Biohazard build thread

I would just tack it to one side with fast epoxy and after that cures fill the other side with thickened epoxy.


[emoji1010] Steve Shannon [emoji1010]

Steve Shannon said:

I would just tack it to one side with fast epoxy and after that cures fill the other side with thickened epoxy.

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I'll do something along those lines.

What turns out to be interesting to me during a build may not be the same as what's interesting to others. In this case, I finally figured out the most effective way to round the edges of balsa fins. For my rear fins, I needed to work a concave edge (the leading edge), which dictated a different approach from what I had been using. It turned out that I stumbled on what is, for me, *by far* the best method I have tried, for any edge, regardless of shape. This is for balsa only, although maybe it would work for basswood. Definitely not plywood, nosirree.

Step 1: throw away the sanding block (OK, don't actually throw it away, those things cost money. But put it aside for now).

Step 2: take a piece of 400 grit sandpaper and wrap it around your finger, like so:


Step 3: run the sandpaper along the edge, side to side. Traverse the entire edge with one stroke, then adjust the angle as necessary and repeat until finished.


Step 4: there is no step 4.

Using the finger in this way offers so much more control than any other way I had tried. This way I can feel exactly what's going on where the sandpaper touches the wood, and the results were incredibly quick and nearly effortless. Such a small thing, yet so satisfying.

Biggest lesson I've learned during this build so far: know when and when *not* to use the sanding block.

Would be interested to know how this technique compares to others'.

Your writing is hilarious! :lol:

It occurred to me that I should check that the depth of my TTW fin tabs was correct. I mean, I measured it pretty carefully in the laser-cutting drawing, but it seemed important to check.

This proved difficult.

I put a single centering ring on the engine mount tube, and stuck it in the BT55. Then, using all three of my hands, held the three TTW fins in place, and looked in the back and tried to see if they were touching the inner tube. No pictures of this process for obvious (I hope) reasons.

I concluded they were a tad (or perhaps a smidge) shorter than they needed to be, so I'll just grab the sandpaper and add on another mm... wait a minute sandpaper does not work that way. I sure wish I had erred a bit on the side of making the TTW tabs too tall, that'd be oh so much easier to adjust. Lesson learned for next time.

So the only reasonable thing I could think to do was to take a bit off the root edges of the fins beyond the edges of the tab, like so:


I did just a bit (it only needed a little), and then repeated my juggling act and concluded that everything was good enough for now. Once the motor mount is glued in (one day I will settle on calling it a motor or an engine, but that day is not today), I'll test again, and sand down the tab until the fit is perfect. Then it'll be a lot easier (remember this comment).

RUT ROW.....Now you're going have to custom fit that ring. Then again, maybe you anticipated that?

Nope, the fins that hold the ring are surface mounted, and should be fine... but actually I won't know if the fit is good until I have them all glued on. I wonder if I erred on the side of making the ring fit too tight (I hope), or too loose (I hope not)?

Great, another thing to worry about. But seeing as how there's basically nothing I can do about it until the time comes, I won't worry *too* much. :wink:

I initially thought about the fit with ring being affected by the fix as well, but then took a look at the pic and you're talking about the rear fins that have outer pods/tubes...not the forward ring, right?



Also in situations like that I've had in the past, I would just get a sliver of wood and glue it to the bottom of the fin to make up the gap...wood glue would likely cover that entire area anyway and often the glue is as strong/stronger than the bt you're gluing it to.

Correct, it's the rear pod fins. Gluing a strip of wood to the bottom might have worked better, I'll perhaps try that next time. But I hope there is no next time.

Nothing much to say about this. Or is there?

(To be continued)

So the rear fins still needed papering, and they would be the first ones with TTW tabs that I would be trying. So I worked up the first fin using my now-perfected process.


