Toaster ovens and their accuracy

[GasGuzzler]

Verified with a remote probe connected to a digital readout I got new for $12. My brand new cheapo Black and Decker is not accurate at all on the dial but I found where it needs to run. The longer it's on the more stable the temp is. The readout has a max temp you can set that will sound an alarm if the temp gets too high.

[Sitzme]

Checked mine with an oven thermometer and set it. Never looked back. Is the oven thermometer accurate? Absolutely! Well as accurate as you can expect for $3! My PC coatings are good so it must be close enough.

[Hossfly]

Checking my old convection toaster last few days and keep the temperature set on 425’, will keep the temperature inside a 500 gr boolit at 400’ for the duration of process. Thermocouple is inside of boolit, crimped in and placed in middle of trey, also cooled to same temperature as next batch.

[slide]

Hossfly, I am glad you posted this. When I came up with the thermocouple method I taped the thermocouple in with high heat aluminum tape. For the life of me I couldn't remember who came up with the idea of crimping, now I know. I always like to give credit to people when they come up with ideas. Before, I would just say that the crimp idea was not mine but it is an excellent idea. I crimp all my t-bullets now!

[oley55]

Hossfly/Slide,

I recall seeing a thread with pics and/or description of crimping the thermocouple into lead but I can't find it now (or maybe it was an ingot preheating thread).

I am trying to understand how this works, i.e. the removal of heated slug/bullet and replacing it with a like room temperature slug/bullet. My 6" long thermocouple passes through a small hole drilled through the sidewall so that the tip is hanging in air just barely above the cooking area. I'd have to reach into a hot oven and try to twist the heated bullet off and then reach in again to slip a new unheated slug back on. All the while, a lot of heat is being lost into the open air.

I am not dissing here, as I can see the merit, just trying to mentally work out the mechanics.

[Dragonheart]

Hossfly/Slide,

I recall seeing a thread with pics and/or description of crimping the thermocouple into lead but I can't find it now (or maybe it was an ingot preheating thread).

I am trying to understand how this works, i.e. the removal of heated slug/bullet and replacing it with a like room temperature slug/bullet. My 6" long thermocouple passes through a small hole drilled through the sidewall so that the tip is hanging in air just barely above the cooking area. I'd have to reach into a hot oven and try to twist the heated bullet off and then reach in again to slip a new unheated slug back on. All the while, a lot of heat is being lost into the open air.

I am not dissing here, as I can see the merit, just trying to mentally work out the mechanics.

The mechanics are really very simple. First you need one or more inexpensive K-type thermocouples; this is a wire that plugs into an inexpensive digital thermometer. Take the end of the wire and insert it into a bullet. I personally don't want it to come off so I cast the wire into the the bullet or any other similar sized chunk of alloy. Check out Amazon- "Proster Digital Thermocouple Temperature Thermometer with Two K-Type Thermocouple" for an example as this unit monitors two thermocouples at the same time.

The thermocouple concept is also very old as it is nothing more than a remote thermometer that is measuring the temperature of an object, and thermometers are about 300 years old. When we place a probe into an oven the probe is measuring the air temperature and not the actual temperature of the bullets. Eventually, thermal transfer will take place and the dynamic load will equalize, so air and bullets temp will equalize, but the question is how long will that take, since your timing should start when the bullets reach temp.

When the probe is inserted in a like size bullet then it gives us a better indication of the temperature of the surrounding bullets. When I say better indication that means most ovens, even convections, have hot spots, so if you are doing multiple racks the temperature between the racks and even on the same rack can still vary. The best solution there is multiple probes.

[oley55]

Dragonheart, got it, so the thermocouple is laying in/on the basket or tray and the lead wire is passing between the door and frame.

I am using my current thermocouple with PID to control the oven temp. I now realize controlling the oven temp and measuring the internal temp of the slug need to be separate functions. Otherwise the oven would reach too high of a temp while waiting for the slug's core temp to catch up. Yes?

