Side vs bottom blast

[Stash]

I met a guy at this past weekend's PABA meeting who swears by his side blast, after starting with bottom blast. I'm currently using a bottom blast rivet forge and am on the lookout (as always) for a newer and betterer tool. I've seen lotsa great ideas for the bottom style and how to fab it up, but this guy had some convincing reasons for making the switch.

I'm not going to open a can of worms about which is better, but am curious about pros and cons, as well as personal experiences.

Thanks

Steve

[brianbrazealblacksmith]

I've used them both and like them both.

[John B]

Hi Stash, I am sure this has been well discussed before on the site, however there are points for and against both styles.

A lot depends on the use you are going to put it to, fuel being used, air source, portability required for shows or demo's, how long your intensive forging sessions are going to take, the design of the hearth/forge itself, and do you have a readily accessible water supply.

Personally I use both types regularly and there is little to choose between the two for performance. It's a "Horses for courses" situation, and what is best for the situation/jobs requirements.

In a side blown, by approaching the forge from the side, you get a longish heat, and if you want to upset the end, you can just approach from the front for a short heat on the stock's end.

The clinker gathers below the tue's airblast and can be easily removed when necessary.

If you go into the technicalities of oxidising, neutral and carburising areas, it is probably easier to locate these areas in a side blown set up.

The main drawback to the side blown is that the front of the tue is subject to very high temperatures (particularly when using coke) and that it will erode unless the tue is cooled by the use of circulating water which necessitates the use of a water tank/combined tuyere. (Not always practical especially at off home site demo's)

This also means the hearth has a bigger footprint/area required in the workshop, if space is at a premium, a major issue.

The bottom blown hearth has the clinker forming over the air supply holes,

The depth and design of the hearth will determine how difficult this makes the clinker to be removed without breaking it up and contaminating the working fire.

Bottom blown do not have much of a problem with erosion of the face due to the heat generated being above the base of the firepot.

The depth and shape of the firepot in a bottom blown hearth also determines how easy it is to remove the clinker, and the type of work that is best suited to the specific design.

On a personal note, I have a 16" square bottom blown hearth, and it will, if required, perform as well on up to 2" Square bar as a 3 foot square side blown or bottom blown, it just has to have the fuel fed in more frequently.


My advice would be to try both and make your own mind up as to which you prefer, you can have more than one hearth, so at least one of each is an option.

Generally speaking side blown water cooled take longer to make and are more expensive than a bottom blown one if you have to purchase materials.

A well made one of either type will give many years of professional use service, if you do not have a water cooled tue on a side blast, it will need sacrificial tuyeres and they can be eroded quite quickly even using coal or charcoal and a hand cranked blower

[NecroSteel]

The main drawback to the side blown is that the front of the tue is subject to very high temperatures (particularly when using coke) and that it will erode unless the tue is cooled by the use of circulating water which necessitates the use of a water tank/combined tuyere. (Not always practical especially at off home site demo's)

Hey John,

You mention that without water cooling the side blast with 'erode'. I've seen side blast (at Vaughans) that doesn't seem to have a water tank and it looks like they sell replacement Tues. How long would the Tue last without cooling do you think and what are the signs\symptoms of the Tue eroding?

N

[John B]

It depends on what fuel you are using, what type of work you will be doing, and how often you use it, so it is difficult to say how long one will last before needing replacement. It could be a matter of weeks, or years depending on how it is used.

Some years ago I used to use a dry tue in a hand cranked (Alldays and Onions)forge, some over enthusiastic person kept on cranking it all day (It was using coal at the time) and a good inch+ was eroded/burnt away from the front face.

Depending on the tue castings internal profile it should work until the hole at the front burns away until the larger cored diameter at the rear is reached when the diameter rapidly increases and this will affect the fires efficiency and it will also be approaching the rear of the hearth,

If you are using coke, I would go for either the bottom blast or a water cooled tuyere, if you have used both types, you may favour one more than the other.

[jonathan king]

Hi Stash
John b is spot on with what he says about the solid sideblast tue iron you should have a look at his bottom blown forge, john sent me some plans its a great forge and is very simular to my bottom blown forge which i use daily as im a full time blacksmith but with a limited space. I would recomend only a water cooled tue iron or a bottom blown forge.
It means you don't have to keep spending money on cast tue irons which are not cheap.

[NecroSteel]

Hey,

I've had a response from Vaughans with regards to how long they would expect their non-water cooled side blast forges to last. They have said that ".. as long as the fire is built correct (eg. 4 - 6" away from the Tue Iron) it should last 2 years+. ".. SO...heck...

The only bottom blast I've used was one that didn't have a deep fire pot so the iron was pushed into a coke heap about level with the general base of the forge, with a bottom blast do you only get forge welding heat inside the fire pot or will you get it higher up?

[John B]

I have yet to build a fire in a side blast forge that stays 4" to 6" away from the front of the tue iron, especially when using coke, what does your experience with them tell you? And was the 2 years quoted quantified? Coke or coal being used for fuel?, and how many hours of forging per day,week or month? and do you want to spend money regularly replacing them? They will wear out, far quicker than the alternatives.