Bollocks. The interior corner where the TTW tab ends came out a bit of a mess. Still three more fins to get it right, thanks to the extra I had cut (that was a rare bit of clear forethought on my part). Although I have since thought of a number of additional ways to fix this, my initial reaction was to wonder why I was bothering to paper all the way over the root edge in the first place, since that edge would be covered by fillets later on.

And so I updated my papering formula again. For the remaining three fins I applied the paper parallel to and just above the root edge (I used a clean edge from the label sheet), and then did everything else the same. This way, I don't have to do any sanding of the paper at the root edge and risk messing it up at all. I don't know why I didn't think of doing it this way in the first place.


Diluted wood glue was applied to the edges as before, and the results are perfect.


And so here is my final (?) papering formula:

1) Round all edges as desired.
2) Clean sanding dust off fins: first use a soft paintbrush to take off as much as you can, then use painter's tape to pull off any remaining surface dust.
3) Apply self-stick label paper to front and back, starting just above the root edge and extending beyond all the other edges.
4) Gently sand excess paper off edges using hand-held paper, no blocks.
5) Apply thinned wood glue to edges, sand smooth when dry.

I think I'm starting to feel about papering the way TopRamen does about glassing. This has me a bit worried.

So the motor mount turned out to be not-so-uninteresting after all. I was getting read to glue it in, and slid it into the BT to do a final check on the fin tab height, when I realized that the electrical tape wrap around the hook was a problem. Doh! I went back and tried to remember why my Estes Centuri, which uses TTW fins, didn't have this problem, and found that the mount had a BT20 (for the 18mm mount) inside a BT50 (for gluing the tabs to). Ah, so *that's* why the mount had two nested tubes in in it.

Well I'm doing a 24mm mount inside a bt55, so there's no space in there for an intermediate tube. So what to do? This is a non-rhetorical question, seriously, what should I do?

One idea I had was to simply cut the electrical tape down much narrower, and then notch the TTW tabs to fit around it, something like this:


If I did this I'd lose the middle 1/3 of the tab root edge for gluing purposes. It'd probably still be strong enough, but I'd like some opinions before I commit to this approach.

Notching around the tape will be fine. If you're flying more powerful motors get rid of the clip completely.


[emoji1010] Steve Shannon [emoji1010]

For an Estes motor hook to be held in place by a CR or body tube, you don't need much...even one 1/2" strip of masking tape laid along the length of the hook (where the other tape starts) and then a thin layer of wood glue applied over the tape and edges (just in case) should be a forever deal.

KenECoyote said:

For an Estes motor hook to be held in place by a CR or body tube, you don't need much...even one 1/2" strip of masking tape laid along the length of the hook (where the other tape starts) and then a thin layer of wood glue applied over the tape and edges (just in case) should be a forever deal.

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That is something I was wondering... I was actually thinking of just putting a layer of epoxy over the hook and that should do it. Maybe I'll go that way; I'm not super enthused about notching the tabs, even thought that'd probably be fine as well.

You'll find slight notching of the tabs in some kits as well.

Here's a good example: Estes Phoenix Bird - step 9 of engine mount assembly
https://www.estesrockets.com/media/instructions/003024_PHOENIX_BIRD.pdf

neil_w said:

That is something I was wondering... I was actually thinking of just putting a layer of epoxy over the hook and that should do it. Maybe I'll go that way; I'm not super enthused about notching the tabs, even thought that'd probably be fine as well.

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While epoxy can work as well, I'm not sure it's better than wood glue since wood glue is more flexible and epoxy is more likely to crack if flexed enough IMHO. Still, either should be enough that you shouldn't have to worry at all since it only really serves to hold the upper end of the hook in place and keep the other end from moving outwards.

BTW - I really love your papering...almost like artwork!

Ah, interesting.

For now, I tried gluing down the hook with 30 minute epoxy, which hopefully will obviate the need for any wrap at all, and I can leave the fin tabs as is. Will see how it looks tomorrow.

So the epoxy route seemed to work. I don't think that hook is going anywhere.


Onward.

