Since the last post, the fan bracket for the heat sink has been completed.

Since it had to fit quite precisely in place below the heat sink on the side lid, I glued a piece of urethane foam in place and cut it to the correct shape and rounded the corners a bit. Then I covered this in plastic film and made the layup over it, wrapped the whole thing in plastic film, and applied vacuum.

I initially only used a single ply, but this didn’t work at all, the vacuum squeezed it and got rid of so much resin there were holes right through the weave. It was also way too flimsy. It had to be redone with two more plies to get it reasonably stiff.

Test fitting the fan holder for the dehumidifier heat sink.

After curing, it fit very nicely to the shape of the heat sink and the side lid, not surprisingly since it was shaped to it. Then the holes for the fan screws and the air passage had to be drilled and cut.

Marking out the position of the fan for cutting the holes.

I realized that it was not going to be possible to use nuts to attach the fan since you can’t get to the inside when the fan is mounted. Instead, I covered the fan in plastic, screwed it in place, and then applied flox around the nuts to stick them in place.

To make it easier to mount the fan, I screwed it to the bracket and then covered the nuts in flox (carefully so nothing got on the screws.)

Once the flox had cured, it was time to mount it by the heat sink. This was done by applying a generous coat of flox around the flange and weighting it in place. I had also drilled 4 holes for nails that ensured that it ended up in the right position.

The bracket has been floxed in place below the heat sink. Here it’s running during a drying cycle. This worked out very nicely.

This ended up working really well. The fan fits perfectly, there’s a tiny gap between the heat sink and the fan holder that can be covered up in tape. You can feel a little air escaping through the gap but I don’t think it does much to the cooling efficiency.

With that, the glass work was done. Since then, I’ve been working on the software. It’s been quite tricky to figure out the best way to get moisture out, but things are converging. I’ll have more to say about that in the next post, but as a sneak peek, this graph shows the current temperatures and humidities:

The filament storage box was now in a state that I could start wiring everything up. Running the wires was pretty quick, but then I had some software work to do before things started functioning. I had stubbed out a lot of the code back when I assembled the circuit board, but there’s only so much you can do without having hardware (or a simulator!) to test it on.

I also still had to glass the inside of the lid before I could add seals to it to make it really tight, but I did verify that the heater and fans work. So far I’ve worked up to a box temperature of 70C, but slowly to give the epoxy plenty of time to post-cure to deal with the higher temperatures. The Pro-Set can be post-cured up to a temperature of 80C for an ultimate glass transition temperature of 95C, so there’s a bit to go yet.

Glassing the inside was a bit tricky because of the sharp corners. I had initially intended to vacuum it, but it actually turned out that the glass conformed pretty well to the corners without it, so I didn’t bother.

The finished layup on the inside of the lid. There’s a flox corner around the entire outside, and the glass is lapped halfway up the flange to give it a chance to conform to the corners.

To post-cure the lid, I strapped it in place while heating the box up to 70C. This took out the small curve it had gotten while curing and made it conform very well to the shape of the box.

The lid had taken on a bit of a curve as it cured, so I decided to “post-cure it in place” by strapping it against the box while heating it up. The heat makes the glass creep a bit and worked perfectly for taking out the curve.

The picture above also shows the electronics enclosure with all the wires. It’s a bit of a mess now, it still needs to get cleaned up. The little MicroOLED display from SparkFun that displays the current temperature and humidity can be seen among the wires. It will be attached to the top of the enclosure, which still needs to get printed.

There’s one more fiberglass layup needed, because the fan that blows air over the exterior dehumidifier heatsink needs a bracket/duct for it. That layup is curing right now, so more on that shortly.

Coming up on the end of fiberglass work, I completed the first layup for the box cover, the outside. This was pretty easy since it’s mostly just flat, but the glass has to go around the edges and conform to the corners. The cloth will go around a 90-degree corner but only barely. Since the side is only 0.75″, there’s not much material for the cloth to hold on to.

The first layup for the box cover, the outside, is done.

I had to go back and wipe the cloth into position a few times but as it cured and the epoxy got thick and sticky, it eventually stuck in place.

One other thing that needed to be done was adding something on the cover for the dehumidifier so it could be held in place. I glassed in hardpoints in the side of the box so now I needed to add something that could hold it in place. I decided to just dremel a hole in the glass and carve away enough foam that I could flox in an aluminum tab with a screw hole in. Cutting the hole was quick work and by filling the hole with very wet flox, moving it around a bit, and then inserting the tab, I could be pretty sure there were no huge air voids.

