[TheForge] Fanning the flames

Sun Dec 19 11:16:08 EST 2010

Thanks Bruce,
The layout and hinge arrangement was pretty much what I had in mind. I'm 
going to keep with the traditional shape  though. I like the way it 
looks, and perhaps I'm over thinking it, but I think it would allow 
better air flow not having "dead" corners.

The ribs I was referring to are not the stiffeners, but additional 
internal members with the same outside profile as the paddles. 3 
paddles, 2 ribs so it's Top paddle, rib, center paddle, rib, bottom 
paddle. The ribs help the leather fold in a controlled way, and provide 
some retention so they don't "puff out" too far.

Obviously you've put a lot of thought into the use of different 
materials for the sides. If naugahyde is the air-holding material, then 
if it cracks from flexing, I wouldn't expect it to hold up regardless of 
where in the "sandwich" it is positioned, unless the other materials 
reinforce it sufficiently that it doesn't crack. I'd also be afraid that 
making a sandwich might make it too inflexible.

I'm going to see if I can find a local tack shop that might do the 
leather work for me. Otherwise sewing the seams will be an unpleasant 
learning experience for me. "Blacksmith sides" of leather seem to be in 
the area of $100 on the internet. Actually it's the sewing that concerns 
me more than the expense.

 From what I've read, valve size is pretty important, and the two 
sources I've cited use different methods of securing the valves. One 
suggests leather hinges with a "keeper" to prevent them from flapping 
all the way over. The other suggests a flat piece of wood on two dowels 
(with a retainer), so the whole valve can be raised, but without any 
possibility of the valve flopping completely over. I kinda like the idea 
of the 2nd method.

If I do make these, I'll post photos of the process.

**paul

On 12/19/10 9:23 AM, Bruce Freeman wrote:
> Paul,
>
> I have had similar thoughts about building bellows.  The 3/4" plywood
> will probably work fine, though you might want to use hardwood plywood
> which, surprisingly, is often no more expensive than softwood plywood.
>
> If I were doing this, I'd shoot for two paddles per piece of plywood.
> Draw ~38" circles in opposite corners of the 4x8 sheet, connect them
> tangentially, and you've got most of the lay-out done.
>
> If appearance doesn't matter, consider using a non-traditional paddle
> shape.  Paddles can be square if you like (though you'll have to fold
> the leather like an accordion at the corners), or any shape you like.
>
> The chief problem in constructing the bellows is not the paddles and
> leather but the nozzle and it's associated block of wood, which must
> allow a good, long-lasting, freely-moving joint with the upper and
> lower paddle, and which must attach firmly to the center paddle.  Get
> that design right and you've got the problem licked.  Traditionally,
> the leather at this point was the hinge, but you might want to use
> steel hinges under the leather to ensure longevity and a good joint.
>
> By "ribs" I assume you mean the cross-pieces on the inner or outer
> side the paddles to strengthening the paddles cross-wise to the
> boards.  If you use plywood of sufficient strength, these would be
> ornamental only, and I don't understand why you'd make them of plywood
> anyway.  Do I misunderstand you?
>
> Naugahyde might work as the "leather," but I'd be concerned that it
> would be too weak.  (Also, you should find out what temperatures it
> can stand -- it might crack in the cold.)  I've thought about this a
> lot, but since I use a gas forge I've never gone beyond thinking.
> What you might do is use a double layer-- cotton "duck" or canvas
> combined with Naugahyde.  The cotton fabric is not completely
> air-tight, but it is very strong.  The Naugahyde is air-tight but not
> strong.  Problem is, the Naugahyde really should go INSIDE to hold the
> air -- which won't look right at all (if that matters).
>
> Alternatively, you could glue the two layers firmly together with the
> Naugahyde on the outside.  Another possibility is to use three layers
> - 4+mil polyethylene inside to hold the air, cotton fabric for
> strength, and Naugahyde outside for appearance.  With the plastic
> layer holding the air, gluing might be unnecessary --  though I'd be
> concerned about leakage between the upper and lower chambers.  Maybe
> you could spread the paddles, glue the plastic to the three paddles,
> then glue the canvas to the plastic over the three paddles, then nail
> the Naugahyde to the three paddles.  Similar problems exist at the
> nozzle end, but this will be wrapped with leather for strength anyway.
>
> Plastic capped roofing nails would be excellent for attaching the
> "leather" to the paddles.
> http://www.homedepot.com/h_d1/N-5yc1vZ1xgf/R-100122817/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
> or
> http://www.homedepot.com/h_d1/N-5yc1vZ1xgf/R-100210019/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
> but they won't look "authentic".  What you want is ~1" circles of
> tinned steel to drive the nails through.  Home Depot sells disks of
> galvanized steel, maybe 1.25" dia., but I can't find them in the
> on-line catalog.  Nailing the leather to the paddles is problematic
> when you use plywood, especially softwood plywood.  You might want to
> drill a small pilot hole for each nail.  Again, if authenticity
> doesn't matter, use construction adhesive instead of nails.  Or use
> construction adhesive, then use roofing nails.
>
> Keep us apprised and let us know how it turns out.
>
>
>
> On Sun, Dec 19, 2010 at 9:00 AM, Paul N<crosspein at sbcglobal.net>  wrote:
>> I'm thinking about building a double-lung bellows as a winter project.
>> (Actually 2 of them, one for myself, and a second to use as a working
>> facsimile at a historic site nearby)
>>
>> I have two references ("The Blacksmith, Ironworker and Farrier" by
>> Aldrean A. Watson, and "How to Make a Blacksmith's Bellow" by Robert M.
>> Heath) The designs are very similar, but not identical. These are big
>> boys, about 38" across, and probably 5' long.
>>
>> I'm wondering if anyone on the list has any advice to offer. I was going
>> to make the paddles and ribs out of 3/4" plywood instead of the 1"
>> planks described in the books. I'm also wondering if I can get by with a
>> naugahyde or similar sides to avoid the expense and maintenance of leather.
>>
>> I'm thinking that if the plywood isn't heavy enough to draw air, I can
>> hang some weight on the bottom paddle as needed. Similarly for the top
>> paddle. I can pile weight on top of it as necessary.
>>
>> This sounds workable, but I'm wondering if anyone tried this and found
>> it disappointing, or perhaps had a suggestion to offer.
>>
>> **Paul
>>
>>
>>
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