Considering how much I love building rockets, it's amazing how many tasks there are that I do *not* enjoy. Cutting tubes is one of them, probably because I suck at it.

For normal square cuts on BT5 - 60 I have my Estes tube cutting guides, which work well enough, at least when I remember to a SHARP BLADE, for cryin' out loud. For this build I needed to cut a 1" ring of BT80, and angled cuts on BT20 for my tubes/pods. Yes, I decided to angle the leading edge of them (not shown in the OR render); not sure if that's a design improvement or not but I thought I'd give it a whirl.

So I thought I'd be clever and, while doing another 3D print job, threw in a couple of custom cutting guides for BT-80 and my angled BT-20 cuts. Apparently I made all of them too small, so I started to sand them out to fit the tubes. The BT80 guide was taking forever, so I gave up and just cut the ring manually. That actually came out OK. For the BT20 cuts, I decided it was worth a bit more effort to get the guide working, so I kept sanding and sanding until I could get the tube in far enough to make my cut.

The piece looked like this:


Here's what it looked like with a tube jammed into it:


Pretty straightforward, right? Well it sucked, bad. It totally didn't work, did not enable me to make any sot of clean cut. Basically, I could not follow the edge of the guide with the knife. So I chucked the cutting guide and did them freehand, and here are the three turds that I produced:


If anything they looked worse in person than the picture. I gave a healthy rub of CA to the inside edges, then attacked them with sandpaper. This was a fine and appropriate time for the sanding block. That fixed everything satisfactorily. Here's a before and after, of sorts:


Not bad. Having gone through this, I have no idea how Scotty Dog makes all those crazy cuts in his scratch builds so cleanly. But I survived, and can move on. I still don't know if angling the tubes was the right thing from an appearance standpoint, but I won't be able to really answer that until it's all built.

I suggest you use those guides as marking guides, mark with a sharp pencil and then cut carefully (and slowly) with a new X-acto blade...remember to cut lightly and slowly and go a few rounds.

BTW - Great idea with those 3D printed guides!

KenECoyote said:

I suggest you use those guides as marking guides, mark with a sharp pencil and then cut carefully (and slowly) with a new X-acto blade...remember to cut lightly and slowly and go a few rounds.

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That's basically what I ended up doing. I found that trying to track the angled path around the tube was very difficult. Maybe I just need more practice.

BTW - Great idea with those 3D printed guides!

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Would've been even greater if it actually worked.

I think the straight bt80 guide might have worked ok if it wasn't so undersized, but the angled guide was an all out failure (not sorry I tried it, though). Actually, after seeing how well it didn't work, I'm left with very little idea how to make a working cutting guide for non-square cuts. That idea is shelved for now.

They do make very good marking guides, if a bit (!) overkill.

Neil, I don't know if it's just something I'm good at or if it's the kind of knife I use. I do know this, those standard X-acto knives don't fit my hand very well and I can't cut with the same accuracy as I can with the break-away like pictured below.

View attachment 293610

I usually make a cutting template out of paper with a formula I can use in Autocad ( not completely necessary ), pencil in where the cut is, and turn out some relatively nice cuts requiring a little sanding. If I were to use that old X-acto knife, they'd look like crap. Maybe you should consider a different knife. It's much like why an SG electric guitar was so much easier for me to handle than a typical Les Paul. It just felt comfortable. Here's a couple examples.

View attachment 293611

Man, you always have great looking stuff in progress on your bench.

Anyway, I actually did use a break-away knife for doing my cutting (not that particular one, but roughly equivalent), and started with a fresh blade, but I still did a very poor job. I think I really just need practice. Something I forgot to do (remembered after-the-fact) was wedge a spent engine in to support the tube more firmly; I did that with some coupler stock when cutting the BT80 and it helped.