To get the tab in the correct place I simply screwed it in place while it cured. This worked really well and one M4 screw top and bottom, in combination with the stainless steel pins that register its position, will hold it very securely.

Close-up of the restraint for the dehumidifier cover. An aluminum tab was floxed into the cover. Mounting the screw while curing ensures the tab lines up with the threaded hole in the hardpoint on the box. The plastic film ensures I don’t epoxy the cover to the box.

Next is the inside of the cover. This will need to go across an inside corner so I think I will use the vacuum technique here, too. That will be the end of the structural glass work.

With the bottom of the box done, time to cover the remaining bare foam on the front. The front is 1.75″-2″ wide so we’re talking applying glass tapes all around. To bond to the sides a loooong flox corner was needed all around the inside and outside, which required a lot of Dremel work to remove the foam and get bare glass everywhere. 

The box front uses flox corners all around the inside and outside, so there was a lot of foam routing needed.

It took a lot of flox, too. I think I mixed 7oz of epoxy before it was all filled. I used scrap BID and just kept cutting tapes and applying until I had two plies everywhere, and then added peel ply.

The layup is complete, including peel ply. There were a few small air bubbles against the flox, but not many.

That completed the main work on the box. At this point all the wiring for fans, heaters, and sensors can be added.

The lid also needs to be fabricated, though. This consists of two blocks of foam, which were cut and sanded so one fits into the opening and the other makes a flange that matches the perimeter. After a lot of sanding, these were joined together with micro and weighed into place.

The box lid uses two pieces of foam, one for the inset and one for the flange.

 Once the micro has cured, the lid will get two layups, one for the outside and one for the inside. Then we’re finally done with all the fiberglass work.

Now it’s time to complete the bottom of the box, fitting the penetration bracket into it.

First, the shape of the bracket was measured out on the bottom of the box, and the foam removed to the depth that would match the bracket using the Dremel. This recess was then beveled to match the bracket.

Since the recess also had quite sharp corners, I decided to try the “Lo-vac” method again. This setup was a bit trickier since I’d either have to enclose the entire box inside the plastic wrap or make some sort of joint along the sides. I used some plumber’s putty to put a bead all around the box a few inches below where the layup would end, circling into the inside.

The trickiest part was the front of the box, which still has bare foam. Trying to press the putty into the urethane foam would just have obliterated it, so I put a bead of sealant along the foam, let it cure, and then gently pressed the putty into it.

I didn’t end up taking any pictures before or during the layup, since things got pretty busy. I was pretty sure getting the big piece of fabric covering the top to conform to the recess would be next to impossible, so I used two narrow strips that went into the recess and just lapped onto the flat part, and then covered those with two large plies of cloth. Once the cloth was on, I used the electric cutter to cut a large hole so it just fit over the perimeter of the recess. This worked pretty well, but it all took a pretty long time and since I also used the  “medium” Pro-set hardener instead of the slow that I usually use, things were getting pretty sticky by the time I was ready to put the vacuum on.

The plies covering the bottom of the box have been applied and the layup is under vacuum.

I also had a hard time getting a good seal for the vacuum. I spent the better part of an hour going around the edges, pressing into the putty, straightening wrinkles, taping the loose edge, and once I also injected some sealant around the hose I finally got it to pull a decent vacuum.

After the layup had cured for 3-4 hours more, I could pull the peel ply off without too much trouble. Here, I’ve already cleaned the threaded hole for the drain fitting in the lower left.

The peel ply came off pretty easily, but the layup has a similar whitish appearance like the bracket in the last post. There are also some air bubbles visible. I think I just took too long and by the time I had vacuum the resin had gelled enough that the dinky little vacuum pump didn’t manage to pull the air out through the cloth. It did conform pretty well to the recess, though.

The holes for the storage fittings have also been cleaned. The hardpoint in the recess is for the mounting screw and has yet to be drilled.

Cutting out the fiberglass over all the threaded holes and cleaning out the threads worked like a charm, this method definitely works. If you get the sealant just the right temperature with the hot air gun, you can actually pull it out of the threads like a plug without leaving much of any residue at all.

Next it was time to drill and tap the holes for the mounting screws in the hardpoints in the recess. Using the bracket as a template, I just marked the locations with a drill, drilled out the holes the proper size for an M4 tap, and tapped them.

Finally, the recess needed to have holes for the inside fittings and tubing cut. I attempted to mark the locations there using the bracket, too, but here I did a fairly poor job so I had to enlarge the holes a bit to get them all to fit.

The bracket with its inside fittings and tubing is ready to mount into the holes in the box.

