Super sucker or half hood for large plate?

[Nick]

I just tore down my old overhead hood, which didn't draw well at all, and am planning a new wider chimney.  One thing I haven't decided yet is if I should make a super sucker or a half hood.  I learned how to smith on a forge with a half hood, and it never seemed to have any problems though it had an industrial forced draft.

 

My chimney will be 12" dia., going straight up about 18'-20' to clear the ridge line.  I have considered a side draft in the past, but have never built one due to one concern.  I sometimes work large sheets of steel, as big as 2' in diameter, and when heating the middle I don't want the box to get in the way, and I'm worried that the smoke under the plate will billow out away from the chimney and into the shop.  With a half-hood it seems like I'd have a bit more horizontal room around the firepot and some smoke could be trapped by the top of it. 

 

Am I correct in how a super sucker would work with these large plates?  Or would the space and potential draft be enough?  Either way I'll have to rivet instead of weld since I don't have a welder right now. 

[Frosty]

Interesting problem Nick. I'm sure it can be done but I'll have to give it some thought. I've never been happy with the way overhead hood draw and have been really impressed with sidedrafts. I have a couple ideas but need to think them through a bit.

 

Frosty The Lucky.

[Charles R. Stevens]

Break out the helments and dig in, Frosty's a think'n!
Sorry I couldn't resist :-D As always, said with love and respect
Frosty, dosnt Brian just use a 10" duct about a 18" off and a foot to the side of the fire pot? Most of the 12" stacks move a lot of air, even if the smoke comes out the sides under the plate, most would find its way up the stack.

[Nick]

Frosty, dosnt Brian just use a 10" duct about a 18" off and a foot to the side of the fire pot? Most of the 12" stacks move a lot of air, even if the smoke comes out the sides under the plate, most would find its way up the stack.

 

There's this set up at Cahas Mountain Forge with a stack right over the fire with a very small hood.  It would certainly be simple to make, but it would have to be positioned at the right height to not be in line-of-sight.  I don't want to have to stoop down to see into the forge.  Do you have a photo of Brian's chimney?

[David Gaddis]

I posted some side draft pics a while back...very interesting for those who have never seen a side draft work.


Carry on

[Nick]

David, looking at this photo you posted, it looks like the side draft will take out the smoke well enough.  But there's the other concern, would you be able to heat the center of that plate?  The super sucker does seem to have a bit more room around the firepot since it's angled over it.

[Charles R. Stevens]

Afraid not, just remember Brian Brazeal mentioning it in a hood descusion thread. Might try PMing him. BrianBrazealBlacksmith.

[JNewman]

I actually replaced my side draft with an overhead hood a couple of years ago so I could have access to all 4 sides.  But when I used the side draft I didn't have problems with my side draft and heating plate,  It was about 8-10" from the center of the firepot.   I did have a hinged shelf of 1/4" plate that hung down from the front of the hood about 16" above the fire to help direct the smoke up the hood.  It was also very nice to have as it helped protect me from the heat of the forge as well as a place to stick material ready to go in the fire.  I think the shelf would have allowed me to move the hood a little further  away if necessary.  If I needed the height above the forge I could swing it up out of the way or even remove it as the hinges were gudgeons and  pintles. 

[kubiack]

I don't see why you could not have a small cut out in the sides of your side draft hood where you could pass the plate through. For that matter what about a side draft hood without a bottom. You could just pile some extra fuel along the bottom outside edges which you could remove when heating plate. With that much chimney I don't think having a little extra open space along the bottom is going to be a problem.

[ThomasPowers]

How about a side draft that mounts from the ceiling and leaves a couple inchs between the bottom of it and the top of the forge table. (or one where you could raise the bottom piece up a bit.)

[petere76]

Nick,

I'm using a 10 inch uptake with a super sucker design . No problem with smoking. 12in should give you some serious draft if its designed right.

All the direct overhead vent systems I see in service have issues with smoking when the stack is not hot or the shop is tight. The sucker designs usually involve a size reduction at the throat opening, I.e. 12 to 10 or 10 to 8, the reduction creates a venturi effect, hence the term super sucker. Most of the direct vent overhead hood designs have side panels and a few older rigs I have seen lower and raise. The modern overhead systems use mechanical ventilation to get the job done. This one shop that was quite cold in the winter, was almost impossible to keep smoke free. You went home coughing for a few days. Try the solid fuel forge section of IFI, they used to have some good photos of different designs.

Peter

[petere76]

Nick,

I'm using a 10 inch uptake with a super sucker design . No problem with smoking. 12in should give you some serious draft if its designed right.

