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Oct 10, 2019, 10:16 PM
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Quote:
Originally Posted by jeffsch
P.S. I have no experience with hot glue.
You'd love it, then! My applicator has two heat settings, and I keep it on low. It comes out of the pointed nozzle as a thick goo, and is great for spot-gluing, like servos into foam, for instance. The heat on the low setting didn't adversely affect the surfaces of either the MPF or the pink foam scrap pieces, and getting the pieces apart again from a 1" bead of it is a chore.
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Oct 11, 2019, 02:07 AM
Danish? Don't U eat that??
DKChris's Avatar
Quote:
Originally Posted by Jay B. Scott
Does anyone know if you can use hot-melt glue on foam without melting the foam? I know I can just try it on a piece of scrap, but I thought I'd let someone with experience chime in. I want to secure my servos with a couple drops of it.
I have built a number of the Flite test planes scaled up to fit 6mm Depron (FT foam is ~4.5-5mm) using hot glue, which has worked great. You will melt the foam a little bit, if you are to achieve a good bond, trick is to keep it minimal, so the glued surfaces are just gaining a bit of "texture". To achieve this I use a temperature adjustable hot glue gun.
Mine is a cheap one , not unlike the one in the attached pic. You can find these all over the place on fleabay, amazon etc. It's not amazing quality, but for the price it does the job nicely. The temp. scale is not to be taken too seriously, but it works fine to refind a previously known good setting. I just experiment with scraps to find a setting that goes well with the type of foam I'm working on.
There are far better quality products out there though. But the pro stuff gets pricey quite fast.
Last edited by DKChris; Oct 11, 2019 at 02:31 AM.
Oct 11, 2019, 04:46 PM
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Thanks, DKChris, for sharing that one. So you can build a whole foam airplane using hot-melt glue. I saw an adjustable temperature gun at Banggood for $14.27. Yours and that one go up to 220 degrees C. As per the pic, polystyrene melts at 240 degrees C. I had my cheapie two-temp gun on low (not sure what that translates into actual temperature), and on my pull test, I couldn't pull the two scrap pieces apart without ripping them up (meaning that it was a perfectly sound bond).
Oct 11, 2019, 04:53 PM
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I fixed my servo arm problem. I'll be using four Hitec HS-55 servos, which these fit.
Oct 11, 2019, 06:42 PM
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I ran out of my regular 30-minute epoxy, so I decided to use Z-Poxy Finishing Resin, which I've never used before. I thought it would just be like my 30-minute epoxy, but boy was I wrong! This stuff is thin, thin, thin! I only had to squeegee it lightly to get it even. I can see why it's so good for laminating balsa wing skins to foam cores, and for use with fiberglass.
Oct 12, 2019, 05:07 PM
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And here's the result of using Z-Poxy Finishing Resin on my nacelle lamination. It's thin like PU glue, but non-expanding. MPF has slight ripples in the manufactured product. Flattening it under pressure on one side of it seems to accentuate the ripple on the other side, which is the side being glued. In any case, the finishing resin is not gap filling, as would be the case with both PU glue and regular 30-minute epoxy. Since I've already had success with 30-minute epoxy, I'm going to go back to that. Those who feel comfortable with PU glue should have no fear in using it to laminate the MPF to the pink foam.
Oct 13, 2019, 01:41 AM
Danish? Don't U eat that??
DKChris's Avatar
Quote:
Originally Posted by Jay B. Scott
Thanks, DKChris, for sharing that one. So you can build a whole foam airplane using hot-melt glue. I saw an adjustable temperature gun at Banggood for $14.27. Yours and that one go up to 220 degrees C. As per the pic, polystyrene melts at 240 degrees C. I had my cheapie two-temp gun on low (not sure what that translates into actual temperature), and on my pull test, I couldn't pull the two scrap pieces apart without ripping them up (meaning that it was a perfectly sound bond).
An important hint is that the PS foam will sort of shrink/collapse and deform back towards being a solid at temperatures a fair bit lower than the actual melting temperature. From what I've read it's called flowing, and starts at the materials so-called glass transition point, which is at 100C for polystyrene. It's not melted, but shapable. Basically it's what makes it a "Thermoplastic" (You can have a look at https://www.creativemechanisms.com/b...ene-ps-plastic for some info, if you like.)

