Coal Forge Design

[Randy]

One of the details that I’ve learned in coal forge design is one of the most important. It’s the function and design of the grate and/or clinker breaker. When I first started forging in the early 70’s I was finding all types of forges and then trying to figure out the reason things were done as they were. Luckily I had a couple of retired wagon smiths that could give me some leads into this information. One item I noticed was all of the different angles to the sides of the fireboxes and the different configurations of grates and clinker breakers depending on the company that made them. In use some constantly had large fires no matter how you ran the blower. These seemed to be the ones with either shallow fireboxes, approximately 2-1/2” to 3-1/2” deep, and/or ones that had grates with slots angled outwards. I also found the ones where I had the most control of the fires were deeper, approximately 4” to 5” deep, and had grates angled toward the center of the firebox. I believe it was the Champion forge that had the best configuration of depth of firebox, angle of the sides and size and angle of the slots in the grate to allow me to have a well controlled fire. This helped to maintain a small fire when needed or a large fire for bigger jobs. See Drawing 1.

I even designed an all steel, not cast iron, firebox and tuyere using the angle, depth and grate design angled towards the center and it worked as good as its cast iron counterpart. My sides were only 1/4" steel plate and I got over 8 years of service from this firebox before the sides warped. When first completed I painted the outside of the unit with heat resistant paint, which only goes up to 1,000 degrees, and a lot of it was still intact when I removed this firebox. A lot of forges were built from the plans in my book and I never heard any complaints, just how well it worked.

Back to designs, one item that I often found was the forges with the solid triangle in the bottom of the firebox which acts as the grate and the clinker breaker. One of the railroad style forges had two straps of leather hanging on the front of the forge. When I inquired about this I was told that they were to hold the clinker breaker lever either to the right or to the left. One way the lever would keep the triangle with the flat on top. This would be for larger fires. The air is forced outwards creating more airflow towards the outside of the firebox. See Drawing 2. If turned in the opposite direction the point of the triangle would be up forcing more of the air towards the center of the firebox therefore creating a smaller fire. See Drawing 3. Yes, as the fire burns it will consume whatever is in the firebox, but the hottest area will be where the most amount of air is, closer to the center. It’s up to the user to maintain the fire using green coal and water.

I had the opportunity to put this to the test this year while teaching a forge welding class at one of the craft schools. Most of their fireboxes had the triangle in the bottom and all had the lever bent so that the flat of the triangle was always up. They complained that the fires were too big and they couldn’t control them. It also made for a very hot shop. So I wired my lever so that the triangle point was pointing up and just that simple move gave me a smaller fire with more control. Forge welding was even easier as there was a hotter area in the center of the forge, not spread out in a large area. They have since heated and bent all of the levers in the opposite direction so that the triangle point is up.

So the old methods are out there, but sometimes we just have to figure out how it works and what purpose it serves, and then share what we learn with others.

[Francis Trez Cole]

forge drawing.pdfHay Randy here is the style I have used for the last few years works great and I have very good control with the damper next time I build one I will have to look at angled fins

[MLMartin]

Thanks for the post Randy. Things like this can often make like a bit easier or a bit harder, but are often overlooked. Its nice to have well thought ideas and observations on things we use everyday.

[Timothy Miller]

Thanks for sharing. I had been using coal forges for years and never knew that. I got a used copy of your dvd with a bunch of tools I bought about a year ago. When you talked about the purpose of the shape of the clinker breaker it was an a-ha moment for me. Its strange to me how there are levels of sophistication to our tools that have been lost to us because of the disruption of the trade during the middle of the last century.

[HWHII]

The fire box in mine I made out of 1/4" stainless, measure up a Champion, and a triangle clinker braker that the point is up also. What you say is right about a smaller more managable fire.