Tag: Tools

Posted on

The easy way to manage T-88 epoxy

I’ve seen all kinds of methods people use to mix up their T-88 epoxy. The manufacturer says to mix the resin and hardener (Part A and Part B) 1:1 by volume, or 100:83 by weight – which are the same thing. Plenty of videos on YouTube and EAA Hints for Homebuilders show various methods, and I’ve read some pretty involved threads on various homebuilding message boards. Some squeeze out equal lines of the two parts. Some cut the bottle tips to different sizes and squeeze out for a measured amount of time. Some have built scales to measure out by weight. Some do it in graduated mixing cups, like the little medicine cups that are easy to find. Some just use “TLAR” – or, “That looks about right”. You can buy T-88 in twin dispensing cartridges that automatically dispense and mix the glue — but it’s something like six times the cost of buying it in bottles, and of course you’re going to waste some each time when you throw out the mixing tube.

I have a bit of an aversion to not measuring epoxy accurately, and estimating and hoping for the best didn’t seem to me like a good plan when building an airplane. I know the precise ratio isn’t super critical; even System Three says that. Still, though, why guesstimate or get “close enough” when it’s so easy to get an exact amount?

I bought some 60cc catheter tip syringes through Amazon. They’re cheap and disposable, though I’ve reused mine a number of times. I fill one with Part A and one with Part B, and usually use a permanent marker to mark the cap for the Part B (darker) syringe, just so I don’t accidentally mix the caps up and ruin some epoxy. I’ll fill them just past the 60CC mark, then stand them tips-up overnight to let all the trapped air bubble up to the top, then squeeze a little back into the bottle or jug until the plunger is exactly on the 60cc mark. Pull the plunger back just a bit to get a little air in the tip, and cap it.

By doing this you can very accurately measure both parts to mix up any desired quantity of glue, from 2 cc up to 120 cc. Gluing plywood spar webs to spar caps? I’ll mix up 20 cc at a time, 10cc from each syringe. Building ribs? About 8 or 10 cc of glue will do two wing ribs, so 4 or 5 cc from each syringe. When the syringes are empty, you can either be a cheapskate like me and refill them, or just toss them in the trash if they’re too grungy to re-use or if you’re Daddy Warbucks and don’t care about the cost. I’ve got two pair of syringes that I use, and each has been refilled probably six or eight times. I just ordered some more syringes, since these are getting a little sticky and I want to keep fresh ones on hand. I use them for other things as well, so it’s never a bad idea to have some around. You also don’t want to run out of glue before you’re done building for the day, so I try to always have at least two sets filled.

Note: Pay attention to the quality of the syringes you buy. The first few I bought were made by B-D (Beckton-Dickinson) or Brandzig, are nice heavy duty plastic, are marked with 1 cc graduations, have good caps, and are generally high quality. The next batch I bought are thin, lightweight, shorter, marked with 2 cc lines, and are generally cheap Chinese crap. I’ll toss these after the first use and chalk it up to a lesson learned. As is almost always the case, it’s better to spend a little extra for good quality.

Posted on

Started on the second spar

This morning I went over to Stu’s and finished gluing the root attach blocks and the blocks for the N strut and flying wire brackets to the spar. Other than the tapered extension for the wing tip bow, that’s all of the wood for the first spar. Once the glue is cured, I can start locating and drilling the holes for the attachment bolts and bushings.

With that done, Stu and I started on the second upper wing spar. The bench has threaded inserts set into the edge, and he’s got a long steel rail that bolts on. It’s 2 x 2 inch square steel tubing with mounting brackets welded on. The rails were designed and built to bolt to the table, then he’s got a steel sled that sits on them that he can use to flatten a large wood slab using a router. We bolted one rail to the edge of the table, overhanging the work surface. Now there’s a long work bench with a straight, level steel rail on one edge.

We glued the groove in the spar cap, inserted the plywood web, then glued the other spar cap. One spar cap is clamped against the rail, then the assembly is clamped in place to hold it straight, flat, and properly spaced at 5-3/4″ total spar height along its entire length.

I think about 10 ml of epoxy is plenty to glue one spar cap groove. I mixed two batches today. I’ve been using 60 ml syringes ordered from Amazon to hold and measure the glue – it works wonderfully. I can very precisely measure out even very small quantities.

Posted on

First spar, continued

It’s been a bit of a learning experience building this spar. The amount of glue required, of course, is one thing – about 45 ml or so, I think, for the whole thing. There are still a few pieces of plywood that need to be glued, most of them for the flying wire and N-strut attachment brackets. Yesterday Stu showed me his pneumatic pin nailer, which I plan to use. It’s not unusual to use staples or small brads to hold wood together while glue cures. This thing shoots ridiculously small wire pins — 22 or 24 gauge, I think — with no heads. They’re just enough to hold the wood in place, and won’t need to be removed.

