More progress on the filament storage box. All 5 sides of the box have been glassed on at least one side, and the dehumidifier circuit side was completed.
The left and right sides of the box have been glassed. The left side has the channels for the air to blow over the cold plate, which made a bit more complicated glasswork than the flat sides I’ve done so far.
The layups for the air channel were a bit tricky compared to the flat sides I’ve done so far. Instead of just wetting out rectangular pieces of cloth, this has numerous corners and edges. The inside of the channel only has a single ply of bidirectional cloth, which is very flexible. When you lay it down so the fibers run at 45-degree angles to the corners, it takes a very small radius, especially on these inside corners where the adhesion to the sides hold it in. I used random scrap cloth pieces and cut them as I went, and amazingly it did not turn out terrible. I’ve verified that both the fan and the cold plate for the thermoelectric element fits.
Closeup of the hole in the side of the box where the 60mm fan will be mounted that blows air over the cold plate to condense water out of the air.
The next step will be to attach the sides of the box, but before doing that I wanted to mount the large aluminum plate to which the old silicone 3d printer heater was going to be fixed. On the TAZ6 this is affixed to the back of the glass printer bed, so I got some sheets of the same adhesive (3M 468MP) and stuck it to a 1/8″ thick aluminum plate I cut out. The aluminum plate is mounted with M3 screws to threads cut into the aluminum hardpoints I mounted into the foam before glassing the back of the box, see the last post.
1/8″ 6061 plate with the old TAZ6 print bed silicone heater attached to the back side.
In the last post, I described the basic idea of the dehumidified filament storage box. I don’t have a lot of time to work on it, so progress is slow, but I’ve done a few layups.
The layup on the inside of the back section of the box. This side has these aluminum hard points, that will be drilled and threaded to hold the hot plate.
The back side is made from 2″ foam to give good insulation against the hot plate and maximum rigidity. That part has been glassed on both sides. I floxed 4 aluminum hard points on the inside so the heater plate can be attached.
A closeup of one of the aluminum hardpoints. They’re made of 1/4″ 6061 floxed in place under the glass.
The right side of the box, where the fan and the cold plate for the dehumidifier is mounted, is partly completed.
The right side of the box, with an outline of the dehumidification passage. The fan sits in the upper left, then the cold plate will go below it, mounted on the top. The passage has a bottom collection point where the condensate will gather and run out, and then the air circulates back up and re-enters the box through the hole in the upper right.
Here the foam has been routed out for the air passage, and the surface glassed. The passage itself will be glassed separately once the surface has cured. There are a lot of corners here so it will be pretty tedious to do.
I started using West System epoxy, which is what I’ve used exclusively for glass work since I bought it back in 2012. However, since the inside of this box will be quite warm, well above the heat deflection temperature of the West System, I decided it would be a good idea to pull out the Pro-Set that I got way back before we moved from L.A. If post-cured, it has a much higher heat deflection temperature up towards 80-100C, so it seems a better choice. It’s not like I’m using it for anything else, anyway.
I was a little bit worried that it would no longer be good, since it’s specified with a shelf life of 2 years, but I mixed a test batch and it cured fine. The hardener has turned very brown, much more so than the West hardener, even though it’s been in sealed containers, but it doesn’t seem to affect the cure.
However, I have been getting a sticky, oil-like layer on top of the cured expoxy, especially the stuff that remains in the cup. I assume this is what’s known as “amine blush”, a byproduct of the hardener reacting with moisture. I’ve never noticed it with West System, but the Pro-Set instructions warn that it’s possible. The high humidity here (I’m working in the garage, too) probably doesn’t help. Maybe I should be doing the layups in the dehumidified room…
As you may remember, my 3D printer is mostly used with Nylon or polycarbonate filaments, since those are strong and works to high temperatures. Unfortunately they’re also very hygroscopic, so they absorb moisture from the air (which we have a lot of here) and then you can’t really print with them without getting blobs and oozing everywhere. You can literally see steam coming out of the nozzle when printing if the filament’s been sitting out.
To fix this you have to dry it before printing, and then keep it dry. I’ve been doing this by keeping the filaments in the oven at ~80C for a day and then storing them in air-tight tupperwares along with boxes of dessicant. This makes it doable, but isn’t really cutting it in the long run.
First, drying a full spool doesn’t actually dry it all, the inner part must not get enough airflow so even after a day it’s not sufficiently dry to print. Since I often print large objects that use the better part of an entire spool, this means that at some point during the print things will start going south as you get into the un-dried part of the filament.
