Donated electric oven - Dedicate to craft/project usage?

[Kmcleod]

There has been discussion of this on slack, but I wanted to make sure we were all on board.

There was pretty unanimous agreement that we want the kitchen range to be gas, but we had an electric range donated in addition to our gas range. there was a proposal to make this range dedicated to craft/making/non-food usage, for things like wood drying, ink and dye heating, plastic slump forming, etc.

Any objections to Todd and I dedicating the electric stove to that purpose, and modifying it to have a proper temperature controller?

thanks,

Kevin M.

[Dave_Schwinn1]

It has been my understand from the start that the electric range was to be dedicated to non-food uses. I was unaware of the idea to add a controller to it but I think that is a splendid idea.

[DVelzy]

If this is such a great idea, why don’t you do it at home in your own oven?

[Kmcleod]

Because most of us use our ovens at home for food… and we don’t have a spare one sitting unused.

[Kmcleod]

Todd and I made good progress on this last night!

We started with an exploratory surgery to identify how the stove was wired from the factory, to ensure that we could isolate the oven functions we were hoping to replace from all the stovetop functions. We also set a goal of maintaining full functionality of all features so that out modifications would not reduce the stove’s usefulness for other things. We also are aiming to be able to safely power it from a single NEMA 6-50 plug, so that it can be powered from any 240v 50amp outlet we have in the space (welding outlet, kiln outlet, etc.). Because standard stove outlets provide both the hot wires for 240v, AND the neutral wire to get 120v, we had to identify what devices/functions relied on 120v as well.

In summary, we learned:

1. the only two devices that use 120v are the “keep warm” surface burner (w/ it’s associated indicator light) and the oven light
2. the following functions require only 240v: oven heating elements, stove top heating elements (except keep warm burner), the left and right burner on indicator lights, the over temperature switches for each burner, and the “surface hot” light and temperature switches
3. the surface burners are not temperature controlled, but instead the dials are a duty cycle controller, that controls the fraction of time on and off (a setting of “8” is 80% on time, 20% off time)
4. each burner has a temperature switch device mounted on it with two switches, one NC that breaks on excess temperature to prevent thermal runaway (wired in series with the burner’s power) and one NO that makes at a lower temperature to turn on the “surface hot” indicator light
5. from the factory, the heating elements are hard wired to one leg of the mains power, meaning that even when off, the heating elements are energized at 120 vac to ground. (This is an important note for anyone who has an electric stove at home, keep your hands off the oven heating elements, even when not on, unplug when you are cleaning).
6. the upper (broil) heating element in the oven has 15.5 ohm resistance, so at 240v is draws ~15.5 amps, for a power of 3.7 kw and the lower element (bake) is 21.5 ohm, ~11.2 amps, or ~2.7 kw. both elements are exposed within the oven without diffusers.
7. the keep warm burner is 100w @ 120v, and the oven light is 40w @120v, so to be able to maintain those functions, but with only a 240v supply (NEMA 6-50 plug only supplies two hot wires and a ground, no neutral wire), we will require a 2:1 transformer rated for 140 VA or more (anyone have one?)
8. there is a microswitch on the oven door lock, that was used by the OEM oven controller to enable the “self clean” function

After the autopsy, we moved forward on the modifications. Most of out time was spent learning, but we did accomplish the following:

1. We installed a replacement power cord with NEMA 6-50 plug
2. We rewired the existing 240vac stovetop functions to be completely independent of the OEM oven controller. The four main stove top burners are completely functional, using the OEM devices, including the duty cycle control knobs, the left and right “burner on” indicator lights, the over-temp safety switches on every burner (except keep warm, which the burner and safety switch run on 120v), and the “surface hot” indicator light and thermal switches (including the “keep warm” burner’s switch, which is in the same 240v circuit as the others, despite the burner and overtemp switch running on 120v). We tested each burner’s operation, and they are working as intended.
3. We isolated the 120v circuits for the “keep warm” burner (and it’s switch and indicator light) and the oven light. These circuits are ready to be powered from a transformer, they have no interconnection or dependance on the mains 240v lines.
4. We removed the OEM oven controller, and replaced the EOM temperature probe with a K-Type thermocouple, leaving the oven ready for installation of the industrial temperature controller circuit.