These holes are just bare foam on the inside right now. Ideally I would coat these with flox so there’s no chance of damaging the foam, but once assembled there’s no reason to be fiddling around with these so it shouldn’t matter. It can always be done later, if necessary.

Here are the penetrations into the (upside-down) box. By having the tubing protrude into the box, the filament won’t have to make a sharp turn as it enters the hole.

Here’s the bracket mounted into the bottom of the box. Only a few of the fittings are in place now, and I need countersunk screws instead of the button-head ones, too. The short piece of tubing with the red cap shows how unused fittings will be closed off so there’s no air entering.

I’ve been worried about how to make these penetrations since I started thinking about making this box over a year ago, but this worked out OK. The fit isn’t stellar but it’ll do. The only thing that remains to do now is glass the front of the box and fabricate the cover. At that point we can actually turn on the heat and see what happens! (To actually put some filament in there, I need to fabricate the holders for the spools that go inside, too.)

It’s been a couple of weeks since the top of the filament storage box was completed. In the time since, I’ve been working on the bottom.

The first thing that had to be done was to add a drain for the water from the dehumidifier. I did this by adding an aluminum hardpoint glued to an aluminum tube, just like I did for the filament storage pockets.

The drain hole for the dehumidifier. The top of the aluminum tube has been capped with duct tape to avoid getting flox into it.

After filleting the area around the tube with lots of flox and letting it cure, I sanded away flox and the aluminum to make a nice shape for the water to drain into (and not out towards the surface.

So the bottom of the box should have penetrations for all the filaments to exit. After going back and forth a bit I decided to make a bracket that could hold push-in fittings on both the inside and outside. The reason for having them on the inside is so that a short length of tubing can go through the foam, enter the inside of the box, and create a transition so the filament won’t scrape against the fiberglass on the inside.

I conveniently had a piece of PVC foam left over after cutting the top and bottom. This was perfectly sized for making this bracket. Each side of the bracket will have 12 of the push-in fittings, so I had to fabricate 24 small pieces of aluminum and tap them with a 1/8″ NPT thread. I also had to make 5 pieces countersunk for the M4 mounting screws that will hold this bracket in place against the bottom of the box.

This piece of foam will have 12 holes on each side where the push-in fittings will screw in. It will also have 5 holes for mounting screws. That’s a lot of hardpoints.

The hardpoints for the NPT fittings and the mounting screws have been fabricated and fit into the foam.

The top and bottom of the bracket has been glassed and peel plied.

To make it easier to glass this bracket, I beveled the sides slightly. I did not have a lot of extra material, though, so even with the bevel there would be quite a sharp turn for the glass to make.

I had recently read about the “Lo-vac” method used by the Cozy Girrls that seemed like it would be useful for this situation. It’s sort of a “vacuum bagging lite” where you use peel ply, paper towels, and plastic pack wrap with a cheap vacuum pump to put the layup under a slight (like 50%) vacuum to help get rid of voids and make the glass follow the foam tightly. It seemed worth a try.

The “lo-vac” layup has been wrapped in plastic wrap and put under vacuum. It does definitely help the cloth conform to the shape of the foam, but also make the “bottom” (the outside) of the layup no longer lay flat.

The plan was to give the bracket a flat outside, extending a bit outside the foam. This would make a surface so the inside layup could get some glass to glass bonding. (Similar to the Long-Ez practice bracket.) I intended to do this in a single layup, but didn’t realize that for this to work I needed to put the  flat part against a surface inside the vacuum bag. As soon as I put the layup under vacuum, the flat part got pulled into a curve.

After partial cure, the peel ply and paper towels have to come off. Normally you can peel off peel ply after a full cure, but the presence of resin-soaked paper towels on the outside makes it far too stiff to do that. I struggled a bit anyway and had to warm the layup to make it easier.

After curing and trimming, the part looked pretty good apart from the non-flat top. However, the layup ended up with a whitish appearance, which typically means it is resin-starved. I’m not sure whether this is just the fact that the peel ply was pushed tightly against the glass cloth and it’s just in the surface, or if the vacuum pulled air bubbles up out of the foam and into the cloth. The layup definitely was not too dry before pulling the vacuum. The part is fine for this purpose, but before using this for airplane work I would definitely have to sort this out.

The finished, trimmed bracket.

The layup ended up with this whiteish appearance that makes it look like it was too dry.

After cure, the glass was cut out from all the holes, the sealant removed, and the threads chased with a tap to clean them up.

