Good oven thermometer for coating

[mjwcaster]

What is a good, accurate oven thermometer to test my convection oven for coating?

And what is a good way to verify accuracy in the needed range (400f)?

I started having issues with hitek and need to verify my oven temp.

Checking reviews of oven thermometers, they all seem to have some bad reviews for accuracy.

Also not looking to spend too much on this, would rather build a pid if I have to spend too much.




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[Grmps]

Buy and / or borrow some thermometers like https://www.amazon.com/Winco-3-Inch-...en+thermometer
place 2 or 3 of them in the middle of the shelf you will be baking on. turn on the oven and adjust the setting until the thermometers read 400°. ( I bought 2 and borrowed 1 to be sure they were accurate).
With countertop ovens, the temperature is affected by the surrounding temperature. anytime there is a bi temperature shift I re-check my ovens.
With Hi-Tek it's always better to bake a little longer than shorter, the worse thing that will happen by baking longer is the coating will get darker. They will still be good to shoot.

First and biggest problem with Hi-Tek failure is people aren't letting the coating get COMPLETELY DRY before baking.

[mjwcaster]

The issue is even with multiple thermometers we are still guessing without a standard. Granted with enough data points we can assume it might be right, but if I try 3 thermometers and they read different, which one do you trust.

I think my oven is close enough from observing its performance and the color change of the coating when set for higher temps/time.

Just would like to prove it to eliminate a variable.

My hitek is definitely dry, either overnight, multiple days or in the sun all day, almost too hot to handle.
Then preheated on top of the oven while it heats up.
I have successfully hitek coated and shot thousands of 45 and 380 bullets up to now, then suddenly it stopped working.
I am leaning towards lead contamination, but not sure yet. I didn’t reload at all over the winter, and when I finally did I had leading.
I think all my issues have been with one batch of lead (range scrap), not sure as it has been a long time and I did not keep great notes.

I have tried freshly cast boolits, probably from the same batch of lead, freshly mixed hitek with new jug of acetone, higher temp, longer cook time with preheated/warm boolits, extra cleaned containers to rule out post cast contamination.

The cooked boolits at higher temp/longer time are discolored/browned just like I would expect from over cooking.

I just want to verify the oven (should do this anyway, but it worked fine when I started using it, so never bothered).

I will use up this batch of range scrap, still works fine when tumble lubed over bad hitek.

Then try another batch of lead.

The failure is strange, seems to pass acetone and even crush test, but I can scrape it off with a fingernail. How it can stay on when I flatten the boolits with a hammer, not get scrapped off when sizing but can scrapped off with a fingernail?

Any way most of this post should probably go in the coating thread, but I wanted to verify my oven and lead before posting all my troubles.
Too late for that now, I guess.



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[mjwcaster]

I am thinking that the best bet for verifying temp/accuracy in this temp range will be pure tin, ~450f.

Unfortunately I do not have any pure tin, nor had I planned on buying any since I have enough solder to last me a long time at my current use.

Looking at melt temp charts, even a slight alloy to tin lead free solder makes a large difference in melt temp.




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[Grmps]

Try using 15% less HiTek mix on your first coat and cut a few seconds off your tumble time.

Countertop ovens, due to the location and style of thermostat are ALWAYS off and vary with ambient temperature.

[mjwcaster]

I already use a thin mix, very light on my first coat, dried very well.
2 coats used to work just fine, but didn’t look very good.
I have tried 3 coats, the third coat makes them look much better, but they worked fine with 2.

It might be something I am doing, but it worked fine for a couple of years, many batches and many thousands of boolits before with no issues.
Something has changed, and I have been trouble shooting this for a while now.
I am basically down to oven temp, contaminated lead, or bad hitek powder.

I realized I have another pot with some left over alloy in it that hiteked just fine before.
I will try to get some cast tonight and test with them.




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[bdicki]

I just put the thermometer from my lead pot in the oven.

[mjwcaster]

I just put the thermometer from my lead pot in the oven.

Only issue is I don’t have a lead thermometer either.
Just been flying by the seat of my pants.


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[gundownunder]

You might need to take this one to the coating forum for expert advise,
but for what it's worth here's my opinion.
If you've tried higher temps and higher times and turned the bullets darker with both, it's not your oven. It may be a variable but not "the" variable.
If you pass the smash test you have adhesion between coating and bullet, and if you pass the wipe test your coating is fully cured.
When you scrape the coating off with your nail, are you getting just the coating, or is there lead coming off with the coating? If lead is coming off with the coating I'd say your lead is too soft. If not, read my first line again 'cause I don't know.

Just as an add-on, I never use range scrap any more. I did when I started casting, but I found it too variable.
If you have a hardness tester and alloys to play with then range scrap is cheap, but I prefer to use nothing but COWW as the consistency is far better.