Diamond Cutter build thread

More time for a thoughtful reply ;-)

Do you have a link to the tutorial? Does this technique suggest thick, medium or thin CA?

I avoid getting CA on surfaces that I want to finish except for edges and tips where I need the strength and the finish isn't going to add or detract that much anyway. CA is a PITA to sand in any way what so ever. I use it to harden the transition part of a Nose Cone to add strength and secure in a screw eye. But I'm not worried about finish in those areas. However even when I do this I'm super careful to not get any CA on the parts of the nose cone to be finished. This is especially tricky where the thin CA may chase the grain down through the balsa and 'emerge' on the surface on the other end the grain.

Wes

Here ya go: https://www.rocketryforum.com/showt...rial-Making-Balsa-Nosecones-Look-Like-Plastic

I used Bob Smith super-thin CA.

It's certainly possible I did something wrong, but it sure felt like I was doing what I was supposed to. I'm still hopeful it'll end up OK, and either way it's not the biggest deal. I've found that I'm fairly tolerant of certain kinds of finish deficiencies. For this rocket there are other areas that I will be much more fanatical about getting right.

I've CAed many a nose cone and like the process described in the linked thread. However, when I do the sharpie trick, I only try to sand off the surface sharpie marks, not the deeply recessed sharpie that gets into pits.

The problem which probably happened here is things go one of two ways with the sharpie, depending on how wet and fuzzy the tip is.

If it's relatively dry and the tip isn't fuzzy, the pits in balsa (which are sealed with CA just like the surface) don't get sharpie marks in them. So, in this case, the idea when sanding is to sand all the sharpie off, leaving behind a smooth main surface that has recessed pits below, without sharpie marks in them. This serves as a substrate for further filling.

If it's a wet/fuzzy sharpie, the ink gets down into the pits. In this case, you have to stop sanding when you see the sharpie on the surface is sanded off but the pits are still dark.

This is a fun build thread. Thanks for posting it. Beautiful design!

Marc

I may have been a bit aggressive with the Sharpie.

I am thinking that next time I will apply a coat of CWF to achieve basic smoothness, and then CA over that for hardness. Then I shouldn't have to deal with all the various pits in the balsa (at least, not as much).

More build updates coming in the next day or two.

This is an interesting technique. I'll have to experiment with it some day. Today I basically do the same thing but with lacquer based sanding sealers. CA sure would make it much harder though.

Hardness is the goal, especially for nose cones. It's easy enough to get the balsa *smooth* by any number of techniques, but CA gives it a nice hard surface that (in theory) should reduce the tendency to get dinged up. We'll see!

Next up: preparing th front transition/canard assembly. My intention was to completely finish this assembly on is own, including painting, before attaching to the payload section BT. I thought it would make painting easier.

I started by marking, the four positions for the canards. I marked them with pencil on the bottom shoulder:

They're numbered because on a handmade part like this, I couldn't assume the shape was perfectly consistent all the way around, so I'd be fitting the canard fins to specific parts of the transition. Each fin was cut, then sanded as nauseum until it fit well enough into its position on the transition. The fins were marked, for now, with tape and sharpie:

I actually had to recut 3 of the fins because they came out way too small after I was done sanding.

Next I applied CWF to the transition and prepared it for primer. As usual I masked off the attachment points for the fin roots first. Determining a straight line across the transition was not easy, and I don't think I got it perfect, but good enough for this purpose:


After priming and sanding, I rechecked the fit of the fins and sanded some more until I was satisfied.


It's not perfect but these are small fins and shouldn't require ultimate strength. They'll be fine once glued and filleted.

By this point I had figured out to mark the fin numbers with sharpie on their root edges.