The final step was to cut the fiberglass over all the holes in the hardpoints with an X-acto knife and then clean up the holes. It ended up working quite well.

With this bracket done, it was time to cut a recess in the bottom of the box and glass it. That’ll be the topic of the next post.

With the sides of the box completed, it was time to glass the top.

The layup itself was pretty straightforward, since it’s just a flat piece of glass that laps onto the sides and back. I added aluminum hardpoints for the screws that will hold the electronics enclosure and another hardpoint that can be used to make some sort of clip for the condenser cover, I haven’t worked that part out yet.

The top surface of the box with the layup done.

The only hard part about these larger layups is that I’m suffering from having too small epoxy cups. For smaller work, my 2.5oz paper cups are pretty good, but when making these larger ones, I have to run over to the hotbox and mix more constantly. I should really get some larger cups, too. (Imagine laying up an entire wing skin using 2.5oz cups. It would take days…) As usual, peel ply was added where the glass laps onto the sides, ensuring a smooth transition.

I put in a hardpoint that can be used to hold the right side cover. Not sure exactly how yet, but it’s there if needed.

As an aside, I got new peel ply tapes from Aircraft Spruce. There are two types of these tapes, with smooth or “pinked” edges. “Pinked” means it’s cut in a zig-zag pattern. When I initially ordered the composite supplies back in 2013, I got a roll of “pinked” 2″ tape, and that turns out to be the wrong choice for fiberglass work. The zig-zag pattern leads to lots of little strands getting stuck in the corners. Apparently, when you do fabric covering of tube-and-rag airplanes, you want pinked edges, because it attaches better when you join fabric together. When using it on top of layups, though, that’s exactly what you don’t want. These new tapes, with straight edges, work way better.

Once the epoxy had cured, it was time to attempt to cut out those wire holes. If you remember from earlier, they had been covered with sealant to prevent the epoxy from getting into the holes. That had also covered the 3-conductor wires for the temperature probes that were now enclosed under the glass.

Using a fresh X-Acto blade, I started cutting the glass, trying my best to not cut into the wires. This turned out to be pretty difficult, and before I had gotten the holes cleaned out, two of the three wires had substantial cuts into the top conductor. I checked the probes and they still work, but this was not a good way of doing this. At the very least, I should have added some heat shrink tubing to the wires as they exited into the hole to give them more resistance to errant cuts.

The wire hole cleaned up. The damage to the insulation of the temperature probe wire is clearly visible.

The other hole has two wires coming out of it. Here, too, I managed to cut into the insulation of the top wire.

The hole that had two wires also had had some epoxy run into it. The sealant must not have covered the entire area, or the epoxy entered from the wire trough between the two wires. It wasn’t too bad, the cured epoxy mostly peeled off the wires pretty easily.

 With the wires extracted, I drilled and tapped the holes for the electronics enclosure, which completes the top of the box.

The four hardpoints for the enclosure have been drilled and tapped.

The bottom of the electronics enclosure temporarily screwed in place to test the fit.

Now I can’t put off finishing the bottom any more, so I have to make a decision on what to do with the filament exits. I also have to add a drain hole where the condensed water from the dehumidifier can exit. Here I’ll use the same kind of tube I used for the storage tubes.

Since the last filament storage post, the storage tube assembly was microed into place. I covered the foam around the hole with duct tape to prevent getting micro on the foam surface, and poured slurry into the holes.

The foam has been covered with micro slurry, and a substantial amount of slurry also poured into the holes so the space is completely filled up when the tubes are inserted.

The idea was to get enough slurry into the holes that it just filled all the empty space when the tube assembly was inserted. I had to trial-fit the assembly a couple of times and add more slurry, but eventually I got to a state where slurry was coming up out of all 8 holes right as the aluminum bracket was going into the hole.

It then took some pushing to get the part seated to be level with the foam surface, wiping up more micro that squeezed out, but eventually I covered it with plastic, but a big weight on, and left it to cure.

The storage tube assembly after cure. The sealant in the holes will be left until this surface is glassed over.

There was more work to be done on the outside of the box. One task was to glass the left side, which has so far been bare urethane foam. This is a pretty straightforward piece of glass with a flox corner on one side. The biggest complication was that the bare foam edge of the 2″ thick back piece was not very level and had to be filled with a lot of micro. It was hard to get that even so there’s a bit of a bump in the glass there.

The left side of the box glassed over. The back edge is a flox corner, while the top and bottom lap slightly onto the blue foam. The glass on the top and bottom will later overlap these. The back region also had to be filled with a lot of micro where the back side didn’t match very well. This fill ended up pretty uneven.