Forge welding in a bottom blast is above and beyond the base of the pot, and thee hearth's table, it depends on the fire's height, and the airflow.
Shallow pots can be welded in as can deeper pots, its how you use them, and how you build your fire.

[jonathan king]

stash all i can say is that my bottom blast forge grate/plate has been in seven years in regular daily use and there is no sign of it burning away plus it will only cost me about £4 to replace. so i wouldn't spend all your money until you try out a few other options. all the best.

[youngdylan]

I've had a response from Vaughans with regards to how long they would expect their non-water cooled side blast forges to last. They have said that ".. as long as the fire is built correct (eg. 4 - 6" away from the Tue Iron) it should last 2 years+. ".. SO...heck...

Somebody want to tell me how on earth to do that. I'm a gas man myself but did rig up a coke forge. I experiemented with a sideblast with a tuyere made from solid 75mm with a 1" hole bored through. Only lasted a week or so. Made a water cooled side blast; lasted years, still going strong now but I much prefer using oxy-propane torch/gas forge/ induction heater to solid fuel.

[son_of_bluegrass]

I've got a non-cooled side blast. It used to be a Weber charcoal grill. I drilled a hole in the side for the pipe and lined the insides with wood ash. The pipe burned back to the ash insulation and has held there for a few years now. I started burning charcoal and since I now have some coal I burn that. The coal produces more clinker which can congeal on the pipe.

ron

[Ramsberg]

I remember reading somewhere that a tuyere constructed of copper without water cooling is supposed to greatly outlast one consructed of steel or cast iron.

It makes sense to me, copper has a rate of conduction around 10 times that of steel(depending on the steel) and reflects almost all of the radiant heat, where as the steel absorbs it, especially if it is oxidized.

Thinking about it I believe that the heat with a copper tuyere is conducted down its length back towards the air entry, which part is cooled by the air flowing in and a natural convection from the outside air.

Anyone out there ever seen a copper tuyere?

Because of the cost of copper I have a feeling that they are very rare.

Having said that I have only used a bottom blast forge, but have always been fond of the idea of a side blast.

Has anyone ever seen a shop with both a side and bottom blast in the same shop? It would be ineresting to try them truly back to back.

Caleb Ramsby

[Conrad Hodson]

I've got a non-cooled side blast. It used to be a Weber charcoal grill. I drilled a hole in the side for the pipe and lined the insides with wood ash. The pipe burned back to the ash insulation and has held there for a few years now. I started burning charcoal and since I now have some coal I burn that. The coal produces more clinker which can congeal on the pipe.

ron

In the designs I've used, erosion of the tuyere isn't a real-world problem. By which I mean, takes a long time to happen, costs nothing to fix when it does. But then, my forges have all been homemade, so there hasn't been any BS about proprietary parts or precision fits.

My first forge uses a thick-walled 3 inch steel pipe that runs crossways through an oil drum. Sand and dirt were shoveled into the drum and packed tight, until they were halfway up the side of the pipe. I drilled some 3/8 holes in a cluster of seven to make a grate in the middle of the pipe. Then I made a form in the shape of an inverted pyramid (just about the size and shape of the top of a concrete pier block), greased it well, and rigged a temporary frame of scrap wood to hold it in place. I poured refractory concrete (which cost way too much money but I didn't have a place I could dig fireclay back then) up to the height I wanted for a forge top.

This forge has lasted me 34 years, and the grate finally burned out last year--all the holes started burning together into one. I took a small rectangle of 1/8 plate, hammered into a arch to fit a piece of pipe the size of the tuyere, and drilled some more holes in it. Then I just cleaned the forge out well, and set the plate in the bottom flush with the original pipe. I didn't secure it in any way, but it hasn't shifted and the forge works as well as ever.

Two years ago I made a portable side draft forge for events. I bought five fairly thin, flat firebricks from a building supply, 2-3 bucks apiece. Two are flat and form the floor of the hearth, two more stand up and form the headwall. The inner corners of the upright bricks I knocked off, making a triangular hole that the tuyere comes through. The fifth brick is upright but on its long side rather than its end, and can be moved depending on whether I want a very small or larger fire. I bent frameworks of junk sheet steel to hold all these bricks, and any broken brick can be slipped out for replacement.

My tuyere for this forge is just a 1 1/2 inch water pipe with the tip forged down into a nozzle, perhaps a 2 to 1 reduction of area. I left extra pipe sticking out the far side of the headwall; if the tip ever burns off I'll just forge another taper on the burnt end and shove it forward a bit.

