Semroc Micron Build 3

Good evening everyone. Boy, was I pleased to see that my blog has thus far received over a dozen views! Then I realized they were me, viewing my posts repeatedly to catch errors. But I’m certain some slip through anyhow lol.

Today I continued to fill and sand balsa. I put a second coat of the thinned CWF on the fin I coated and sanded yesterday, and thus far today have put the CWF on the nose cone and the other three fins. 

I sanded the fin I filled yesterday. For one coat it felt pretty smooth IMHO. I coated this fin and sanded it a second time for this shot:

I think it feels almost to ready to paint with primer. I do still need to sand off some residual CWF that collected along the fin’s root edge while it was hanging down drying. Also note the new dimple in the side of the fin. I skewered it with its music wire holder while reinserting the wire to recoat it. A second fin was later inadvertently so treated.

Then I filled and sanded the nose cone. Here are before and after shots with before sanding obviously on the left:

I’ve coated it with CWF for a second time and it’s drying again right now. 

Meanwhile at the beginning of today’s session (or first shift, it depends on what my dear wife Bridgid has planned tonight lol) I also coated the remaining three fins with CWF and let them dry. I like the Apogee guy’s music wire technique. Here’s what the three fins looked like right after coating:

As you can see I again put it on quite heavily. Remember last night I made passing mention of how I thought the excess CWF would sand off just fine? Well, it actually did, at least on the first fin and the nose cone. Anyhow the three remaining fins are now drying as well. I’m giving them an hour before sanding them down. I’ll post a photo of one after it’s dried & been sanded, filled and sanded one more time. Then these should be ready to paint along with the nose cone.

Somewhere along in here I found time to try and fill the body tube spirals with the CWF. I decided to use another tip from Apogee and use the back of a #11 blade in a #1 handle to fill in the spirals - more on this later. I found out after I started that there are indeed spirals in the plural, extending parallel down the body tube. I’m sure there’s some painfully obvious mathematical reason why there must be more than one spiral, but I for one was mildly surprised to see this.

Oh wait I forgot - I marked the fin attachment lines next. I used my good old Estes tube marking guide (#302227) to make the necessary little marks around the base of the body tube. Then I extended the lines up the tube a ways, I just eyeballed the length, and I’m hoping like hell I drew them long enough. After all, I could have gone totally old school and cut out the fin marking guide, destroying the instructions, and then wrapping the guide around the tube to mark it. Or I could have gone high tech and photocopied the guide out of the instructions, cut that out, and used it to mark the tube precisely. But hey - I’m Not-So-Good and proud of it, damn it! In the photo on the right below, I’m using an Estes Ultimate Tube Marking Guide (#002228) to rest the body tube on my lap while I extend the fin lines with a pencil. My trusty kitty-cat Cry Baby watches me like a hawk, looking for the slightest tremor, in which case - she’ll pounce!

As seen above, these little marks would be extended into equally spaced lines along the tube upon which to mount the fins. I read one fin mounting technique that suggested scuffing the body tube with a little #0 steel wool along these lines to help the glue on the fins adhere to the body tube. But I took care of that later, when I sanded off the CWF I filled the spiral with. 

Here’s a photograph of the body tube before any sort of preparation. Can you see the spirals?

Yeah, me too. So for the first time I tried the aforementioned method of teasing the thinned CWF into the relatively shallow body tube spirals. It involves dipping the blade of your knife into the CWF and then drawing the back of the blade along the spiral, depositing CWF along the way. As a corollary to what I mentioned above, you have to do this twice, since there’s two spirals! But it turned out to be fairly easy. In the video, the Apogee guy outlined the spirals with a mechanical pencil before starting to fill them. I didn’t bother with this, as I predicted (correctly, as it turned out) that this was going to be a mighty tedious process.

I’ve been concerned all throughout this process that I had thinned the CWF too much but as it turns out it seemed to be thinned to just about the right consistency to deal with both filing the all the balsa and the body tube spirals as well so I was pretty pleased about my lucky guess, though I have no way to precisely repeat the dilution I now have. I wish I had mixed up a lot more of the stuff lol.

So I started filling in the spiral:

As you can see, I my technique has lots of room for improvement! But overall I was surprised how simple it was to fill the spirals this way. I was griping about how tedious the whole thing was the whole time I was doing it of course. But it was soon all done and here’s how the tube looked while drying:

Next I let the tube dry for an hour, then sanded the tube gently with a nice flexible sanding sponge I have. I have no idea what grit it is but it worked great for this purpose. Here’s the finished product:

It appears that the spirals have filled in pretty well, to my eye. But I’m really uncertain because if I run my fingernail gently up and down the tube I still sense slight indentations. I’m hoping a heavy coat of primer will fix this. Maybe the CWF was a bit too thin for this application, however, because it appears excess water has leached into the tube from the filler in spots. So I’d prefer to avoid repeating trying fill the spiral with CWF if I can.