So the only things that remain to be done to finish our modifications are:

1. Obtain the last few parts (transformer, Indicator lights, some fuses, etc.).
2. Make a bezel to mount the oven on/of switch, temperature controller, and indicator lights in the space the OEM controller had occupied.
3. Mount the SSRs, mount the safety relay, and wire up the oven controller circuit (per the attached diagram).
4. Calibrate the thermocouple, test the circuit, and calibrate the temperature controller’s PID.
5. Wire up the 120v oven light and keep warm burner to be powered from a transformer
   looks like this will end up being a nice and quick project to add some nice capability to the hive! and no more worrying what inedible science project someone has done in the Hive kitchen!

Thanks,

Kevin M.

[Todd_Fegelman]

Thanks Kevin!
Excellent summary.

• Todd

[Jim]

Hi Kevin (+):

Thank you for your original post from last week and the detail in your latest update for your intent (as far as it goes) both on the mailing list. It makes me realize how we’ve all fallen into the multi-channel, silo echo chamber trap of SLACK and have overlooked the original broadcast utility of the single-channel mailing list (which has its own faults). I have an input and a request for your consideration, if we all still go to this legacy official communication site.

The input regards thermal gradients inside a closed oven. I don’t yet know the temperature tolerance band you are shooting to have, but from experience, you may ultimately want to consider an oven with a convection feature, either OEM, added, or home-built. The capable fan setup that will appropriately circulate the heated air inside the closed cavity will help even-out and reduce the somewhat small (but still potentially significant?) static top/bottom thermal gradient and make the full volume between all eight corners of the internal cavity closer to the same temperature setpoint, if such nominal differences matter for your intended use. To use a food example, as you know, a sheet of biscuits will cook differently when placed on the top rack or the bottom rack and you won’t get the same results if you cook two sheets of biscuits (one over and one under) at the same time. The shape and bulk of the item you are heating also has an effect. That is why angel food and bundt cake pans are shaped like donuts and bagels. And yes, convection can add its own unintended effects. Going for exact uniform browning across a large sheet and balancing the difference at the outer crust and center of a large loaf/roast are both interesting challenges.

The request is a separate concern that you consider to have a safe fume exhaust. Yes, venting and convection can be somewhat in opposition. An oven cavity typically vents into the room at the stove top. Kitchen installations typically (per code?) have a vent hood over the appliance location. I do not (yet?) know where you intend to place the oven (in different rooms at different times or at one dedicated/already_chosen location?) and the cord reach to the nearest NEMA 6-50 wall outlet. I do not know what normally out-gasses from the wood drying, ink and dye heating, plastic slump forming, etc. of your intended applications. I wonder if the normal operating smell from the craft oven may not be as pleasant as freshly-baked chocolate chip cookies. Due to the unique nature of a craft oven, you should also consider the potential equivalent of an unexpected dumpster fire inside such an oven. Please make appropriate provisions for normal and worst-case venting in consideration for hive members in our space and even other tenants in the building. Murphy also says it is highly-likely, at a most-unexpected-moment, you will experience the equivalent of a blaring smoke alarm, smoke-filled kitchen broiler oven-on-fire incident that may be even less pleasant (and more serious) than a tray of burned biscuits. Again, I do not know the scope of your intent, but this is especially important if you envision extended (dare I say un-attended?) multi-hour, overnight, and/or multi-day heating cycles. You are a responsible engineer, but it would be nice to have additional assurances that such a craft oven will indeed be a safe and good addition in the space.

