My RCBS "Pro Melt" Lead Pot Story...
- Thread starter seagiant
- Start date
seagiant
Member
Hi,
By Bi-Metal Probes, I take it you are talking about the Thermocouple...
If what you are using them for, is wrecking them that much, then shorten the time they are used before replacement.
It is not the PID's fault.
The other thing is, in a Home Shop, whether for a Lead Casting Pot, Temper Oven, or a Gun Kote Oven, no failures of the Thermocouple, have I heard of or experienced myself?
At the end of the day you have to decide what YOU trust, and gives you the results you are happy with.
RicinYakima
High Steppes of Eastern Washington
No but when the thermostat lets the temperature vary over 100* between off and on, it is a problem.
RicinYakima
High Steppes of Eastern Washington
When Uncle Russ built my first PID in the early '00's, I was horrified when I just stuck the probe into my faith Lee 10 pounder and found out it varied 100*. Then I put it into the RCBS 20 pound bottom pour and found out not matter what I set the thermostat at, it maxed out at 670* and the over heat switch opened.
You'se pays your money and you'se takes your chances.
Facts and knowledge can be much scarier than wishes and hopes.
You'se pays your money and you'se takes your chances.
Facts and knowledge can be much scarier than wishes and hopes.
And that is why I use a PID. Call it peace of mind
KeithB
Resident Half Fast Machinist
A PID stabilizes the temperature a lot quicker when adding sprues and fresh material to top up the pot than a thermostat. Mine will do one slight over-temperature swing and then stabilize. I usually run my 20lb pot about half empty before I top up. Sit the mold on the hotplate to keep the temp right while the furnace gets up to temp. Meanwhile I do whatever culling and sorting is necessary, drink some coffee, use the can, etc, knowing I can start making good bullets right away after a minimal wait.
Measurement without calibration is fine as long as it's accepted to be relative, as @Mitty38 has stated. Using ONE thermometer for process temps, like using ONE tape measure for an entire furniture project is an example of this being a age-old accepted "standard." Who cares if your foot is the same size as the king's foot if you're not measuring for the king?
This is also true though for electronic control of process heating. If a TC is lying to you - being off by several degrees, it's no different than a mechanical thermometer lying to you, because it's relative and you adapt or adjust, often without even realizing you're doing it or that your instrument is "off." You can build a perfect piece of furniture with a janky tape measure - as long as you use the same janky tape measure for both the drawers and the openings into which they fit.
With a regular thermometer or a TC and electronic control, you can and will have the very same issue. Note that I didn't call it a "problem." A few degrees is no big deal. Being experienced casters, we'll all know when the instrument has gotten too bad.
I replaced my original TCs out of a bunch of discarded TCs from up to twenty years ago, until I ran out. Eventually, they all started reading way off - noticeably off because at "725F," my alloy was too hot. I was getting finned and frosted bullets. Your TC (or thermometer) can be off a bit and you may never notice. No big deal - it's relative. Same thing can happen to a regular thermometer.
Having a digital readout I can glance at, not fumbling with a thermometer and letting the controller maintain my process variable are three pluses over a thermometer - for me. And, again, I got all the stuff for free out of a dumpster.
The processor is doing a bunch of math, really, really fast.
We're doing it by guess and by golly - intuition and experience.
seagiant
Member
Hi,
But...Would that not be related?
If your Lead Temp is more steady and at optimum Temp, won't your Mold?
I would think so?
Maybe but . . . Probably not if not PID controlled. A consistent Goldie Locks mold temp is the secret to good casting. The Goldie Locks mold temp is easier to maintain with a steady pot temp but the bottom line is . . . Mold temp.
KeithB
Resident Half Fast Machinist
If you continuously monitor your mold temp as you go through a casting cycle you will see the how fast the temperature changes during the fill, solidification, and after bullet drop out. Lots of heat loss (more than double) if you keep the mold blocks open vs closing them quickly after dropping the bullet. The temperature and heat loss in a mold explains why newbies that go too slow and want to examine their bullets with the mold open never seem to get good bullets. It is as @Rick and others point out mold temperature is far more important than the melt temperature.
Aluminum conducts heat very quickly too, so it's a little more important to keep that pace - don't hurry, don't dawdle, find the optimum and be consistent.
seagiant
Member
Hi,
Yes, I was referring to using a PID to help keep a more consistent Lead Pot temp.
As I said, fought from using a PID for years, and now that I have one...
See, that looking back now, as a mistake!
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JonB
Halcyon member
I'm on team PID.
I joined it about 3 years after I started casting with a 20lb Lee bottom pour pot.
I can't speak for other brands of furnaces, but a stock 20 lb Lee pot temp climbs as the alloy level lowers, due to the placement of the heating element and the thermostat thingy. example, if you set the pot to 675º (measured with analog thermometer) when the pot is full, and you cast until the alloy level is at 25%, the temp will likely be around 800º
...A PID cures that issue.
and yes, without a PID, you can just continually turn the Lee down ( a tiny bit) every 10 pours or so, I've done that before I got a PID and what a pain that was. I could seemingly keep the alloy within ±50º ...a PID will keep it within 5º or less, without me having to do anything.