Second, the “air-tight” containers aren’t, and even if they were you have to open them and put the spool into the little box on the printer I feed it from. This means the dessicants get saturated, even though I have about a pound in there. You can dry them, but that gets old, too.
The net effect of this is that I basically don’t print stuff unless I have a big project that warrants baking filaments and dessicants. These days time is a sparse commodity so streamlining this would do wonders for being able to use the printer as an everyday tool.
So here’s the plan:
I’m going to build a large, insulated box where I can store several spools of the filaments I use most often. This box will have a heater that can heat the entire box to 80C to bake the moisture out of the filaments. It will also have a dehumidifier, essentially a cold plate where the moisture in the air will condense and then leave the box. The box will have outlets with teflon tubing where the filament will feed directly into the printer. The tubing for filaments that aren’t used can be stuck back into the box to seal those holes. This way, filaments will be continuously baked and kept dry.
A rendering of the filament storage box in Fusion 360. The square in the back is the heating plate, the holes on the right for the dehumidifier.
For making the box, I will make use of some of the foam and fiberglass I have for the on-indefinite-hold Long-Ez build. The heater will be the old heater plate for the 3D printer, which is capable for 360W at 24V. The dehumidifier will re-use the thermo-electric cooler from the long-defunct Wine fridge (see the first ever post on this blog!)
An internal fan will circulate the air internally, and on one side of the box another fan will blow air into a passage that contains the cold sink of the thermoelectric cooler and then comes back out into the box.
Finding fans that are OK with being put into an 80C environment is a bit tricky but Mouser has a few. The humidity and temperature in the box and after the cold plate will be monitored with the same kind of sensors that I use for the weather station. Controlling it all will be, of course, an Arduino.
Both software and hardware-wise, I already have most of what will be needed for this project, since the functionality is some mix of the weather station and the epoxy hot box. I did need to buy the fans and a power supply (for the 12V thermoelectric cooler and fans, for the 24V I’m reusing the one from the 3d printer.)
Sorry for this wall of text, but I wanted to give an outline of what I’m going to do. I’ve started making some parts, so hopefully I can give a first progress update soon.
In the last post, I talked about the painting of the room. However, since we hustled to get the room habitable, we skipped the closets. Before the Swedish grandparents arrived for their visit this year, we wanted to get that done.
As you may guess by now, this entailed first stripping a bunch of lead paint.
The closets have been stripped. That’s the most painful part of the job done.
After stripping, it was time for 2 coats of primer and 2 coats of top coat, Bermuda Blue for the walls and Royal White for the trim.
Closets are done and the room is now complete.
We completed the closet well in time for the grandparents’ arrival and the “library/guest room” is now complete… with the exception of the closet doors, of course. There are imperfections, obviously, but overall we’re very happy with how it came out.
As usual the grandparents visit was occasion for getting some more home improvement done. More on that in the next post (which hopefully won’t take months.)
Wow, posting’s really dropped off this year. Hard to get the time to do stuff, even harder to then actually write something about it.
When we ended the last post, I was going to show you the room painting project that we continued with after replacing the windows. The first, and most painful task, as always, was to strip all the lead paint. If you look back to the previous post you know we already went through this with the windows. The wall and ceiling is a lot more surface area but it’s actually a lot quicker to do flat areas and not have to worry about corners and edges, so it took us a few days.
To be able to work the ceiling efficiently, we constructed a platform from a few 2x4s that we could span between the ladders.
To get the ceiling done without breaking our necks we made a platform hanging between the two step ladders, and we used the Speedheater movable arm attached to a tall metal pole on wheels. That way you don’t have to hold it up, you just move it from place to place and scrape the areas you’ve heated.
The walls and ceiling have been stripped, ready for priming.
Once all the old paint was off, we repaired some termite damage and filled every seam between the planks with sealant to have an elastic seal there instead of a gaping hole where the planks move.
In general, there was not a lot of termite damage found, but this area of the ceiling was pretty bad.
To make sure we got a uniform, well-primed base, we elected to go with two coats of the Eco primer/undercoat. We rolled it on, but they recommend a foam roller for this and that obviously won’t get paint into the grooves between the planks, so before rolling we had to go through and hand-fill the grooves with a brush. This easily made it take more than twice the time compared to if we’d just had a big flat area.
