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.

After 4 sides of the box were assembled, it was just the top left. This should have been quick but was delayed by the need to first bond the bracket that will hold the circulation fan to the inside surface.

Had I designed the box today, with the intent to use the bed heater, I would have made it 10mm taller, since now there is basically no space between the heater bed and the top and bottom of the box. The circulation fan must be mounted quite far back in the box to not obstruct the filament spools (it will still prevent that section from fitting a 3.5kg spool, but 1kg spools and smaller will be fine) and this means even the single ply of its mounting flange had to be cut down to not protrude into the tiny space between the heater bed and the box ceiling.

Once the fan mount had cured in place, I smeared micro on the edges of the box top, slid it in place, and weighted it down with some aluminum stock. Before adding the corner tapes, which would preclude me from weighting down the edges, I wanted the micro to cure and hold it in place.

Adding the corner tapes was a bit more unwieldy now that only one side is open, but not a big deal.

The top of the box (flipped upside down) has been bonded to the rest and corner tapes applied.

A closeup of the corner tapes for the box top. As with the bottom, I had to take care to not get epoxy in the threads for the heater bed mounting screws.

I had initially cut 1″ thick foam pieces for the top and bottom. Since then I realized that it’s pointless to skimp on foam thickness since it’s just going to lead to unnecessary heat loss and more power use, so I’ve been planning to add an extra foam layer to the tops and bottom.

I don’t have enough of the tan urethane foam left, so I had to start using some of the much stronger (and more expensive) PVC foam that is meant for the Long-Ez structural parts. They come in 3/4″ and 1-3/4″ thickness so by adding a 3/4″ layer to the tops and bottoms those will end up 1-3/4″, which seems reasonable.

The way the sides overlap, these foam pieces will also cover the edges of the 2″ vertical sides. These edges were quite uneven (it’s hard to cut the 2″ foam precisely at a right angle) so it would also cover those imperfections.

But before adding that, I also needed to figure out how to get the wires from the controller into the box. There are three penetrations needed: One into the main compartment, for the heater, the heater bed thermistor, and the circulation fan. Another into the dehumidifier loop before the thermoelectric cooler, for the dehumidifier fan and one of the SPI temperature/humidity sensors. And finally one for the second temperature/humidity sensor after the cooler.

One possibility would be to glass in some sort of tubing, maybe PTFE, so that the wires can then run in those. Trouble with that idea is that PTFE tubing is kind of stiff, doesn’t stick to the epoxy, and in any case I don’t have any in the size needed to fit all the wires.

I decided to try another method. Instead of embedding tubing, I could use tubing just to make a channel in the micro, and then remove it. I have some 3/8″ tygon tubing left over from water cooling the computer. This has an OD that’s about what I need for the wiring, is really flexible, and is also not a material the epoxy will adhere to. Worth a shot.

The box top with cutouts for the electrical wiring, ready for the extra foam layer.

Two of the penetrations are simple, straight shots through the wall. The one to the dehumidifier fan, though, has to pass inside the wall for a while to get to the location where the entrance hole in the enclosure will be located. I drilled a hole up to the top of the side foam, and then removed foam along the top so the tubing would fit under the new foam block once it was added.

Closeup of the three sections of tubing that will create the holes for the wiring once the space around them is filled in with micro.

Actually bonding the foam block in place turned out to be quite a job because of the very uneven top that required a lot of filling. (In fact, there was so much filling that I’m now out of micro.)

I started the process by pouring micro slurry down the wire holes to give it maximal time to sink all the way down and get into all the places around the tubing. But it turned out I was mixing micro and filling for pretty close to 2 hours so there wasn’t much concern for that.

The extra layer of foam microed in place on top of the box. This is after all the weights and clamps holding it in place were removed.

The sections of tubing poking out of the foam block. The lone piece at the back has already been removed.

Once everything had cured it was time to see of that tubing would actually come out like I hoped. It turned out to not be a big deal getting the two straight sections out, I basically just pulled and twisted a bit and the popped out.

The long run, though, was a bit trickier. Since it runs in an “S” shape, there’s no way to get good leverage on the middle section, and even some quite violent pulling and twisting didn’t seem to do anything. I got the idea to spray a little bit of WD-40 in between the tubing and the micro, and that did the trick and it popped loose quite easily.

