Round or Square ?

D

dancalvin

Well-Known Member
Which forge shape is the easiest to heat up and maintain heat ? I've been playing around with some stacked firebrick and had mixed results . I was wondering if a round chamber would be more efficient .

Dan
 
A round chamber will be the most efficient, the most important thing it gives you is a good vortex of heat when angled into the curve of the forge, as apposed to your heat being shot into a solid wall with a square forge, it gives you even temp throughout the forge as apposed to a few hot spots in the square forge.
 
If your looking to use a forge for Bladesmithing purposes, round is the ONLY way to go. The main issue with an "angular" forge shape is burner placement....there simply is not way for a burner to enter the forge chamber that doesn't in one way or the other direct the flame at whatever work piece you put into the forge. This isn't a problem if all your doing is forging mild steels. However, with carbon/alloy steels it creates issues that many do not even realize....that being hot/cold spots, sometimes of several hundred degrees difference within a very small area. This is over simplifying it, but in essences you can literally way overheat one area of the steel, while an adjacent area is not heated enough. A forge of circular design, with the burner(s) set up at a tangent will provide a much more even and at the same time an "indirect" heat, which means "gentler". Often the differences of forging "straight" steels in a round versus square forge are not all that noticeable to the inexperienced Bladesmith, but as an individual gains experience and knowledge, the differences become evident. Those who started their Bladesmithing careers with forges of a circular design rarely understand the difference, but a person who started with a square shaped forge, then converted to a round design will often rave about how much better the round design is for Bladesmithing.
 
There are any numbers of things that will be a matter of taste for each smith, I see no sense in any of the vertical cylindrical designs, but users of them have issues with the horizontals that I favor, so everybody will have their own reasons a rationales for what they prefer. The one feature that cannot yield to alternate rationales or opinion is the fact that corners make cold spots, so not only do I totally agree with what has been said here, I believe the facts also totally support it. For most operations that we do with our steel choices even heating is most critical, with the only exception being localized heating for specific forging operations where one doesn't want to overheat thinner sections that are already forged, but this is dealt with by adjusting our forging techniques ans sequences when making the transition from coal to gas. With no concern for vortex action or even heating many square forge designs simply have the flame coming straight in and directly onto the work- this is a no no for blade forging, avoid any design that has the flame blasting directly onto the side of your blade.

All gas forges should work off reflective or conductive energy, the flame does not do the heating of the blade, the flame heats the walls and either has it reflected to the center (wool line forges) or conducts it to the center (hard refractory lined forges). It should be immediately obvious that a cylinder will send this heat back to the center in the most even fashion. A flame entering on a tangent and creating a vortex around those outer walls will increase this effect even more, thus my strong preference for a design that allows me to pass the steel down the center of that vortex instead of through the side of it.

In short, I know - too late, you can bank on what Thunter and Ed have told you and add my vote to the count.
 
I have been reading this post with some interest , I have several forges gas, coal , a round one and a square one and a flat pan forge with crank blower. Once my forge gets to welding temp I see no major difference in thier ability to heat. Once the doors are closed on my forges there are no cold spots, I believe there may be some minor diff. but, not enough to make any great difference in my opinion. I also heat with coke and I lay my swords and knives right on the coal s and flame ??. The key to even heating is to keep your blade moving . Another thought I had was , I have been to a few steel mills and have never seen a round forge , they are all big square boxes ? Fellas I am not disputing your experience , I just have had some different experiences . I was traditionally trained in japan as a young whipper snapper of 17 . I was taught to put blades directly in the flame and coals . My gas forge runs at 20 psi and gets to forging temp in about 5-6 min. My round forge does vortex the flame but I fail to see any advantage ? once you get to 2000 or so degrees . Mainly what my interest is , in the various forging techniques some smiths use . One thing I do agree , I always heat my steel edge up , in the flame and then flip it to heat the spine . Never directly on the side of blade and always keep it moving . I really dont have a problem with hot or cold spots , I work in the early evening so I can see any uneven heating spots on blade .I Dont use any heat sensing equipment I go by color and magnetism the old fashioned way ... Thanks for the interesting and thought provoking post . Bubba-san
 
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My square chambered " stack " of firebrick seems to be functional . But , as with most things I build , it will be evolving until I get where I like with the operation . I plan to build a round chamber soon , to tinker with .
When I get back to full speed in the shop , I will report back , with results
 
My experience is only limited to my square NC Tool "Knifemaker" forge and my charcoal forge but I have had no problems with either in getting the temps and results I want. I have never used a round Gas forge so take my comments for what they are worth. Square works for me. Besides, it was a birthday gift from my Wife a few years back so I dare not say that it doesnt work.
 
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