The first coat of primer is on. It gets absorbed a bit into the wood so to get a uniform base, and more durable paint, we did two coats of primer.
With the second coat of primer, the base is nice and uniform. Here we’ve started painting the trim along the ceiling with the Royal White flat paint we’re going to use for the ceiling.
Once everything was primed, we rolled the Eurolux ceiling paint. This is the same Royal White color we use on the trim for windows etc, except it’s flat instead of shiny.
Because the Eurolux acrylic paint dries quite quickly, it was difficult to not have the paint dry between filling all the plank joints and doing the edges, etc. It helped to do this as early as possible in the morning so it wasn’t so warm.
It was really difficult to edge and roll the main areas without the paint beginning to dry, so we did the corners and top/bottom early….
With the ceiling done, we proceeded to the “Bermuda Blue” wall paint. This was applied in two coats, rolled in the same way as the ceiling.
After the first coat of blue you can start to see what it’s going to look like.
Two coats of blue done. I think at this stage we’d also done the first of the two coats along the baseboards.
Finally, with two coats of blue done, it was time to crawl along the baseboards and paint them using the same shiny Royal White paint that’s used on the window trim.
The final product, with the room back in usable shape.
The room got done right at the deadline, which was the inlaws arriving. They did have to sleep in the office one night while I did the final coat on the baseboards, but that seems like a small price to pay to get such a nice guest room! We’re really happy with how it came out. Maybe we should move out of the master bedroom and in here now just to experience it!
So there’s been a 5-month hiatus on posting, but things have been happening. I’ll try to catch up.
During November, the grandparents came for their usual month-long Hawaii visit, and the task my Dad and I decided to tackle this year was to replace the old counterweighted “sash” sliding windows in the two rooms in the main house. The real objective was to remove the lead-based paint on them, since they are high-wear surfaces and the paint had started to crack and peel. The paint in the “library” is especially deteriorated, not just on the windows; it’s peeling all over the walls and the ceiling. But the windows were a start.
This is one of the original sliding windows (also used as a whiteboard…)
Rather than attempt to strip the paint from the existing windows, we decided it was better to switch them out for jalousie windows. Literally every other window in the house use jalousies and they are superior for the amount of airflow they provide. The only issue with our existing ones are that they are aluminum and have pretty severe corrosion. For that reason we chose to go with Palmair windows made by Breezeway. These use vinyl, powder-coated aluminum, and stainless steel, and the mechanisms are protected so they’re not exposed directly to the elements. They also seal much better than the old metal ones that don’t really make a tight seal between the slats.
The Palmair windows are also reasonably priced, at least compared to the other vinyl alternative one of the local window dealers had, which were almost 3x as expensive. We just had to drive over to Lowe’s in Kona to get them.
Getting the old windows out was an interesting exercise. To remove the sliding windows out of the frame, you had to break off the nailed-in-place wooden trim that held the windows in. Then you had to cut the ropes to the counterweights, tie a knot in them so the counterweights didn’t drop to the bottom of the window, and then take the inner window out. The outer window was then held in place with rectangular wooden rods that were fitted in a slot in the window frame. With the windows removed, you could open an access panel in the side of the window frame so you could reach in and grab the counterweight, cut the knot in the rope, and pull the weight out. These weights were large bullet-like chunks of cast iron, when you slid the window up and down they would clang against each other like some heavy-duty wind chime.
First step was to take the windows out. This required taking the inner window trim out at which point the inner window can be removed, the center trim taken out, and then the outer window taken out. Note the stumps of rope which are still holding the counterweights inside the window frames.
After removing the counterweights and putting the access panels back, we were left with a window frame with a slot all around the perimeter and holes where the counterweight pulleys had been. These needed to be covered, so we fabricated plywood sheets for the sides and top of the window frames.
Both windows are out. We also removed one of the planks from the window frame to see what it looked like inside. There was what I assume is 70 years of dust on the bottom of those cavities, but no termite damage. The sides of the window frames have slots for the trim and holes for the counterweight pulleys. These were covered with thin sheets of plywood.
With the side plywood panels mounted, we temporarily mounted the new windows to make sure they would fit and to figure out exactly where to mount the frames. To get the bottom of the windows to seal, we’d also need to add a piece to extend the bottom of the inside window sill outward so we could add weatherstripping against the inside of the bottom of the glass.
