PID Controlled Forges..... Thoughts and advice


"The Montana Bladesmith"
Generally I don't do a lot of offering unsolicited advice, but because of past, and more recent experiences, I believe it's appropriate. Over the past several months, I have fielded MANY phone calls and emails from individuals seeking my help/advice in finding/fixing problems with PID controlled forges they have built. I have become somewhat frustrated, because these type of forges simply are not capable of working as most anticipate they should, and when I try to tell individuals that, they get defensive, and several have even "gone off" on me. I don't want to be this way....but I am nearly at the point where I want to simply refuse to help anyone with these PID controlled forges.

For those who don't know what a PID Controlled for is..... essentially its propane forge, which uses a solenoid valve, with a PID Controller to turn that solenoid valve on/off. The idea behind it is to be able to set or adjust the controller to make the forge maintain a given temp. While this might seem a great idea in theory, the results are often very different in practical application. In short, an individual's expectations generally far exceed the capabilities of this type of forge. Were it not for the variables inherently involved with the uses of a forge, these type of devices MIGHT be viable, but for the most part they are simply a "money pit", that create more problems then they solve.

Nearly every request for help I've received begins with "As long as I don't put anything in the forge, it holds the set temp, but when I put steel into the forge the temp overshoots or undershoots the set temp way too much." Therein lies the problem with PID Controlled forges... the variable of mass that a person introduces (in the form of a bar/billet of steel), and how much/often that mass is removed, reinserted simply cannot be anticipated by the controls, causing the unwanted temp fluctuations. It's actually very simple, but its very difficult for most to understand.

OK, having said that, the next issue is the number/amount of parts this type of forge requires...... way more parts, and way more complicated then a simply designed, single burner forge. To put it bluntly, when it comes to a propane forge, the more you overtake the plumbing....the easier it is to stop up the drain. There's just more to go wrong, more parts to connect (and possibly connect wrong), which generally creates a overly complicated device, which just opens the door for more and continuing issues/problems.

I have to believe that many seek to build these types of forges in hopes of dodging the learning curve when it comes to forging, and even though I do my best to explain to those who've sought my help/advice, that there simply isn't a "magic bullet" that will eliminate the learning often just bounces off, and the individual struggles along, trying to chase a unicorn that they are never going to find.

My advice is this..... before you spend the money and time to build a PID controlled forge, think hard about it, and temper your expectations to a realistic level. It MIGHT be helpful in a limited number of scenarios in your shop, but it WILL NOT be all you anticipate/expect. There is a reason that experienced Bladesmiths build/use forges that are of simple designs..... it's because they work, and because those simple designs keep on working, without presenting constant problems/issues. Do yourself a favor.... if you're thinking of building yourself a propane forge, steer clear of overly complicated designs, and ALWAYS, when it comes to building a propane forge....stick to the "KISS" principle.


Very well stated Ed. I thought about going down that path. After a lot of research and playing around with a prototype I chuck the idea. A PID once you have it together with a themocouple becomes a nice fancy thermometer. It does have a viable use for me in that configuration. Thus not a total waste of money.

Fred Rowe

Well-Known Member
They can be a challenge to build, but if you enjoy a good challenge don't hesitate to build one.

They do have advantages more than just being a high priced thermometer. I've built two dual stage forges; which is a forge that has a primary or manual side and a high or pid controlled side. The basic idea is to set the manual side to just below the desired "set point" temperature, such as: you want a set point temperature of 2100 degrees; you set the manual side to where it reaches a temp of 2050. Then set the pid controller to the desired or "set point" temp of 2100 degrees.
With the forge pictured both gas supplies are switched, the manual and the pid controlled sides with the gas "main" controlled using a rocker switch with a green indicator light.

You can see in the wiring diagram that this forge set up is wired so that if the electric goes out the gas shut off automatically.

If you build one of these dual control forges its important to give yourself the ability to adjust each burner separately. The Chariot runs on three [3] burners and not the five shown. Each burner has its own needle valve located just before the burner nozzle. In order to tune a blown forge you have to be able to tune each burner separately.

I took one of the air volume controls out; I found, because the temp settings are so close there is no need for both.

The real advantage to a dual stage forge is the recovery when you add cold metal to the forge. The pid controller turns on and injects gas to over come the drop in temp and stays on until set point is reached.
This forge will hold set point temp to within 5 degrees at all times. It makes forging at specific temps a real pleasure.

Don't attempt one of these unless you like a challenge, they are that. But once its built they are a pleasure to operate. We have around 650.00 in the Vulcan's Chariot.