Vinland 3 Smelter Build

For the next in the Vinland smelt series, the material for the furnace walls has been changed. Course sand (dug locally) was mixed 50 / 50 by volume with the powdered potter's clay (Bell Dark). The finished furnace walls are roughly 5 - 7 cm thick.

View of smelter work area, boxed in to rough size of the Furnace Hut at L'Anse aux Meadows	Slack tub positioned to duplicate size and position of an unexplained large pit from the archaeology.	Using a 22 cm diameter tank as a form. End of the first course of clay.
Showing bricks placed inside to stablize the furnace, plus allow the tank form to be moved higher.	Packing the gaps with dry wood ash. This both helps the furnace keep its shape and draws the moisture from the clay.	Full height of build at 65 cm total.The exterior will be wrapped with sheet metal to prevent slumping.

On forges, chimneys - and blowers.

I often get direct questions related to specific problems in blacksmithing. I often will turn those responses into blog postings (to share the information, after the work of writing them!)

...I saw your videos on youtube and in the one explaining your shop ''set-up'', I noticed you are using an updraft hood..
I've heard alot about side-drafts and how they do the job way better then the other one.
I'm halfway done with building an updraft for my forge, and I was planning to use a power ventilator or something like it, to help it suck up the smoke.
- Samuel

In case you have not seen it, the reference is to this YouTube segment:

Sam Asks: Does your hood work well? ...what kind of ''fan'' do you use?

I have a chimney set up adapted from an 1880s book on smithing.

There is a roughly 12 x 12 square pipe that extends from the ceiling with a second piece about 11 1/2 x 11 1/2 , maybe four foot long, that fits inside this. The smaller section ends in the more or less chopped off pyramid that is the hood. Thats maybe a foot top to bottom and extends to about 2 x 2 feet on the lower edge. Originally this inner section was counter weighted. The cable eventually eroded in the coal smoke, so now it takes two hands to lift the hood. (The hood piece is not heavy, it just binds if you try to lift it with one hand.) A simple pin through a hole holds it in place.
Now I can actually drop the hood tight on to the top of the forge table. That would pretty much get every last bit of the smoke contained. In actual practice, I lift the hood all the way up to give me about three feet of clearance for cleaning and setting a new fire. Once lit, I drop the hood down to about 18 inches above the forge table. This is quite effective for gathering the smoke during normal forging operations.

The use of a blower to extract smoke is important in this set up.
In the ceiling space above the enclosed forge room, I had installed a large furnace squirrel cage blower. (These prove pretty easy to gather at the dump - at least around here.) That type of blower has two circular inputs - one on either side, and one large output in the middle. The output is roughly 12 x 10 inches. This is fixed to another section of rectangular duct that runs at right angles to the line of the chimney. In my case this piece sticks out through the end wall of the building.
As the blower has two input sides, I boxed in the side opposite to the one attached to the forge hood. This ends in a simple trap door that opens down into the forge room on the ceiling. In warm weather I open this, thus pulling room air out at ceiling height. This not only grabs any smoke the forge hood might miss, it also pulls a lot of the hot air out of the room as well. Needless to say, come winter I need to work with that trap shut.

Exterior View: On the lower left (partially obscured by the tree) you can see the output vent from the blower. The straight line passive stack shows on the upper right. The wedge shaped piece of metal diverts our heavy snow fall around the base of the chimney.	Interior View: The retractable hood in the full up position. To the upper right can be seen the open 'hatch' that leads to the blower to extract room air.

Although this set up on its own does certainly extract all the smoke from the forge, I have also extended the line of the forge chimney straight up through the roof using a length of 10 inch diameter stove pipe. This ends in a standard fire place style cap (to keep the rain out). This second vent point actually will actually extract most the smoke during the forging sequence - passively.

I don't know exactly how much air the blower pulls - but it is a HUGE amount. Enough that you can not keep much heat in the shop come winter. This presents is own problems here in Grey County.

Sam Asks : Do all the side-draft (users) exaggerate the weak abilities of the updraft hood?