I joined it about 3 years after I started casting with a 20lb Lee bottom pour pot.
I can't speak for other brands of furnaces, but a stock 20 lb Lee pot temp climbs as the alloy level lowers, due to the placement of the heating element and the thermostat thingy. example, if you set the pot to 675º (measured with analog thermometer) when the pot is full, and you cast until the alloy level is at 25%, the temp will likely be around 800º
...A PID cures that issue.
and yes, without a PID, you can just continually turn the Lee down ( a tiny bit) every 10 pours or so, I've done that before I got a PID and what a pain that was. I could seemingly keep the alloy within ±50º ...a PID will keep it within 5º or less, without me having to do anything.
Winelover
North Central Arkansas
When I was using the Lee 20# bottom pour pot, never let the alloy go down to 25 percent. Halfway, is about all I can manage at one sitting. Need to get up stretch my legs and take a break. This is the opportunity to add sprues and or more clean ingot alloy. Let pot get return to molten alloy, flux and resume casting. No thermometer or PID necessary. It's all about feel, gained from rote.
Another way to control pot temperature is to add sprues, back to pot, directly after cutting. I do it, this the way, when ladle casting.
Mold is up to optimum casting temperature when you can cut sprue with just a gloved hand.
YMMV
Another way to control pot temperature is to add sprues, back to pot, directly after cutting. I do it, this the way, when ladle casting.
Mold is up to optimum casting temperature when you can cut sprue with just a gloved hand.
YMMV
Two excellent points, @JonB .
I've been aware of the temperature rise as the pot empties for a long time and didn't even think to mention it.
I don't even know where they put the t-stat in the, but it surely isn't in the molten metal. You stick a TC right into what you want to know the temperature of, which is a huge plus.
It's not that the LEE pots are poorly designed, but just crude, because crude works. Some may be surprised just how crudely a lot of process-heating controls work. Most residential ovens are probably not all that precise or consistent. Don't get me started on toasters - and the LEE pot is really about as sophisticated as a toaster.
I've been aware of the temperature rise as the pot empties for a long time and didn't even think to mention it.
I don't even know where they put the t-stat in the, but it surely isn't in the molten metal. You stick a TC right into what you want to know the temperature of, which is a huge plus.
It's not that the LEE pots are poorly designed, but just crude, because crude works. Some may be surprised just how crudely a lot of process-heating controls work. Most residential ovens are probably not all that precise or consistent. Don't get me started on toasters - and the LEE pot is really about as sophisticated as a toaster.
Petrol & Powder
Well-Known Member
The Lee pot is as sophisticated as it needs to be.
And while the temperature of the alloy goes up as the mass of alloy in the pot goes down, I can keep the temp close enough with the crude thermostat provided. Like a lot of things, if you pay attention to what you are doing, it all works. Yes, you have to anticipate the temperature swings in all of that mass and get ahead a little bit, but it’s not rocket science.
Coming from a generation where instruments like digital thermometers, tachometers, digital scales, and other instruments were luxuries, you learned how equipment was operating by sight, sound, FEEL, and results. The more precise information we have at our fingertips the more precise information we seem to need (or more to the point - want).
There are mechanically inclined folks that can feel when an engine is operating perfectly in tune with the load. There are people that can solder, weld and braze almost instinctively. There are people that can turn a regular old wrench and maybe not hit a precise torque rating, but they never strip a thread of have a fastener work loose.
We might be setting the measurement bar a bit too precise only because WE CAN, not because we need to.
And while the temperature of the alloy goes up as the mass of alloy in the pot goes down, I can keep the temp close enough with the crude thermostat provided. Like a lot of things, if you pay attention to what you are doing, it all works. Yes, you have to anticipate the temperature swings in all of that mass and get ahead a little bit, but it’s not rocket science.
Coming from a generation where instruments like digital thermometers, tachometers, digital scales, and other instruments were luxuries, you learned how equipment was operating by sight, sound, FEEL, and results. The more precise information we have at our fingertips the more precise information we seem to need (or more to the point - want).
There are mechanically inclined folks that can feel when an engine is operating perfectly in tune with the load. There are people that can solder, weld and braze almost instinctively. There are people that can turn a regular old wrench and maybe not hit a precise torque rating, but they never strip a thread of have a fastener work loose.
We might be setting the measurement bar a bit too precise only because WE CAN, not because we need to.
JonB
Halcyon member
When I'm casting 41 cal 255gr ranchdogs with a 6 cav lee mold, that pot goes down quick, even when dropping the hot sprues off the top of the sprue plate into the pot. When using a mold like that, I often get to 25% or less, before stopping to add a bunch of cold ingots and taking a coffee break.
When I'm casting rifle bullets, all those details mentioned are the exact opposite.