Alternate title: I looked inside a corroded air tank and now I kind of wish I hadn’t.

During the disassembly of our thermoforming machine, we noted with worry that the compressor doesn’t have an air dryer between it and the tank, and that the tank is installed in such a way that the water drain valve is basically inaccessible. So any water in the compressed-air system (and due to basic physics, there definitely will be some) would have accumulated in the tank over its years of service.

A short while ago we got far enough in the rebuild to test the compressed air subsystem. Not surprisingly, the compressed air tank leaked and could not hold pressure. Upon closer inspection the leak appears to be rust perforation implying the inside is pretty rusty. So we replaced the tank instead of trying to patch it.

But I was curious: OK, it’s rusty. But how rusty? During a lull in projects (waiting for some parts to arrive) I pulled out the angle grinder, attached the cutting wheel, and merrily started making sparks.

As I made progress cutting, I noticed chunks of degraded metal were falling out of the gap I had cut. Not flakes of rust – chunks of varying color and texture. This is my first hint things are about to get ugly. Once I cut enough to pull away the end of the tank, we can see inside.

That’s far more corrosion than I had expected. And while most of the inside surface qualifies as “rusty” the bottom part deserves a stronger word. I can think of a few, but the only one I am willing to put in print is “Yuck”.

This sight is something I might expect to see in a home plumbing project fixing the sewer pipe. And this stuff has the soft squishy consistency of… well, the kind buildup you’d find in a sewer drain. This is not something I expected to see inside a piece of industrial equipment.

This layer has built up across the entire bottom part of the air tank.

I had originally thought it’d be neat to find the other side of the perforated hole but I was not in the mood to dig through this muck. Even while wearing gloves.

So let this be a lesson to everybody: If you have a compressed air tank, be sure to drain the water out of it regularly, or this might happen to you!

(Cross-posted to Hackaday.io)

We got far enough wiring (and re-wiring) the thermoforming machine to perform an integration test of the low-amperage parts of the machine. This covers almost everything except the heating element.

On the previous test of the compressed air subsystem, we found a leak in the air tank. The leaky tank has since been replaced and this will be a test to see if it works with everything else.

The vacuum subsystem had also been partially tested earlier. For the previous test we only got as far as the vacuum table solenoid. This time we also have the vacuum lines between the solenoid and the vacuum table.

The relay panel had been tested with the following configuration:

• 24V bench power supply as the input.
• Manually connecting the control wires in turn like an old style telephone switchboard.
• Multi-meter reading the output.

This time, the test will put the relay panel in a more realistic configuration:

• Power will come from the 240V AC to 24V DC power supply on the DIN rail.
• The control signals will come from the manual operation toggle switch panel.
• And the most exciting part: the outputs are going to the actual air and vacuum components!

There was much anticipation and trepidation when the power switch was thrown the first time and we see LED indicators on the power supply indicating the system was live. Every switch thrown was a “Will it work?” mystery. The test did its job, exposing a few wiring errors. Fortunately none of them were damaging mistakes and all were trivial to fix.

At the end of the evening, we could control everything except the heating element using the manual operation switch panel: Move all the air cylinders, open and close all the air valves, and activate the electromagnets that hold the frame closed.

We still have lots of things on the to-do list, including some air leaks to track down and fix and plenty of wiring tasks. And there’s still the big intimidating heating element looming in the near future. But all in all, a wonderful morale boosting step on the journey to completion.

(Cross-posted to Hackaday.io)

When we started on this thermoforming machine rebuild project, one of the first things we did was to open the control panel. We looked at the nest of wires back there and tossed the whole tangled mess. Those control wires were a basket case we’re happy to leave behind. But the rest of the machine – the power cables and such – looked OK at first glance.

Unfortunately, they don’t look as good after the second or third glances. Sometimes it’s not a glance at all – it’s seeing (and feeling) them fall apart when we worked in the machine. We expected the wires to be old, and kept our eyes open for signs of aging wires. We just didn’t expect to see them quite so often! This particular example was from the back of the air compressor. When we wanted to clean up the air compressor, we had to disconnect these wires. The act of moving the wires for access and removal broke the age-hardened insulation in many places. So now we have to replace it.

Every time we get to work on a new area, we find that a new bunch of wires need to be replaced. We’re rapidly approaching the point where it might be easier to rip out every single wire and restart from scratch.

Wiring is tedious work, part of why good electricians make good money. For us, it’s a very real threat against project completion. We’re interested in having our own thermoforming machine, but that interest tends to drop every time we discover 2 new wiring tasks for every one completed. It’s a race to complete before everyone loses interest in the project.

Hopefully the work will be much easier – or at least more rewarding – once the wiring is complete.