JimD

[Kmcleod]

Hey Jim! Thanks for the thoughts! it sounds like your thoughts break down into one of four items, so let me break them down a response with my thoughts one by one:

1. Slack vs. Mailing List - Slack adoption definitely slowed our mailing list traffic, somewhat as-expected. I think we also saw another dip in activity when google recently re-vamped the web interface for the mailing list, and they made it so those of us who choose to not get the mailing list sent to our emails can no longer respond via mobile device web browsers. This all probably deserves it’s own thread though…

2. Recommendation to add a forced convection fan for more uniform temperature - I absolutely agree that this could be a great improvement! though, without testing, its hard to say how much. the Thermocouple is installed in the top left rear corner of the oven, so it’s likely to read a little hot compared to other parts of the oven. I personally do not have any specific need or use for this project myself, so I can’t say what will or will not be sufficient. I just saw that people were excited to have a non-food oven available to use for making stuff, and figured an industrial temperature controller would offer a nice improvement on both the reliability and accuracy of the thing, but also the safety of the tool (after that autopsy of the OEM circuitry, I am VERY uncomfortable with the safety of home ovens, haha).

It would be VERY easy to add a blower/fan into the circuit. It could be wired up with it’s own switch, or so that it was on whenever the temperature controller was on. A convection fan from another oven would work, or possibly a draft inducer blower from a furnace would be a good candidate.

Seeing as I don’t have any immediate need for that additional temperature uniformity though, and I don’t have one of those fan on hand, I’d say we punt this as a future improvement if the need or opportunity ever arises.

3. Recommendation to add ventilation - I am 100% on board with this thing having a vent hood over it’s home, whenever it gets assigned one! That said, not all activities that involve heat require ventilation! In fact, kitchen OVENS do not require external ventilation per code, only cooktops do, due to a cooktop’s increased likelihood of introducing aerosol greases into the air when cooking food.

Of the use cases I mentioned in my proposal however, I don’t think any fall under the umbrella of requiring ventilation. To address them individually:

• Wood drying - Wood drying is typically performed at low temperatures of around 120°-220°F. This process temperature is well below the flashpoint and smoke point, so there is little to no concern of combustion gases developing. I have found no references indicating significant VOCs are emitted from wood at that temperature range, and in fact, this document states the temperature range where small amounts of VOCs begin to escape due to vapor pressure starts at 356°F, again, well above the process temperature. Additionally, this manual for wood drying kiln operators mentions many safety precautions, but does not mention any special precautions to take due to VOCs, even when inside the hot kiln.

• Wood Stabilization - the most common product I have heard people use for this is called ”cactus juice”. Their instructions recommend oven drying the wood to remove moisture prior to treatment, and then oven curing the resin after it’s been absorbed by the wood. They state that the product does not emit dangerous fumes, however, they do recommend using an oven dedicated to non-food use. There is note that for a short period (10-15 minutes) of the curing process, they say that some people find the smell to be mildly unpleasant, but that the smell does not bother most people and dissipates quickly.

• Ink and dye heating - this is really a stovetop item, and doing it on this stove is identical to doing it on a hot plate or any other heat source. There are a million dyes in the world, but RIT is the dye I have most familiarity with, and they state that all their dyes are 100% non-toxic.

• Plastic slump forming - this one is tricky! Some plastics DO emit bad vapors when heated! That said, we also have a vacuum former, and slump forming is identical to vacuum forming with this respect. If you stick with plastics suitable for vacuum forming, slump forming should be not more risky.

I would argue that yes, we should eventually build a vent hood that exhausts outside to go over the craft oven/range to help with odors and noxious fumes from some potential use cases. However, based on the list of activities above that do not require active ventilation, it still seems worth it to get the oven set up and usable now, so that it’s less work for the person who decides we need a vent hood!

I’ll also note that we had a stove and cooktop (and a gas one, which even more so needs exhaust) at the old building for 10 years without a vent hood, and the aerosol grease from cooking is far worse for people than most activities likely to be done on this craft stove.

