Box Bellows size recommendations

[Michii]

Hey guys!

My first ever post in this forum, so hello to all you awesome people!

So, I want to make a simple box bellows for a Jabod forge, and I'd like the blower to be as compact as possible. However, I'm not sure how compact I can make it while still having enough power to reach welding temperature. So far, I have already designed something I like, inspired by some YouTubers, with dimensions of 50cm x 22cm x 20cm. I assume this might be too small?

Also, what coal should I buy to get started? Is there something you guys would recommend for newbies?

[JHCC]

Welcome!

There have been a couple of good discussions of box bellows on the forum already, such as THIS ONE and THIS ONE.

One of the other sources I've seen for a classic Japanese fuigo gives dimensions of approximately 36"/90cm long x 12"/30cm wide x 20"/50cm high. Given the substantially larger cross-section, that bellows would be moving over three times the volume of air for the same distance of pusher travel as yours. 

Of course, how large or small your forge and bellows are depends greatly on what you plan to forge. Are we talking about welding 8mm square for basket twists, 30cm round bar for ship anchors, or something in between?

[Michii]

Hey JHCC, thanks for the answer!

To the question of what I want to do with it, for the start, just small stuff to get a feeling for blacksmithing. I'm really interested in knifemaking, like most new people to blacksmithing lol, but I know that's something I can do properly just do when I already have some experience with blacksmithing. So, as for now, I just want to try to make some simple stuff like hooks, a bottle opener,  fire poker, and so on.

 

This is btw the design im going for, like from the youtube channel "Mr. Chickadee" 

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[Frosty]

Welcome aboard Michii, glad to have you. 

When asked what size stock you want to heat, saying small is too vague, small for me and small for the Bremerton Navy yards are tons apart. Large as in an aircraft carrier anchor or small like a 40' sloop? 

It is MUCH easier to offer you useful suggestions if we have a better handle on size, 8mm, 12mm, 25mm. all carry a world of good info. When burning coal or even charcoal I forge welded 12mm and smaller with a fire the size of my fist and smaller and 25mm. + in a fire the size of the one in your pic above.

What you wish to burn makes a big difference, not only how Much air but how fast the blast is. Coke REQUIRES a pretty strong nearly continuous blast, where coal might require a pretty fast blast if it's broken too finely. Charcoal likes a gentle blast, not a lot of air and definitely not fast. 

With a little tinkering you can build a charcoal forge that draws it's own blast so you don't need a bellows of any kind. You do in fact need a valve to control it. 

Frosty The Lucky.

[Michii]

Hey Frosty, thanks for your answer, i think up to 30mm would be a good start for me.

[Frosty]

Uh HUH. Pick up some small pieces of 30mm. to see how much work is involved in moving that much steel. I usually start guys out on 3/8" or 10mm or if they're bruisers 12mm.

If you start out trying to work heavy stock or with heavy hammers there's a much better chance you'll give it up as too hard and painful. Starting with small stock lets you develop hammer control and the necessary muscles while you learn how to get steel to do what you want. Lighter stock moves faster and easier so you get to learn the basic lessons faster and failures cost less.

Hmmmm?

Frosty The Lucky.

[Michii]

Thanks for the help Frosty, then i will probably stay with the compact blower and try to weld some 10mm pieces for the start ^^

[Frosty]

Something to think about before deciding on the small bellows. You can always push slowly if you want just a little air from large bellows but it's a LOT of work to push little bellows fast enough to get lots of air out of it.

Frosty The Lucky.

[JHCC]

Frosty's last piece of advice is well worth keeping in mind. Remember also that there's not much difference in the amount of work involved in making a small, medium, or large box bellows, just in the size of the pieces. In your situation, I would go with something along the size of the box in the Mr. Chickadee video.

Remember also that you can substantially improve the performance of your bellows by (1) minimizing air leaks and (2) making the mechanism as easy to operate as possible. Any air that escapes around the edges of the plunger or through the joints in the box or the tuyere is air that's not going into the fire. Any effort that goes into overcoming friction or inertia is effort that's not going into moving air. Make sure that all the joints are tight, that the valves move easily and seal effectively, that the working surfaces of the inside of the box are as smooth as possible, and that the plunger can move freely without losing too much air around the edges. I gather that the original Japanese versions have the edges of the plunger wrapped in fur, and I've heard tell of modern versions that incorporate a gasket of innertube rubber.

[Michii]

Thank you very much guys, i'll keep that in mind!

[Irondragon Forge ClayWorks]

Also adding a little lube, like bees or candle wax to all sliding area's helps in sealing and reduces friction.

I can't control the wind, all I can do is adjust my sail’s.
Semper Paratus

 

[Frosty]

You could put the piston on rollers and tack a leather "skirt" around it to seal on the blast stroke. If the "skirt" opens enough for air to pass on the back stroke you won't have to make a flap valve to do that job. Hmmmm?

A forces air source (blast) is probably the simplest thing to make in the whole craft, an old pillow case makes a great sack bellows. An open ended bucket and a pond makes a terrific bellows. Hang it open end down with a flap valve in the closed end so air can flow in and one at the end of the tuyere so it doesn't draw fire and hot gasses back into the hose and you're golden. Enlarge that to a 55gl. drum with weights and you have a continuous blast a couple few minutes long, need more? add more weight.

You can have the neighborhood kids wave fans at a funnel shaped collector connected to the tuyere or like I did on the Resurrection River aim the collector into the wind. 

Making air is easier than you'd believe.

Frosty The Lucky.