Designing a Solid Fuel / Gas Hybrid Forge

[Gundog48]

I've been wanting to build a new forge for a long time, my current one is very substantial, too substantial really! It's built inside of a large bus brake drum, with a 1" thick steel firepot and about 6" of refractory cement. It's really cumbersome to move around and doesn't really fit the bill. 

I want to switch to a simple 'tray' type forge as I've crudely drawn below. Angle iron rim with a 1/4" steel plate 'table' with a heavy steel firepot dropped in. I'm quite keen on using solid fuel as I find it quite versatile and would be great for my larger, decorative projects, plus the smell just makes me happy. Convenience is a big factor with these things though, as well as cleanliness. I hate those times where you need to leave the forge for a while and have the option of letting it burn out and relighting, or trying to keep it going and wasting fuel. I'm eager to do more knifemaking and similar small items too, so a gas forge would be really handy here.

What I'm thinking is of building a traditional solid fuel forge, with a removable refractory-lined 'tunnel' with a gas burner fitted. I would probably have a few locator pins in the forge table for the tunnel to drop into. I feel that this option would give me the versatility of being able to switch between solid fuel and gas, and also allows me to run on solid fuel with some added insulation, but having the ability to take it off to work with larger projects.

Has anyone tried something similar? The only problem I can really see is the lack of refractory lining on the forge table itself. I've never run a gas forge so don't know what level of insulation would be required. One option would be to line the forge table with insulation underneath the steel surface, or to slip a couple of fire bricks in when using it in that configuration.

Just to be crystal clear, I don't intend to use both gas and coke at the same time as I've seen discussed before, but to operate it in discrete gas or solid fuel configurations.

[Irondragon Forge ClayWorks]

In all probability, it would do neither fuel well. It would be better to build a separate propane forge and use the coal forge as the table when running it.

[Buzzkill]

I think I understand what you are attempting to do here, but I do not see the practicality of such a setup.  The floor definitely needs to be insulated when running your gas.  Typically the recommendation for the floor would be 2 layers of 1 inch thick 8 lb. density ceramic fiber blanket covered with about a half inch of insulating refractory material, such as Kastolite 30.

These materials would not likely hold up well with repeated use in a solid fuel forge, so that would mean you'd need to drop in your gas forge floor before installing the tunnel overhead.  Now you have to clean out the coal, coke, and ash away from the area so you can place the gas forge components somewhat level and avoid burning your solid fuel at the exhaust openings.  In addition you've got your gas source and hoses to deal with and the possibility that you'll knock your burner out of alignment while installing the tunnel and hooking things up.

Unless space is so limited that you can't build a separate small cart or table for your gas forge I think you'll find that in the long run a separate forge for each type of fuel is a far better option as IF&C has suggested. 

[ThomasPowers]

I know a bunch of smiths who use their coal forge as the "bench" to set their gas forge on.  No reason to try to force one forge's parameters on the other. If space is extremely limited; put a shelf under the coal forge to store the gas forge on between uses.

I use a propane grill cart for my propane forge's table, it was free. I junked the grill and put a sheet of 1/8" steel where the grill had been and set the propane forge on it.  Easy to move around as I made it easy to remove the propane forge it's easy to transport too.

[pnut]

Have you thought about  using a removable table top that fits in the rim of the forge table so you have a solid flat surface to set the gas forge on when you want to use it and set the removable table top against the wall and put the gasser under the solid fuel forge when you're done and your coal forge is ready to go again.

Pnut