4. Fire Safety - This one is a hard one to make generalizations about, and as I mentioned, I personally don’t have a specific use case in mind for this temperature controlled oven. However, I have done dye work, plastic slumping, and similar activities in other ovens in the past. Most of those, I absolutely would not leave unattended any more than I would the laser, plastic former, or a pot of a cooking stove.

My assumption is that the worry about un-attended, long-term use is related to Todd’s desire to use the oven as a wood drying kiln to prepare blanks for stabilization. I have never done this process myself, however, let me share what I have learned about it and my thoughts on it.

The cactus juice product does recommend 24 hours of drying in a non-food oven at 220°F prior to processing. While intuition does make leaving any flammable material in an oven seem unwise, I do think it’s worth evaluating the actual process, and that there is a strong argument to be made that it is safe. Fire requires three things to burn: fuel, heat, and oxygen. And at first glance, it seems like you are putting at least the fuel (wood) into the heat (oven), however, that neglects to consider how much heat is required. Wood’s flash point and smoke point are both at 570°F or higher, so a process temperature of 220°F is really quite safe, particularly with a reliable PID temperature controller controlling the process.

There may also be concern about the risk of flammable material contact with the surface of the heating element. This is also mitigated some by using a PID controller. In a thermostatic temperature controlled oven, you will end up with a longer element on times resulting in target temperature overshoot and high element surface temperatures, but a PID controller will limit the element on times, thus reducing peak element surface temperature as well. The risk of direct element contact ignition can also be further mitigated by simply placing the wood within a metal container, in the middle of the oven, so there is no risk of it falling down on the heating element.

If the wood is placed in a metal container in the oven, that additionally addresses the third requirement for combustion: oxygen. Placing the wood in something like a roasting pan or buffet tray with a lid will prevent oxygen getting into the mix. The moisture being driven out of the wood will displace oxygen already in the container as well, resulting in an atmosphere around the wood that is too low in oxygen to support combustion.

Between the low process temperature, fuel confinement, and low oxygen atmosphere, the risk of fire is very low for the process of drying wood turning blanks.

That’s all I’ve got for now, I’m open to further debate, but I think regardless of the outcome, it’s clear that a non-food stove top and a non-food oven will be valuable tools in our maker arsenal.

Thanks,

Kevin.

[MalcolmM]

Not sure where to post this, because this oven safety discussion makes me ask an overall safety question: if a naive (or forgetful) user can endanger people or equipment, shouldn’t the caveats be made known at the point of use? Perhaps by posting a reminder of key points with any additional details or explanations in an always-present manual? I know we should and can assume a degree of intelligent life on Earth, but smart people do dumb things especially when their expertise is elsewhere. Yes, we have some training for some tools, but both the teaching and learning are imperfect. The same is true for all the equipment and materials at the Hive. Is there a safety officer / policy / practice to maximize safety and minimize risk to Hive and its leadership? I would be willing to help. (BTW, I am from time to time impressed by thoughtful and well-researched Hive posts like some in this thread.)

[Kmcleod]

Todd and I made further progress today.

We have now installed the 120v transformer and wired it up, so the keep warm burner and the oven light are now functional.

We also got the main power components for the oven heating elements and temperature controller (the SSRs and the safety relay) mounted, but we have not yet wired them up. We have a few small parts on order that should arrive Friday, we are hoping to have the full system wired up (and possibly calibrated) this weekend.

Thanks,

Kevin

[John_Clark1]

Malcom,
Good questions. I am currently the COO (Chief Operating Officer) and I am “responsible for managing the safety, security, and tidiness of the physical space”, quoted from the bylaws. That probably makes me your man.
At one time I remember someone was referred to as something vaguely like a safety officer. If there is one I am not aware of it but certainly I should be. Some of the tools require certification. Certification is primarily safety training. Some people also do more actual training than others in the process. We could certainly use more training. We could also use more people to step in and help. Both safety and learning are a continuing process. You are right that smart people do dumb things. Sometimes even when they actually are experts. I speak from my own experience.
Next time you are at the Hive see if you can find me and let’s talk about how you can help. Even ideas help.

