Testing my Therometer and other things that perplex me.

[Colorado4wheel]

So everyone keeps saying "you should not need to cast at 800F to get good boolets. The other thing that perplexes me is that no mater what my Lee pot needs to be above 725F to not freeze the spot. Then I started wondering about Zinc contamination causing spot freeze (read that on this forum). I think that is a long shot. My pot doesn't drip. It's perfect. Bullets look good at 800F. So I decided to test my Lyman Thermometer. I live just under 4700 so I think water boils at 205F around here.

http://askville.amazon.com/fast-boiling-water-cool/AnswerViewer.do?requestId=784336

I stuck my Lyman Thermometer into a pot of boiling water and it read 222F. Seems odd to me. It was a rolling boil. I tested several others. My two good food ones both read 204F.

So now I am second guessing if I am even casting at 800F. It would help explain why my spot freezes at such a high temp. Any other thoughts?

[MT Gianni]

I can get good boolits @ 700F with my thermometer. It is a basic bi-metal 100-1000 made for a Bacharach burner adjustment kit in the early 70's. Design and size is almost the same as Lyman. I use a thermometer as a reference. If I am not getting good fillout, I check the reading and adjust the thermostat to my needs. Repeatability of my thermometer is much more important to me than +or- 25F @ 750F. I want the alloy temp to read the same when it is 725 each time I put the probe in. I would not expect great accuracy from a bi-metal thermometer @ 20% of it's scale, ie boiling water. I would check it with the melt point of pure if I was concerned with calibration accuracy as that is closer to 50% of its scale rating [1000F]. Let me know if this doesn't make sense.

[Colorado4wheel]

I don't have anything "pure" to test it with. I do have some Linotype that I have not used for anything.

[edler7]

My pot doesn't drip. It's perfect. Bullets look good at 800F.

Why fix something that isn't broke ? It might not be exactly 800F, but it's making good boolits. Use it as a reference point for your alloy- when the thermometer says 800, it's time to get busy.

[geargnasher]

Here's the key, regardless of thermometer accuracy:

Cast boolits at the temperature that is 100 degrees above the point that the alloy JUST BECOMES FULLY LIQUID. The temperature of the alloy will remain constant from the point that it just starts to sweat beads to the point that the last crystal of the last element on the last phase of liquifaction melts, then the temperature will start to climb. Watch carefully as the alloy melts, stir it, observe the "thickness" and grainy-ness of the texture. It will suddenly become smooth as the temperature starts to move upward. The point it's at when it starts to take on heat again is the full-liquidus point.

This is an excellent rule for any ternary alloy, regardless of balance, from stick-on wheel weights to the type metals. 100 above the end of the mush phase will keep you from overheating the alloy, ensure it is at a good flow temperature, maximize the usefulness of the tin content, and keep your pot flowing well. If it won't flow out of the spout at 100 over full liquidus, you have other problems.

Even if your thermometer is 150 degrees off, it will still be good enough for measuring relative temperature.

Gear

[Colorado4wheel]

So the lead becomes liquid just before 640F. With out a fan blowing on my the spout is free flowing around 725F. If I let the melt cool at all it will freeze up pretty easy at 725F or maybe even a little higher. Doesn't give me any breathing room for adding even preheated lead. If I keep the lead flowing off and on while I add more hot lead the spout doesn't freeze till just under 700f. Seems kinda high doesn't it?

[Dannix]

It's the difference between accuracy and precision. Your thermometer may not be accurate, but if it's precise, you can still use it as a frame of reference.

[MT Gianni]

So the lead becomes liquid just before 640F. With out a fan blowing on my the spout is free flowing around 725F. If I let the melt cool at all it will freeze up pretty easy at 725F or maybe even a little higher. Doesn't give me any breathing room for adding even preheated lead. If I keep the lead flowing off and on while I add more hot lead the spout doesn't freeze till just under 700f. Seems kinda high doesn't it?

That does seem high. My ww are liquid at 550F.

[Colorado4wheel]

I guess I keep casting at the temperature that works. Before someone asked why I cared. EVERYONE says "You don't need to cast that hot" But it appears I am only about 50F hotter then the recommended temperature. I have been trying to figure out why that is. This is range scrap. It's not WW or great lead.

[btroj]

What you are missing is this- it doesn't matter what your thermometer reads, it is the fact that your thermometer allows you to KNOW what relative temp you are at.
Listen to what Gear said. Note the temp your thermometer reads when the lead first begins to melt. Add 100 to that and you have a good temp to cast at. it doesn't really matter what the temp your thermometer reads at the beginning of the melting as long as you can know when you are 100 degrees over that. If the thermometer says it is at 800 when melting begins then cast at 900. That is an exaggeration of the error of your thermometer but it illustrates what Gear was saying.

[Colorado4wheel]

I get that. I just am not sure it's that far off. Maybe it is. I am going to try casting at 750F. I also knocked some burrs off my vent lines on my molds. Maybe that will help as well.

[btroj]

In the end do what I do. Find a setting for your pot that works and leave it alone. Mine hasn't been changed in years. Don't ask what temp is at, I don't know. It is "hot enough", so says my moulds. No thermometer.

[Colorado4wheel]

Just cast a bunch more. My molds and lead just like the 800F # on my thermometer. Thats just the way it is. I tried a lot of thing to try things at 750 or below. It was just hit or miss. 775-800 was the sweet spot.

