D. Fogg
Chuck Patrick
It was not without some trials and errors along the way. First, I had chosen 1050 medium carbon steel for the stock to work with and I was not that familiar with it. There are some good reasons for this choice of steel, first being that it has a TTT of about 3/4 of a second to get below the nose of the curve and therefore is very responsive to the clay coating applied to the back of the blade. In my earlier test blades, I was able to get a clear and dramatic hamon, but was not really happy with the softness of the back. If not properly hardened, the blades bent too easily, but I began the trip hoping to find the right combination to overcome that handicap. Another clear advantage of this steel was that it would stop an edge crack from propigating through the hamon and made the blade virtually indestructible.
Swords have a unique set of requirements and the right choice of steel must take these into account. In use the edge of the sword is likely to get chipped. Because the edge is under tension, once the integrity of the edge is broken, it will break quite easily. This can be demonstrated by chipping the edge with another piece of hardened steel and then striking the spine of the blade over the anvil. In my test pieces, 1050 would stop the crack and despite numerous hard blows to the spine the crack would travel no further than the hamon. I was also able to place the blade in a vise and bend it 90 degrees at the crack and back without it breaking. This showed me that the steel was capable of withstanding actual conditions.
Another requirement is that the edge be hard enough to cut through tissue, bone and even metal without chipping. Edge holding is not as important as it would be in a using knife, but if the edge is too soft it will not cut cleanly. Again my tests showed that the steel would get hard enough to perform well. I do not have a Rockwell tester, but from looking at the charts and by checking with a file, I estimated that it would fall into the 58-60 RC range.
Prior to the class, Chuck and I made several test blades attempting to solve the soft back problem. We converted one blade to banite and it would support the weight of two men, over six hundred pounds, without breaking, but we were unable to subsequently reharden the edge without softening the back too much again and it this condition it would not stop the fracture.
We also tried several methods of flash quenching in water, interrupted quenches, but still ended up with soft pearlite structure in the back. Finally we reduced the thickness of the clay to a minimum and quenched in water until all color had left the spine of the blade. This produced a hard edge and tough back, making a mix of pearlite and martensite in the area under the clay.
D. Fogg |
Chuck Patrick |
We had twelve students with twelve forges going at once. The shop was a converted milking parlor comprising one long open room with the forges going down each side and steel layout tables in the center. Each station had a coal forge, anvil, and post vise. There were a few gas forges available, but most of the students worked with the coal. When all the fires were lit and the hammers were beating on metal, it was a factory.
I demonstrated first, showing how to shape the point and begin the bevels. My technique involves working with a heavy hammer, minimum four pounds and preferably larger, and constraining motions by locking the hammer arm to the side and striking with the forearm and not wrist. Also the arm holding the work is locked into the side also and the piece is moved by rotating the hips. The hammer face should strike in the same spot and the work moved. Attention has to be paid to the height of the work piece so that it is flat on the anvil and the handle is not tipped up or down creating a bend in the blade which will later have to be straightened. In the manner of the Japanese, I like to wet forge. Wet forging is simply keeping the anvil face and hammer covered with water while forging. The water does not cool the blade but helps to blow off the scale and keep it from being beaten into the hot metal. Scale is uncompressable compared to hot metal and will leave craters in the finished work that can be a problem. I also like to keep the scaling down by working in a rich fire and at lower heats.
Forging steel is the beginning of the heat treating process and as much care should be given to the temperature of the steel as is given the actual forging. I like to progressively reduce my forging temperatures until in the finish forging I am working just above and below critical. I feel this goes a long way to refining the grain of the steel. Care must be taken not to drop too cold or stresses can be built into the steel and so you should cycle right around critical.
I like to work in small sections, beginning at the point and then forging the bevels by laying the unforged steel on the anvil and forging into the already forged section. If you try to forge from the already beveled area to the unforged area, the thicker unforged section will curve the blade every time and create problems. It is helpful to straighten and true the blade before it returns to the fire so that you don't end up chasing your lines and can start from a good straight line.
