Double (not Great) bellows

[Archie Zietman]

Okay, I think I have figured out a design, thinking along the same seesaw pronciples. I'll just draw it up and then post it.

Here is the design, hopefully it makes sense.

[Wayne]

I use a pair of single action bellows when I am doing my medieval demonstrations, what I have found so far roughly runs as follows - two single action bellows worked by hand from the rear are good for Roman and Dark age.
Two single action bellows operated by the crank mechanism are good for medieval and upto about 1550 period when you start to get illustrations of double action bellows from german illustrations.
For VERY late medieval - early Tudor the book De Re Metallica by Agricola has very good instructions and sketches of the construction of single action bellows.
On my own set up the bellows are weighted with stones with the bellows furthest away from me being just slightly heavier to help on the up stroke of the lever.
The main pivot bar of the crank has to be angled - higher at the back than the front, I will have to measure mine as I cannot remember if the angle of the bar matches the angle of the top board of the bellows when they are half inflated or fully inflated, this angle is needed because of the twisting effect you get as the crank pivots.
I original thought this angle was only shown by the artist in an attempt to show as much detail as possible, but I found out the hard way it really is needed.
If I can figure out or someone can point out how to post pictures I will send some of my set up.

[Nick]

Wayne, I'd love to see pictures of the setup! Do you have a digital camera or know someone who does and can upload them? If so, and the pictures are on your computer, click the "manage attachements" button below the reply window and you can load the picture. Otherwise, upload it to Photobucket and you can then post the URL here (posting it with [img]pictureURL[/img] will post the picture here directly.)

[Wayne]

Ok,
If this works,, here is a shot of my medieval forge. With this set up I can cover most of the middle ages, by attaching my double action bellows I can cover from mid 1500's through to 1800's and by replacing the woden set up with my metal set up I can cover the Victorian to almost the present day.

[Wayne]

Oop's,
Not quite right but you should see what I mean

[jake2431]

If I'm not mistaken, Wayne, that first image is exactly what Nick is looking for, and what is pretty much happening in the medieval artwork.

[Nick]

Wayne, that's exactly what I've been looking for, thank you! When you said the pivot bar has to be angled, are you refering to the bar I've marked in blue? Also, if that's the case, is the pump lever attached to the crossbar and the pivot bar, or is it just resting on the pivot bar?

What's the bronze colored thing on top of the bellows nozzle? Is it just a weight to keep things from shifting? What kind of valves do the bellows have, and do you get a continuous airflow or puffs?

Lots of questions, but this is the first time I've seen this kind of setup recreated!

[jake2431]

Very cool! I can't wait to understand exactly what is going on as well.

[Wayne]

Hi nick,
Thats right, I call it the pivot bar as every thing runs off of it.
The pivot, crossbar and lever are all fixed - imagine a crucifix with one end of the pump lever attached just short of the right arm. You then cross the lever over the pivot until the handle is in a comfortable position for you and then it is fixed where crosses. On my early version I used to lash it in place but it has a tendency to work loose as the day progresses so now I fix it in place with screws sunk in and the hole closed with a small dowel pin to hide it.
On the underside of each bellow there is a hole about 4'' square. this hole is closed with a square of plywood about 6''square, on the underside of the plywood I have glued suede leather which has about a 7'' square and this helps to seal the hole.The hinges for the flaps are leather also.
There is a flap of suede leather pinned to the top of the bellows where the air comes out - it is hidden inside the metal cones and is there as a precaution which so far has not been needed. to give you an idea of scale the bellows without counting the metal nozzles or the small handle where the ropes attach are 40''long 18'' at the widest point and open up to 20'' if I made any more I would probably make them slightly longer and deeper but not wider to give me a slightly larger air flow, with a little practice you can get a near continous air flow going with the air stopping only as long as it takes to change the stroke.
This forge will happily handle up to 1''square and will burn charcoal,coal or coke without problems and I can fire weld on it.
To hold the bellows to the frame there are metal brackets on the frame under which the bellows sit on - two under each bellows and I put a couple of screws into the underside of the bellows to fix them - not terribly authentic but the public cannot see them.
All of the frame is held together by mortice joints and knock out pegs.
Remove the coals, lift out the fire pot and the floor tiles lining it ( a friend is a potter and makes copies of medieval floor tiles) just a single layer suffice for me .
Lift out the metal sheet the firepot sits on - this in turn sits on four pieces of angle iron around the edges of the frame.Lift off the hood, knock out the pegs and it all the forge and frame breaks down.1 front,2 sides,1back, 2 bellows supports,2 cross braces for same,1 rear frame,1hood and 1 pivot/crank.
The wattle and daub effect is what you guys call hybrid adobe or papercrete -70 parts pulped paper,10 parts sand,10 parts soil and 10 parts cement ( the measurements do not have to be exact) there are several sites that tell you how to make it. Put it onto the frame and let it dry, it is flexible, fire retardent,waterproof and (fairly) light weight. The unfinished hood is deliberate it shows the public the construction and helps dissipate the heat away form the canvas.
The bronze coloured thing is actually my medieval drinking mug.
I hope this helps
Wayne

[Wayne]

Nick,
Forgot to mention, if you are coming over to leeds and plan to hit the royal armouries give them a call first as tucked out of sight they have a first rate reference library which is or at least was when I last went open to the public ( but they tend not to tell people this fact), but you would need to find out the opening times and days. They also have a photocopier there and for the price of the paper are not to adverse to assorted tomes falling on to it.