It was at this time that I realized I couldn't build and paint the canard assembly on its own, because I really needed to fill in and smooth out the joint between the transition and the payload BT, which was to be a glue joint. This would not do:


I glued the transition and filled and sanded, and then also built up the other edge with CWF to sharpen it up a bit. Then I had the brilliant idea of applying a bit of CA on top of the CWF for strength:


That was a mistake, as it was basically impossible to sand down smooth without affecting the surrounding un-CA'ed wood. I did as well as I could, then stopped and cut my losses once I determined that I was starting to make things worse. It won't be too bad of a defect but I nonetheless curse my foolishness.

So, nothing left to do but get the whole thing ready for primer, which should be applied this Sunday. Ready for action:

Today, in a very narrow window of opportunity, I applied primer and the first bit of paint.

First: Duplicolor Filler/Primer on nose cone and tubes. Being in a hurry, I only sanded down the primer for the two pieces that were getting painted: the nose cone and the rear transition.

After sanding, my accursed nose cone was looking not-bad:


I've found that, after sanding with 400 grit, a good rubdown with a paper towel gives the primer a good smooth final finish before paint.

Next, I applied Rusto 2x Key Lime to the nose cone and the rear transition. Here's how the nose cone came out:


That is pretty good I'd say. The color is in the ballpark of what I was trying for, and I got a good smooth grain-less finish for the most part, though there are some imperfections. Good enough.

The transition came out nice, although paint showed some rather nasty imperfections that I carelessly overlooked beforehand.


Unfortunately, in my haste it didn't occur to me to at least sand the primer directly adjacent to the transition before painting; now I'll have to mask the paint and sand very carefully.

Why paint the transition first? I simply thought it'd be easier to do a good job on it before there were fins all around it. Also, it'll greatly simplify masking tasks later.

When suitably cured, both the NC and the transition will get some Future, and then the transition will be masked for the remainder of the build, to protect it. The nose cone will not be glued in (since the top is a payload section, so it will simply be put aside until the end.

A final note on color: I was trying, as best I could, to get a color match to a Stickershock color. Key Lime had potential to be at least vaguely similer to Mark's "Alien Green". Well, as it turns out, it's not a great match, but it'll have to do. Here's the nose cone with a vinyl sample:


The vinyl is quite a bit darker. That'll be fine for the name, but I'll have to decide how to handle the bands on each side of the transitions. That decision will be for later.

Anyway, it's exciting to see some color. On to the fins!

Time to attach the canards. I must admit that this part of the build has been the most frustrating by far. Doing it is easy; doing it *right* has proved difficult, and I've had to live with some imperfection.

First I sanded the primer off the payload section and the edges of the transition, and noticed that I really did a number on the transition last time when I was adding filler and CA. All kind of nicks and scratches and bumps. Well it's gonna stay like that, because I have a limit on the number of times I'm willing to go back and do more rounds of filling and priming. Given my limited opportunities to spray, any extra rounds could cost me weeks.

Next, I really wanted to make sure the root of the fins were straight, and aligning the bottom point of the fin (at the deepest part of the transition) with the two ends had me stumped. Eventually I remembered my fin jig (full discussion coming later), which solved the problem perfectly. Like Wes's butterfly fins, my jig is designed to hold two aluminum angles at the proper position to clamp onto fins. So I stuck a scrap piece of balsa and used it to mark the point on the transition where the bottom of the fin goes, after I eyeball-aligned the gap between the angles with the pencil marks at the end of the transition. Hard to explain, but it looked something like this:

Satisfied I finally had good alignment marks for the fins, I went and checked the fit of the fins *again* and did some more sanding until they were as good as they're gonna get, which is to say nowhere near perfect. Here I'm not worried because they should not require excessive strength, and the fillets will fill in whatever gaps remain.

And here we are, after attachment with a generous bead of Titebond II:

If you view at full size you can see an obvious gap in the lower right, at the aft edge of the fin. You'll also notice the fins aren't exactly the same size. Argh!

And now the gaps are gone, and everything looks great:

I'll probably do one more round of fillets just for good measure, but they're lookin' good. Titebond M&T is my savior.