I also had to glass over the opposite side by the dehumidification duct, where the foam edge of the 2″ back piece was also still bare. Because of the difficulty of getting the micro fill even on the left side, I decided to split this into two cures.

First, the depression was filled with dry micro and covered with peel ply. This was a trick I was reminded of when I recently watched the “Building the Rutan Composites” movie on Youtube. By covering the micro with peel ply, you can smear it out evenly without the surface rolling up when you scrape it. This makes it way easier to ensure you get an even surface. You simply add more micro and use a straight edge to smear it until it’s even. If you get extra micro, it simply gets scraped off the edge.

The foam edge being covered with micro. The object here is just to get enough micro to fully fill the depression.

The dry micro has been covered with peel ply and scraped to be even with the glass edges.

Once the micro has cured, the peel ply was removed, the edges cleaned up and some excess micro that had migrated onto the glass sanded off.

Since the back edge should be a flox corner, I had to then dremel off the micro and foam in that area to get a clean joint with the glass on the back face. Dremeling through the micro is substantially harder than just getting rid of the foam, but not a big deal. This now makes a very nice channel that can be filled with flox, and then two plies of BID were added.

Here, the fiberglass cloth has been added on top of the micro and the flox along the back edge (top edge in this picture). Peel ply has been added to make sure the edges of the glass were clean.

The next steps are to glass the large top and bottom areas. The top is ready to go, but the bottom still needs to have the penetrations for the filaments to come out of the box made, and I still haven’t decided exactly how to do that.

The work on the filament storage box has lately focused on what to do with the filament tubes when they’re not used.

The box will fit up to 8 1kg rolls of filament (or 4 3.5kg rolls), and those filaments will exit the box in PTFE tubing through the bottom of the box so they can be routed to the 3D printer. The question then was what to do with the filaments that aren’t being used.

Since we are trying to keep humidity out of the box, leaving those tubes open is a non-starter. One could imagine just capping them with a plastic cap, but that would push the filament back into the tubing so you couldn’t get it out without opening the box and feeding it out again — which would also defeat the purpose of not introducing humid air.

Instead, I decided to make 8 “holding tubes” on the side of the box. These will be short aluminum tubes with the same push fittings that are used to hold the tubing at the exit end. The filaments that aren’t being used are then just pushed into these fittings. Because there is space for the filament past the fitting, the filament can continue to poke out of the tubing so you can get to it when you want to use it.

The fittings I’ve bought have a 1/8″ NPT thread, which is about 9mm diameter. I ordered some foot-long pieces of 10mm ID, 12mm OD, aluminum tubing and cut these into 8 roughly 75mm long pieces. Since the ID of the tubing is larger than the thread, there will be no interference, so all I had to do was machine 8 holes into a piece of 1/4″ thick 6061 bar stock. (Except before I could do that, I had to resurrect the CNC mill which hadn’t been reassembled since I moved it from the garage to the basement.)

I was also a bit rusty on the CNC side (and Fusion360 has now decided to nerf the “Personal Edition” that is free for hobbyists to use so you can no longer export jobs that use several tools. I mean, come on…) so it took me some time to get up to speed, but I got it done.

The tubes have been capped with JB Weld and are test-fit in the bracket, to make sure they are nice and snug.

After cutting the 8 tubing pieces, I capped one side of them with JB Weld. This ensures that when they’re epoxied into the foam, the inside won’t fill with epoxy. I also had to fill the threads in the bar stock with sealant, since it will be glassed over when mounted into the box. The sealant will be cut away along with the glass covering the holes after cure, and the pipe thread cleaned up with the tap again, but this way no epoxy will get into the threads and the tubes when glassing it.

The blue foam was milled out to fit the 1/4″ bracket and then had the 8 holes drilled into it so the tubes would fit. When mounting, I’ll fill these holes with slurry and any excess slurry should be squeezed out.

The tubes have been epoxied in place.

Finally, the tubes were glued in place with 5-min epoxy so they won’t pop out during assembly. The whole thing is a bit of a tight fit pushing into the foam, but it does fit. 

This is how the tube assembly will fit into the bottom of the box. The sealant used to plug the pipe threads on top is also visible.

I’m still debating whether to mount this in place ahead of time or do it while glassing the bottom. Doing it ahead of time is a bit less stressful but having cured slurry on the foam is a bit harder to deal with when laying the glass over since it’s difficult to ensure it’s perfectly even. I think people deal with this by masking the foam around the area with duct tape so you don’t get any in the foam, which sounds like a good method.