I also found that the spar has about 1/8″ of gradual taper toward the tip end. That was a builder error; it’s supposed to be a constant 5-3/4″ across the entire length. When I assemble the other three they will be correct. It’s not a critical error; I can fix it with shims when the wing is assembled. It’s even noted in the plans that ribs may be shimmed where they attach to the spar. It’s just been an inconvenience. Before I found that taper we’d cut some reinforcing blocks that fit between the spar stiffeners to a constant length. Some needed to be sanded, some needed to be re-cut because they were too long. That’s when I measured the spar height more carefully. I had just measured one end and a spot partway down the spar before — I guess it didn’t occur to me that it would have a taper to it. Everything else is good, there’s no bend, twist, or warping, so it’s good to go.

Other minor things — the plans call out 120-1/4″ for the spar length, but the main caps are 120″. Obviously the quarter inch at the tip isn’t going to make a difference, I’ll just make sure both spars are exactly the same length.

I’ll go over tonight and finish the assembly of this spar, and hopefully get started on the next. I also need to find my box of 4130 steel tubing and see if I’ve got the stock I need to make the bushings for the wings. There are bolts through the wing that hold the attach brackets for the fuselage, struts, and flying & landing wires. All of the holes need steel bushings through them. Simple enough to cut and file to size; I just need the right size tubing. I bought a “grab bag” assortment of random tubing cut-offs from ACS a while back to see if I could learn to weld. If I’ve got a couple feet of the sizes I need, I can use them for this.

Posted on

A few more false ribs

I glued up two more last night, and will do two more tonight. That will make 18 down, with 20 19 more to go. I’ll typically take some time at lunch to cut out the cross brace pieces and get everything set up. Then after work I’ll mix up some T88 and glue the ribs up, then let the glue cure overnight. By the next morning I can pull them out of the jigs and start again.

I’ve run out of cross-brace stock that’s been sanded down to 3/32″, so I’ll have to stop while I retrieve the small shop vacuum from the project house where it is now and run some more 1/8″ stock through the drum sander. It’s a pain, yes, but it has to be done.

I’m already debating where to go from here, once all of the false ribs are finished in a few weeks (maybe). I could start on the tail, but that will require a 4 x 8 work surface. The wing spars will require a longer bench, at least 12′ long. I may instead start working on cutting out the large number of nose ribs that will be needed, and the other high volume plywood parts. It’s awfully tempting to set up my CNC router again for that part, but I doubt that I will. I’d have to translate the outline from the printed plans into G-code for the router, and quite frankly I think by the time I got that right I could cut them all out by hand. I’ve seen a couple of guys use a router and a flush cutter to route the nose ribs from a pattern. I’m a little concerned about the radius on the inside corners where the nose rib glues to the false spar. I figure I could either sand a matching radius there, or touch up the corners of the nose ribs with a bandsaw or something. I’ll cross that bridge when I get to it.

Posted on

Bending wood and building ribs

I got two false ribs glued up last night and pulled them from the forms today.  The new razor saw arrived yesterday afternoon, so that was nice to have.  I’m leaving all of the ends of the top and bottom capstrips a little long.  I am planning to just build a sled for the table saw out of MDF, with dowel pins or wood blocks to locate the ribs for the four cuts I’ll need, referenced to the main spar and rear spar.  That’s one cut for the nose, one for the trailing edge, and two for the tail ends of the false ribs.  That can wait until all of the ribs are finished, maybe later depending on how cold & crowded it is in the garage.  They really don’t NEED to be trimmed until I’m ready to assemble the wings, so that may be a while yet.

I figure I’ll get two, maybe three false ribs out of a pair of capstrips that would make one regular rib, so I’ll have plenty of opportunity to use whatever method I do finally end up using to pre-bend the wood.  Over the past couple of nights I’ve tried a couple of methods of bending capstrip.  The other night I ran a bucket of the hottest water I could get from the tap.  It was probably 140 F or so, coming from a bar sink just a few feet from the water heater.  I put half a dozen capstrip pieces in there, let them soak a couple of hours, and put them on the bending forms.  That seemed to work well, with no broken pieces.

Last night I added a gallon or so of hot water to the bucket, just to top it off some more.  The water would have been lukewarm at best.  I soaked another half dozen strips for 12 hours or so.  Of the six, one snapped as I was bending it in the form.  That’s about what happened the last time I tried soaking in cold water, so obviously that’s a waste of time and good spruce.  Won’t make that mistake again.