A common mistake is to fail to set the angle on the bevel by raising the bar up from the anvil. You have to set the angle otherwise the bevel will be establish on the hammered side and remain flat on the reverse. I found it helpful to work to your weak side first, setting the bevel and then switching sides. I need to make a sketch of this, but will have to add it later.
The forging proceeds down the blade in three or four inch segments, taking care to watch the lines and true everything up as you go. I do not attempt to forge to the final edge at this time, but rather want to establish the bevels and profile for the blade. It is important to forge equally on both sides. If you fail to do it, the blade will begin to twist because you are drawing more on one side than the other. Also, by forging equally on both sides balance the stresses on the blade.
Another common problem encountered is keep the blade from curving radically. The old addage about never beating on the edge is foolishness. You can beat on the edge without creating problems, but obviously you have to correct for any upsetting. I use the lenght of the anvil to take the curve out of the blade laying the section that is curving on the anvil and lightly tapping it back straight. When the edge is thinner, I use a wooden or rawhide mallet and a wooden block so I won't mar the blade or edge.
When you approach the tang end of the blade it is time to reverse your grip, you will know when it is time because it is too hot to handle comfortably. It is difficult to continue the bevel line from the forged section without running into the problem of the thicker section curving the thinner beveled area, at least for me, so I begin at the far end by forging the tang. On the katanas the bevel is just and extension of the blade bevel. The only consideration with the tang area is that it be tapered in all directions to the area where the fittings will seat to the blade. I don't go to great pains to set the notches just rough them in, but I do spend a considerable amount of time shaping the tang. The tang takes a lot of stress since it is fulcrum point for the blade and it is wise to make it as strong as possible and forging to shape is the best start.
Working back from the tang, forge into the blade and join the previously forged area. I like to let the blade cool at this point so I can handle it comfortably and look at it from all angles. It is amazing how different steel looks when it is cold from when it is hot. This will give you the opportunity to see where you need to work and to plan you finish forging.
When I begin to final forge the blade, I use the same hammer, but use lighter blows. I am looking to bring the metal down to the edge, straighten all the lines, crisp up the bevel lines and remove any hammer blemishes from the rough forging. It is slow and careful work, but will greatly shorten the finishing time when the blade is cold. The final shape of the blade is straight. The curve will be established during the hardening process.
As a final step to the forging process, I cycle the whole blade from critical temperature to below 1000F for at least three times in the air. This thermal cycling will reduce the stresses in the blade and help to further refine the grain structure before hardening. I do not anneal my steels and if they need to be further softened I will heat the blade to 1300F and hold for a long soak.
Since there were no real grinders at the Folk School, I decided that we would make these blades by hand. This was quite a shock to the full time makers who were attached to their belt sanders and to the new comers who hadn't done much hand work before, but it was also a good learning experience and I felt essential to really understanding the swords. Too often we rush out to buy power equipment to do a job missing some of the basics of the craft in the process. I began making Damascus by hand with a hand hammer and continued for several years until I could no longer keep up with the work. This gave me a feel for the steel and the process and also made me appreciate the final product. Damascus has never been bar stock for me, it remains special and it feel it is because of this early start.
I had requested that the students bring files, stones and paper to the classes, but we took Tuesday morning to forge out some Japanese style scrapers called sens to use for the stock removal. The sen is very similiar to a draw knife used for wood. The blade has two handles or tangs extending from a flat center cutting area. The best cutting tools are flat ground on one face and have two cutting edges front and back. The bevel is quite acute to the edge, but is concave for strength. They are meant to be used sharp and work with either a push or pull stroke. We made ours up out of leaf spring and oil hardened them, drawing for 1/2 hr at 325F to take the curse off the hardening. Most of the ones we made worked quite well, some better than others, but I think that all who gave them a fair try, found it to be a much fast way of getting the stock off and the flats set than by filing.
