Edge-gluing polystyrene to cardboard?

[SolarYellow]

I got the dumb idea that if Estes can make fins out of polystyrene, I should be able to cut nice, smooth, perfectly flat fins out of Evergreen polystyrene sheet. Easy to fabricate. Don't have to color it, but can if you want.

I have some fins made. Cut from 0.030 sheet for BT-20. I like them, and I liked the process. They are flat and smooth. No paint required. All good.

Now to attach them. I'm trying to stick with a clear adhesive so I can just rely on the color of the BT and fin without any paint required.

The preference for clear appearance led me to set aside JB Weld plastic epoxy because it is opaque and grey. I don't really trust my BSI on the non-porous PS without making a bunch of holes in the root edge to act as rivets. I'm assuming CA, even the thick stuff, will end up being too brittle to survive landings.

I know Estes recommends what in most cases works out to be the red-tube Testors for sticking its PS parts to BTs, but my gut says that will not work well here. Lots of reports of it getting brittle over time and not holding up as well as pure solvent weld to rocket abuse.

I tried E6000. Glued a test fin to a sanded BT scrap piece. Went back and added fillets. Found it to remain flexible when cured, which meant it was more subject to peeling failure. Also, it peeled cleanly right off the edge of the fillet where I hadn't sanded off the glassine. It stuck much better to the PS, but I'd have been happier with a little more solvent melting/welding at the interface.

My next attempt is going to be Duco cement. The last time I saw it was when I was a kid, but the local Ace Hardware has it in stock. I've read that it dries hard. Thinking the solvents should work well on the styrene. Have read that the formulation changed a few years ago, making it stiffer and quicker drying, but that it is possible to thin it with acetone and make it act like the old formulation, which I may try in order to get a little more soak into the sanded BT and solvent welding at the interface with the PS.

Anyone else have any bright ideas?

 

[dhbarr]

JB has plastic Weld and plastic Bond. I thought one of them was fairly clear.

 

[cbwho]

If you want nice perfectly flat fins without painting. Take a balsa board, take colored printer paper, white glue. After quick shaping of the balsa board, put glue on the paper and wrap the board around the leading edge. Rub it and pinch the edges. Put beneath books to dry. Trim edges with scissors. Perfectly flat, colored fin, and strong. No paint, very little sanding.

 

[DigBaddy]

Attach with CA, then tiny epoxy fillets.

 

[teepot]

Would styrene glue stick to paper. Or is it only for styrene to styrene? I but some styrene panels on a BT a few builds ago. I used CA IIRC. Might have been Testor's too.

 

[SolarYellow]

The Duco cement surprised me. It's about 80 percent solvents and mostly nitrocellulose for the rest. Figured it would bite into the PS really well. Not at all. Used plenty, did the double-glue method (like with aliphatic wood glues) per the instructions for porous surfaces. Let it dry overnight. In the morning, the Duco was nice and hard. With hardly any force applied, the PS fin popped out, leaving a perfect print of itself in the dried Duco, almost like it had been coated with mold release. Utter and complete failure.

Figured, what the heck. There's the red tube of Testor's sitting there. Glued the test fin to the chunk of test BT. Let it sit overnight, pulled some fillets with the Testor's when I got up in the morning. Fillets came out pretty well. It's nicely self-leveling. About 15 hours later, when I got home from work, I checked it. The fillets, made with a flat-blade screwdriver, had shrunk to a just-right concavity, and the glue felt nice and hard. Applied some lateral bending force to the fin, and it flexed and stayed there surprisingly easily. Bent it back, also pretty easily. Took the test to a destructive limit. It turned out the flex and yield was all in the fin. The fillets were quite rigid and kept their shape well, but the PS material had absorbed solvent from the cement and been softened while the fillets got reasonably stiff. All the bending was right at the root of the fin, just above the fillets, where the solvent had affected the PS material. Maybe if I had a month to wait, the PS solvents would absorb back out of the PS and leave it at full strength, but it's possible it would never reach full strength.