[slide]

oley55, you can go to amazon and order a digital thermometer with a thermocouple. The thermocouple is thin enough it will not interfere with the oven door closing. You are correct to lay the t-bullet close to your bullets that are baking. One thing, use an already coated bullet for your t-bullet. I worked with the inventor of hi-tek and we found out that a coated bullet will absorb and hold temp at a different rate than a uncoated bullet. I tested powder coat and found the same thing. On the thermocouple, drill your hole in the base of the bullet and then squeeze the bullet down on the wire. Works real well. If you need to you can remove the bullet and replace it with another. I have several thermocouples that have been taped in for going on four years now and still haven't come loose. Not very pretty though. When I hatched this idea the tape is what I started with until Hossfly came up with his idea. I recommend only one t-couple. You are going to have hot and cooler spots even in a small convection oven. Trying to watch a couple will drive you jack batty. With this setup you will know approximately what the temp of your bullets are. Follow the mfg. instructions. If your powder says 20 minutes at 400f you will be able to do that.

[Dragonheart]

Dragonheart, got it, so the thermocouple is laying in/on the basket or tray and the lead wire is passing between the door and frame.

I am using my current thermocouple with PID to control the oven temp. I now realize controlling the oven temp and measuring the internal temp of the slug need to be separate functions. Otherwise the oven would reach too high of a temp while waiting for the slug's core temp to catch up. Yes?

Yes, the oven would overheat if the pid was monitoring the bullet temp, so the PID needs to monitor the air temp just as any regular oven does. You want a constant oven air temperature to be 400 degrees F. regardless of the dynamic load. Meaning you can cook 50 bullets or 5000. The difference is the time it takes for the dynamic load (the bullets) to reach 400 degrees and stabilize. Since the dynamic load is absorbing energy and assuming everything equal 5000 bullets are going to absorb more energy therefore will take longer to stabilize at 400 degrees than 50 bullets. The thermocouple is just a bullet thermometer measuring a like kind and quanity of alloy, so it stands to reason when your "bullet thermometer" stabilizes the surrounding bullets have also stabilized, with the exception that a large quanity of bullets on multiple levels won't all stabilize exactly at the same time.

Basically, your bullet thermometer is just like sticking a thermometer into your casting furnace to measure the temp of the alloy. When the alloy comes to temp you pour. Same principal, when your bullets come to temp in the oven you start the timer.

[Mr. Woodchuck]

I don't trust oven thermometers, and furthermore, the only temperature that's important is the bullets themselves. I bought a handheld laser style thermometer on clearance from Sam's club for about $6.00. I set my ovens on 425-450. I'll crack open the oven door and "shoot" the laser probe at the bullets. Once they reach 395-410, they're done. I've learned how long it takes to usually get the bullets to these temps, so I set my timers accordingly, allowing for time to open the oven, shake the pans, and turn them about half way through. I use the laser each and every batch and the results are consistent. My Oster ovens are finicky. Sometimes they run hotter than other times and ambient temperature doesn't seem to cause the variation.

[charlie b]

That works well enough unless you have a basket full of bullets and cannot use the IR to 'see' the bullets in the middle of the batch. That's where a thermocouple is ideal.

[slide]

Mr. Woodchuck. Use whatever works for you. That is a smart way to do it. I have to agree with charlie b. I ran into the same problems as you trusting the thermometers,especially those little cheap oven thermometers. Get five of them and they all read different. I was using hi-tek at the time and temp is critical. Just couldn't get it to come out right. After quite a few failures I came up with the t-couple bullet which has worked very well. It will only cost you around twenty bucks or if you have a muti meter that has a thermocouple you can use that.

[Mr. Woodchuck]

I can see how the thermocouple bullet would work, but I generally bake one batch right after the other and having to remove the bullet, let it cool, then put it back in the oven each time would be a bit tedious. A good laser thermometer is about as easy as it gets. But be aware, that some laser thermometers are junk. I bought 2 different ones several years ago from Harbor Freight and they were garbage. Guaranteed to never give the same reading twice.

[slide]

You don't have to let it cool. It will stabalize. I have used mine that way when I do multiple batches. It will take a little bit for the bullets to come up to temp. and by that time everything will be leveled out. I will say again, If you are happy with what you are doing then by all means keep doing it. Now you have another option if you choose to try it. There is more than one way to skin a cat as they say. Good luck!