The two wire penetrations to the dehumidifier. You can actually see my fingers through the left hole.

Now I just have to avoid getting epoxy into those holes when I glass over the foam. I think people have successfully used a slug of silicone sealant that can be popped out once the hole is cut in the glass.

Next step is to add the extra foam layer to the bottom side. There are no complications on that side, I think, but I can’t do it until my shipment of micro arrives from Aircraft Spruce.

After starting to assemble the filament storage box, I was distracted by the house fumigation and repairing the Flightradar24 antenna, but this weekend I finally had time to apply the corner tapes to the inside corners.

This is pretty simple, the idea is to apply a strip of fiberglass cloth to join the two sides in the inside corners. To make a smooth transition that the glass can follow, a small bead of micro or flox is used in the corner.

These thin BID tapes are cut at 45-degree bias, so the fibers go diagonally across the tape. This makes it conform to shapes much better, but also means that the strip can be stretched and squeezed a fair amount. Care has to be used when applying the tapes since it’s easy to stretch it as you push it into the corner. It’s also a bit tricky to make sure the tape ends up centered in the corner.

The 4 sides of the box with corner tapes applied to all joints. I also added peel ply to ensure a smooth transition and no sharp glass needles poking up at the edges of the tapes. The tape in the lower right is intentionally short since there needs to be room for the box ceiling on that side.

The only complication was that the screw holes for the heater bed plate are quite close to the edge, close enough that the corner tapes would cover the threaded holes. Getting epoxy into these holes would obviously be no good, so I initially covered them with pieces of painter’s tape, cut the cloth to clear the hole, and also cut the peel ply to avoid getting wet epoxy anywhere near the holes.

The corner tapes and the peel ply were cut to not cover the threaded holes that hold the heater bed.

Once these have cured, I can mount the final side of the box. Stay tuned, I hope to keep the momentum going now.

Progress on the filament dryer was stalled over the summer since all free time went into the repainting of the room. The next thing to do on the box itself was to figure out a way to mount the internal circulation fan, figure out how to run the wires, and assemble the panels into a box.

I’ve been putting off assembling the box since it’s sort of the “point of no return” in case something goes wrong, and I wanted to make sure I knew how to run the wires since it’s easier to make pass-throughs through the foam boards before they’re assembled.

In the end, however, I decided that I should just make the fan mount and affix it to the inside of the box top, and then put everything together to get the project moving again.

The circulation fan is an 80x25mm fan that will be mounted vertically to the ceiling of the box, blowing air down to set up an airflow inside the box. To not obstruct the filament rolls, it has to fit fairly tightly against the ceiling, which isn’t optimal for airflow since the fan has to suck the air in somewhere.

To mount the fan, I made a square bracket by laying glass on top of a 1″ thick 90x90mm large foam piece, folding it down along the sides and then out at the bottom to make feet. By cutting out a big circle in the “top”, and then cutting most of the sides away, the fan can suck air in through the slits on the sides. The airflow area is a bit smaller that I would like, and the fan definitely has a slightly choked sound when tested, at least at full speed. However, I don’t anticipate it needing to run very fast at all since all it needs to accomplish is to make sure all the hot air doesn’t stay at the top, so I think it’ll be fine.

This is the bracket that will hold the 80mm circulation fan.

With the fan mount done, I started assembling the box. After some test fitting, tedious removal of all the peel ply, and trimming some edges that weren’t quite straight, I went for it. For starters, I assembled the left and right sides, the back, and the bottom. This is easy to do on the table, and adding the top can then be done by flipping the box upside down and adding the top in the same way.

Eventually all the inner corners will get glass tape to hold them together, but to avoid disturbing the shape when doing that I started by adding flox to the foam edges and moving then against each other to “glue” the joints together. Checking that everything was square, they were temporarily fixed in place with a few large nails through the sides. 

The box with the cured flox but no corner tapes yet. The top of the box won’t be mounted until the corner tapes are done, since it will be much harder to access the inside at that point.

This worked pretty well. It was a little hard to fit the pieces with the flox in the joints since I’d deliberately made the flox quite dry so it wouldn’t run out of the joint, and I ended up getting little gaps in places where the flox had’t conformed. That’s not really a big deal, though, since the real strength of the joints come from the glass tapes. I can also backfill the holes in the joints from the outside before glassing that.