Assuming, or course, we get there…

(Cross-posted to Hackaday.io)

Around the periphery of the vacuum table on the thermoforming machine, the previous owners built a perimeter using L-brackets. The presence of the frame made sense to help seal in the vacuum. The mystery is the height: The vacuum table and its surrounding frame are the same height as the combined height of the top and bottom parts of the frame holding the workpiece. We had expected the vacuum table to be aligned with the bottom part of the frame, since that’s the height the workpiece will be held at. As this frame is double the height, it would have impacted the workpiece on the way down. We’re left scratching our heads figuring out why this is desirable.

But that mystery isn’t important right now. Since we intend to put this machine to work on low-volume hobbyist projects, we will want to change the size of the workpiece frequently. This would be difficult with the existing system, since changing the size of the workpiece means changing the surrounding frame, greatly increasing the up-front setup work. It might be fine for a commercial production machine but such a barrier on a hobbyist machine would probably mean we’d be too lazy to actually use it.

We’re bouncing around a few ideas that should make it easier to change the size of the work piece in the machine. All of those ideas are incompatible with this existing taller-than-expected frame, so it needs to be removed.

A few jabs with a metal putty knife got things going and the frame popped off shortly afterwards.

Then the tedious part starts: the putty knives went to work scraping off the sealant that was liberally applied to the bottom of the frame.

Part of the motivation to invent a new vacuum sealing system is visible here: this surface is quite scratched up and rusty. To make it seal properly with the old system, we need to remove all the paint, sand things flat, and put on a new smooth coat of paint. If we can avoid that work with a clever new sealing system, we’d be happy.

(Cross-posted to Hackaday.io)

Since we just tested the air subsystem and found problems that will probably require buying parts from McMaster-Carr, we decided to perform a vacuum subsystem test with what we already have on hand to see if we need to add anything else to the shopping list. Only some of the fittings and vacuum lines have been replaced, and the vacuum table itself is in pieces, but we can put together enough to test the vacuum pump, the accumulator tank, the solenoid-actuated vacuum valve, and the fittings and lines connecting them.

We were happy to see the system could generate vacuum beyond an indicated 25 inches of mercury. This measurement is taken with a grain of salt coming from the old vacuum gauge that was on the machine. But while the absolute value (“25 inches”) might be suspect, the relative value is still useful information. We shut off the vacuum pump and went to work on other things. After 15 minutes, the vacuum held steady enough that there was no visible movement of the needle.

The next test is the rate at which vacuum is generated. We don’t need it to be super fast, but we don’t want it to be the limiting factor in cycle time. As soon as the softened workpiece is pulled against the mold, the vacuum should start building back up. It can continue doing so as the completed workpiece is removed and the next workpiece is loaded and heated. By the time the next piece is heated, we want to have sufficient vacuum in the system ready to go instead of having to wait.

Using the solenoid, we opened the valve and admit air into the system, dropping the vacuum down to an indicated 5″ Hg. We closed the valve and started writing down the vacuum reading relative to a stopwatch.

The recovery rate is acceptable. After one minute it was back up to an indicated 23″ and 90 seconds brings us to 25″. It didn’t have much grunt beyond that – it took double the time (an additional 90 seconds or 3 minutes total) to reach 26.5″, where the needle stopped moving.

We expect a new pump to recover vacuum more quickly, and provide a stronger vacuum, than this tired old thing. But this performance indicates the vacuum pump will not be the limiting factor in our cycle time and that’s good enough.

(Cross-posted to the Hackaday.io project page.)

We’ve just completed the milestone of replacing the compressed air fittings and lines in the thermoforming machine being rebuilt at Tux-Lab. We replaced the fittings because we expect the old air seals within them to have decayed with age. Since we have everything disassembled, replacing them now is relatively easy and reduces many potential points of failure.

The same logic also applied to replacing lines carrying compressed air throughout the machine. For extra bonus, the new air lines are blue and the old ones are green, making it instantly visible which pieces have been replaced.

Once the compressed air subsystem was buttoned up, we wanted to do a subsystem test. Since we have yet to wire up the 220V power distribution, we can’t run the built-in air compressor just yet. So we unplugged the output port of the air compressor and plugged that into the shop air.

Loud hissing announced the presence of a leak in the system. We felt all around the newly installed air lines and fittings, but the source of the leak wasn’t any of the new stuff. We eventually located the source of the leak to the compressed air tank that we had not yet touched. Before this test, the quality of the air tank was a question mark. Now that we have finally pulled it out and gave it a good look, we have answer to that question!

During disassembly we noted there was no air dryer between the compressor and the tank, so moisture would have collected in this tank. There is a fluid drain port (not visible in this picture) but it doesn’t look like it has ever been used. This hole implies the inside of the tank is a rusty mess and a hole patch repair would only be a futile short-term solution. If we want a self-contained machine not dependent on shop air we will need to replace this tank.