Having the whole canard/transition assembly done is another major milestone. This rocket may yet get finished.

Finally, I stumbled on this thread over on YORF, which discusses how lousy 5-minute epoxy is. Of course that is what I used to install the motor mound and rear transition. Hooray. I don't think there'll be a problem because the assembly is glued in so many ways that there is a lot of redundant strength in there, but I don't want to take any chances so I acquired some Great Planes 30 minute epoxy and applied a nice fillet to the aft centering ring, like so:


Couldn't really complain about having to do that since that's why I recessed the centering ring from the end of the tube in the first place, to preserve room for a fillet. On the front centering ring, inside the main BT, I will attempt to apply a Titebond fillet, if I can successfully maneuver a remote-control glue applicator (i.e. a dowel) 11 inches from the end of the tube. I'll do what I can, and I probably won't ever worry about it.

Next steps are to apply the key lime paint onto the front transition and get to work on the main fins.

Neil:
I guess what you missed in the instructions was that you Will have black spot remain as they show were the Low spots and indented grain are located. Once you sand to the point you have these spots, it's time to apply another coat of CA. Blacken or Blue marker and repeat the sanding process. Within about 3 coats of CA you should get to a very smooth glass like finish. I do not use the Markers but CA coat Nosecones, Transitions and fins all the time.

One thing I like to do before starting the CA process is to use Miniwax Wood hardener to toughen up the sap wood between the grain which remains rather soft after CA soaking only. Stinks to high haven but really hardens up the sap wood.

Hope this helps a little

Neil,

From my perspective everything looks great! Yeah there are gaps and alignment issues, but a bit of fill and we can't see them. Keep moving ahead and don't be too critical of yourself. We're gonna love the outcome!

-Tim

Micromeister,
I think what bugged me most is how poorly the second coat of CA seemed to be sanding. However, the results seem pretty good, so I can't complain. I can't ascertain how much of a hard protective layer I achieved, but it came out looking nice. I will definitely continue to work on this technique with balsa parts in the future. Gotta use up this bottle of thin CA somehow.

Tim,
No worries, I'm happy with the way things are going, although I like to identify the deficiencies as I go so I can try to improve in the future. My results are usually pretty good although not museum quality, and I'm fine with that.

Well, this was easier than I thought, although I suppose I should wait to see the results before I congratulate myself. Here's the transition/canard assembly, masked and ready for some Key Lime paint:


After that's painted and dry, I'll need to do the inverse mask (covering the Key Lime only), and then paint the whole thing metallic black, then mask the payload BT and paint the fins silver. But there will be more building to do before I get to all of that.

While checking out the assembly I noticed that one of the canards is canted a bit. Shouldn't be a problem, and only visible if you sight down the body, so in other words basically invisible. But I would definitely say that fitting the canards in and gluing them straight was really a surprising challenge. If I ever made another one of these, I'd have to do some more thinking about what technique to use to do it right. I'm not yet sure what that technique would be. Anyway, unless you inspect it unreasonably closely, the assembly looks good. It's now down to the quality of masking and painting to determine the quality of the end result.

Question... Couldn't you have just sprayed the Lime directly without masking? Then mask the Lime and apply Black (the lighter green being easily covered by the black).

Yes, I could, and if I think much more about it I might conclude that I should. But then I'd have Key Lime under Black under Silver... I somehow didn't want the extra layer of paint there; I build heavy as it is and hate to put excess paint where I don't have to, at the cost of a little extra effort.

Staring at what I just wrote, it seems a little stupid. That's not much of a paint savings.

Anyway, it could turn out to be a bad decision if I fail to do a good enough job on the next round of masking, and don't achieve a good sharp edge between the key lime and the silver. So we'll just call this a motivator to be extra-diligent on the next round. We'll see how it goes.

In general, this build has a trickier paint sequence than I've tried before. It's been interesting thinking it through, and I'm sure there'll be plenty of good post-mortem analysis to do when I'm done.