In addition, we needed to fabricate extensions to the inside window sill so it would go all the way to the glass. Because this would have sit on top of the outside portion of the window sill, which is inclined by about 13 degrees, it had to be made in a trapezoidal shape to lie against the tilted bottom and line up with the horizontal top of the inside of the window sill. Making 7 of these pieces with the correct angle and thickness by hand seemed like an iffy prospect, so we tilted the vise in the mini mill and used it as a “guide” so we could slide the pieces through the mill and have it take off the appropriate amount of material.
The window sill needs to be widened since the new windows set further out. The existing base of the windows is inclined about 13 degrees, so the trim pieces need to be shaped like a right trapezoid. The mini mill was set up to be able to make the 7 pieces in a reproducible way.
The outsides of some of the window frames were also in such bad shape that rather than try to get the paint off and make the wood look decent, we replaced them. Stripping the outside paint was quite a chore, it’s quite resistant to the infrared heater and you have to heat a lot to get it to soften. The wood is also quite rough so the scraper can’t get the entire paint layer off like it could on the inside where the old paint came off easily.
Having finished the woodwork, we needed to paint the windows, inside and out, before mounting the windows. This seemed like it should be quick, but took quite a while. The inside window frame was first painted with Brushing Putty (which I’ve talked about before) to mask some of the very coarse grain in the wood. This needs 24+h of drying, then sanding. Then the oil primer, which needs another 24+h of drying, and then two coats of the Eco “waterborne alkyd” paint. Since the outside is brown and the inside white, you also could only do one side at a time since otherwise you’d smear the paints into each other.
Before mounting the windows, the window frames were treated with Brushing Putty, sanded, and painted with the same Eco Brilliant Royal White paint that is used in the kitchen. With all the coats and drying time, this actually took over a week. (This also explains why there weren’t any blog posts at this time since the thing under the big cloth in the corner on the right is my computer…)
The outside of all windows are painted Tudor Brown. We’ve previously used a Benjamin Moore glossy latex paint for this, but we’ve not been happy with it as it remains sticky for a very long time and does not seem to hold up well to the elements. Instead, we got a satin version of the same Eco paint we’re using for the internal white trim, matched to the BM Tudor Brown tint. This is an alkyd paid so dries to a hard, weather resistant surface. Hopefully this will hold up better outside.
Since my parents were staying in the other room, we couldn’t get started there until we were done painting and had the windows mounted. This took quite a while longer than anticipated so by the time we could get started on the other room, we only had one week left until my parents went back home to Sweden. This was enough to get the wood work done, but not the painting.
After finishing the 4 windows in the office, we moved on to the 3 windows in the library. As is evident in this picture, the paint in this room is in really bad shape, flaking and molded. More on that later.
Since the paint on the walls and ceiling was in such bad shape in this room, peeling and full of mold stains, we decided that this was a good opportunity to repaint the entire room instead of just doing the windows. So we started stripping the walls. This actually didn’t take too long, with the Speedheater you can cover about 1m^2 per hour, when you don’t have to deal with trim and corners and stuff. The windows went a lot slower.
Holding the Speedheater gets very tiresome after a while, you basically hold it in one hand and strip with the other which is hard on your shoulders and wrists. As we discovered how hard this job would be, we ordered the “arm” that holds it so you only have to reposition it and not hold the weight. However, it didn’t arrive until the job was mostly done. I’ll make a separate post about the repainting of the room.
Nearing the end, the windows in the library are painted and the windows are ready to be put in. As you can see, we’ve also started stripping off all the wall paint. More on that later.
Finally, the windows can be mounted, here two are done and I’m just about to start working on the third. The only thing remaining is to cover the small space between the top glass and the top of the frame. This will have to be done similarly to on the bottom, but is not urgent since only in a major hurricane would the wind blow hard enough that rain would hit the window that high up under the eaves.
In the end, I think this was a major upgrade. The old windows weren’t just peeling, when the wind was blowing they also would shake in their mounts, giving off a rattling sound that isn’t so nice if you’re trying to sleep there. The jalousie windows will give a lot more airflow (although we haven’t had occasion to need that since it’s been “really cold” here. Cold for Hawaii, that is.) The new paint also looks really nice. I can’t even imagine how nice the whole house will look when we’ve repainted all the trim, door frames, baseboards, etc with this paint. So we’re really pleased with the new windows. Stand by for the next post about painting the room.
