Semroc Micron Build 4 Part 1

Good afternoon everyone! As mentioned previously I finished filling and sanding the nose cone and remaining fins. Here they are:

The nose cone has an unfortunate gouge in its bottom just above the shoulder, the result of an unwise choice to use a flat sanding block on this curved surface. Viewed close-up, the fins still appear to have a number of imperfections to the eye, though to the touch they are glassy-smooth. So with this bird I’m going to go with the two coats of CWF on everything except the body tube spirals and see how the painting comes out. I’ll paint it after assembly and will start with two heavy coats of primer. I have to go to Lowe’s to pick up some new glossy white, the base color I decided on. If you noticed, the package art shows a cool large retro red & white checkerboard body wrap decal. Some older reviews of the kit I read complained that this decal wasn’t included and Semroc must have listened because my version of the kit does have this decal. So it will look best, IMHO, against white (although did I mention I’m color blind lol?).

As you saw previously, I attempted to use the thinned CWF to fill the body tube spirals. I took a closer look today and was not satisfied, there were still obvious unfilled areas in some spirals so either I didn’t direct the blade right into the spiral upon the first application, or I sanded all the dried CWF away. So I decided to try and refill one of the spirals after all, the one that on initial inspection still appeared most egregiously grooved:

I’m now waiting for this to dry so I can sand it down again. Did you notice the subtle little bulge now in the tube, maybe a third of the way up? Here’s another angle, before I reapplied more CWF:

Along with the bulge, note the new small indentations at the aft end of the tube. There’s a story behind all these, classic stuff for me...

First of all, l’ll start by saying that I recently read the Handbook of Model Rocketry by Stine et al, and it wisely emphasizes the wisdom of always following the instructions. Well, I ignored this right off the bat on this kit because I stampeded right to sanding and filling the fins. This actually took me to about step 7 lol. The real first step involves tying the Kevlar thread around the thrust ring, then gluing the ring into the body. Here’s the indicated parts (along with the launch lug, screw eye for the nose cone, and shock cord):

You mark the included empty engine casing 1/4” from an end. This mark is used a a gauge to know how far to push in the thrust ring, after applying glue around the inside of the body maybe 2-1/2” up with a finger or stick or something. Here’s the ring after the Kevlar is tied on:

The instructions emphasize pushing the thrust ring with its Kevlar tied around it into the fin end of the body tube, then smoothly inserting the marked empty engine casing up to the mark you made, then immediately withdrawing the casing. If you don’t do it smoothly, the ring can “freeze” in place in the glue and become impossible to move.

Do you remember in my first post where I predicted that the Kevlar tied around the thrust ring shouldn’t be a big deal? Well, when I inserted the ring into the end of the body tube there was a mild apprehension at the back of my mind about how the ring, with its additional functional outside diameter contributed by the Kevlar, would slide into the tube. The Kevlar cord itself feels like it may be coated with wax or something but at any rate it slid in with some resistance and then - the whole thing froze up about halfway in!

It’s a shame no one was taking video the next few minutes - I was in an absolute panic. I couldn’t push the thrust ring in deep enough. I couldn’t withdraw the motor casing. Those little indentations at the aft end of the tube are molar marks, from where I tried to bite the empty casing to get it out. Then I banged on the casing with something one last time and it advanced - all the way flush with the end! Now I’m really screwed because the thrust ring has been pushed TOO far into the tube. So I took a length of 1/2” dowel I had and started banging the whole assembly violently down onto the dowel, trying to get everything back out.

Finally the empty casing started to emerge. I got it knocked back out to the 1/4” mark again, grasped the empty casing and this time it slid easily out. Of course I have no idea where the actual thrust ring ended up unless I measure it from the outside lol. This is easy to do because if you look closely at the last photo you see a distinct line along part of the bulge in the tube. This is where the Kevlar cord wrapped around the thrust ring in all this process. It reminds me of a snake that’s swallowed something. But I’m afraid that the ring has ultimately ended up too far forward for the rocket to be flown as it is now because I think the CG would now be too far forward, both for flight stability and also because if the motor is too far forward it will be exceedingly difficult to extract after a flight.

Anyway, I’m breaking for now because I have to return to work. I suppose the next step will be gluing on the fins - I need to check with the instructions lol. I was thinking about using a technique I read of involving sort of tacking on each fin with CA (superglue), then filleting heavily with wood glue. I could do this, and try filleting with the Tite-Bond Quick and Thick Multisurface Glue, which is supposed to make excellent fillets. But I’m going to save that for the Baby Bertha and proceed with the epoxy putty fillets on this little Micron.