First time forge build

[Cyp]

Hello!

First off, I am little more than a complete beginner with 20-30 hrs at an anvil between two classes this year. I certainly have much to learn.

With that said, I am in the process of building myself a forge. I am using Wayne’s propane forge design with a forced air burner. I intend to begin forging tools to satisfy my tool acquisition syndrome and enable my hobbies. I plan to begin with tongs, chisels, gouges and drawknives but I also would like to be able to make hardy tools, hatchets, hammers, etc. 

I have materials and supplies on order including 20# kast o lite 30, 8# ceramic blanket 1”thick, fumed silica, and matrikote. 
 

I plan to use a 5 gal air tank (slightly smaller than a 20# propane tank) as the forge body that is approximately 10” in diameter and 24” long. Using the basic guidelines for lining it, I expect my forge volume to be roughly between 450 and 550 cu in with the ability to increase that volume based on Wayne’s hinged body design. As far as the forge body is concerned, I have so far only cut it in two along it’s length. 
 

As far as the burner goes, I have made a ribbon burner using John Emmerling’s design. I followed the directions on Wayne’s site with some deviation. Using 3” square tube, I cut a length to 8”. The home store I bought black pipe from did not have 2”, so I used 1 1/4” instead. When it came time to mix the mizzou, there were conflicting instructions between the manufacturer and Mr. Emmerling. Foolishly, I chose to follow the manufacturers instructions. This made for a very dry mix that is not appropriate for making a ribbon burner. As you can see from the attached pictures, there is a gap between the castable and the body. Luckily, I have plenty of mizzou to make another cast. 
 

I would still like to use forced air on this forge, mostly because I have already purchased the blower to do so...but I have some questions that I have not been able to find reliable answers to.

How critical to the function of the FARB is the larger pipe? Is there a reason I should not use smaller pipe?

How critical to the function of the FARB is the inside baffle? It seems there are conflicting opinions on whether it is necessary.

Since I have to redo the casting anyway, could I get away with an even smaller ribbon burner? Maybe 4 or 5”?

Is it unwise to use a simpler design for a blown burner? Not that I am unwilling to cast a new burner, but in a small forge, could I get away with a straight pipe? Would a baffle be necessary on a straight pipe?

I appreciate any input!

Cyp

[Latticino]

A couple of quick points that may be of help:

• Before recasting I would look into use of refractory cement to close up those small gaps.  If you are careful about differential thermal expansion in that area (avoiding rapid changes in temperature) it should work.
• Mixture pipe size for a forced air burner is not as important as for a naturally aspirated one.  You just need to have sufficient gas and air pressure to overcome the added pipe friction.  If using bottled propane the gas pressure shouldn't be an issue.  The air pressure available is dependent on the blower you selected.  I recently switched to a much larger high pressure blower and see significant improvement in heat output.
• A 20" forge interior is quite long for a gas forge.  Your forge will be quite long and narrow, perfect application for a ribbon burner, but you will likely want a longer burner than typical, not a shorter one.  I used the same type of air tank for my current FAB gas forge, but cut out around 6 inches (wish I had cut away more).  I have a single 1 1/2" burner on mine and get up to forge welding temperatures (but I use an unusual system with residential pressure natural gas and a commercial mixer/regulator).
• Your Mizzou mixture doesn't look that bad, possibly not packed down well enough during the casting process.

[Cyp]

I double checked my tape measure skills, the forge body is only 16”. I plan to cast refractory proud of the steel opening, so this would probably put me closer to 300 cu in forge volume.
 

I thought about refractory cement/mortar to patch the burner. When I cast this one, I used 4# of mizzou. I put 3# into the mold, and 1# into the burner body and flipped it onto the mold. Tapped it well to settle and left it. The castable seems well attached to the body, but I’m not confident it will stay that way. 
 

I have the medium blower from Blacksmith’s  Depot. I’m not sure of the pressure, but the volume says up to 125 cfm. 
 

If I understand correctly, your burner end is just 1 1/2” pipe?

[Latticino]

Essentially yes, but it is actually a 1.5" pipe size heavy wall stainless steel flame retention burner head originally manufactured by Eclipse (I believe):

Note: the 125 CFM blower is the one I originally used in my setup, which was upgraded to a larger blower recently.  It may still work for you, but take care with your air ducting.