The problem with any side draft chimney set up is getting it built correctly. There is no doubt that a properly designed side draft will preform like a vacuum cleaner. I have seen some that will actually suck smoke back down towards it and out!
The main thing with a side draft is getting the correct proportions of smoke hole to shaft size. To get that magic draw, the proportions of side opening to chimney square area needs to be in the range of 1:3 to 1:4. (So smaller opening than the size of the chimney) If there is not a large enough difference, the chimney stack will just not draw correctly. The exact details of the construction can effect the potential draw as well (like too much rough mortar left on the inside surfaces when using brick. All that being said, I have seen extremely good results using a straight piece of 10 inch diameter pipe with a brick sized hole cut in side. There is sure to be some relationship between the placement of the inlet opening above the forge table. Most I have seen are located with the bottom edge of the cut out about 4 - 6 inches above the table surface.
A passive chimney set up of any kind is also effected by roof layout, local setting, variations in wind and weather. The exact placement of the chimney stack above the roof line is important, as is the orientation of the roof line to prevailing winds. Placement of near by trees can effect function of a chimney. Rain or dry, hot or cold, direction of wind a given day, all can combine to sometimes render even the best passive draw chimney ineffective.

One thing to consider (??) is that with a side blast, the chimney stack has to sit to one side of the forge fire, and fairly close to it. This may or may not interfere with the placement of a working piece into the fire as desired. Not a problem with smaller objects, or generally for linear ones. May be a consideration with larger 3-D pieces. (This is another reason I set up the hanging hood arrangement - I can work pieces potentially from all four sides of the forge.) Bear in mind that most likely the weight of your chimney stack will bear down on that side of the forge table as well. In the classic 'traditional' forge, the heavy brick construction is not because of the forge itself, but required to bare the weight of the brick chimney above. Of course there are ways to limit that, but now construction is becoming more complex overall. (Balance that against the light sheet metal construction of the galvanized sheet I chose for my set up.)

I think the comments about the weakness of the straight line, passive chimney are fair - when compared to a correctly designed (!) side draw chimney. However, my system is essentially a powered blower extractor. No real comparison in terms of raw volume of air moved between it and even the best designed passive system.

Sam Asks : Does your shop end up full of smoke?

No.

First off, remember that there is only a significant volume of smoke generated during the initial 'coking up' phase of working with a coal fire. I can easily lower that hood close to the top of the forge table, grabbing 95 % of the smoke generated for those first few minutes and the blower ramming it out through the side vent. That extra hatch in the forge room ceiling pulls out a good volume of room air - and any of the remaining smoke with it. After coking, working a fresh fire does not produce that much smoke. At that point I could actually turn off the blower and allow the straight line stack to passively vent the fire. (In actual fact, I just leave the blower on all the time I'm working.)

I had suffered lung damage from working in a living history museum (unnamed for liability issues - but its the large one in Toronto). The health standards there were absolutely Victorian. The management at the time acted as if they thought Ontario Health and Workplace Standards did not apply to them! I quit that position, the longest season and highest paid artisan interpreter job in Ontario, largely over these horrible safety conditions.
The problem there was two fold:
First, the chimney itself had been built like a fire place - NOT correctly like a forge. The chimney actually tapered in smaller for the first three feet or so. This resulted in hot air being piled up as it tried to enter and rise, filling to overflowing with smoke. To make matters worse the proportion of bottom opening to stack cross section was almost exactly backwards. The straight stack section (above the constricting flare) was about 10 x 12 inches. The opening at the bottom was about 16 wide by 18 inches high (so a 2.4 : 1 ratio - against the optimal 1:4!)
Second, the chimney top was :
- located on the east side of a building with prevailing winds from the west
- ended lower than the building ridge line
- a tree on the west side had grown up to almost 1/3 higher than the building peak.
The net effect of all that was that nine days out of ten, the wind blew over the top of the tree, slanted down on to the building ridge, then effectively blew back DOWN into the chimney. This was such a problem (compounded by the management's insistence that it was all due to my lack of skill!) that I ended up contacting over 30 other living history museum blacksmiths from all over North America, I got replies from most of them describing their own forge and chimney layouts for comparison.

