I am sufficiently curious now to sacrifice my last bit of 1/16" balsa sheet to a science experiment. I'll post my progress here.
Plasma Dart II Build Thread
- Thread starter neil_w
- Start date
-
- Tags
- build build thread
Help Support The Rocketry Forum:
Two pieces of 1/16” balsa, 4x4” each:
Glued together with a *thin* layer of TBII, wrapped in waxed paper and placed underneath this pile:
I am open to suggestions of what to do with it when it’s dry.
Glued together with a *thin* layer of TBII, wrapped in waxed paper and placed underneath this pile:
I am open to suggestions of what to do with it when it’s dry.
Ah, Horowitz and Hill! Great stuff....
Suspend the square by its' edges on two tables. Tie a string to a container or bucket. Loop the string around the center of the square and load the bucket with weight to failure. Do the same with 1/8" thick solid balsa. Note which sustained the most weight at failure.
Titles not chosen at random.
PS run the string perpendicular to the grain of the solid balsa.
Or use an extensometer if you have access to one.
Nytrunner
Pop lugs, not drugs
Without question it should be stronger. There's the adhesive properties to contend with also. You've created a composite.
Next do an 1/8" with paper on each side
Or my favorite, balsa with 1/32 basswood on the sides
Next do an 1/8" with paper on each side
Or my favorite, balsa with 1/32 basswood on the sides
If one can find it, how about 1/8" styrofoam with 1/32 basswood on each side?
- Joined
- Aug 27, 2011
- Messages
- 11,639
- Reaction score
- 6,290
It worked quiet well with my “Squirrel”, which had a huge multicurved literal “tail” fin
https://www.rocketryforum.com/threads/the-squirrel-2-almost-perfect-flight.146038/
Regarding @neil_w making a big dual balsa plywood sheet, it would likely work. Following challenges
1. Strong tendency to warp, so you have to get an even coating of glue and then find a way to keep the pressed flat and tight.
2. The strength of the bonded wood is a great asset in flight, but it is a PITB to cut with an exacto blade. May even be a bit tougher than standard thin plywood. Hence I tend to cut two identical shapes with orthogonal grain directions and glue them together.
Regarding @neil_w papering a sheet of balsa and then cutting.
Yes, it is do-able. It is messy (I am not the fastidious type and end up smearing some glue on the outside of the paper, which totally defeats the purpose of smooth finish). Biggest issue is the fact that you have to do bother sides at the same time to prevent warping, and again still have to hold it flat and tight while it dries.
Mounting the Fins
The final bit of construction before painting commences is to mount the fins. Following process is shown for the first fin.
1) Sand the fin tab to fit. One accidental benefit of the tab design I used (flush with front of fin) is that it is easier to get the tab root to sit flush on the body tube, since the front can float up or down as needed, with very little visible effect.
2) I had planned to remove the glassine layer from the fin mounts on the main BT before attaching the warp tubes, but completely forgot. So, instead, I inserted a flat jewelry file in from the rear, and scuffed up the appropriate area on the BT. not as good as glassine removal, but I think I got it scuffed up a bit.
3) Glue fin. Finally got to use my fin guide, which fit pretty snugly over the full rear assembly.
4) I had a thought: could I get internal fillets in there?
Answer: yeah, sort of. I took a scrap of 1/16" square dowel lying on my bench, applied a line of glue to it, and carefully threaded it in there. Then I laid it against the root and turned it a bit, transfer a decent amount of glue onto the joint. I think it was enough just to ensure that any gaps in the root are filled.
5) Remember those little crescent pieces I made in a previous post? Time to sand those to shape and glue them in. I slopped some glue in there and pushed the piece in until it hit the fin tab, about 1/2" in. Then applied some fillet glue around the seam to fill in all the gaps. In a kit, these pieces would be laser-cut and a lot less work, although sanding 1/16" wood goes pretty quickly, especially when a precise fit is not necessary (these are not structural.)
6) Fillet the seam with the warp tubes.
One down, two to go. Starting to look like a rocket.
The final bit of construction before painting commences is to mount the fins. Following process is shown for the first fin.