All righty, I have to go sand off the last coats of CWF now. I probably won’t blog photographs after sanding them, at least tonight but I’m posting pics of them tomorrow if not tonight.

Semroc Micron Build 2

Hi again, hope everyone is well and safe and sequestered from the dreaded virus. So to my surprise, my music wire showed up today! It turns out that I serendipitously ordered just the right size. When I looked for “music wire” I found out that there are a TON of different diameters available. So I searched for “music wire rocketry” and I got some hits but none specified a diameter. So as I mentioned in my last post I guessed on 0.025” diameter wire. It arrived in a long tube, which actually would make a decent rocket itself. I thought I had ordered 5 pieces but it turns out I had ordered 5 packs of 6 pieces, each 36” long, so now I have a bunch of this stuff lol.

As I mentioned previously my goal was to insert a piece of the wire into the root edge of a fin, to be able to have something to hold it with as I paint on thinned CWF. It turned out that this diameter wire fits perfectly into the root edge of my fins! In retrospect, considering that the thickness of this balsa stock is 1/16”, I could have calculated that it would be ok but I’m not that nerdy.

So here’s a photograph of a piece of the wire. It’s resting diagonally across the fin stock:

I had already cut a piece of it down into 6” lengths. That’s the rest of a little bundle of the wire in the top of the pic. For some reason they look all rusty but they really aren’t.

Here is a pic of three of the fins after removing them from the stock and sanding them lightly. I had read somewhere what a delight Semroc fins are as far as the quality of the balsa goes and that’s really true. I don’t know if you can tell from the photograph but they look like they’ll require little filling:

The next step was to thin some CWF. Mine came in a squeeze tube. I had no practical way to measure out a portion of the CWF so I just squirted some in to a little plastic container and mixed it well. I just eyeballed the water and at first I put too much in so I added more CWF. My goal had been at first to reach the consistency of mustard but I went way past that. After adding the second aliquot it did reach the consistency of the thin Chinese mustard one often finds with delivery food. I didn’t photo the end result of the mixture because I couldn’t think of a way to convey its consistency with a still photograph, and I’m too lazy to video me pouring it from one container to another or something fancy like that.

But overall I was happy with the end result. I used a cheap paint brush to swab the thinned CWF onto a fin while I held it by one tip. Then I held it by the music wire to paint that tip, and inserted the other end of the wire into an edge of my newly-arrived Super Big Bertha’s box:

As you can see, I put it on a little heavy. It’s collected at the bottom of the fin and looks perilously close to dripping off onto the carpet at any second lol. My lovely wife Bridgid may not be so cool with model rockets after all when I’m done with this build lol. I believe the excess CWF will dry, however, and sand out ok. If not: well,”Not-So-Good” is part of my blog’s name, isn’t it?

Semroc Micron Build 1

Hi again everyone! It’s still me, Grumpy Doc. I’ve changed my job. I no longer work in Urgent Care and now have my dream job with a Medical Marijuana clinic. We’re doing telemedicine at present and since I’m at very high risk for contracting COVID-19 I’m loving that. We may have to go back to office visits but I don’t mind - I love my job. All that being said, I refuse to change my name to Happy Doc, that would be too much.

As you can see I’ve changed the name of my blog to reflect my current passion - model rocketry. I’ve been flying model rockets since I was 12. I was quite ignorant starting out, lighting model rocket motors with a piece of fuse and kitchen matches or even better, a purloined lighter. I would insert the fuse, light it and run like hell but turn around in time to see the launch. This type of “ground support equipment” was of course completely prohibited by all the National Association of Rocketry safety rules and presumably at 12 I was old enough to read those but the fuse was way cheaper than a real launch controller with batteries and so on, and thus more immediately available on an allowance of like a dollar a week. It would have taken weeks to save up for the proper equipment after all lol.

Anyway I flew model rockets until my teens, then again in my 20’s after finishing college and while working as a medical technologist. At age 27 I went to work in Riyadh, Saudi Arabia in 1986. I think model rocket kits were available in Saudi but no motors or launch equipment (of any type lol) were. When I came back home for medical school in 1992 I resumed the hobby & built a few, IMHO respectable scale models: an Estes Saturn 1B, a Mercury Redstone and a Space Shuttle with a little vacuformed shuttle that detached at apogee and spiraled down gently just like it was supposed to. I launched all of them of course and gave no thought to the very real possibility of the sudden sickening loss of a rocket on which I had spent hours and hours and days and weeks on, trying to get a nice finish for once. But that risk is likewise a very real part of  rocketry’s appeal to me in an odd sort of way.