It’s been two years since the last time progress was made on the kitchen. We still didn’t have any cabinet doors, and recent developments have caused this to be a more pressing matter…
Here’s the recent motivation for getting doors on the cabinets. At least the lower ones.
We had focused on the lower cabinet doors the last time we made a push, and gotten to the point that they were all primed. Over the past 18 months I did the final sanding, so they were bascically all ready to be painted. It’s kind of silly they’ve been sitting so long, but otherthings came in between.
In any case, it was now time for the final push. If you need to remind yourself what the cabinet doors looked like when we started, you can go back to the original post. First, there are two coats of the white Eco Brilliant on the frame. This is the same paint we used for the rest of the kitchen framing, super shiny but that also means you can see every little imperfection.
The cabinets with Eco Brilliant on the frame. Every little dust speck and imperfection shows up here, so it’s pretty humbling.
The Eco paint is really nice to work with, dries pretty quickly and has no odor. Once the door is painted, it gets to set up while horizontal, and once it won’t run the doors are hung up to minimize the amount of dust landing on them.
The doors were left to dry in the dehumidified room (but with the dehumidifier off to not make them shrink too much.)
With the frames done, the next step was the green Eurolux paint in the center (not sure what the term is in English, in Swedish it’s called the “dörrspegel”, door mirror.) This is a matte paint, so is a little more forgiving when it comes to the surface. On the other hand, you need a steady hand to cut the edge against the white so it actually took quite a while to paint.
Painting the green centers of the doors.
With two coats of those done, the painting stage was over. Next: drilling holes for the hardware.
Back when we trial did the first door, my Dad and I made a fixture out of a large MDF board that mounted to the table of the mini mill. I cleaned that out and reminded myself what the measurements were. It might be overkill doing this on the mill, but it meant that the holes would have the correct spacing and that the handles and hinges would just fit right. Once I had the procedure down, it probably didn’t take longer than doing it by hand since then you have to be very careful.
The first step was to drill the two holes for the handles, 128mm apart.
First step was to drill the two 4mm holes for the handles. By clamping the door against the guide, aligned with the mark, the position was reproducible to reasonable accuracy. What’s really important is the relative location of the holes since that determines whether it will fit or not.
The hinges used a 35mm boring bit to cut the hole for the “cup”, and two small pilot holes for the screws that hold them in place.
Boring the hole for the 35mm hinge cup. This needs to be at least 13mm deep, and the doors are 18-19mm thick. It’s not super close, but there’s not a whole lot of margin.
I did all this by hand-typing commands in to the mill, and there were only two screwups. I mistyped the spacing for the hinge screws by 1mm in one instance, which wasn’t so bad. The more serious one happened when I typed a “z” instead of an “x” and crashed the drill chuck into one of the doors. Luckily it was the inside, since I was drilling the hinges, but the new servo had enough torque to push the 2.5mm drill clean through the door before it broke off. The tip did poke through the front, but only barely, and it’s the lower hinge down by the floor, so it’s not very visible. I’d worried about doing something like this, but considering what could have happened (like drilling a 35mm hole straight through the door) it’s not so bad.
In contrast to the holes in the doors, the holes for the hinge clips in the frames had to be hand marked and pilot drilled, which took a while. I completed this without any screwups, although in one case I managed to precisely hit the head of a screw that we had used when adding the cover pieces around the range…
Mounting the hinge plates in the door frame. This was a manual measure-and-drill procedure.
The first door is in place, eight to go.
The hinges have a bit of adjustability in every dimension (in/out, up/down, left/right) so it’s not a disaster if the position of the hinge plate varies by a mm.
It took basically two full days to do all the drilling and mounting, but now all the under-counter cabinets have doors!
All the under-counter cabinets now have doors!
There’s definitely some variations in the gaps, so you can tell that it’s all hand-made, but it looks pretty good! An unexpected result is also that the kitchen became noticeably brighter compared to having those black holes under the counters.
So what’s next? We’ll savor the completion of this long-standing project for a few days, but there’s more to do. We could start working on the above-counter cabinets (not just the doors, but the cabinets themselves still need to have the lead paint stripped, too) and have those done in another … 4 years? I think the more pressing ones, however, are the few full-height cabinets to the left of the counters. One of those hold all the cookware, and having Axel pull down the 18″ cast iron skillet on his head would probably not be good.
After fixing the main wheels, there was also some things to attend to at the back. We’ve had a replacement for the ridiculously dinky tailwheel since before I became a co-owner but never mounted it. Since we were doing wheel work anyway, we decided now was the time.