Before using the sen or files, we knocked off the scale with rough stones. I had found some cheap oil stones at a flea market and they worked fine. Knocking the scale off revealed the hammer imperfections and bevel lines. Once most of the scale was removed, we turned to the scrapers. It is a bit difficult to get them started since they need to establish their own bite before they really start cutting the metal. I have pulled a shaving off a katana three inches long with my sen and end up with a pile on the floor when I am finished shaping the blade. I brought my sen to class and it had sharpened two katanas and a tanto before requiring anything more than a light touch up.
Final shaping of a sword with hand tools is hardwork. I have to work through my impatience and settle into the rhythm of the tools before I can appreciate the process. It is very peaceful and satisfying not to have a motor running everytime you work. I find going back to power tools stressful after a time of working only with hand tools. Because the pace is slower, you also get a chance to thinking about what you are making, anticipating problems and developing a connection with the piece instead of simply producing it.
Often new knifemakers jump into the craft without ever having made a knife from scratch. I think this is skipping an important learning phase and doesn't teach respect for what they are doing. The connection with the past and with a time not so caught up in the frenetic pace of today's life that was appealling to me when I first started forging and I am glad that I was able to experience and appreciate it.
The scraper sets the lines of the blade and prepares us for the files. Going to the files we begin to refine the blade. At first the file takes the tops off the scraper cuts, but soon it is into the meat of the steel. I like to use a draw filing motion that is not in the books. I hold the file in both hands and push/pull it at right angles to the work. While this may seem contrary to the way a file was designed to cut, it produces a smooth flat finish and rarely gauls. I also use light strokes and do not bear down as hard as I did with the scraper. I begin with a bastard mill file, though if a lot of material needs to be removed I sometimes use a magic cut file. After the bastard mill file you can go to a smooth file and this will save you time when you transition to stones.
After, the lines have been set and are crisp, I begin to work the flat of the bevel to the edge. It is helpful to sight along the edge and find the center line. Cutting a minibevel to establish the center line will give you a guide when you begin cutting to it along the flat of the blade. This is a common practice when grinding a blade and it works well with hand tools too.
I should mention at this time about how to secure the blade while working on it. In my shop, I have made a sturdy and functional tool for holding long blades. It is made from a drill press vise to which I have welded a 1" angle iron roughly 24 inches long. The vise is located in approximately 6" from one end and the angle is welded using nickel rod for the cast iron and welded to the inside base and fixed jaw. I pad the surface of the angle with thin leather and pad the top, moveable vise jaw with neoprene. When I am working, I clamp this tool in my bench vise. Using a vise in a vise is very versatile, sort of vise versa. Sorry. Anyway, you can then clamp the blade securely while you are working on it. A bit about vise safety. A blade clamped in the vise should have the edge and point behind the back up support. It is very dangerous and can hurt you badly. Whenever I leave the workpiece, I remove the blade from the vise, everytime. For the class at JC Campbell, we used 2x4's held in the post vise clamping the blades down with c clamps.
In the class, we hardened the blades in the as filed condition. You can take them through the first stone, but any further will just create work for yourself. The secret of the Japanese katana is its ability to hold together even if the blade chipped or damaged. This is accomplished by a process of selectively hardening the blade through the application of clay along the area that is to be left unhardened. The Japanese smiths were very creative when it came to building strong, unbreakable blades. By carefully combining steels of varing carbon contents, sometimes using five or more different steels in the construction of their blades, they were able to adjust each portion of the blade for the maximum service. Since we were working with a piece of homogeneous steel, we attempted to achieve similar results though careful heat treating.
I won't pretend to know all the secrets of the clay formula, but I have found that any refractory that will stick to the blade and still be easily removed after hardening will yield satisfactory results. I prefer to a high temp mortar mix from A.P. Green Industries called Satanite. It comes dry and may be mixed with water to provide a tenatious clay with excellent insulating characteristics. I also use #36 premixed mortar cement from A.P. Green. #36 is an air setting mortar and has higher shrinkage than the Satanite, but is popular with many makers. I heard about it from Michael Bell and again from Bob Engnath. For the class, I brought a tub of the #36.