Thanks,
John Clark
Hive13 COO

[John_Clark1]

Kevin,

For several years I have been working on a somewhat similar project, a controlled temperature toaster oven. Some of the things that I’ve come across might end up being useful to you.

I tried using a PID controller on a toaster oven, expecting that the D (derivative) part should be helpful in keeping the temperature from overshooting too badly. To my great disappointment the temperature overshoot by over 100 degrees (F). Just something to look out for. I did not spend a lot of time trying to tune the controller but I did use the self-tuning function to set it up.

I also made measurements of my own stove, which is very similar to the one you are working on. I have attached a spreadsheet of the temperature profile with the thermostat set at 400. I was mainly interested in how long it took to preheat, how stable it was and how fast it cooled down.

200923.xlsx (27.6 KB)

[blundar]

PID tuning is some science and some art. I too made a toaster oven with temperature control and was able to get it to the point of following a typical reflow profile within ±2C or so. Plenty accurately enough for soldering. I also need to deal with PID controllers at work quite a bit in the context of their use in automotive control systems.

One of the key factors that isn’t often discussed in getting stable temperature is to try to align the speed of your feedback loop with the speed at which changes in the system can happen. A good place to start is to make temperature measurements from a typical ambient temperature running at full blast. Graphing this out, you’ll see that there is a maximum rate of change in terms of degrees/second. Using your maximum rate of change and desired accuracy, calculate a feedback loop cycle equal to approximately the desired accuracy divided by the maximum rate of change. i.e. if you want 1C accuracy and your maximum rate of change is approximately 2C/s you wan 1C/ (2C/s) or 1/2s for your feedback loop speed, i.e. how often you compute your PID error terms in order to change your process variable. The other thing that I’ve found is that the P term massively dominates for stable temperature control in a oven type scenario. I tends to produce a lot of overshoot and undershoot. D is largely unnecessray.

if you need further PID tuning help, lmk. There are more mathematical ways you can work on it but simple rule can get you there pretty quick.
-D

[John_Clark1]

These are not necessarily full thought out or well phrased but an attempt at a starting point.
Questions and observation:
What kind of temperature ranges do you expect this to be used at and is there something to limit going beyond that?

One big concern is someone at the Hive doing something crazy stupid with it and I don’t know how we can prevent that. Ideas would be welcome.Seems like some degree of supervision may be needed.

How hot will the electronics get when this is in operation? Should there be a fan or something to keep it cool? My thoughts for my toaster oven project was to keep the electronics in a physically separate enclosure.

SSDs, like a lot of semiconductors, typically fail in short circuit mode. A frightening thing in an oven that is capable of self-cleaning temperatures. A simple thermal cutoff is worth considering.

An actual cutoff switch that disconnects the unit from the power would be a really good idea. Both to truly disconnect it for the power in case of a problem but also to be able to shut it off and disconnect the electronics from power line transients.

[Bradman]

Excellent topics. I think it would be worthwhile to create a list of topics and then discuss each one. I’m not saying we debate for hours on the color of the buttons, but a real discussion about what could happen. Nice thing about thought experiments is that they are free. (Just time).

While we will never make anything totally idiot proof (seems to be an endless supply of ever improving idiots ), we can walk through different scenarios before they happen (or cause them to happen while we watch).
Here are some of my thoughts.

My primary concern is fire and fumes.

What happens if the power cycles? Does the system shut down/reset/go crazy?

What if sawdust or wood particles fall onto the lower burner? Will they ignite?

If a small fire does start, will the oven just happily keep working?

If a larger fire does start, what do we do? What could happen? What if no one is there? Fire propagation and smoke generation.

What if someone puts improper stuff inside (treated wood, sappy wood, etc)?

Could some accidentally set crazy temps? Either by mistake or hitting the wrong buttons?