Anyway, the short (after the long) of this was that when I established the Wareham Forge as a full time business and constructed my own workshop, I was painfully aware of the dual problems of coal smoke and chimney construction. The use of what is basically a simple powered negative pressure system for my forge is a result of all this.

Spears for Vinland

One of my current (paid!) jobs is to make a number of pieces for the Encampment program at L'Anse aux Meadows NHSC. This year's additions are a set of spears and shields - five of each. There are also a group of arrows being made up by Mike Kleinknecht . (Forging the arrow heads was detailed on an earlier posts : ONE / TWO / THREE.)

The spears are made in two basic patterns, forged from mild steel. There are two of a shorter javelin head, about 6 inches in blade length. The other pair are longer, slashing heads, these closer to 9 inches in blade. All are full socket type. The last of the set (seen at extreme right) is a more leaf shaped blade. This I forged from antique wrought iron - the material that is more likely to have been used for the originals. From a distance there is no difference, but close examination shows the distinctive linear grain in the actual iron.
On all the spears, the sockets were forged separately from standard schedule 40 mild steel pipe. The heads were forged down to a short stubb tang. That tang was forced into the hot cone of the socket, which when cool was MIG welded and ground smooth. That last is 'cheating' in terms of historic method, but in practical terms, you can't tell the difference in appearance between the MIG and a proper forge weld. (And yes - I have made these up with forge welds in the past.)
I deliberately chose NOT to polish the blade surfaces down to remove all the forge pitting. This shows primarily along the spines of each blade. The logic here was to preserve as much as the original thickness of the material as possible. Each of the blades was forged from 1/4 x 2 inch flat stock.
The shafts were purchased from a London Ontario supplier, Relics. They sell a very nice quality, straight grained ash spear shaft, for about $45 CDN. (Watch out on the shipping cost - I had the order picked up)

(Additional comment)

Jason asked:
... How are the heads fastened to the shafts? Just shaped and forced on hot? Riveted?

The heads are basically friction fit. The end of each shaft was tapered with a draw knife to the basic shape. I then fit the sockets down, rotating them as I did so. This would scrape some of the internal fire scale on to the wood, marking the high spots. These were then reduced with a course file. Repeat until pretty much the whole taper is being marked (indicating a tight fit). Normally fitting the socket back on to the shaft, then tapping the base of the shaft is enough to firmly mount the spear head.
As these are going into a living history situation (where I know from past experience a certain amount of abuse is almost certain) I did cheat at this point. Each socket got a liberal coating of epoxy before I did the final setting of the head. After this was hard, any excess was trimmed with a knife. The epoxy is this invisible, but ensures the heads will not work loose.

(Additional comment 2)

polymarkos asked

...how did you make nice conic shapes out of the black pipe for the sockets?

Carefully!
The trick to getting long tapered shapes out of pipe is to hammer quickly and using gentle strokes - with a lighter hammer. I use a 800 gm / 1.5 lb weight as my primary forging hammer. Working down into a conical bottom hardie tool also helps speed the work. There is a short photo description of forging long tapers to points out of pipe on an earlier blog entry : Forging Rush Tips - which also includes a video clip of the process.

Clay at L'Anse aux Meadows?

This is a response to a comment by one of the regular voices on the Early Iron Group discussion.

Do you make a difference between loam and clay?
We always use loam mixed with sand and other things (when needed).
I am sure that the inside of the furnace wall participates at the proces. I dig out the loam as close as possible to the ore bank.

Loam has very less lutum and clay minerals but much iron combinations.
If you mix it with (lots of) sand it dries very quick and you can even start firing it while it is still wet.
I am curious about the situation of loam and ore near the excavation of that oven in LaM.

Thijs.

