Tag: Band saw

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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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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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Miscellaneous work

Today came and went without mixing up any glue. I sorted out the nose plywood, then went through all of the aileron pieces and got them cleaned up, marked, and re-taped for the three remaining ailerons. I got the aileron spar web and marked it for the notches to clear the ribs, then brought it home and started cutting those notches on the bandsaw. I pulled a wingtip bow down and checked its fit; it looks like minimal trimming will be needed.

I also collected all of the aluminum pieces I had at Stu’s shop and brought them home, and cut the ends on the bandsaw. They’re all CAW2 pieces, I think — I need to dig out the rest of the pieces and get them all drilled and finished off. I’ll finish them on the belt sander and Scotchbrite wheel before priming them. My little 3D printed guide button worked great for this. I don’t recall if I described it or not, but it’s just a 1″ diameter by 1/8 thick disk, with a 1/4″ diameter by 1/8 thick nub in the center. Put the little piece in a 1/4 bolt hole, and the larger piece gives you a perfect guide for shaping the end of the bracket with a 1/2″ radius. They’re disposable if you nick or break one, and only take a little while to print up. I’ll probably print a few more in case I destroy any while using the belt sander.

I spent some time trying to determine whether the wing walk pieces will be of any use to me or not. The plan sheet and plywood supports all seem to be made for some earlier version of the wing. The notches on the supports don’t work (or even come close to working) with the root blocks on the main spar or rear spar. The forward plywood bits are too long, and even if cut off don’t match the curve of the wing ribs. There are supposed to be three installed forward of the spar — but that would only work if I removed one of the false ribs. I still don’t know what I’ll do for the wing walk. I do know that 1/4 plywood for the rear portion would need some curve in it, and I’m not sure about that. The plan notes say to nail it in place until the glue dries… ::shrug:: This is why I’m considering a laminated layup with some wood and maybe a layer or two of carbon fiber.

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Cold weather musings

Haven’t done much on the plane for a few days now. We have been in the grips of a winter storm, followed by a cold snap. We got several inches of snow; anywhere from a couple inches in the front yard to maybe 2′ drifts closer in to the house. The temps throughout the 3-day weekend never got above -7, and the wind was blowing. This is not weather conducive to going outside for anything non-essential.

During the last build session, I tried cutting a few of the bushings needed for the wing. The results were not great. While a chop saw will go through and make a beautiful clean cut, it will also randomly launch the cut-off piece somewhere in the shop, often with a nice big chunk out of the end. Not what I was after! I did get one bushing cut successfully, and another done after much filing to get it down to its final size.

After doing some research, I believe I’ll end up building a band saw sled to cut the bushings. I can make it with a nice end stop to cut the tubing to consistent lengths, and it should make it relatively easy to get an acceptably square cut. I’m hoping the cut ends turn out clean enough to dress with a brief time with some sandpaper.

The bloody compass is still very slowly seeping fluid. I suspect the face plate is not perfectly flat. I think for now I’ll leave it, but at some point I’ll need to drain, disassemble, and maybe use a thin coating of Aviation Form-A-Gasket on the black rubber seal. At least everything works well, it looks great, and the LED light is quite effective. I have no idea why I’ve invested so much work into a mag compass, to be perfectly honest… but it’s been an entertaining project. I just like restoring old things.

I’ve had no success at all getting answers out of “CKD.aero” regarding the pricing and availability of parts and subkits for the Celebrity. I’ve been trying to get pricing for the wing tanks so I know whether to plan on using them or not. It just feels like Fisher got bought by people who have no clue what to do with it. The website has been stripped of any pricing or availability information. It took me weeks to get anyone to even respond to an email, and despite a couple of promises I have yet to get a useful response from anyone. I guess I’m on my own. It’s a shame, but I did decide to build from plans; I think I’ll be able to muddle through.

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It’s damn cold outside!

I’ve been wanting to get back to building ribs.  The garage bench has been piled too deep to get anything done, and now it’s been below zero for over a week solid.  Insulation or no, it’s damned cold out in the garage.  Too cold for epoxy to cure, and too cold to work.