The clay works by providing a barrier to the quench, effectively slowing down the cooling rate so that the steel does not completely transform to martensite during the quench. Most modern eutectoid steels have a long TTT transformation time and the clay is not as effective as it is with the medium carbon steels. 1050 is particularly sensitive to the clay since it has to get below the nose of the curve in under a second to fully harden. By running a bunch of tests, we were able to determine that a thin layer of clay, around 1/8th inch, would stop complete hardening of the blade, create an interesting temperline and leave the back tough and relatively springy. All blades hardened in this manner will take a set if bent too far, but it is very important not to make the backs too soft or they will bend with nearly every cut. I have seen old blades that were easily bent in the hands and I do not find this acceptable. If it is too hard it will not stop the propagation of a crack so there is a balance that has to be struck. Obviously the Japanese smiths confronted the same problem hence the complex billet constructions.
A light, thin wash is applied over the entire surface of the blade. This is done with a brush which has had the excess water flung out and then is dipped into a thin clay mix. After this has dried enough not to be runny, a thicker layer of clay is applied to the back of the blade using a spatula. We used a broken bandsaw blade, but an old table knife will work as well. A layer about 1/8th is applied uniformly down to within about one third of the distance from the cutting edge. You can be as creative as you like with the application of the line remembering that if it is too busy, you may lose definition to the hamon. Since I wanted to stiffen the back of the 1050 all clay was scraped from the spine of the blade. This allows it to harden helping to control the curve and make it more flexible without being soft. On a tip from Bob Engnath, I wrap construction wire in a spiral down the blade and then go back and cover the wire with the clay that surrounds it. This wire is not necessary with Satanite, but helps the #36 stay in place when it is heated. The clay is then left to dry a bit before putting it into the heat treating forge.
You need a fast quench to harden this steel and water is the best choice. I was using brine, but Yoshindo says in his book that the clay has the same wetting effect as the salt and yields good results. It is best to use distilled or rain water for the quench, but lacking a rain barrel, we used water from the tap. My quench tank is made from plywood that was caulked and sealed with polyurethane. It works fine though it did leak because it had dried out during the trip. You should build the tank long enough to get the entire blade and tongs into it without a problem. My quench trough is 4'x1'x1' or maybe a little bigger. It is wise to dry run the quench before you apply the clay so you know what the movement will be and to see if everything will fit.
I built a gas fired, digitally controlled furnace to harden the swords. The design came from a conversation with Howard Clark and were modified to suit my needs. The controller is a small 1/16 DIN Microprocessor-Based Auto-tuning Control series 965 from Watlow. Omega offers similar controllers and they run around $200. These controllers allow you to establish a set point temperature and sends a signal to a gas solenoid valve turning the gas on and off as it approaches set point. The solenoid valve I use came from White-Rodgers and is in normal close postion until activated by the controller. The solenoid I use is a low pressure valve and runs off a 1/2 lb regulator. The plumbing on the value is straight forward. I use a K type thermocouple to provide input to the controller. For this system I decided that I would install a sparkplug ignition and placed sparkplugs at the two burner ports. They are constantly fired by a standard furnace transformer.
For the forge, I used a 12" diameter pipe 36" long for the forge, cutting in two burner ports approximately 8" from either end. I also cut a vent in the center and welded a chimney over it. The vent helps control the atmosphere and also draws the heat to the center of the forge to equalize the heating. I lined the inside with 2400 degree 1" blanket of Inswool from A.P. Greene and coated it with a layer of high temp mortar mix. I also made a bed of soft firebrick along the bottom and cut grooves in the block to support the blades. The block also serves to break up the flame from the burners and stops it from making direct contact with the blades.
The burner is begins with a 100 cfm shaded pole blower connected to a 6" length of 1 1/4" diameter iron pipe. In the center of the pipe, drill and tap for a fitting to connect the gas line. I do not use an orifice, just straight in. The pipe leads to a T and then 6" straight pipe, elbows, 4" straight pipe to a bell reducing fitting 1 1/4" to 1". I welded on pipe to the outside of the burner posts to support the burner heads and lock the burners in place with a set screw. The burner and the transformer are connected to an outlet strip which is then plugged into a surge suppressing outlet strip which powers the controller. I mounted the controller and another digital pyrometer inside a utility box.