I have one of those Atlas saws but since the blade isn't deep enough to go all the way through the tube I'm not sure when I'll be able to use it. Perhaps a very fine hacksaw or coping saw blade would be good for diagonal cuts, if I support the tube and maybe paint it with some CA first to prevent fraying. For the freehand cuts like the one in your second attached picture I think, again, I just need to practice.

At least I was able to clean these up with sanding, but I definitely want to do a better job with the initial cut than I did.

Paper templates are good alternatives to use for marking...just cut out the template, tape around the tube, hold in place, mark with a pencil and you're good.

As for cutting tubes, just practice on scrap first and I really, really recommend using an X-acto knife with a new X-acto blade...that sucker has such a sharp little point that it's no joke and you don't even need to support the inside of the tube - repeated light passes is the key. IMHO a Snarky is s good kit to learn using paper templates and angled cuts or try to dig up build threads on it.

This year I've likely hand cut more tubes than most people here in trying research for a new line of kits (a bit on hold now and it wasn't a spiral fin...however maybe it will be now ).

Despite my less-than awesome experience CAing my last nose cone, I decided to try it again. CA, then sand, then CA again, then sand again. Just like last time, I found that I had a very difficult time getting the surface smooth. This time, though, I tried something that someone (can't find the post, unfortunately) said he had done with success: apply CWF *after* the CA. So, I first painted my CA-ed (but not smooth) nose cone with a layer of thinned CWF:


Then sanded it down until it felt pretty smooth. Here is what it looks like:


If you enlarge it you can see there are quite a lot of "low" spots that the CWF filled in. It feels pretty good, and I think it'll paint well. I mainly hope to get some surface hardness from the CA. Anything is better than the soft raw balsa, which seems to attract my fingernails like a magnet.

The point is not quite as sharp as it used to be because, ah, well things happen. I didn't *want* it to be so sharp so I intentionally rounded it off a bit, yeah, that's the ticket.

I think next time I'm going to try the epoxy route: CWF, then sand, then apply a thin layer of epoxy, then sand. But for this built I *think* I'm in decent shape.

I tried that same approach just a couple days ago with a balsa coupler. Soak with thin CA to harden, sand, then CWF to fill, sand smooth. The coupler was going to be painted metallic silver so it needed to be smooth for sure.

I think I have another balsa nose cone that I may try thin CA with as well. But more carefully next time as(they're right!) the thin stuff can soak through the balsa to your fingers, leaving three fingers glued to your part in about two seconds.

Hmmm, putting on ca, then sanding it off sounds really inefficient, like sanding an m&m. Did you try sanding sealer? I've used it and slightly diluted Elmer's Wood filler on balsa and ended up with a finish like plastic. Once you are done sanding, then harden the outer surface.


[emoji1010] Steve Shannon [emoji1010]

Steve Shannon said:

Hmmm, putting on ca, then sanding it off sounds really inefficient, like sanding an m&m. Did you try sanding sealer? I've used it and slightly diluted Elmer's Wood filler on balsa and ended up with a finish like plastic. Once you are done sanding, then harden the outer surface.

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Others seem to do better with the CA than I do. But I think my end result is pretty good, and it really isn't that much work. I'm definitely inclined to try epoxy, if I can solve the rotisserie problem.

Aaaaand the motor mount is in. I used 30 minute epoxy (the only kind I use these days) and it slid in beautifully. I remembered to wipe any stray epoxy off the mm tube, so it wouldn't get in the way of the fins. I also remembered to position the engine hook between two of the fin slots, and also made sure that the epoxy holding the hook did not extend under either adjacent slot. Yay me.

Here is a rather uninteresting picture of the result:


I recessed the mount about 1 mm from the tube end, and applied some of the leftover epoxy as a little fillet. Not really necessary for strength I don't think, but gives it an extra bit of finish. The rear centering ring is paper, so it's nice to seal it over with some sort of glue either way.

I peeked into the other end of the tube with a flashlight and the forward centering ring seems to have created a nice fillet of its own when squeegeeing the epoxy as it was inserted.

Good to go.