Brainstorming what/how to try one or both of the epoxies. The BSI 30-min has the advantage of being clear, but may only be able to achieve a mechanical lock on the PS of the fin. The J-B Weld 50133 Plastic Bonder is made specifically for plastics https://www.amazon.com/J-B-Weld-50133-Tan-1-Pack/dp/B009EU5ZNO , but is not clear. May just have to compromise and do some after-fillet coloring. (This is all part of a no-paint finishing strategy I'm trying, hence the desire for clear adhesive and fillets. Having to apply color after applying fillets would be a significant compromise of the objective.)

 

[BEC]

Attach with CA, then tiny epoxy fillets.

+1 for this.

This is also how one attaches thin carbon plate or G10 fins to paper tubes (as often used on competition altitude models).

 

[dhbarr]

The J-B Weld 50133 Plastic Bonder is made specifically for plastics https://www.amazon.com/J-B-Weld-50133-Tan-1-Pack/dp/B009EU5ZNO , but is not clear.

This is the other one I mentioned up thread.
https://www.jbweld.com/product/plasticweld-syringeApparently there's also
https://www.jbweld.com/product/clearweld-syringeWish they had a better naming schema, hard to keep straight.

 

[lakeroadster]

The Duco cement surprised me. It's about 80 percent solvents and mostly nitrocellulose for the rest. Figured it would bite into the PS really well. Not at all. Used plenty, did the double-glue method (like with aliphatic wood glues) per the instructions for porous surfaces. Let it dry overnight. In the morning, the Duco was nice and hard. With hardly any force applied, the PS fin popped out, leaving a perfect print of itself in the dried Duco, almost like it had been coated with mold release. Utter and complete failure.

Figured, what the heck. There's the red tube of Testor's sitting there. Glued the test fin to the chunk of test BT. Let it sit overnight, pulled some fillets with the Testor's when I got up in the morning. Fillets came out pretty well. It's nicely self-leveling. About 15 hours later, when I got home from work, I checked it. The fillets, made with a flat-blade screwdriver, had shrunk to a just-right concavity, and the glue felt nice and hard. Applied some lateral bending force to the fin, and it flexed and stayed there surprisingly easily. Bent it back, also pretty easily. Took the test to a destructive limit. It turned out the flex and yield was all in the fin. The fillets were quite rigid and kept their shape well, but the PS material had absorbed solvent from the cement and been softened while the fillets got reasonably stiff. All the bending was right at the root of the fin, just above the fillets, where the solvent had affected the PS material. Maybe if I had a month to wait, the PS solvents would absorb back out of the PS and leave it at full strength, but it's possible it would never reach full strength.

Brainstorming what/how to try one or both of the epoxies. The BSI 30-min has the advantage of being clear, but may only be able to achieve a mechanical lock on the PS of the fin. The J-B Weld 50133 Plastic Bonder is made specifically for plastics https://www.amazon.com/J-B-Weld-50133-Tan-1-Pack/dp/B009EU5ZNO , but is not clear. May just have to compromise and do some after-fillet coloring. (This is all part of a no-paint finishing strategy I'm trying, hence the desire for clear adhesive and fillets. Having to apply color after applying fillets would be a significant compromise of the objective.)

I'm wondering if you would have drilled a series of small holes through the polystyrene to allow the Duco to flow through the holes if that would have acted like small rivets to hold it all together.

I'm surprised @Dotini hasn't commented on this thread? He glues plastic fins to cardboard BT's for his Magnus Effect birds.

 

[SolarYellow]

I'm wondering if you would have drilled a series of small holes through the polystyrene to allow the Duco to flow through the holes if that would have acted like small rivets to hold it all together.

I'm surprised @Dotini hasn't commented on this thread? He glues plastic fins to cardboard BT's for his Magnus Effect birds.

If I'm going to drill holes for glue rivets, I'll just use epoxy.

Will have to search on @Dotini's threads and see if he posts how he glues the fins. Thanks.

 

[lakeroadster]

If I'm going to drill holes for glue rivets, I'll just use epoxy.

Will have to search on @Dotini's threads and see if he posts how he glues the fins. Thanks.

We talked about this technique a while back. Combining this (the BT modification, not the kevlar) with the glue rivets, you'd think it would be hell-for-stout.