1) Sand the fin tab to fit. One accidental benefit of the tab design I used (flush with front of fin) is that it is easier to get the tab root to sit flush on the body tube, since the front can float up or down as needed, with very little visible effect.
2) I had planned to remove the glassine layer from the fin mounts on the main BT before attaching the warp tubes, but completely forgot. So, instead, I inserted a flat jewelry file in from the rear, and scuffed up the appropriate area on the BT. not as good as glassine removal, but I think I got it scuffed up a bit.
3) Glue fin. Finally got to use my fin guide, which fit pretty snugly over the full rear assembly.
4) I had a thought: could I get internal fillets in there?
Answer: yeah, sort of. I took a scrap of 1/16" square dowel lying on my bench, applied a line of glue to it, and carefully threaded it in there. Then I laid it against the root and turned it a bit, transfer a decent amount of glue onto the joint. I think it was enough just to ensure that any gaps in the root are filled.
5) Remember those little crescent pieces I made in a previous post? Time to sand those to shape and glue them in. I slopped some glue in there and pushed the piece in until it hit the fin tab, about 1/2" in. Then applied some fillet glue around the seam to fill in all the gaps. In a kit, these pieces would be laser-cut and a lot less work, although sanding 1/16" wood goes pretty quickly, especially when a precise fit is not necessary (these are not structural.)
6) Fillet the seam with the warp tubes.
One down, two to go. Starting to look like a rocket.
So why not graduate to a coping saw or coarse bladed jeweler's saw?
A good hobby saw should be able to handle balsa and wood glue. I've used it for separating the nozzles and transitions from the Estes plastic nose cones. And for cutting body tubes (with masking tape). Invaluable tool.
If you mean the saws I think you do, they're great for straight cuts and, for the same reason, useless for cutting curves.
For curves on harder wood you would have to graduate to power equipment for best results.
Subjectively, my laminated piece feels less rigid than 1/8" balsa against the grain, but at least as good and probably a bit better than 3/32" balsa. And of course it feels the same no matter which way I bend it.
I don't know if I'm going to do full rigorous strength testing, but I will definitely do some cut-testing. If I can't cut it cleanly with my usual snap-off blade, I'm not interested in using it.
One thing I noticed is that my waxed paper had a crinkle in it and that put a nice dent in the surface of the wood; easily fillable with CWF, but still. Make sure to use clean, unwrinkled waxed paper for pressing.
I don't know if I'm going to do full rigorous strength testing, but I will definitely do some cut-testing. If I can't cut it cleanly with my usual snap-off blade, I'm not interested in using it.
One thing I noticed is that my waxed paper had a crinkle in it and that put a nice dent in the surface of the wood; easily fillable with CWF, but still. Make sure to use clean, unwrinkled waxed paper for pressing.
Is this a perimeter of basswood? Like a strip veneer that woodworkers put on the fronts of shelving? Do you get it in strips?
My new favorite is 3/32 balsa sheet, framed around the perimeter with 3/32 square hardwood, and then papered with white glue. I don't worry about warping, but just iron it flat with a monokote iron and it reactivates the PVA glue.
Interesting. What scale of rocket do you use this in? I assume it's an MPR sort of approach. Framing the balsa with hardwood seems like a lot of effort, not necessary for LPR (and forget it for curved fins). On the other hand, 3/32" balsa is pretty skimpy for MPR, even papered.
Got any examples where you're used this technique?
That's a matter of prefference. I find it much to easy to screw up with power tools; because they let you go so fast, a little splip off angle can have me over the line before I know it. I'd rather go slow and careful with a hand powered coping saw, outside the line, and get to the final shape with a file and sandpaper.
It was in a MPR rocket, and I was wrong, it was 1/8" balsa. Here is the example. I read 3/32" in the previous post, and that number inserted itself into my brain.
And you're right, it would be very difficult for curved fins! I guess you could get fancy and laminate thin strips around it, but that seems like a lot of work. But I bet it would be strong.
Ah, I followed that thread but glossed over that particular step. Those came out really nice. Looking forward to seeing that one fly (well, virtually, at least, via pics and/or video).
