Which type thermocouple to insert into bullet?

[psychodad]

Wanting to insert a TC into a bullet to monitor bullet temps in oven. What type TC are you guys using? I assume it is the "sheathed" type and not one with an exposed junction?

Do you just throw it in the oven with the rest of the bullets and let the wires hang out the oven door?

[JonB_in_Glencoe]

I use a analog kitchen oven thermometer.

[kevin c]

K type is what I use. It’s a pair of insulated wires ending in a small metal bead which is the business end of things.

I drill a small hole in the base of the bullet, insert the bead and wedge it with a couple toothpicks. The wire trails out the oven door to my multimeter.

[psychodad]

It’s a pair of insulated wires ending in a small metal bead which is the business end of things.

I guessing that was a plain unshielded thermocouple since it just had the two wires and a bead (spot-welded junction). I was afraid the lead may short out the TC and prevent it from reading properly. I plan on casting the TC into a bullet.

Thanks

MODS, I probably should have posted this under the "Coatings and Alternatives" thread. It would be more applicable there for those wishing for better monitoring of their bullet temps during baking. Feel free to move at your discretion.

[Hick]

Not sure why you want to monitor the temperature of the bullet during PC-- the inside will always be cooler than the surface-- and its the hot air at the surface in contact with the powder that cures the powder. But-- if it adds to your confidence level its worth it. Many of us who have PC'd thousands of bullets don't worry about it.

[psychodad]

.... But-- if it adds to your confidence level its worth it.

Actually I'm using HiTek and trying to improve my process. I'm transitioning from a full size oven to a mid size convection toaster oven and I'm over cooking the bullets. Coating is curing fine but colors are too dark. I've seen others on here talking about casting a TC into a bullet to see the actual temp of the bullet. Just trying to figure out if they are using a TC with an exposed junction or one with a sheath cover. I've order some with the exposed junction. Guess I'll find out Sunday when they get here.

[Hossfly]

I drill a hole in several different size boolits of similar cail. To what I’m curing. Exposed bead type, and close down by mashing down. Doesn’t short out the 2 dissimilar wires at all. When the center of that boolit gets to the desired temp the coating is cured to the point of passing the smash test, and I mean passing like flat with no splitting or cracks.

Just lay in the middle of boolits and hang out the door. Bought a roll of this thermocouple wire and ends from Grainger and make your own. Cheaper and you can have a few different ones to work with.

[psychodad]

I drill a hole in several different size boolits of similar cail. To what I’m curing. Exposed bead type, and close down by mashing down. Doesn’t short out the 2 dissimilar wires at all. When the center of that boolit gets to the desired temp the coating is cured to the point of passing the smash test, and I mean passing like flat with no splitting or cracks.

Just lay in the middle of boolits and hang out the door. Bought a roll of this thermocouple wire and ends from Grainger and make your own. Cheaper and you can have a few different ones to work with.

Thanks for the replies.

I ordered some TC's (exposed type) with connectors from Amazon. I think I'll try to cast one in a bullet first.

I am curious how you spot weld the two wires together when making your own TC? Those little suckers are hard enough to wrap around a screw terminal!

[Mike W1]

You'd need 2 dissimilar types of wire. That creates a micro voltage that can be measured. Not a do-it-yourself project!

[20:1]

The core temp of the bullet is irrelevant to the finish being baked onto its surface.

Honest.

[Carrier]

Thanks for the replies.

I ordered some TC's (exposed type) with connectors from Amazon. I think I'll try to cast one in a bullet first.

I am curious how you spot weld the two wires together when making your own TC? Those little suckers are hard enough to wrap around a screw terminal!

Any I’ve made I use silver solder to make a bead end.

[BattleRife]

Thanks for the replies.

I ordered some TC's (exposed type) with connectors from Amazon. I think I'll try to cast one in a bullet first.

I am curious how you spot weld the two wires together when making your own TC? Those little suckers are hard enough to wrap around a screw terminal!

I have made a few dozen type K thermocouple connections with a GTAW (TIG) welder. I put the biggest diameter tungsten I had in the torch, with the end ground to a flat face, set the amps just about as low as I could get them, then just held the twin wires together and tapped them on the electrode, just to get a quick flash of arc.

But, that is not the correct way to do it. I eventually bought a capacitor-discharge spot welder, and hooked it up to a block of graphite. I touch the wires to the block, then press the discharge button. A burst of current melts the tip of the wires, and burns a bit of the graphite to create a little cloud of CO/CO2 around the hot joint, for just a second. The result is a nice bead. It's a thousand-dollar machine, so not justifiable for the average Joe. That's why I started with the welder, until I knew I had a market and would be making lots of thermocouples.

[danmat]

Buy some Hi-Temp thermocouple wire, skin inch or two of the ends.
Take 2 pair of needle nose, start twisting wire.
Grab beginning of twist with pliers and finish tightly twisting with 2nd pair about an inch.
The silver would work but not needed.
Sheath type coulpes were not prevalent in the industry until the early 70s if I recall right, prior to that they were all made in house.
We used ceramic insulators with 2 holes in them of various sizes and lengths and spot welded the ends with machine made for this.
Made many emergency repairs in the middle of the night with the twist method to keep a unit running until I could get a new one made and installed.
We are casting boolits not sending a man to the moon.

[kevin c]

The core temp of the bullet is irrelevant to the finish being baked onto its surface.

Honest.

Runs directly contrary to the advice given by the inventor and producer of the HiTek coating, but then, what does he know…

[20:1]

Runs directly contrary to the advice given by the inventor and producer of the HiTek coating, but then, what does he know…

In the 8 to 12 minutes at 400 degrees Hi-Tek recommends for baking?

7. Once the bullets are fully dried and the oven is set, put them in for 8-12 minutes to cure the coating.

https://hi-performancebulletcoatings...-instructions/

[kevin c]

I’ve read those instructions, three times I think. That’s what I started out following, and it’s all good advice.

I’ve also read the massive HiTek thread three times. That’s where Joe Ban, the creator of HiTek, suggested using thermocouples inside test bullets as a good way of judging when the cure is complete. It seemed to me, too, that bullet surface temp over the recommended time to cure should do it, but apparently not. Some of it may be that the metallics in some of the coatings reflect heat more than the nonmetallic versions of HiTek, and that there are multiple coats applied. I do know that some of my colors cure in 8 minutes and others in 12 minutes, and that’s with the same bullet weight and design under the same environmental conditions, and that it was the thermocouple in the bullet core that told me that, confirmed afterwards with the wipe and smash tests.

Coating and baking batches of 10,000 casts, twice each, over massive sessions, I’m glad to shorten the baking cycle by a third.