After this discovery, we disconnected the air line from the output port of this tank and hooked that up to shop air. It allowed us to test the rest of the machine.

• The mechanism to move the heater rearward seems OK.
• The mechanism to move the heater forward has a leak that needs to be investigated.
• Trying to move the heater forward/back repeatedly showed no problems (aside from the above leak.)
• The mechanism to move the frame up/down each seems OK individually.
• Trying to actuate up/down movement rapidly would cause the two sides of the air cylinder to fight each other. We are missing an air relief mechanism somewhere in the system. Either we forgot we removed something during disassembly, or an existing relief mechanism has plugged up.

(Cross-posted to the Hackaday.io project page.)

I help where I can in the Tux-Lab effort to rebuild the old thermoforming machine. I’ve been doing more learning than helping, though, since others have more experience with industrial machinery than I do. The initial goal is to get things up and running under manual control, and we’ll tackle automation later.

That doesn’t keep us from chatting about ideas for the automation effort, which is roughly divided up into three tiers of complexity.

At the low-end, we can drive it with a PIC micro controller. A modern PIC should be more than capable of duplicating the level of automation that existed in a decades-old machine. It would be the lowest-cost solution, if the cost difference was significant enough to matter.

The mid-tier option is an Arduino. It should be the easiest to get up and running due to the components already integrated on an Arduino board and the large existing library of code we can draw upon.

Both of the above would offer the option of reusing the control panel as-is, which would be important if we wanted to preserve the exterior appearance of the machine. At the moment it is not a goal to do so – we are not a museum and see little value in historical preservation on this machine. Especially since it’s a huge mess of wires in there.

So, as can be expected of a bunch of tinkerer types, the dreams started getting wilder and wilder. It wasn’t long before we started talking about a touchscreen-controlled thermoforming machine that is network-connected for job monitoring and logging. Which leads us to the high-tier option: a Raspberry Pi with the matching LCD touchscreen.

The team has members with experience in PIC programming, and in Arduino programming, but we’re light on Raspberry Pi programming expertise. Since this is something I wanted to learn to do anyway, I volunteered to investigate.

In the short term we’re still focused on the manual toggle switch operation mode. In the medium term we might still implement Arduino control. And that might be a good enough place to stop, but I wanted to see if we can turn the wild dream into reality.

One of the projects on the Tux-Lab to-do list is to revive a thermoforming machine. Purchased cheaply in non-working condition, it has potential to enable some very interesting projects. It has been gathering dust while waiting for enough interest from enough people to reach critical mass to start the project. I think we finally reached that point! We pulled it out of the corner it’s been sitting in, and merrily started pulling everything apart.

I thought we would document the original condition as we pulled things apart, but it quickly became apparent there’s no “original condition” to document. The wide range of age and quality of components made it clear it has seen continual modifications in its decades of service. The decision was made to go all the way back to fundamentals.

The bottom cabinet held the air machinery: a vacuum pump and an air compressor, each with an associated accumulator tank. They had all been bypassed with external connectors, which was not a vote of confidence in their functionality. We were hopeful that the previous owner(s) just wanted to reduce noise and vibration by hooking into their shop’s existing compressed air and vacuum lines.

The vacuum pump turned and could pull 26 inches of mercury, which is quite acceptable. The air compressor pushed out 40 psi, which was rather was less so. Fortunately a disassembly and cleanup was enough to help it push 100 psi. The two air tanks are question marks.

There are two air cylinders in this machine: One moves the thermoforming frame up and down, the other  moves the heater front and back. A quick test of both revealed they move and no air leak hissing was audible at either of their end positions.

The thermoforming frame was designed with two electromagnets to hold it closed. We assumed the magnets were broken because somebody installed some Home Depot quality mechanical latches. But we were able to energize the coils and feel it hold. Maybe the failure was in the control circuitry, maybe it doesn’t hold strongly enough for some task. We’ll find out for sure later.

The brains of the machine are the clearest indication of the age. We see a lot of discrete logic components and no indication of a microcontroller at the heart of it all. The control panel has a button “Automatic” and we wonder what that used to do. For the moment we will not worry about it: the initial milestone is to get it up and running in manual operation mode. If we get around to implementing an automatic cycle, we’ll pull in an Arduino or something modern to orchestrate the various bits and pieces.

On the assumption that old air hoses and fittings will be leaky, they will be replaced with new parts. The air valves should still be good and will be used until proven otherwise. Same for the big honkin’ contactors (240V, 40A) in the back to control the heater.

Orders have been placed for replacement parts – once they show up we can install them to get a better idea of how everything will (or won’t) work together.

(This project is cross-posted to Hackaday.io)