So…  there’s a perfectly good work bench down in the basement.  8′ long and rock solid, built by Dad back in the 1960s.  It’s been pretty much completely covered up for the past several years with a collection of parts, partially-disassembled or -assembled prototype projects and assorted debris from the side business I was running, plus a CNC router that took up about 3′ of it.  I have cleared most of it off (much of it into a trash can).  The CNC machine is shelved for now; I’ll maybe resurrect it when needed at a later date.  It will probably come in handy for cutting the instrument panel and/or nose ribs.

The next issue is containers for the geodetic rib braces.  There are 24 braces used in each rib, all of which are of course slightly different.  Just enough so that none are interchangeable.  I was using paper cups to hold them in the garage, but it’s a completely unsatisfactory solution.  In the basement I think I’m going to try stapling taller plastic cups along the back edge of the bench and see how that works.

I’m not moving power tools down there from the garage, so new geodetics will be cut with a razor saw.  We’ll see how that works out…  it’s one of those jobs I wish I could set up a machine or fixture to do.  It’s 24 different lengths with over 40 different angle cuts, so I’m not sure how I’d make that work.  Even cutting them out in batches on the band saw meant fine-tuning each one with a sanding block before assembly.  It’s fiddly work and tedious as hell.  Classic gusseted ribs would be a whole lot faster and easier to build.  If I were starting this over I’d probably just depart from the plans and build them all that way; I’d probably have them all done by now.

 

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Bending more capstrip, and glue efficiency

Last night I tested out the upgraded steam box door with an hour of steam.  While that was going on I grabbed a chunk of scrap 2×4 and cut a second bending form.  I wasn’t happy with only being about to bend three lengths per run of the steam box.  I really need a better blade for that band saw…  this one is cheap, and while it will claw its way through a 2×4 it’s not something I would want to do regularly.

But — I have two bending forms, which means I can now do six lengths of capstrip at a time, so I won’t run out as often.  The steamer seems to work pretty well.  It’s not quite as perfect as if I had attacked it with a planer, jointer and an attitude of complete professionalism…  but I don’t have a jointer or planer, and even if I did what that steam would do to cheap flat sawn boards would be a real downer.  It works.

On the last several ribs I’ve been taking a different approach to gluing.  Early on I found that trying to glue up two ribs in one night meant working with epoxy that was starting to get a little stiffer than I would have liked.  I was using a popsicle stick to carefully spread glue in the groove, then on the braces, and assembling.  I was also having to fit each brace piece as I went along.  Each rib seemed to want about 10cc of glue, but I was getting a fair amount of it running down onto the plastic on the jig.

Now I pre-fit all the braces and mark them with their location.  I mix up the glue, dip the ends in the glue and put them in place.  I can work a lot faster and make less mess.  I’ve been seeing more left-over glue than I would like, as much as half what I mixed up.  I think about 7.5cc of glue per rib is more than enough.  I mixed 15cc for one pair of ribs and only had a little left over.  I’ve also been more careful about the glue mixing.  I had the ratios close enough to work well, since T-88 is not too critical.  Still, the darker B component was getting used faster than the A, and that tells me I’m not getting it completely right.  The stuff is pretty viscous, B much more so than A, and it takes a while to level out in the mixing cup.  Now I’ve been squeezing the B part into the mixing cup and walking away for a few minutes while it levels out.  Then I add the A component, walk away again, check back in a couple of minutes.  I can get it dead on 50/50 that way.  I may see about building a 100:83 balance scale to get it even closer.

 

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Second jig built

Yesterday I did a little shop cleanup.  Not a lot, just enough to get done what I wanted to do.  I cut a length of 3/4″ x 3/4″ pine and cut a bunch of 1-1/2″ blocks for the second rib jig.  I got the work bench partially cleared off.  The box from the R/C Cub went underneath, and the plans sheet and wings were moved to one end of the bench.  I now have roughly half the bench covered by model airplane wings, while the other half is being used to build the real thing.  ‘Murica, as my kids would say.

So, I built the second wing rib jig.  I used the first rib from the first jig and blocked everything up.  I used some plastic sheet Lisa had picked up underneath it to prevent the glue sticking things together.  When it was all finished, I mixed up 20cc of epoxy and glued up two ribs.  That’s going to work as long as it stays cold, but the glue was gelling by the time I was finished.  If it warms up at all there won’t be time to do two at a time, unless I can find a way to pre-glue the capstrip grooves a lot faster.  I wonder if thinning out a portion of the T-88 and brushing it into the grooves would work.  For that matter, I wonder if pre-gluing the grooves is even necessary.

