Building an accurate tempering oven

[wizard69]

Nice Video;

I've spent years in industry working on process ovens of different types and have to say you did pretty good for you first crack at a improved toaster oven!!! A few comments:

1. If you expect to e leave the oven unattended, you should seriously consider an over temperature safety of some sort. There are options here but some of the over temp controller look a lot like a PID controller but they are a slightly different animal. You should use a mechanical relay in the safety circuit too.

2. Somewhat expensive to buy but might be needed here is high temperature insulated wire. You will find out if pretty soon if the wire insulation going to the heaters or other hot parts of the oven, start to melt down. It is the insulation that goes.

3. You will want to fix that fan as soon as possible. The constant stop and start is not good for the motor. However what might be more important is that air circulation makes a huge, massive difference really in an oven. Even with a fan and fancy ducting it can be hard to keep an even temperature profile in an oven. In a home shop it is pretty hard to tell just how good or bad a temp profile will be in an oven as you need lots of thermocouples carefully distributed to validate. however you can run many test cycles with the one thermoucouple /display you do have with the probe located in different parts of the oven. You may be surprised to find hot/cold spots.

4. Thankfully in regards to #3 above you have insulated nicely. This is huge for oven control ability.

5. Doors are always a problem even on huge process ovens. You could most likely improve the oven with a better door though I'm not sure it would be worth it.

6. Thermcouples do fail and it doesn't hurt to have a spare or two on hand. Of course once you have the spare the original never seems to fail. However thermocouples (TC) are the are a likely item to be changed in an oven over time. Having a TC that can be plugged into a jack on the back of the controller box can be a useful way to quickly swap a TC.

7. This was over 40 years ago so things may be different today, this was also the USA, but I took an industrial electrical course held at a local tech school. A couple of nights a week for a time period I don't remember. Even though I eventually got a 2 year degree in electromechanical technology, that little bit of after work effort has really paid off over time. As they say a little bit of knowledge goes a long way. I'm not sure if anything similar is offered in the UK and frankly the rules are likely a bit different over there, but if such a course is available it can really help with understanding the "industrial way" of doing things.

8. The suggestion above about using your sell phone camera is a fantastic one! I'm a certified old fart, set in my ways, yet more and more I will break out the cell phone to record the state of something before tearing it apart. More importantly for an old fart is that it is often a better magnifier than a real magnifying glass. That is i regularly use the cell phone to record small hard to read or even inaccessible labels on parts and then blow them up on screen into something readable. When the smart phone craze first hit I never thought I'd have a need but now it is almost a daily tool to make use of.

9. It is almost always better to sketch up an electrical schematic before building up an electrical circuit! Even a terrible artist will benefit. That and make use of a wire numbering system recorded on that schematic. Save the schematic, in fact file copies of it, placed in multiple places. You will love yourself 5 years later when having to do maintenance on the controller.

10. Always make sure your grounding is correct. You should have wires grounding the control cabinet, its loose panels, the oven chassis itself (including the covers) and the inner chamber.

In any event a quick 10 to help out anybody going this route. Frankly I might have to take the route you have and just go out an buy a proper oven as finding a used one, that is big enough, seems to be next to impossible.

Again very nice work. Now all we need to see is a nice set of blades coming out of that oven.