At the physical site of L'Anse aux Meadows itself there is not any clay material present. On the actual Viking Age occupation area, the location is a sea shore, with a narrow bank that rises up out of the shallow water. The bank is maybe 30 metres wide. This bank then falls away into a bog, so imagine a thin crescent shape that runs along the sea. So what you have is a combination of fine stones and sand at the water line (a fine gravel). The core of the bank (especially around the furnace hut where the smelter is) is mainly sand. This is topped with a layer of compressed organic material - peat. The bog side is of course peat as well.

Looking roughly north, out over the Marine Terrace at L'Anse aux Meadows NHSC.
The Norse occupation area extends bit more to the right than is seen in this image. The white area with benches seen to the right centre is roughly were the charcoal pit was found, just below it, dug into the stream bank, was the 'Furnace Hut' and its iron smelter.

There is a clay bank in the area. I personally have not seen this, so can't tell you exactly how close it is, or exactly what consistency or kind of deposit it is. A couple of the local people told me about it. One of the staff members at Norstead (an attraction in the area) had been digging the stuff out and building and firing simple hand built pots out of this clay. It looked like a pretty clean low firing grey clay. Most certainly this clay deposit will be some form of water deposited material, my guess is that it would be along one of the many streams in that region. The Norse would certainly have had to have hand carried the stuff a good distance!

From what I saw at Ribe (with Michael Nissen) and Heltborg (with Jens Olesen) the situation in Denmark is quite different. What I observed at both those locations is quite deep underlaying clay and sand layers making up the whole ground. This base material had organic material mixed with it as the top layer, often pretty thin in places. So when you stuck a shovel in, you pretty much got some combination of clay, sand and bits of vegetation. For the Heltborg symposium in 2008, Jens had a pile of clay that they had just used a front end loader to scoop out of the side of a hill. That stuff was almost pure clay, we actually had to add extra sand to it - just as it came from the earth. I was quite amazed! (Denmark, the land of iron riches.)

So I think what you are calling loam is a mixture of materials that does not naturally occur at LAM (and most certainly not around here where I live in Wareham - some 3000 km away!)

We have been adding straw (typically wheat stocks that are gathered up into bales after the crop is harvested), chopped into roughly 5 - 8 cm lengths. Our typical mix is roughly 50 % dry powered potters clay, mixed with an equal volume of the straw. Add enough water to let you manipulate the stuff by hand. Normally we only add sand to balance the water content (like if we use too much water by mistake - its hardly exact). My experiences absolutely agree with yours, the inclusion of vegetation in the form of plant stems both helps to hold the constructed walls together against cracking, but also allows any steam to vent into the hollow stems (or out through the channels) to reduce cracking as well. We also have repeatedly gone straight from building wet cobb mix walls straight to the pre-heat with split wood with no real problems.

Working with straight clay is another matter. Twice we have used boxes of prepared potters clay, which comes pre-mixed as large blocks, soft enough to hand work, maybe 20 x 15 x 25 cm. (Smelts in October 07 and the last one on October 11 09) We cut these with a dry wall saw into thick slabs, about 5 cm thick (so 'brick' shapes, about 15 x 5 x 25) These were stacked, on end, a rough octagon shape, then smoothed over at the edges. As there is nothing to help let the steam escape from inside the 5 cm thick mass, there were plenty of pops, cracks - and flying clay pieces, as the pre heat was underway. Pieces as large as a golf ball flew as far as 5 metres a couple of times! Too exciting. As I mentioned in the last short report , having the clay construction surrounded by stones and packed with sand / ash mix, both held the structure together and helped to keep (most) of the combustion gases inside the smelter.

We have had excellent results with the clay and chopped straw cobb construction. Individual furnaces have been re-used as many as five times with only minor repairs (around the tuyere area). The structures stand up to Ontario winters, by just putting a cover over the top to keep the snow out. Once the walls have gone through a smelt sequence, they pretty much sinter into a rough ceramic and are pretty durable. Built at our normal 7 - 8 cm thickness, they are strong enough to be self supporting. To construct a furnace at 25 cm interior diameter and roughly 60 cm tall requires about two and half 20 kg bags of dry clay. The cost for that around here is about $30 CDN.