This whole furnace can be built from off the shelf parts for under $350 and the controller also is used to run a smaller high temp salt pot that I use for my smaller blades. With the controller and the spark plug ignition, I am able to control the temperature accurately from 200F to 1900F holding a 20 degree margin.
After the clay had set up enough so that it would not run or slide on the blade, it is put into the furnace. The furnace was set at 1600F and was up to temp before we put the blades in. The blades were put edge down in the grooves on the brick. When the forge is running it sounds like it is breathing. The flame cuts on and off as it maintains temp. Adding the spark plug ignition is really nice because all you have to do is push a button and it comes on. At heat treating temperatures the flame would ignite by the interior heat of the forge, but as a safety factor it is nice to know the spark plugs are firing.
To
hold onto the blades, we needed a specially designed pair of
tongs, ones with an offset so that the blade could be thrust into
the quench tank and the tongs not get in the way. Chuck forged
out a pair in about half an hour that worked great. Besides the
offset to the jaws there is a lip that comes back at a right
angle to pick up the bottom of the tang on the sword.
The blade slowly comes up to temp. When the back is at critical, we raised the blade out of the groove and let it come to the same color as the back. When I first went to the controller, I made the newbie mistake of relying on the controller to tell me when the blade was up to heat. What the controller is telling you is the temperature of the thermocouple and you have to calibrate your eye to that color and match it to the blade to be sure that you are at temp. This allow for heat treating in varying light conditions and is quite accurate when you get use to it. The eye is still the best judge of temperature because you can see if there are hot or cold spots and will notice subtle changes over the blade.
When the whole blade is at the proper hardening temperature, we were shooting for 1550F it is rapidly removed and quenched in the trough of water. It is held beneath the water and moved gently back and forth until all visible color has gone from the back of the blade, then it is taken out. If there is still color when taken out, it goes back into the quench again for a few seconds and then removed. Working quickly, you take all the clay off the blade and then check the edge with a file. If it has hardened it is then transfered to the low temp salt bath for tempering.
We do not really want to soften the steel at this point, but do need to relief the stresses created by the hardening, so we set up a salt bath at 325F and drew the blades from 1/2 to 1 hour. This seems to give the best hardness and toughness for this steel. Each steel will have to be treated differently. After the blades were done tempering we checked them again with the file and if they needed straightening we did that over the hardy hole on the anvil using a hammer. The back is soft on this style of blade and they adjust easily. I like to sharpen the swords at this point and go cut something. My standard tests involve cutting 2x4 pine or fir. I like ones with knots because it is hard on the edge and will tell you quickly whether you have the edge geometry and heat treatment right. If I happy with the performance of the blade it is real and I can proceed with the finishing. If I am not happy with it, it can be restraightened and rehardened. We had to do many of the blades over during the Folk school class and didn't lose any.
After the blades were hardened, we began to polish with stones. For this I recommended using red brick EDM polishing stones in 120,220,320,600 grits. I buy my stones from Manhattan Supply Company. These stones are designed for tool and die makers to clean up molds and dies. They are a synthetic stone and quite soft, but they cut well and are very useful for cleaning up and polishing blades. I use then on all my blades and find they are especially useful for cleaning up the transition radius between the flats and ricasso on western style knife grinds. With price of sheet abrasive going through the roof, stones are a fine alternative. The stones wear more evenly and cut best when used with a light touch. I add a synthetic grinding fluid to the water to keep them from loading. I first heard about these stones from Steve Hoel, a superb folder maker. Steve stones and hand finishes all his blades and achieves amazing tolerances in his folders. Our objective with the stones is to polish out the file scratches, moving from the coarser grits to the final polish.
When polishing with either stones or paper, it is best to work at a 45 degree angle to the blade and reverse the direction with each change of grit. By polishing at different angles you can see the previous scratches and insure that all of them are removed before moving on. I also like to reverse the direction of sanding from the bevel and the back so I can clearly see my lines. It is sometimes hard to see all the scratches and I recommend working in a good light. I have a combination of natural light coming from a window by my bench, indirect light provided by florescent lights and a direct light source that can be move to different angles so that you can see the blade in all aspects. It is amazing how those scratches can hide in the light and one thing you can be sure of is that they will never go away if you miss them.