I don’t like to go down crazy paths (what if someone puts a plastic cup with gasoline in it, or ammunition) but I don’t think it is unreasonable to think someone could put a creosote soaked piece in the oven, or sawdust falling off a freshly cut piece. At my old work () we did these things called Failure Mode Criticality Analysys. It got into things like likelihood, detectability, consequence, etc.

My best example was when I was in charge of installing an Ammonia injection system and we installed a 2000 gallon tank to be filled with anhydrous ammonia. I noticed it was in an area with fork trucks zipping around unloading materials. We ended up installing concrete barriers and a water spray system in case a fork truck hit the tank.

Happy to talk more.

Brad

[Kmcleod]

The temperature controller we are using is an ITC-100HV, it’s manual can be found here. I also posted the intended circuit diagram both earlier in this thread and in the #electronics channel on slack. Several of these questions heavily suggest that those things were not reviewed before posting these questions/concerns. Please do your homework on your questions before asking me to spend time addressing each and every thing that pops to mind (the responses below took me several hours to put together, time I’d really prefer to put on more productive tasks).

1. What kind of temperature ranges do you expect this to be used at and is there something to limit going beyond that?

   • Kitchen Ranges are typically limited to a maximum setpoint temperature of 500-550°F (260-288°C). The self-cleaning function of most kitchen ovens operates at 900-950°F (482-510°C) (sufficient to burn away organic compounds).

   • Ovens without self-cleaning function typically have insulation rated for 1000°F (538°C). Ovens with the self cleaning function typically have insulation rated for a few hundred degrees higher.

   • The controller is configurable for many applications, read it’s manual if you want to know more. The parameters diP and diL let you set the minimum and maximum setpoints a user can enter, I was planning to set them to 50°C (122°F) and 285°C (545°F) respectively. HiAl is used to set the high temperature alarm setpoint, which I was planning to set to 350°C (662°F). That alarm point is high enough that it will prevent trips on overshoot during tuning, but is well below the insulation rating.

2. One big concern is someone at the Hive doing something crazy stupid with it and I don’t know how we can prevent that. Ideas would be welcome. Seems like some degree of supervision may be needed.

   • I am not willing to design a tool around the possibility of someone doing something idiotic. We are all adults, and can be responsible for what we do. Nearly every single tool we have at Hive13 can be misused in a way that is dangerous, but with very few exceptions, we all collectively agree that it’s still worth having them.

   • Again, we are adults, we do not need “supervision”. notes/signs that state a device’s limitations as a reminder may be appropriate, but please have faith in your fellow makers.

3. How hot will the electronics get when this is in operation? Should there be a fan or something to keep it cool? My thoughts for my toaster oven project was to keep the electronics in a physically separate enclosure.

   • I plan to borrow Dave B.’s thermal camera during testing of this thing, both to check surface temperatures, and to check component temps and look for poor connections in the power circuits.

   • I have seen many toaster oven projects done that the electronics are mounted within the original control console without issue (including Hive13’s own solder reflow toaster oven). I also modeled this circuit on ones used for controlling electric glass furnaces and kilns, which operate at vastly higher power and temperature, and they all had the electronics mounted in enclosures right on the side of the kiln wall without fans.

   • We will check with the thermal camera, and adjust the design as needed, but the power components are all mounted on a panel behind the oven and the back panel has lots of vents, they will get good airflow.

4. SSRs, like a lot of semiconductors, typically fail in short circuit mode. A frightening thing in an oven that is capable of self-cleaning temperatures. A simple thermal cutoff is worth considering.

   • It is a myth that SSRs tend to fail shorted, in reality it depends on the specific product, but it’s about a 50/50 split on how they fail.

   • That said, take a look at the circuit diagram. The two SSRs act as redundant safeties, current cannot flow through the coils unless BOTH are on. The only way the temperature controller would lose control is if both SSRs failed on.