If for some reason you think it's really a mistake to mask the fins off the way I did there, please do let me know. Seems like a judgment call, unless I'm overlooking some major pitfall.

No, you will just have to be careful masking.

If you haven't already, I suggest you read some of Micromeisters painting posts, especially his technique of applying clear acrylic matte to seal tape edges before applying each successive color--it's a lifesaver!

Have read them, haven't tried it yet though.

so, what kind of diamonds does it cut?

(wait for it)

MACH diamonds, of course!

GlenP said:

so, what kind of diamonds does it cut?

(wait for it)

MACH diamonds, of course!

Click to expand...

Ha, if I had thought of that in the first place I might have worked some mach diamonds into the paint scheme.

[hurries off to start playing in OpenRocket]

Those converging-diverging transitions are basically the shape of Mach diamonds, that is what I thought inspired them. I was thinking of adapting the body tubes used for a Dr Zooch kit flame fins assembly to look like that, but it probably would have gotten too heavy, and I did not want to spend more time on the flame fins than the actual rocket.

Oh, good point. Yeah, it was intentional, just what I had in mind. Yeah, that's the ticket.

I'm loving this build, great looking rocket!
Will we be seeing it at Great Meadows sometime?

Nate

nute said:

I'm loving this build, great looking rocket!
Will we be seeing it at Great Meadows sometime?

Click to expand...

Absolutely, unless I butcher the paint job so badly that I'm embarrassed to show it in public. Not out of the realm of possibility!

neil_w said:

Absolutely, unless I butcher the paint job so badly that I'm embarrassed to show it in public. Not out of the realm of possibility!

Click to expand...

I don't know, that's a pretty nice looking paintjob!
I'll look forward to seeing it!

Nate

Me too.

Here's the transition after masking tape removal.

Looks good but I am a bit concerned about whether the paint was adhering tightly at the mask lines. If not, I'm gonna have a heck of a mess later on.

Probably shoulda painted the whole thing green as suggested. Fingers crossed.

Fin papering is in progress and should be complete tomorrow.

Let's make some fins.

First I had to cut and assemble the main fins, which I chose to make out of two pieces because it seemed like the right thing to do, with grain parallel to the leading and trailing edges. My big concern was cutting them precisely enough to fit together properly.

After cutting the two pieces, I placed them against a straightedge (in this case the ever-useful aluminum angle) to test that the two pieces fit together *and* would sit flat on the root edge. I then sanded until everything seemed correct, like so:


The leading and trailing edges were rounded; the edges on the inside were left square. Just because.

Then I glued the two pieces together while holding them against the angle, to *guarantee* that they really came out straight (of course they didn't come out exactly straight). I did a bit more sanding after assembly to get the root to sit as flat as possible.

With all four fins glued, it was time to have my first adventure with papering fins. Because it seemed so darn easy, I chose to try Avery self-stick label paper (hereafter referred to as SSLP). Mine were half-page sized sheets, which turned out to be a good size for one of these fins. I was a little concerned about dealing with the rounded fine edges, but it seemed manageable. Here goes.

1) Lay the fin on on the sheet of SSLP, with the leading edge in the middle:


2) Fold the SSLP tightly over the leading edge, trying to keep it as tight and flat as possible:


Here I will note that the SSLP seems to lie flat on the balsa with almost no fiddling. No bubbles, no creasing, no nothing. Super-easy. For now.

3) Rough-trim the excess:


4) Sand off the excess. For the trailing edge, it turned out to be surprisingly easy, despite the curve. I was pleasantly surprised. However, the paper didn't cut in the same spot on each fin, probably due to the variance in the edge shape:

To get to this point was ridiculously, almost embarrassingly easy. It is at times like this that I can feel Murphy lying in wait for me, ready to pounce.