[williamwaco]

Two thoughts:

1) Based on your comments, it is possible your thermometer is not correct.

2) It could also be related to where in the pot you measure the temprature. I am assuredly NOT a thermometer expert. I got my first thermometer only a month ago but I have noticed several troubling issues.

( Lee 4-20 Pot)

With a full pot, the temperature can easily vary over 150 degrees from the bottom of the pot to the top.

Adding a couple of pounds of sprue cuttings or new ingots will lower the temprature 150 to 200 degrees.

Stirring the melt with the thermometer probe will change the reading.

Touching the bottom or lower inside of the pot will change the reading.

I have settled on taking temprature readings like this.
Stir the pot vigorously with my fluxing spoon.
Place the probe all the way to the bottom of the pot one half inch to the right of the spout opening ( Because I am right handed and because that is where the actual metal that enters the mold will come from.) I hold the thermometer there until the needle stops rising and then raise it about 1/4 inch and wait for it to stabilize again. That is my "official" reading.

Notice that if the pot element is heating the needle will continue to rise until the element clicks off.

Now the bad news. After taking a stable reading in this manner say -750 degrees. I begin casting with a six cavity mold. After about ten minutes of casting without adding any sprue back to the pot, the temprature ( at the spout ) will drop by 100 to 150 degrees.

I have not been able to pin down the variance between the temperature at shich the pot turns off the element and the lower temperature at shich it is turned back on but I am reasonably sure it is at least 150 degrees.

It is entirely possibe in my experience that you could measure a temperature of 725 when you start casting and it could easily be down to 525 within 10 minutes.

And yes, I have trouble with the spout freezing too. I keep a little butane fire starter handy to thaw it out.

[Colorado4wheel]

Mine is very consistent. I stir with the thermometer. But I let the entire setup stabilize. I read the temp about 1 inch off the bottom. I never change the temp setting once I get it stabilized. I never add much to the pot unless I have seen the put temp creep up. It used to move around a lot till I noticed that I was causing the problem by constantly adding stuff and fiddling with the dial. The less you do to it the better you are. I heat lead in another pot and transfer it to the main pot. Using this process the temp stays relatively stable (+- 25F). Thats as good as it gets for this thing.

I have decided the Lee pot sucks. I want to get a magma. While casting with the Lee 20 lb pot, when the primary pot is 1/2 empty (which is too low in my opinion) The other pot has not recovered from the lead that I have added back into it. So I am constantly balancing waiting for the second pot to heat the lead so my primary pot doesn't cool too much. It just a sucky system, but it's better then letting the primary pot cool or fluctuate because I am adding cooler lead into it. I am feeding two 4 cav molds at the same time. So I do go pretty quick.

[btroj]

I don't ever add lead while casting. I wait til the pot drops to a point where I feel it needs more added. I then add lead and walk away. While the pot comes back to tmp I inspect bullets, get a drink, or do something else. I find a watched pot never melts......

[MT Gianni]

Interesting comments Williamwaco, my Lee 4-20 raises temp as it drops. If I don't change settings I am 100 F hotter by the time it drops to 1/2 full. You might try insulating the top of your pot with foil hat to help hold heat in.

[Colorado4wheel]

I should mention that I have the probe area insulated with some spare insulation. I think drafts and the heat from the pot cause it to vary more when that gap isn't insulated.

[williamwaco]

Interesting comments Williamwaco, my Lee 4-20 raises temp as it drops. If I don't change settings I am 100 F hotter by the time it drops to 1/2 full. You might try insulating the top of your pot with foil hat to help hold heat in.




That sounds like a very interesting and inexpensive modification to try. thanks

[Colorado4wheel]

Insulating the probe works better on my pots then the Hat. I have a hat, it helps hold some heat in during the heating up phase.

[Old Caster]

I have a Waage pot setting next to my RCBS and I constantly add lead based on the column height because I almost always pressure pour and don't want the pressure to change much and I want my temperature to stay the same. The Waage is 800 watt 20 pounds, so it keeps up no matter what I do. The Waage's are very accurate temperature wise and I think only cost about $200. It is surely the best ladle pour pot available. -- Bill --

[blikseme300]

Repeatable results are what we are after, no matter the reading value. Accurate calibration plays no role in the results. I have a PID system and I don't care what the value is on the read-out. I know what number to be at to reproduce prior casting results. Is the value on the read-out accurate? I don't care as I can reproduce consistent casting every time the desired set-point is reached.

I have noticed that a "settling period" is required for consistent results. The temperature differential between the bottom and top of the pot as well as the proximity to the heating elements affect the sweet spot greatly. That is why my thermocouple mount always places the tip at very close to the same spot each time. Consistency is key here, IMnsHO.

I now have a smelting setup that is so predictable in casting outcome that is almost boring. Boring is good as any changes can be fixed easily as there are a lot fewer variables than if things are done loosely.

Many of the prior posters here echo my experience that repeatable results are what we need to aim for and not absolutes in read or measured values.

When I was a newbie I over researched things and tried to stick to absolutes. As an engineer I thought this was "the only way". Anybody here do old school BBQ? You learn to be quite humble real quick if you want to stick to absolute values. There are nuances that defy measurements. Same with boolits.

My 2 1/2c

Blisem