Door configuration question

[jmeineke]

I'm resuming work on a forge I started a while back and wanted to get some opinions on whether or not to use the ends that I cut off to make doors. I've seen several designs that have hinged doors on the ends and want to see what you all think.

For the back one, I was planning on just making it solid - no holes, just open or shut (and insulated) to accommodate long pieces. For the front, I've seen square holes cut out (and have heard that they don't last long), so I was thinking of doing the same with the front as I'm going to do with the back - just insulate it and leave it solid with the thought that I could use it to slow cool pieces; just shut the forge off and close the doors. So, the front door will be open all the time while forging and the back will be open or shut depending on what I'm working on.

Additional info:

Will be using two 3/4" burners
Length, 18.5"
Diameter, 10"
Plan on lining with 2" of Kaowool and using fire brick at the bottom; final ID should be around 6" making it in somewhere in the neighborhood of 520 cubic inches

[SoCal Dave]

You will lose a tremendous amount of heat by having the front door fully opened. With the door fully opened, It will be difficult for you to reach the upper temperature limits needed at times for forging. By having a smaller opening in the front door, you retain some of that heat and you must have an opening of some kind. Look at other models and look at the relationship of the door to the smaller opening. You should be able to figure out the right proportions for your forge. Good luck.

[pkrankow]

Put a small hole in the back door so long skinny stock can pass through. Make the hole convenient to plug with a firebrick, so measure your soft bricks. You can cut the soft brick in a manner that lets you have 2 or 3 opening sizes or fully closed.

Phil

[jmeineke]

Another thing I'd like feedback on is the size... I'm thinking I got a little too ambitious with this thing - 18.5" is going to cost a lot to run and to insulate. What's a good size for your average weekend warrior? I'm not going to me making swords or anything really long, so I'm thinking 12" might be a good number (Kaowool comes in 12" wide strips, so it makes sense to shoot for about that size).

Thoughts?

[SGensh]

I'll attempt to add a couple of photos of a fairly simple front door configuration I've been using on the small freon can furnaces I've been building. On my larger furnaces I like guillotine type doors.

This is basically just a half door which covers the top of the front opening of these small furnaces (opening is a bit more than 5" in diameter). The door is made of a piece of rigid refractory (Insboard here) held in place with two simple sheet metal parts which are screwed to the single hinge. If you copy this idea slice a groove in the board for the sheet metal flange with a hack saw or something similar so it doesn't split. If you don't have an easy source for rigid refractory you could sandwich ceramic fiber blanket over a sheet metal door instead to do the same thing. You may notice that the hinge pin is extended to provide a handle for opening and shutting the door. I like to use stainless for the handle since it has a fairly low heat transfer rate and you can operate it with a bare hand even after hours of operation. The door in the upper half of the opening relflects a lot of heat back into the forge which would otherwise escape while still allowing enough exhaust area for good burner efficiency. I just use a small opening in the back of these with a plug made of kaowool or such. The furnace in the photos is the test mule in my shop and has been running with the same uncoated lining and base brick since October of 2009. That's the third piece of door refractory in hundreds of hours of operation by several users.

You asked about furnace size so I will say that I was surprised to find that I use this tiny forge more than I use my larger two burner, it's just so practical and economical for a lot of work. I hope this helps. Steve G

(Glenn, I hope this post is OK as I do sell a few burners and forges and I don't want to violate the rules. Please feel free to delete it if I'm out of line. Thanks, Steve)