   • I do not currently have it drawn this way, but we could also wire the NC terminal of the controller’s alarm relay to the main power relay’s coil, so that power is cut before the SSRs if the temperature controller enters an alarm state (such as over temperature)

5. An actual cutoff switch that disconnects the unit from the power would be a really good idea. Both to truly disconnect it for the power in case of a problem but also to be able to shut it off and disconnect the electronics from power line transients.

   • Take a look at the posted circuit diagram, the circuit does this for the oven circuit. The controller is isolated when the power switch/breaker is in the off position. The power switch does not directly cut power to the SSRs, but turning it off cuts power to the relay coil, which has the same effect without requiring a massive 40 amp switch on the user interface.

   • This configuration is also VASTLY safer than the OEM configuration, in which a single SPST relay controlled the oven elements, leaving them energized at 120VAC even when the oven was switched off.

   • The other circuits (surface burners, keep warm burner, and oven light) are all essentially unchanged from the stock configuration, if they are safe enough for a kitchen, they are safe enough for us.

6. What happens if the power cycles? Does the system shut down/reset/go crazy?

   • I will test this, but I believe the controller either resumes at the last programmed setpoint temperature after power is restored, or the controller enters an idle state.

7. What if sawdust or wood particles fall onto the lower burner? Will they ignite?

   • A reminder: I am not doing this modification with any specific purpose in mind, but to make something useful available to our members. I’d prefer to leave defense of any specific usage to the person interested in that usage.

   • However, I addressed this concern in my reply to Jim’s questions/concerns, please re-read that.

   • Note that this scenario is virtually indistinguishable from the oven’s self-clean cycle, because the oven’s chamber is oxygen deprived, no sustained open flame is able to develop.

8. If a small fire does start, will the oven just happily keep working?

   • I don’t know how happy it’d be with a small fire inside it, but yes, it would keep working. Again, this is virtually indistinguishable from the oven’s self-clean function, and no sustained flame would be possible due to oxygen deprivation.

   • If the fire was large enough to raise the temperature inside the oven above the alarm temperature setpoint, the controller would enter an alarm state and shut off the heating elements.

9. If a larger fire does start, what do we do? What could happen? What if no one is there? Fire propagation and smoke generation.

   • This question could be asked of literally everything at Hive13 that we leave energized. In fact, those “air filter” blowers that have been built have been found in the space left on, with the bearings clearly failed and overheating to the point they were scorching hot to the touch.

   • Please read my response to Jim above for more for my thoughts on the unattended use and associated fire risk (and mitigating factors).

10. What if someone puts improper stuff inside (treated wood, sappy wood, etc)?

    • See my responses to question 2 above.

11. Could some accidentally set crazy temps? Either by mistake or hitting the wrong buttons?

    • See my responses to question 1 above.

    • The biggest risk I see here is that the controller only functions in Celsius, so if someone didn’t notice that, and entered 220, assuming °F, they would actually be setting it to 220°C (428°F), nearly double the intended temperature (but still well below the flashpoint of wood). I believe the best mitigation to this possible error is labeling and signage.

    • Even if that did happen, all of the logic and safeties discussed above are still in place. The oven would still be well below the “self clean” temperature it’s designed for. The material placed in the oven would be ruined, but the oven is designed to withstand and contain burn off of organic compounds at 900-950°F (482-510°C), much more severe than our controller configuration will allow a user to run it at.

[Kmcleod]

oh dear… copy and paste really messed with my numbering and bulleting… oh well

[Bradman]

Just for clarity, I thought we were trying to generate a list of questions first then decide what were the right questions to address and then talk about it
I did not ask, or expect you, to answer every question I posted. Sorry if it came across like I was throwing rocks at your house.
I’m actually very happy to see stuff getting made.
As I’m not in leadership, my comments/questions are just dust in the wind.

Stay safe and healthy.

[Kmcleod]

No worries Brad, also, I do not think it matters whether you are on leadership? We are all equals, and everyone deserves to feel safe, right?

[blundar]

All animals are created equal but some animals are more equal than others, duh.