And the heat transfer into the foam is dependent on the size of the deposited glue glob. I usually start out with my personal glue gun set at ~"160C" with the foam I use, and at that setting I will be able to put down a fairly suitable amount of glue for a typical size build step before the first part of it gets too close to cooling and hardening for assembly, but I can still also cause the foam to withdraw and create gaps at the seams, if I concentrate it in too large globs of glue in one place, such as in an attempt to bridge a gap etc. To do this successfully I would turn down the heat further and build up the glue slowly, waiting for it to harden between applications. In fact I would probably just try to jam a foam bit in the gap instead, and try not to use very much glue, as stuff gets heavy fast.
It ends up being a bit based on experience and gut feeling. To be perfectly honest, the main point of building foam planes with hot glue is to be able to build fast, with less emphasis on looks and low weight.

I've also built 1 FT plane and some other Depron planes using mainly UHU Por, a foam safe contact cement, which did turn out prettier and lighter, but it also was more cumbersome, as I either had to wait for the cement to become tacky and live with the 1-shot chance of getting assembly just right, or glue it wet and use extra effort taping and clamping stuff in place, as the glue takes too long to dry for it to be possible to just hold it in place till it hardens, as you can with hot glue.

In the end, your choice of glue ends up being a personal weighing off of pros and cons, and you will simply end up choosing what fits your personal pace and style of building. Personally, I like to pick a glue that fits the separate build task. For the FT planes, I just wanted it to go fast and get flying. Since mine did not have paper covering, they still ended up well on the light enough side, and flew/fly just fine.
Last edited by DKChris; Oct 13, 2019 at 02:17 AM.
Oct 13, 2019, 04:43 PM
Registered User
Hey DKChris--I just noticed that your avatar has the exact same shapes that Jeff used to align and interlock his wing halves in the center. But the bottom piece's shape and the top piece's shape are in two different places, so that you can't laminate the top and bottom pieces together on each wing half first, and then push the one half down on top of the other to lock them together. I had to cut off the rounded side edges of the "male" part on both the bottom and the top parts, and slide them together from the side, in order to build the wing in two separate halves. The spar complicated that even further, because it had to stay in one piece from the beginning. And thanks for the in-depth discussion of hot glue. Definitely an underrated glue for what it can do.
Oct 17, 2019, 05:55 PM
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Fuse Work Beginning


I realize it isn't going to be this easy to get my wires run when the wing is pushed into place for that part of the final assembly. My eight wire connectors from the wing will be sitting inside the 1" square center opening of the wire channels on the wing bottom at the time the wing gets attached to the fuse. I'll pull them out one at a time with tweezers.
Oct 17, 2019, 07:17 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
Looking good!

Pretty neat how you opened up the space in the aft fuselage for the receiver.
Oct 19, 2019, 12:12 PM
Registered User
They say, "Planning is half the battle." For me, set-up is everything. The fuse starboard-side piece of MPF has three hatches--two large ones--that cause the piece to be particularly flexible. It has to be pinned in place with the hatches inserted temporarily to maintain its shape, or else the hatch openings will inevitably be warped, making it a nightmare to put the hatches in place once the lamination is cured.
Last edited by Jay B. Scott; Oct 19, 2019 at 12:23 PM.
Oct 19, 2019, 12:46 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
Beautiful work!
Oct 19, 2019, 02:29 PM
Registered User
Jeff, thank you so much as always for your continuing support! I'm just glad my major laminations are done.
Oct 21, 2019, 09:22 PM
Registered User

Carbon Fiber Reinforcement


Here's Monday's work. The extra reinforcement is because I'll be pushing the airframe beyond the normal limits with my "go faster" power system.
Oct 21, 2019, 09:27 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
Love to see your craftsmanship. Thank you for keeping us posted.


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