Quick and Dirty Steam Box

For a current project I need to steam bend some pieces of Bolivian Rosewood, and the problem is that I have neither steam bent anything nor have a steam box handy. For about $25 and an hour of work, here is what I came up with.

For parts, I used
     -42" of 4" diameter, schedule 40 PVC pipe for the body of the hot box,
     -1 4" end cap
     -1 pair of a threaded cap and coupling that it screws into
     -1 4" female-female coupling (not pictured, to join the screw coupling and pipe)
     -12" of 2" pipe
     -2" 45 degree elbow
     -$1.50 Kettle from the thrift store (half off... What a deal!)

I would have gone with a shorter length of pipe had the hardware store been able to accommodate the length I needed, but they could not so I'll save the extra for something else. The reason I went with 42" is because I plan on using the tube for etching patternwelded longswords (given the infrequency I obviously need a steam box).

Despite what seems to be common in other PVC designs, I will not be drilling holes in the length of the pipe for dowel supports. This limits the pipe to the single purpose as a steam box and is not strictly necessary. While I am cutting my boards to width just barely smaller than the inner diameter, they will be off the bottom of the pipe, although I could also have made some removable supports to slide in underneath to keep the bottom face open to steam circulation.

The ends both need holes drilled in them to release steam and prevent it from rupturing violently. I don't have a functioning power drill, so I turned to the brace.

The first hole is sized to fit my thermocouple probe so I can track temperature throughout the process. A regular meat thermometer will work fine provided it can accurately measure around 230 (F).

Probe test fitted. No need to make the hole overly tight.

Next up I drilled three holes of arbitrary size (9/16") on the other side of the end cap. These will be the primary steam vents. Never having done this before, it was a guess as to size and number, but this combination worked well.

Originally, I intended the elbow to fit inside the kettle mouth itself, but that clearly did not work out. To remedy this, I cut a piece of pipe to join the two.

This little bit is enough to keep it snug inside the kettle, but not too deep as to inhibit the steam flow by dipping below the surface of the water.

Here we come to the most difficult part (for me working with hand tools). I had to drill an angled hole in the threaded cap to join the elbow to the steam chamber. Due to the complex surface, it was difficult to position the bits in such a way that they effectively drilled. This took a majority of the time, but would have been inconsequential with a drill press or power drill.

Even using the largest bit I have, the hole was slightly undersized for the 2" PVC to fit into. So, deburring and widening a hair with a file opened it up to the perfect size.

What a fit!

And that's the finished box! (or pipe)

Naturally, I tested it on some scrap wood before committing to the real thing. For the actual steaming, I will be building a support to hold the kettle end of the pipe due to the softening of the smaller 2" pipe during use.

A rule of thumb for steam bending wood:
For every inch of thickness, steam for an hour.

For my purposes, I will be bending 1/8" wood, which comes out to 7.5 minutes, but with the 1/4" piece I tested, I may go longer.

If I were to use wood of this width, I would use supports to keep it higher in the tube. However, it is only a test so I did not care to go through the wasted effort.

The test was of mixed results. Taking the wood out of the steam box, it felt about the same in terms of moisture content and rigidity as it did going in. I was not able to bend it in the tighter inner corners of the frame, but it also did not break. Perhaps I need to wet it first? I'm not quite sure...

Jewel Steel

Tamahagane, in Japanese a term for the result of a smelt yielding a very high carbon steel bloom, translates in English to Jewel Steel. Height and diameter of the reduction furnace, air pressure and by extension temperature, fuel quality and type, and the type, refinement, and size of the ore all play an intricate part in the production of bloom, each of which can dramatically change its resulting properties.

I had the opportunity to join Mark Green for an experimental magnetite smelt which resulted in a beautiful, carbon rich bloom of surprising yield. Magnetically separated, crushed magnetite was used as the sole ore source, which averaged between 50~60% iron. Typically, ore with less than around 80% Fe is not worth the effort of smelting due to the low yield. Additionally, this magnetite was high in Aluminum Oxide at around 20% despite cleaning and separation. To accommodate the magnetite, the stack was extended by an extra 12 inches for a total of 48 inches from the floor to the top. Because of the extra volume of charcoal, the pressure, and subsequently volumetric flow rate of the air was also increased, which caused the smelt to run a bit hotter and faster than the lower stack.