5) To seal the edges, I chose good old Elmer's Carpenter's Wood Glue. It was suggested that CA doesn't play particularly nicely with the SSLP, and Titebond doesn't sand too well, so Wood Glue it is. On the root edges, I allowed myself to be a bit sloppy, since those areas were going to be covered by fillets eventually. On the other edges, I tried to get the glue only a couple of millimeters off the edge. This turned out to be harder than expected, because the wood glue gets really sticky really quickly. I just couldn't control it as precisely as I wanted to. When I was finished, it looked OK but a little messy, and I hoped I'd be able to sand off the excess. I also had a bit of trouble getting the label to adhere around the very sharp leading point of the fine. No matter what I did, neither stickem nor glue wanted to hold it together. Somehow, though, when I was finished, they all seem to have settled down and stuck. Ok then.

6) Finally, I sanded. Some of the messy areas did indeed prove hard to sand, and I didn't get them perfect. However, the other bits came out good, and the sanded wood glue made a really glassy smooth edge on the trailing edge (I didn't care so much about the edges "under" the fin, although they came out fine too).

At this point I'm thinking success, and boy oh boy was it easy compared to sanding CWF. Nothing left to do but prime, so I masked off the root edges and a couple of millimeters up each side, and sprayed my usual Filler/Primer (I ran out of Duplicolor after the first side, so I did the other half with Rustoleum. Both seem to perform about equally).

They sanded up really nice and I think I am declaring victory. They also feel really strong, despite the spindly point in the front.


Sanding revealed the high spots, like at the glue joint between the two halves of the fins. No matter, all is well.

Oh, and while I was priming the fins I did this, because why the hell not:

Fantastic job with the papering - I think it looks great from here! :clap:

Thanks. Without your professed enthusiasm for the technique I never would have tried it, so thanks for that too!

For me, attaching the fins is always the highlight of the build. This one had a little extra juice because (a) what it took to get to this point, and (b) this would be the first real test of my custom fin jig.

As my first experiment with 3D printing, I designed a jig in TinkerCad and printed it through 3dHubs. Doing the design was incredibly fun; TinkerCad is stupidly easy to use although it can be challenging to do some things very precisely. Ultimately the precision of the print ends up being the limiting factor, so that was not much of an issue. I got the jig printed in 100 micron ABS, cost me about $12 with local pickup. Here it is:


It's sort of a modification of the Estes tube-marking guide, with the big difference that it's designed to hold 1/2" aluminum angles (mine where 1/2"x3/4"), and the angles create a clamp for the fins. This part is specifically for 3/32" fins; I also made another one for 1/16" fins. The only difference is the thickness of the central spine. Obviously this is a 1-fin-at-a-time jig.

You start by strapping the jig to your body tube, using the slots provided to thread through some Velcro straps:


What comes next seems to be a matter of preference. You can either hook in the angles first, and then install the fin into the "slot" they create, or lay the fin down and then clamp the angles around it. I tried both, and think the latter might work a little better. My pictures show the former. Here are the angles in place, held in by medium binder clips. Note that due to the very long fins, my pieces of angle weren't quite long enough to reach to the end of the jig. Didn't make any difference, although in the future I'll try to avoid this, just to make sure the angles are clamped as securely as possible to the jig.


The angles are positioned so they extend just past the end of the fin. After the fin is in place, I put a little clamp on the angle ends, and the fin is most assuredly not going anywhere.


Overall I'm pretty happy with the way it worked, although on the BT-60 it did not sit quite as securely as I had hoped; even with the velcro straps pretty tight, there was still a bit of play in the alignment of the jig on the tube. Possibly I should make the "wings" a bit longer, so it overlaps the tube a bit; it does this with anything smaller than a BT60. I'll probably try that on my next version (if there is one). This would be dicey on anything larger than a BT-60, although in those cases I'd probably be using 1/8" fins anyway, so I'd need a larger jig for that.

Finally: while gluing on the fins, I noticed that despite my best efforts, the root edges were not perfectly aligned and flat. So there was a bit of gapping in some parts of the root/tube joint. Generous filleting should take care of that.