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:
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…
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.
- 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.
- 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.