Replacing the tailwheel looked simple until we realized that it did not have a hole for the bolt that holds it to the titanium rod that makes up the tailwheel spring. Drilling this hole so that it matched the hole in the rod was not going to happen lying under the tail with the plane jacked up, so I took it off and brought it home so I could rig it up in the mill. I’ll let the pictures tell the story.
This is the titanium tail wheel rod mounted up in the mill. By moving the mill until the drill went clean through the rod, I knew it was in position.
Once the drill was in position, the tail wheel was mounted on the rod. The 1-2-3 block under the tailwheel ensures that it’s orthogonal to the drill.
Then the 1/4″ spot drill was used to start the hole and ensure the drill wouldn’t walk since the hole was being drilled into a convex surface.
And finally, the hole was through drilled, passing cleanly through the existing hole in the rod.
The new tailwheel, test fitted to the rod.
So that was not a big deal. But just as we were about to do this, Sonex came out with a Service Bulletin that said that failures of the two small screws that hold the steering link, at the top in the final picture above, had occurred and that the should be replaced with AN bolts instead. This required drilling out the threads in the aluminum tailwheel mount, so the tail wheel went back on the mill.
The tailwheel back on the mill, this time to drill out the threads for the screws that held the steering link.
While we were at it, we also replaced the steering link. The steerable Sonex tail wheel is linked to the rudder, and the old tail wheel also had this steel link that used loose bolts as “bearings” and that had ground against the bracket that holds the rudder cable and steering link. Sonex builder Peter Anson makes a much better link that uses rod-ends and completely eliminates any binding and play in this link, so we ordered that.
The new tail wheel, complete with new hardware per the Service Bulletin and the new steering link.
Finally, the new tail wheel is back on the plane.
With that we now have new wheel bearings, new brakes, and new tail wheel. The wheels felt really smooth just rolling the plane back and forth, and the brakes worked to stop it, so I guess the next thing is to go for a short taxi to see how it works when you get everything rolling a bit.
The “one thing” left to do on the Sonex was to fix the left wheel brake, which was stuck. Well, ok, the left tire also kept losing pressure. Finally co-owner Andy and I managed to get down there and jack the plane up so we could take the wheel off.
We had wondered about how to safely jack up the plane, and after reading how other people had done it ended up putting a 4×4 across the fuselage bottom immediately behind the gear. Then we jacked this up with a lift and put jackstands under the 4×4. It seems quite secure, especially with the lift in place since it gives a large support area for the 4×4, even if the jackstands themselves were to fall over somehow.
This is the lift we used to lift the plane off its gear. The jackstands are not in place yet.
Once we got the wheel off, it became apparent that this would be a somewhat larger job than anticipated, because … you guessed it: corrosion. It turns out not only was the brake arm rusted completely solid, the races of the conical wheel bearings were also rusted. That just was not acceptable, so off both wheels came off.
Everything down there was just in terrible shape. Apart from the left brake being frozen, the wheel bearing being rusty, and the tire having a slow leak, the brake drums were severely rusted all over and the aluminum wheels had pretty bad corrosion, too.
We left the plane on jackstands and I took everything home for a basic cleanup. There was so much caked brake dust everywhere that it was hard to see how bad the corrosion really was. The wheels can be split so the tire and tube can come off, and then the brake drum separated from the wheels. After some ultrasonic cleaning, it was clear that the left brake was a goner. The shaft for the actuator was completely frozen on the bushing and, instead, the bushing had spun in its mount and was now loose.
The brake drums look almost acceptable after some serious rust removal.
I dunked the brake drums in rust dissolver and left them for a week, after which they looked a lot better. The inside actually did not look that bad, and there’s barely any wear noticeable. The outsides, however, have “cooling fins” machined into the perimeter, and those were completely pitted. It took several sessions with Naval Jelly and the Dremel wire wheel before they were reasonably rust-free. Apparently they initially had a black oxide surface and that is completely useless here in Hawaii. Instead, they’re now painted with high-temperature “BBQ” black paint. This paint may interfere slightly with getting rid of brake heat, but it’s not going to be worse than a thick layer of rust.
The drums were painted with high-temperature paint. This will hopefully prevent them from rusting right away again.
