted — along with varnishing the wings — before calling these two wings “done”. Oh, and I’ll need to get the final torque tube bushings milled out and mounted.

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More aileron structure

Getting the CW35 aileron nose ribs located perfectly in the aileron is critical to making sure the aileron is straight and consistent with the other wing. Today I slid the torque tube into place and checked the fit of all the pieces that I can at this point. After making some adjustments to the holes in the CW36 end plates, I glued the three CW35s in place in the middle of the aileron. The next step will require cutting the trailing edge to install the aileron end caps, so I want to make sure the torque tube location is easily and consistently reproducible.

I think at this point I may just bolt the torque tube bearings in place (I have a set of 3D printed temporary pieces) and cut the last piece of AL tubing in half. This will let me work with a much shorter and easier to handle piece of tubing while setting up the ailerons.

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CAW2 brackets

Over the past couple of days I’ve gotten all 14 of the CAW2 brackets shaped. I had drilled all of them already, but the ends needed to be rounded off. One end of each will be hidden inside the wing, but some will have one end exposed so I wanted them looking decent.

I designed a radius guide to help with the bandsaw and sander. It’s just a 1″ diameter disk, with a short 1/4″ button on the center of one face. Stick the button into the hole on one end of the bracket, and the guide is there to show a 1/2″ radius all the way around. My original idea was to use them to scribe a line to follow when finishing the ends. I had 3D printed a couple of them, and found it was just as easy to just leave it in place and work around the edge. Inevitably, of course, you end up nicking one so I printed up a batch of 9 more. I used 3 of them to finish off the CAW2 brackets.

Given that there are a bunch of other brackets to finish, I’ll definitely try the scribed line approach as well. Overall, though, I’m pleased with the results. I used the bandsaw to lop off the corners, then shaped the ends with a disc sander and finished them on a Scotch-Brite wheel. I had planned to paint them, but I may not. I’ve still got a batch of metal etch and Alodine (Bonderite 1201, to be precise), so if it still works I’d like to just give them a conversion coating that weighs nothing; that way they are protected from corrosion but only the exposed parts get paint. I’ll probably try a test piece to see if the Alodine still works; if not, I’ll get some self-etching primer and use that instead.