After I have set down a good 320 grit polish with the stones, I will switch to Japanese style water stones. I am not a sword polisher and can not justify the expensive natural stones a professional polisher uses, but am quite satisfied with the synthetic stones now commonly found in woodworkers supply catalogs. They also come in a variety of grits, but I use only the 400 and 800 grit. These stones need to be soaked in water before they are ready to use. I prefer to use distilled water and recommend adding a bit of baking soda to the water to help prevent rusting. I also have found it helpful to buy some plastic trays and keep each stone in its own tray. This helps prevent contamination by grits from the coarser stones.
The water stones are usually quite large 3x6x1 inches and I have found that they are more easily handled and that I can get more life from them if I cut them to smaller sizes using a masonry blade in my saw. The water stones cut very differently than the EDM stones. You will notice the hardened and unhardened portions of the blade pop out when you begin using these stones. Still alternating the direction of the strokes for each grit, I get a good 800 grit polish over the entire surface of the blade. These stones wear quickly and care must be taken to keep them flat so that they won't wash out the bevel lines. Also, the motion with these stones is to the edge, rounding in to sharpen as you polish. Be very careful not to slip or you will christen the blade with blood.
After the final water stone is finished, I switch to 600 grit wet or dry paper, wet and sand lenght wise on the blade. I cut the sheets into inch or so wide strips and pinch them over a sanding block of hard flat material. I like corian blocks because they are not bothered by the water and are flat and thick enough to get your fingers on. I make my sanding blocks 1 inch wide and around four inches long. The paper is used wet with considerable force and the paper is rotated frequently as it begins to lose its cutting action. During this process the edge will begin to polish brighter than the softer back and you should continue to polish until all the scratches have been removed and the back is beginning to shine. While this process may seem to take forever the first time you attempt it, it gets much faster with practice.
At this point a light etch will really help pop out the temperline. I use a very dilute wash of ferric chloride , Archer etchant from Radio Shack, cut 2 to 1 with distilled water. I soak a portion of paper towel and rub it briskly over the entire blade. I am not trying to etch the blade as much as bring out the temperline. You have to acquire a touch with the ferric so that you don't darken some areas more than others, but it doesn't take long to figure out and can really make the temperline jump. When you are satisfied with the etch, rinse the blade and neutralize the ferric with a spray of ammonia. You can tell the ammonia is working by the blue green colors it turns up. Rinse again and dry the blade thoroughly.
The next step is 1500 grit wet or dry paper. I get these papers from my local autoparts store, but they are readily available. Again using this paper wet, go lenght wise over the entire blade paying more attention the area above the temperline than below. This will bring the back of the blade into high polish. If you wipe out the temperline redo with the ferric and repolish.
The final step is to go over the back of the blade with a fine paste polish. Some folks use rubbing compound on a cloth, but I like to use Simichrome a chrome polish found in most motorcycle shops or through mail order knife supply catalogs. Continue with the paste until the back of the blade is dark and all the 1500 grit scratches are wiped out. You can go over the hardened portion, but only lightly to remove the oxides from the etch. A popular finish on the Japanese blades shows a frosted edge, bright hamon and darkly polished back. You can approach this look with careful use of the paste polishes. Another polish used to darken the back of the blade can be made by using red rough buffing compound and light oil.
Now is the time to look over your work. Carefully inspect the blade for areas that need work. It is helpful to look at the blade in full light and also indirect light, tipping the blade so that the hamon is clearly visible and so that you can inspect the surface from every angle. If you find an area that needs work go back to it until it is right.
This blade finish is quite attractive, easy to maintain and a lot less expensive than a traditional polish. While nothing can duplicate the incredible view into the metal that a well done traditional polish reveals, this method is attainable by anyone with simple tools and the willingness to work.
That's all for tonight