The aluminum wheels also had pretty bad corrosion, especially where the brake drums had been mounted. I cleaned the mounting surface up with the wire wheel but otherwise there’s not much to do. I tried using the aluminum equivalent of Naval Jelly, but it didn’t seem to make any difference whatsoever. This corrosion is unsightly but not bad enough to affect the structure of the wheel. The wheels also aren’t visible when the wheel pants are on.
I was wondering how to get the bearing races out, since I don’t have a suitable puller. I was trying to find someone in our EAA chapter that had one, but eventually I decided I would just try to heat the wheels a bit and see if I could get them out. Indeed, it turned out that after some mild torch heating, I could pry them out. The new ones dropped right in with heat, too, so that turned out to be easier than expected.
The new bearing races slipped in cleanly after the wheels where heated a bit.
With that, the wheels were ready to be put back together. The only hitch was that one of the wheel bolts were bent enough that it did not want to go back into the hole. (I had to pound it out, initially, too.) So I have to find a 3″ 5/16 bolt somewhere. At least these wheels aren’t actually aircraft parts so they don’t use AN bolts which we definitely can’t find locally.
The wheels were massively unbalanced, so I took advantage of the wheel balancer that I got a while ago to be able to change the tires on the bikes. Spinning the wheels this way also gave me an opportunity to make sure the brake drums were reasonably centered, since they’re only held by the bolts which do not provide very precise positioning.
The only thing I’ve not been able to figure out is the leaky tire. I dunked both inner tubes in water and saw no leaks. Maybe there was some junk in one of the valves that blew out when I emptied them? I guess we’ll see.
We’re at three months since the last post… We were in Sweden for almost two months, introducing Axel to the grandparents, and after coming back I’ve not had time to write. I have however made progress on an upgrade for the mini mill that I started planning at the beginning of the year: replacing the stepper motors with servo motors.
While the stepper motors generally have worked well, I notice that I do lose steps during jobs. This becomes obvious because I frequently drill holes as the first operation, and then as the last operation run a chamfer mill over all edges. If the chamfer and the drill isn’t concentric, you can easily tell by the chamfer width changing around the perimeter of the hole.
Since steppers are open-loop systems, the motion controller tells them to do something and then you assume that it does, there is no way to detect or correct if the motor misses a step due to insufficient torque. Servo motors, DC motors with a built-in encoder, are closed loop so they will not lose position as long as they have sufficient torque to follow their commands, and if they can’t, they will tell you. This is a big advantage when it comes to the robustness of the setup.
Their construction also gives them better efficiency, especially when stationary where they will only draw as much current as necessary to hold position, while a stepper generally burns full current holding position.
The drawbacks with servos are that they are significantly more expensive than stepper motors and that the setup is more complicated. However, a line of servos called ClearPath are made for replacing stepper applications. They have integrated controllers and are controlled with step and direction inputs just like a stepper driver. This means the motion controller can control them in exactly the same way as it does steppers, which is great. This means I could continue to use the open-source G2 controller on the Arduino Due I’ve used for the steppers.
While the Arduino did not have to change, everything else did. The servos run at 75V and require a linear power supply instead of a switched one because they can better handle the large peak currents drawn by the servos when the accelerate. The Clearpath motors also use optically isolated inputs and outputs that require at least 5V to run, a lot more than what the 3.3V Due can output, so I’d need a new shield with driver transistors for all the outputs.
This is the new shield for the G2 Due, with connectors for the three servos, limit switches, spindle control, coolant control, and the Arduino monitoring the motors for shutdown.
There was also the question of how to handle motor shutdowns. If a stepper loses a step, it’ll keep going, so the result is likely not catastrophic. If the servo runs out of torque and can’t keep its position to within the allowable tracking error, it’ll fault and disable itself. Since having one axis on the mill suddenly stop while the others continue is unlikely to be a good experience, I wanted to a way to stop all the motors if one of them shut down. The ClearPath motors have a feedback line that indicates whether the motor is enabled or not, and can also output the current motor torque as a PWM signal.
My solution was to design a circuit that would raise a feedhold input to the G2 controller if any of the three motors shut down. That way the job would be halted, all axes (and the spindle) stopped and then you could recover. I initially attempted to design a collection of logic gates that would do this, but once I realized the motor feedback could also tell me the motor torque, which would be a useful indicator to know whether the motor is operating close to its limit, I decided that the most flexible way to do this was to take one of my Arduino Pro Minis and add it to the circuit.