Cockpit Decal Update
So, after thinking about it, I indeed was able to do some scripting to help fine-tune the cockpit decal, which I could see was not perfect. I started with an equivalent shroud template to my balsa transition, then marked on it the exact locations where it would join the black stripes on the body. It looks like this:
I then superimposed my existing cockpit image:
I don't know if you can see the defects or not, but I what I see in this image matches exactly what I see on my mock-up body tube. And so I cleaned it up in Paint.net. Here's the before and after inside the editor:
And here are old and new IRL:
I think you can see it there in full-size: whereas the old one was very good, the new one is *perfect*. I fully understand no one would ever have noticed this on the real rocket, but why not make it as accurate as possible?
So, after thinking about it, I indeed was able to do some scripting to help fine-tune the cockpit decal, which I could see was not perfect. I started with an equivalent shroud template to my balsa transition, then marked on it the exact locations where it would join the black stripes on the body. It looks like this:
I then superimposed my existing cockpit image:
I don't know if you can see the defects or not, but I what I see in this image matches exactly what I see on my mock-up body tube. And so I cleaned it up in Paint.net. Here's the before and after inside the editor:
And here are old and new IRL:
I think you can see it there in full-size: whereas the old one was very good, the new one is *perfect*. I fully understand no one would ever have noticed this on the real rocket, but why not make it as accurate as possible?
Wow. That is truly some attention to detail. That's what separates the great from the good.
Sometimes it's just fun to geek out. I sure have gotten good use out of the shroud generator script...
Three fins finished (warp core test print included just for fun):
I made a small error on the top fin, where the slot was a bit extra long and I inadvertently pushed the fin to the front of the slot. As a result, the rear is about 1/8" in front of the back of the warp tube. Very annoying but not tragic. By the time I realized it it was too late to try to correct.
Almost ready for paint.
I made a small error on the top fin, where the slot was a bit extra long and I inadvertently pushed the fin to the front of the slot. As a result, the rear is about 1/8" in front of the back of the warp tube. Very annoying but not tragic. By the time I realized it it was too late to try to correct.
Almost ready for paint.
- Joined
- Oct 8, 2016
- Messages
- 2,835
- Reaction score
- 1,211
Think drill (variable speed hand drill is best) + sandpaper.
Start with a dowel longer then you need and chuck it in the drill. Cut a 1.0"~1.5" long strip of sandpaper (320 or finer) about the width of finished dowel length and folded in half without creasing.
Pinch open end of sandpaper between thumb & index finger, insert chucked dowel into sandpaper loop and rest curved portion of sandpaper on the dowel.
Run drill at lowest speed for short intervals and tug lightly on pinched sandpaper strip. Also shift the position of the strip often.
Check diameter of dowel between intervals.
Easy Peasy.
If you do that a lot, like model shipbuilders and such, you can get a metal drawplate for relatively cheap.
https://www.amazon.com/gp/product/B018RH0Z6Q/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Thin down one end of the dowel, poke it through the hole, grab with a plier and pull, pull, pull.
Laters.
https://www.amazon.com/gp/product/B018RH0Z6Q/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Thin down one end of the dowel, poke it through the hole, grab with a plier and pull, pull, pull.
Laters.
Interesting tool, I didn't know such a thing existed. Have you used one on wood before?
I tried it on the dowels for a Semroc Sat 1B. It has an LES tower made of dowels and you are supposed to manually shave it down to the proper size. Ran into the same problems that Neil did.
Well, I guess there is a learning curve because my results using this tool were not good. I read somewhere that model shipbuilders use this to construct custom spars for their sails. Guess I don't have the touch.
EDIT: On second thought I withdraw the suggestion. Was trying to throw ideas out there, but if I can't get good results (even though others have) then I shouldn't have mentioned it.
Well, I guess there is a learning curve because my results using this tool were not good. I read somewhere that model shipbuilders use this to construct custom spars for their sails. Guess I don't have the touch.
EDIT: On second thought I withdraw the suggestion. Was trying to throw ideas out there, but if I can't get good results (even though others have) then I shouldn't have mentioned it.
Last edited:
My ability to overlook straightforward solutions is unparalleled. [emoji849]
I applied another (final) round of Quick and Thick fillets to the fins. The placement error I made on the final fin is really bugging me, but there’s nothing to be done about it at this point.
It seems that in every build I am required to make at least one boneheaded mistake.