Throughout the smelt, 19 total charges went in, totalling 51.8lbs of magnetite and 83.75lbs of charcoal plus the initial fill of about 30lbs. The result, 11.25lbs of dense, high carbon bloom ranging between 1~1.1% C.

Due to the nature of the magnetite and likely the high aluminum content of the slag, tapping the furnace was initially difficult, with a thick, sticky slag that did not flow easily.

After a few taps, the slag began to flow more readily. Inside the furnace, the slag bath was very large and active, bubbling and spluttering wildly as it crept higher and higher.

Through the tuyere, the bloom (dark spot) is visible the charcoal faintly visible on top. This is the first clear shot of a bloom I have managed to get through the tuyere. Throughout the smelt, droplets of slag were visible leaping around inside the furnace, sometimes splashing onto the tuyere orifice and needing to be knocked off. During extraction, we found a large plate of slag and bloom impurities along the side with the tuyere about as large as a dinner plate.

When the time came to pull the bloom, another great volume poured out of the bottom, forming a fiery lake of boiling slag.

Left behind, a tentacley beard sat in the opening that would later birth the bloom.

In extracting the bloom from the furnace, a large portion of the wall fell away. Not unexpected, the wall had become fragile over the course of several prior smelts, and all throughout the day grew cracks spouting gouts of flame that crept steadily higher and higher. 

Already a hot day, the radiant heat put off by the opened furnace and the bloom is immense. Weighing in at 11.25lbs, it was like a meteor that could burn you from simply looking at it.

Cut in half with an axe, the two pieces were cooled and weighed, and then tested for carbon content. Consistently, the bloom sparked well into the hyper-eutectic range, around 1~1.1% carbon.

In the beginning it was unclear whether or not the bloom would yield good steel, or if it would turn to the cast iron range with the amount of air to compensate the higher stack. A few changes may be implemented next time, but the test of pure magnetite was overall very successful. 

Sharpening: Spokeshaves

In the wake of a recent project and beginnings of a new, I had significant demand for a wonderful tool that I do not get the occasion to use as often as I would like. Spoke shaves are very similar to planes in that they have a straight, removable iron that sits at a fixed angle in the throat of the tool. Unlike planes, however, the iron is usually significantly shorter, making it much more difficult to use sharpening jigs. For that reason, I sharpen blades for the spokeshave freehand.

This spokeshave belonged to my grandfather, an old Stanley No. 52 that has seen a fair bit of use through the years. Because there is a spot or two of rust in various places, I'll be cleaning that up while I have it in mind.

First, I find the angle of the edge bevel. For spokeshaves I like to keep it around 25 degrees, and this one happens to be at 24, so I'll hone what is already here. Finding the angle can be tricky if it is rounded or uneven. To get a gauge for it, I lie the iron flat on the stone and lift gradually, watching for the first sign of contact between the edge and the stone, rolling on the back corner of the bevel. There, I lock my arms at my sides and use my entire body to pass the steel from one end of the stone to the other.

The progression I use is 220#, 1000#, 5000#, 8000#, leather strop

A few passes revealed that the corners are a bit more heavily worn than the belly. Not a huge deal, as I like to have the corners a hair farther back anyway to prevent digging in on pieces wider than the blade. To facilitate this, I curl my index fingers around the iron, pressing on one corner with each thumb, again locking my arms at my sides. (sorry, don't have a third arm to photograph it)

While the 1000# stone is out, I use it to resurface the face of the spokeshave. The rust was a little deeper than I thought, so it took some time to polish. If I were to do it again, I would have dropped down to the 220# stone first, especially to fix the very slight convex surface from side to side.

Here are the blade and body after 1000#.

More sharpening and stropping to bring the edge to a razor. At this stage, I also slide the blade flat against the stone to polish the back edge and remove any burr that might have formed.

Light is the best way to check how even an edge is. On things this small, it is fairly easy to get a planar bevel, which will reflect the light in a uniform strip without any distortion or waves.

That's all! Reassembling the spokeshave, setting the depth, and it's ready for use again. From here out, unless the edge is particularly dull, I will not drop below the 1000# stone, and it should take significantly less time to bring back up to shaving sharpness.