The Arduino code watches the enable inputs to the motors as well as the feedback from them. The feedback consists of a 45Hz PWM signal where 50% duty cycle is 0 torque, 5% is 100% peak torque in one direction and 95% peak torque in the other. If the motor is “in position” meaning it’s stationary and just sitting there, the output is 100%, and if it’s shutdown or disabled, the output is 0%.
The strategy is that a motor whose enabled input is high but whose feedback has been low for at least 1/45 s is in shutdown and should trigger the feedhold. This is done with a simple state machine that keeps track of whether the motor is “disabled”, “enabled with feedback low”, “enabled with feedback high”, and which times out into an “alarm” state if the “enabled with feedback low” persists longer than allowed. By measuring the time in the feedback high vs low states, the PWM is measured and this is used to adjust the intensity of three LEDs that give a visual indication of how much torque the motor is outputting. If a motor goes into the alarm state, a red “shutdown” LED illuminates so it’s obvious which of the three motors caused the alarm condition.
This seems to work quite well in tests, the only problem is initializing the state at boot, if the motors are already enabled. The code can always be found in my Arduino repository if anyone’s interested.
When I removed the old Z-axis stepper, I discovered that the coupler had cracked almost completely through. It only took a little axial bending for it to split into two pieces. It clearly would not have lasted much longer.
As I removed the steppers from the mill, I also discovered that the Rocom coupler that connects the Z-axis motor to the ballscrew had cracked and was close to splitting in two. This clearly is fatigue cracking and might be related to the fact that there is some wobble in the ballscrew thrust bearing, so there’s more flexing here than it should be. Crashing the machine into the workpiece and into the hardstops also probably haven’t helped…
This is the motor for the X-axis (the Y uses the same model). It is one of the smallest and cheapest Clearpath motors, the SDSK-2311S. This motor did not have enough torque for the Z-axis.
This wasn’t actually a big deal, because when I tested the motors on the Z-axis it became clear that they didn’t have enough torque to overcome the combined effect of the friction in the ways and the weight of the mill head, so I had to order a different motor that trades speed for torque. The larger motor also has a 0.375″ shaft as opposed to a 0.25″ one, so I would have had to get a new coupler in any case, even if the current one hadn’t cracked.
When I tested the XY motors on the Z-axis, it became clear that it needed a larger motor. This is the SDSK-2331S, which trades a lower max RPM for more than twice the torque (and more length.) It’s a bit more expensive, but not much. It also has a 0.375″ shaft, which required a new coupler.
I got the couplers with the CNC Fusion kit. They appear to no longer be in business, but I found you can order them directly from Rocom. However, buying a single one from them costs $100 compared to the ~$25 I paid CNC Fusion. Apparently they must have a large volume discount…
The servos do use a lot more complicated cabling than the steppers did, so there was a lot of connector crimping going on.
Once the electronics were done, I needed to make the cables. The motors use a 8-pin MiniFit connector for the signals and a 4-pin one for power. Then I needed internal cables to go from the board to the connector on the back of the box, too, so I ended up doing a lot of crimping.
The circuit board with all the connections hooked up. It’s quite busy inside there now.
Once I found a couple solder bridges on the circuit board, worked out some kinks with the Arduino code, and adjusted the motor settings in G2, it seems to run well. The servos really haul, I’m now running a max jerk setting that’s 4x what I ran with the steppers, and 50% more speed. The XY axes now traverse at 15000mm/min, while the Z-axis, with its lower speed motor, maxes out at 13000mm/min. I loaded up an old job just to see what it would look like:
The one thing I haven’t figured out yet is whether it’s possible to keep the position in case a motor shuts down. The fact that it’s shut down of course means that it’s no longer holding position, but the motors still keep track of their position commands and there’s a setting where they will return to their commanded position when they’re re-enabled. I haven’t tested this but, if it works as expected, it should be possible to move the other axes during feedhold to clear the spindle and re-enable the motor that shut down. It would then return to the position it should be and it might be possible to resume the job, which would be awesome.
Even if it’s not possible to resume the job, not losing position means that it can be canceled and restarted with suitable changes and the work coordinate system would still be valid. This is in contrast to the steppers where a lost position in practice means that you need to re-measure part zero. In principle, it would be sufficient to just re-home the axis, but the limit switches are only repeatable to something like +-0.2mm which usually is not good enough.
I’ll report back with how this works out once I’ve gotten some time on it, but for now this looks like a great upgrade.