This morning I pulled both ribs from the jigs.  You can’t tell them apart, and you can’t tell them from the other four I had done.  Any differences between the six ribs I have done are slight enough they can be removed by sanding.  So, now I can double my production rate.

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#2 rib glued

I spent some time cutting geodetic braces.  I stacked five of the thin capstrips, laid out the parts along them, and cut them with the bandsaw.  I now have enough parts to make half a dozen more ribs.  It’s slow going with the geodetic capstrip, because each one has to make three passes through the spindle sander to shave them down to 3/32″  Holy crap that’s tedious.  I may try using the table saw when the thin strip rip jig arrives.  Even if I can get them close enough to just make a single pass on the sander it would be a huge improvement.

I tried a different technique for applying the glue.  First I dry-fit all of the parts to make sure I didn’t end up with a brace with glue all over it that needed to be trimmed.  I marked the top and bottom capstrips with a pencil to indicate where the groove needs to be glued.  Then I pulled them out of the jig and used a trimmed-down popsicle stick to apply epoxy to the grooves.  Back into the jig, with the front and rearmost vertical pieces in place since those are impossible to install with the capstrips in the jig.  Then I proceeded as usual, installing all the other parts with epoxy.  It worked like a charm, and resulted in no glue running down where I didn’t want it.  We’ll see how this rib looks when I pull it out of the jig tomorrow…  and we’ll see how closely it matches the first one.  In theory they should be identical, but I’ve  never done this before, so…

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First rib glued!

After a couple hours of cutting and sanding geodetic pieces, I finally mixed up a little T-88 epoxy and glued up the first rib.  Kind of a milestone — the first full size wooden rib I’ve ever built.  Can’t wait for tomorrow when the glue is hard enough to pop it out of the jig.  Then we’ll see whether this one gets used on the airplane, or used for destructive testing.

Cutting those geodetic pieces is a lot of tedium.  Even more so since I didn’t aend the strips before cutting, so I then had to sand each piece individually.  next time I’ll clean up the capstrip prior to cutting.  I was cutting two pieces at a time, with the capstrip stock taped together.  I may go for 4 or 6 pieces at a time as I get better at it.  And, I need a better solution for holding the pieces.  I knocked three of those cups off the bench at various times while assembling it.  Things will be a lot easier if and when Pete’s R/C Cub gets off my workbench.

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Finally — the first shipment of spruce!

The UPS man just delivered a 30# package of spruce capstrip from Aircraft Spruce.  I can now — finally — start building.

The first step was to set up the table saw to groove the top and bottom rib capstrips for the geodetic braces.  They need a 3/32 x 3/32 groove cut on one side.  Getting the saw set up to cut a perfectly centered groove was trivially easy, and it gave me a reason to install the zero clearance throat plate on the saw for the first time.  Not wanting to experiment on the expensive spruce, I cut a couple of strips of pine the exact size of the capstrip and used one to set up the saw for the right depth and spacing.  The strips are small enough that rather than trying to use a push stick to feed it all the way through, it works out best to feed most of it through in one direction and then flip the piece around and feed the other end in.  The saw is set up precisely enough that you can’t see where the transition is between the grooves cut from the two ends.  It’s perfect.  With that done I grooved a dozen pieces of capstrip and decided that would be good for a limited test run.

I’ll also need a bending jig for the capstrip, since the top piece needs a pretty good curve toward the leading edge.  I could really probably do it dry, but I’ll feel better knowing that the wood is less stressed during assembly.  Better to put the curve in beforehand, I think.  The spruce is flexible enough that I don’t think there will be a problem with the bottom pieces, but we’ll see how it works out.  I cut a bending fixture from a chunk of scrap 2×4 — it split on the end as I was finishing up the cut, so I figured what better time to mix up a spoonful of T-88 and epoxy it back together?  After all, the glue joint should be stronger than the wood itself.  We’ll test that out.  Once that glue cures and I get some capstrip soaked in water and bent, I will finally be able to finish blocking in the rib jig and start cutting the geodetics.  I’ll need to also set up some sort of rig to sand or plane the ends of those down to 3/32″.

The grandkids are coming over Saturday to get some help with their Pinewood Derby cars.  Looks like a full-on woodworking weekend.