In 1999 I finished residency and the rocketry got put away. At that time I had been in the process of stepping up to larger rockets and motors. I bought and started an Estes Master Series Mercury Atlas. It’ll probably never be finished - some centering rings I had already installed are now kind of warped & stuff but we’ll see. I bought an Estes Master Series Jayhawk I’ve opened but never started. I looked last night and the cardboard shroud stock is kind of moldy but I think I can use it. I bought an Aerotech Initiator starter kit with the mid-powered Initiator rocket. This is mostly finished, though I had somehow lost its nose cone over all my moves. However thanks to eRockets.com (thanks Randy!) I was easily able to replace this. But aside from a few D powered flights I never got anything more powerful off the ground.

During all these years I always launched strictly solo, or with my cousins or a few friends. I have never attended any kind of sponsored or NAR sanctioned launch. Then in 2017 I married the woman of my dreams. Bridgid. She’s 100% behind my re-involvement in model rocketry. And now we live in an area with not one but TWO really awesome and extremely active local rocket group - Southwest Ohio Rocketry Association in Lebanon, and the Wright Stuff Rocketeers. They both launch about an hour away. I’ve met several of the members of WSR on their Tuesday night Zoom calls and everyone is extremely nice and helpful. And so far they’ve tolerated all my dumb questions that I’ve asked the group online. They recognize what I learned in medical school, dumb questions are easier to fix than dumb mistakes.

They’re just now resuming launches in our area tomorrow Saturday May 30 2020, following the recent and relative relaxation of COVID-19 Public Health orders. Of course I have to work but I’m definitely planning on making a launch somewhere ASAP. I have 5 birds RTF (all Estes BTW): a Saturn V RTF, a Satellite Interceptor, a D Region Tomahawk, a Mammoth, and a Trajector. I have some motors but only up to a couple of D12-5’s. Thankfully I understand that motor vendors are frequently at launches!

But now to the point of my new blog - documenting the building of model rockets. My first build will be the Semroc RetroRepo kit, the Micron. Originally released by Centuri, it was similar to the Estes Astron Mark II and cost $1.25. I love that because I can actually remember those days lol.

Here’s a photograph of the kit panel (actually, printed on the instructions):

I love the totally retro appearance. The kit is a pretty straightforward build, starting with the motor mount. This kit uses a Kevlar thread tied around the thrust ring. The thread is later attached to the elastic cord part of the recovery apparatus. That’s new to me but I don’t think it’s going to be a major speed bump or anything. 

My goal with this build is to try and perfect all the fundamentals of building a model rocket. In particular I plan to experiment with using carpenter’s wood filler (CWF) to fill the body tube seams and the fins. It’ll be my first experience with this technique. BTW, as the build progresses I believe why “Not-So-Good” is part of this blog’s title will become obvious lol.

I saw some videos on the Apogee site describing how to use carpenter’s wood filler to fill fins and body tube spirals. It looks to me like I’m going to have to use two different dilutions of the CWF. For the fins, the stuff the Apogee guy used looked just like mustard to me. Another blog post said to try 2.5 parts CWF to one part water but I don’t think I’ll try to actually measure it, I’ll go with appearance. Another post also suggested whipping the water in until the CWF is like canned cake frosting but I like the mustard analogy better. On the body tube spirals I think I’m going to need thinner CWF. On another Apogee video, a guy used a syringe to apply thinned CWF along a tube spiral in a continuous line. But I think it was thinner than the fin CWF. I don’t have a syringe so I’ll just have to play around with this.

Along with filling these I’m going to try using epoxy putty to fillet the fins. I want to photograph each step of all this to see exactly where and when anything goes wrong. I also want to document the painting process, typically my finishing downfall of late.

So now I’m facing a dilemma. I did remove the fin sheet and did an initial light sanding with 220 grit. Now, I really should thin some CWF and brush it on the fin stock. I would like to follow the example I saw on an Apogee Components Advanced Construction video, which involves at this point removing all the fins and using filler on one fin at a time. The idea is to avoid warping which might ensue were one to paint only one side of the fin stock and wait for it to dry. This actually already happened to me when I built my Satellite Interceptor so I do want to avoid a recurrence. The video suggests inserting a short piece of music wire into the fin’s root edge then using that as a little handle to hold the fin while you paint all but the root edge with thinned CWF. Then you stick the free end of the music wire into, e.g.  the edge of some corrugated cardboard to let it dry. I like that. I’ve ordered some music wire but I have no idea if I got the right size. Probably not, but we’ll see, it’s 0.025” so I hope that’s not too thin. 

So I want to start the kit right away! But I just checked and saw that my music wire hasn’t yet shipped. So unless I can think of a workaround I suppose I’d best wait for the wire to show up. 

I may be back shortly to post a pic of the fin stock I already sanded. But probably not.