 

[David_Stack]

Since the polystyrene is that thin, would it be possible to slit the body tube and then insert the fins into that slit? The additional bonding area may be sufficient to offset limitations in your adhesive...

 

[SolarYellow]

We talked about this technique a while back. Combining this (the BT modification, not the kevlar) with the glue rivets, you'd think it would be hell-for-stout.

View attachment 563671

I remember those posts. I'm gluing 0.030" fins to BT-20. I don't think my skills would make that approach work well at this size. I also prefer my Kevlar to be readily replaceable.

Glued another test fin with red-tube Testors last night and pulled fillets this morning. I'm going to do the CA/epoxy tonight, then leave them both the heck alone for about a week and a half. Maybe the Testors solvents will work their way back out of the PS by then. Will test both to destruction and decide how to finish building this little rocket.

 

[David_Stack]

Another option might be to pick up some of the polystyrene angle stock as sold by Evergreen (https://evergreenscalemodels.com/collections/14-35cm-opaque-white-polystyrene-angle), use the proper adhesive to attach 'flanges' to the fin along the root edge, and then glue that assembly to the body tube.

It would look similar to the fin attachment used on the Aero Hi sounding rocket. See https://www.rocketryforum.com/threa...d-through-the-wall-fins….177017/#post-2373286 for an image.

 

[SolarYellow]

Another option might be to pick up some of the polystyrene angle stock as sold by Evergreen (https://evergreenscalemodels.com/collections/14-35cm-opaque-white-polystyrene-angle), use the proper adhesive to attach 'flanges' to the fin along the root edge, and then glue that assembly to the body tube.

It would look similar to the fin attachment used on the Aero Hi sounding rocket. See https://www.rocketryforum.com/threads/love-kits-with-pre-slotted-body-tubes-and-through-the-wall-fins….177017/#post-2373286 for an image.

That's a lot more weight and drag than a simple fillet. One aspect of the build is I'm looking to maximize apogee with a C6-7, so keeping weight at or below optimum mass and minimizing drag are important elements. Will be using a fly-away launch lug.

I do plan to build an IQSY Tomahawk at some point with fin brackets as groovy and scale-like as I can figure out how to make them.

 

[David_Stack]

That's a lot more weight and drag than a simple fillet. One aspect of the build is I'm looking to maximize apogee with a C6-7, so keeping weight at or below optimum mass and minimizing drag are important elements. Will be using a fly-away launch lug.

Guilty as charged on the weight aspect (maybe*), but if you choose angle stock with smaller dimensions it may end up completely covered by your fillet.

* - Perhaps the polystyrene is actually lighter than whatever you are using to make your fillets, the amount of fillet material displaced would weigh more than the polystyrene 'flanges'.

Failing that, as I suggested earlier; slit the body tube so the fin is set within it (not TTW since you are building MD, but embedded into the wall of the BT). You could insert a dummy motor casing when you install the fins to ensure you still have clearance for the motor after the fins are glued in.

 

[Dotini]

Although I've built and flown extensively with styrene, I'm modest enough to say it's not been entirely successful and I'm still experimenting to this day. Edge glueing is the worst, and I've generally tried to use T-sections and/or angles to broaden and reinforce the root joint. I think one of my biggest mistakes is to paint the styrene, generally with 2X, and I think this may be causing the plastic to become brittle. My latest plan is to avoid flanges, tack with red Testor's, lightly fillet with it, then make a heavier fillet with the JB Weld epoxy for plastics mentioned above.

 

[SolarYellow]

One aspect of the JB Weld Plastic Bonder is it foams when it cures. So unlike the Testor's, which shrinks as it dries, and regular epoxy, which stays the same size and shape as it dries, the JBWPB will expand.

 

[Dotini]

One aspect of the JB Weld Plastic Bonder is it foams when it cures. So unlike the Testor's, which shrinks as it dries, and regular epoxy, which stays the same size and shape as it dries, the JBWPB will expand.

Thanks for the tip. I've used Gorilla glue (no good for styrene) extensively in the past, so I'm familiar with working with expanding glues.