I am building a double-lung bellows from 2 x 10s, tongue-in-groove.  Over all dims are 48" x 34", length of top and bottom air chamber center of hinges is 40" x 34".  I am concerned one and one half inch thickness of the top leaf may be too heavy to rise properly.  I know this is a bit late now to think of this, but i would appreciate input on this from other experienced bellows builders. I used jointed 2 x 10 wood to stay authentic.

                                                                               thanks for your input,

                                                                                coachwhip24

Sounds like it should work ok... Just make sure that you have good airtight chambers and that you valves are at least 10x10 with good seals, and snap open and close.  

be a lot more work to pump, why not 3/4" T&G? I have never seen a 19th century one using boards that thick!  Can  you share the one(s) you are using as a model?

The design is not my own, rather a copy from memory of my father's bellows.  I have always used a canedy-otto blower on my forges.  I became feed up with these trinket making blacksmith associations and decided to start up a blacksmith club devoted to making useful tools and implements. No samurai swords, 2 foot long Bowie knives, and no pineapple handles nor key chains.  An authentic williamsburg or 18th century style forge, no power hammers.   I intend for each member to start out with a pile of scrap iron and forge a set of working tools.  So, I needed a set of large heavy bellows, hence the thicker wood.  

                                                                            coachwhip24

Coach ...,

Would a pulley work for lifting the top leaf?

Just a stray thought that might be out to tea.

Welcome aboard, you'll fit in just fine.

SLAG.

Slag: You lift the top leaf by pumping it up with the bottom leaf. The weight of the top leaf maintains a constant flow of air. When a harder blast is required you can put a weight on the top leaf.

Frosty The Lucky.

Frosty,

Gotcha. Thanks.

How about a lead boot?

SLAG.

If the top piece is made from 1.5" wood I doubt he will need more weight to push down on it unless his out flow orifice is too small. I was going to look up the one they build in De Re Metallica, mid 16th century, but my copy is out on loan right now.  I'll see what Moxon has to say about it this weekend.

I made mine from 3/4 based on commercially sold ones; it was in a Museum at the OKC fairground as I recall.  As for powerhammers they date to 700 years before Williamsburg; but not having water power available a team of trained strikers will take it's place.  Working alone is very ahistorical!

Agreed Thomas, 1.5" top leaf shouldn't need more weight and in fact need a way to reduce the blast. I've only ever used a bellows a couple times and they were made with 1"x or 3/4" plywood and supplied a nice blast. It's easy to increase the blast by continuing to pump once the top chamber is full, I was surprised that the increased blast continued for a little while after I quit pumping. I'm not sure what pressurized in the top lung, maybe the leather inflated like a balloon but it lasted a while.

I watched a fellow at a ren faire demo use too small a bellows, maybe 2" long and heart shaped. It didn't have the volume for a decent forge fire, puff up your fireplace sure but not a forge fire. The blast only lasted maybe 5 seconds once you stopped pumping and it only had a decent blast while you pumped.

I think bellows are an exception to the rule and bigger is better. Just bear in mind I'm a propane forge guy.

Frosty The Lucky.

Bellows are really a complex design to get the best out of them; further confused by the fact that almost any design will work somewhat.

My double lunged bellows could blow a billet welding fire to forge welding heat just using my pinkie, (did it for a bet once); a friend at a historical site used a double lunged bellows that ended up  with him needing shoulder replacement.

My best suggestion would be to try a number of both old and new versions and decide what works best and then create your design.  It's not hard to spline boards and of course with the modern routers/shapers you can do tongue and groove easily; but the old specialized planes still work!

Except for the size of it creating difficulties in transportation; I loved demoing with my double lunged bellows, the crowd is impressed and you could pump up the top chamber and turn and talk to the crowd while it slowly descended and kept the fire hot!