All the direct overhead vent systems I see in service have issues with smoking when the stack is not hot or the shop is tight. The sucker designs usually involve a size reduction at the throat opening, I.e. 12 to 10 or 10 to 8, the reduction creates a venturi effect, hence the term super sucker. Most of the direct vent overhead hood designs have side panels and a few older rigs I have seen lower and raise. The modern overhead systems use mechanical ventilation to get the job done. This one shop that was quite cold in the winter, was almost impossible to keep smoke free. You went home coughing for a few days. Try the solid fuel forge section of IFI, they used to have some good photos of different designs.

Peter

[Nick]

Thanks for all the input.  After looking at a bunch of side drafts and hoods, I think I will be building a super sucker, but not yet.  I've decided that I'll wait to build any side draft until I get a welder in my shop, I'm sure I can build one by riveting but I think I can do a better job with welding, especially the top collar.  For now I'll build a small hood (haven't decided exactly how I'll shape it yet), but I can replace it easy enough.  If I need more space once I do get a side draft I can just fire up a portable forge and use it until the piece is shaped enough that I can use it on the main forge.

[David Gaddis]

There has been several statements about a tight shop and smoking. What is being said has to do with "make-up" air. That is the air that fuels the flame/heat. If your shop is not allowing in fresh air to feed the fire then nothing is going to work properly. It is a matter of physics. There must be a renewed amount of air to fuel the fire, then any type chimney might be able to work.

 

A side draft does not require a venture ...but may work better with one. To "prime" a chimney, ie. start it to drawing upward, some people must burn a paper bag or similar object inside the chimney. An almost instantaneous gush of updraft is felt as the drawing effect is operational.

 

I do not have a supersucker but a sidedraft. If redoing my project I would like to have my sidedraft a few inches above my forge so that I could easily work a plate under the edge of the sidedraft. And YES I would highly suggest a sidedraft if: 1) Chimney support may be a problem 2)Overhead access is a problem 3)looking across the forge would be a problem because of low straight tube chimney like Brian Brazeal has. And BTW...Brian does not have a chimney on all his forges, while we all know that his forges get a very good workout without complaints from users. That should be a situation to consider too.

 

 

Cary on

[Nick]

Replacing the air in my shop isn't a problem.  It's in a walled-off bay in an old barn on the property, and I can see daylight between most of the wall boards.  I'm going to close some of the cracks and make the ceiling a little tighter, to better hold the heat in the winter, but it will still be quite open. 

[Frosty]

The biggest problem I see trying to get a stack to draw smoke generated UNDER a large piece of plate is channelizing the draw. Left to it's own devices the smoke is goig to escape all round the plate and a stack is only going to draw from one location but the draw will be 360* around it. Yeah, that' barely makes sense to me and I know what I wanted to say. Sorry.

 

Lets say we can see the air being drawn into a stack, whatever kind it is, The stack produces a low pressure zone so air is drawn to it. Without channelizing the draw is 360* in 3D, a sphere. Typically a side draft works better because the opening is smaller so the velocity of the draft is higher. A hooded stack is drawing from a much larger area so the overall velocity is much lower, except where the hood joins the stack.

 

Get smoke evacuated from under a plate means you either have to make a strong enough draft to draw equally from the entire perimeter and this includes the volume UNDER the plate. I can think of a couple possible method: #1, build a screen that wraps around the entire plate from the floor up and has one small gap where the stack can be connected. There will have to be gaps so make up air can enter the screen deflector so the stack will draw. Call that Channelization plan (1)

 

#2 doesn't sound so good to me but. . . Perhaps branching the stack so several side draft inlets can be placed around the edges? Yeah, I odn't think much of it either. <sigh>

 

That's about all I have right now, in the back when one of my jobs in a welding shop was torching plate. We'd lay one of the sacrificial sheets of thin stock on the floor, lay 4x4s on it and lay the plate on the 4x4s. Then mark the plate and I got to spend time on my knees torching. Well, smoke would sometimes billow out from under the plate and the only way to control it was to lay the exhaust hose at one end and set up a window fan at the other. the 4x4s made a relatively confined channel and the forced draft from the fan blew the smoke to the exhaust hose. It still smoked but that made it tolerable.

 

Sorry Charles, not much of a brainstorming session, you can put your helmet away. . . For now. <grin>

 

Frosty The Lucky.

[MLMartin]

For smoke removal while working plate.

 

Is your forge right next to a wall? If yes then what about installing a low pressure exhaust fan maybe 18" - 24" size right through the wall and then placing a fan on the opposite side of the room pointing in the same direction. This would help push all the smoke that billows from around the large plate in one direction and out of the building. You could use a exhaust fan with louvers so it could be closed while not in use.

 

I would still recommend a super sucker hood for normal work that fits in the fire pot. I have one and it works great. I used Stainless steel and 12" duct straight through the roof. My super sucker is hanging from the ceiling by the duct. It just sits right behind the fire pot and floats about 4" off the forge table.