Posted on

Ready for ribs

Well, the work bench is cleared off — well, at least enough to get both jigs on it.  I’ve got a couple dozen sticks of geodetic brace stock shaved down.  The epoxy syringes are filled.  All I need now is a razor saw and a steam setup.

Yes, I have a razor saw.  Somewhere.  I pulled it out during the kitchen remodel, and I remember seeing it in a box of tools we were using, but now I can’t find it.  It’s a Zona, good quality but inexpensive.  A new one is on the way.  Two, in fact; one medium and one fine tooth.  I also have a steam box that I built for the capstrips, but I’m unsure whether I’ll use it in the basement.  It takes bench space (which I now don’t have down there), and drips water out the end by design.  I’m thinking about ways I can use it vertically.  I had looked at rigging up a piece of pipe or something with a heating element for hot water, but it looked like an awful lot of extra work considering I’m over halfway through the ribs.  I’ll probably need it for the tail and wingtip bows as well, but I’m not entirely sure yet how I’m going to steam 6 to 9 foot long strips of wood.  Tonight I tried soaking half a dozen capstrips in a bucket of hot water for an hour — we’ll see how well that worked. 

Posted on

Mixing epoxy

I’ve been mixing epoxy in the little plastic medicine cups using “craft sticks” (think Popsicle stick).  I thought I was doing a pretty good job of stirring, spending some time scraping the sides and swiping along the bottom corners of the cup to ensure everything was mixed up.

Last night I mixed up about 2 cc of epoxy, mostly just to try out my new syringe dispensers.  I let it sit in the cup with the stick propped up in the center.  Today I popped the slug of glue out of the cup.  Lo and behold, there are sticky spots around the edge!  Nearly all of the glue is perfectly hard and cured, but there is just a tiny little bit of uncured epoxy right around the bottom edge.  Apparently the stir stick is not a good tool for making sure ALL of the material gets mixed together.

In light of that discovery, today I did another 2 cc sample.  This time I did the mixing with an acid brush with the bristles trimmed down to about 1/4″ to 3/8″.  After mixing I cleaned the brush out with a little MEK, just to see if that would be worth doing or not.  We’ll see how that one turns out after the epoxy has had a chance to cure.  Acid brushes are pretty cheap, so even if the MEK cleanup doesn’t work out it’s not a big deal.  You can buy the brushes by the gross for around $0.12 to $0.15 each.  But what will I do with about 950 craft sticks?  Good thing I have grandkids.

 

Posted on

Prep work

I’ve been away from building for a while dealing with a remodeling project, the annual condition inspection on the RV-12, Oshkosh and few other odds & ends.  At Oshkosh I discovered that the wood shop guys had actually saved my miniature wing rib from last year (2016).  I brought it home with me, of course.  Last night I pulled the staples, cleaned it up and sanded it, and gave it a coat of clear polyurethane.  I figure it will make a nice wall decoration for my office.

Last night I also started cleaning up some of the enormous mess in the garage so I can get back to building.  I’m not quite there yet, but tools are slowly making their way back into drawers and onto pegs.  It may take a few more days, but it will be nice to get back out to a garage that’s not a complete disaster.  There are 14 wing ribs hanging on the wall, and the guy on the Biplane Forum is catching up with 11 finished.  He can work faster, since he can pull his ribs out of the jigs as soon as they are stapled.  I need to step up my game!

I did pick up a good idea from that discussion — using cut down acid brushes to mix & apply the epoxy.  They’re cheap, and it looks like I might be able to get more precise application of the glue where it’s needed, in the amount needed, with good penetration into the wood grain.  I’m anxious to try that, I have a handful of brushes here.  And, I got some of the epoxy  into 60 cc syringes so I can dispense exactly the same amount of each component.  I know it’s not terribly critical with T-88, but I still want to be as accurate as I can.

Posted on

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.

 

Posted on

Fixing up the steamer

I built two more ribs last night and took them out this morning; I’m up to 14 now.  I’m trying to 3D print some clamps too use on one of the jigs that has locating blocks too thick to use the small red sprig clamps I bought.  of course first I have to fix the 3D printer…

When I used the steam box, the door warped — no, curled outward.  I flattened it out, but because everything isn’t perfectly square it really only fits on one way so I can’t just flip it over.  Tonight I cut a couple of 3/4″ square stiffeners and epoxied them to the outside of the door.  I need to bend some more pieces of capstrip, and I can’t do that until the door is usable.  We’ll see if this is enough or not, should be interesting at least.