Both of these work well, both are very simple, neither one of them cost much at all. I teach my students that forges are the easiest of all the major tools to make for themselves, and that they shouldn't think that a forge should add much of anything to the price of a blower. The most expense I ever had for a forge was about 50 dollars for that first one, then I learned better. The first portable one I made was for an garden arbor installation, for heating collars before assembly.
A student and I built it in a 5 gallon steel bucket, with a hand-dished grate, the top of a propane tank for a firepit, and junk plumbing parts for the air supply and cleanout. Total cost less than five dollars, and it lasted four years. The little side-draft I use now cost about 20 dollars, but that was with store-bought firebrick and black paint to make it look pretty for the tourists.

Conrad Hodson

[Sweany]

What Conrad said, steel pipe is cheap, keep it simple.

[Conrad Hodson]

We all have our preferences, but the fancy factory-made forges I've used don't even seem to _work_ as well as the simpler ones! Most of the little one-piece rivet forges and the like have no depth of firepit at all, and you have to build this huge mound to get out of the oxidizing zone.

Did you ever see that book Aldren Watson did--The Village Blacksmith? Wonderful drawings, lousy history (seems vague on whether he's describing smithcraft as of 1750 or 1900!), and the back of the book has appendices for building a bellows and a forge.

Well, the forge he draws and describes is this huge brick monstrosity, indoors with a big fixed hood. It would cost a couple thousand dollars to build unless you had an awful lot of old brick available. And after all that, you'd have serious limits on the size of curved pieces you could heat, because of the massive hood. And unless you built it dead center of a thirty foot wall, you'd have a nightmare trying to heat midsections of any long bar.

Personally, the only fixed forge I want has to be freestanding, with plenty of room around it. Recently I had to make a whole bunch of U-shapes in 20-foot bars! I have a smoke hood, but it goes up and down on counterweights and isn't connected physically to the forge at all.

There are forges that are no more than holes in the ground, with a buried run of timber bamboo or junk pipe feeding air from bellows to a homemade clay tuyere tip. There are also African smiths who do really nice work with those forges, and they didn't spend a dime on them. If you'd rather stand up while you work (I do) then make a raised platform of adobe/rammed earth. If you want to splurge on a few firebricks, you won't have to rebuild the firepit, but that's really all you might ever have to buy.

"The more you pay, the more it's worth" is strictly for suckers--but there's so much of that attitude poisoning our society that it's easy to drift into the trap. With our toolmaking and problem-solving capabilities, smiths are the last people on Earth who should fall for that one!

end of rant,

Conrad Hodson



Conrad Hodson

[Grafvitnir]

Conrad, I like your idea of forging the end of the pipe to reduce it

What fuel do you use? I know using charcoal will do nothing to the pipe; mine has last quite a while without any damage. Coal may take a while; but someone told me that using coke will burn the pipe maybe even in one session. Have you used coke in any of your forges? I haven't tried either coal nor coke so still don't know what will happen. That's why I ask.

Thank you.

Rubén

[Conrad Hodson]

In the little side draft unit, I've been running wood charcoal mostly(the forge was built for historical demo purposes), with occasional doses of coal when my charcoal supply has run short. No signs of tuyere erosion yet, but I don't have that many hours on the forge yet.

My non-portable bottom draft forge, the 30-year model, has run on coal most of its life, except for a couple of years when I was using commercial coke to see how I liked it. I never really noticed much difference in corrosion, but then I don't water my fire much, or leave the forge exposed to the rain. It stands to reason there's much more chance of corrosion from sulfurous/sulfuric acids if water leaches through green coal than through charcoal. On this note, while my forge has corroded very little, the sheet steel on the coal _scoop_, which sometimes gets left in the coal bucket, has needed replacement twice.

As for other fuels, I learned on gas (someone else's) and then discovered solid fuel, and never went back.
Ask the gas guys about their problems--the only one I've heard about is the way welding flux erodes their refractories.

Another solid fuel is bark. One of my mentors, who was nearing 80 when I met him, taught me how to use Douglas fir bark the way smiths did in lumber camps here in Oregon, a century or so ago. The bark is almost as clean as charcoal--I didn't notice corrosion problems and clinkers were few and far between. Basically he used a larger deeper firepit, about a gallon in volume; he said the fuel was less dense so you needed more of it. And he would throw in some supplemental coke or charcoal to reach a welding heat, but the bark could get you up to the edge of yellow. Can't beat the price, especially around here, where you can clean a hundred pounds and more of bark off one log car on the rail siding a block from my house...so far that's my best effort in being self-sufficient/sustainable WRT forge fuel, though I've been meaning to make more charcoal in the coming year.

Conrad Hodson

[Conrad Hodson]

My non-portable bottom draft forge, the 30-year model, has run on coal most of its life, except for a couple of years when I was using commercial coke to see how I liked it.



One amusing thing I forgot to mention--during my coke-burning experiment I ended up startling some of my friends by mentioning I was going up to Portland to buy some coke. They gave me that "I didn't know you were into that stuff" dubious look.

Then I mentioned I was going to buy 400 pounds of it. They looked at me with new respect--they had no idea I was a big shot....

Then I explained that the coke I was buying was "Pittsburgh Black" with a street value of $500 a ton.

Conrad Hodson