By Matthew ParkinsonDownload Tutorial
Steps in forging a blade to shape.
Step 1 forge the point
Step 2 forge the profile of the blade
Step 3 forge in distal taper (distal taper is taper in thickness from base of blade to point)
Step 4 forge in bevels
Step 5 set in the tang or grip area
Step 6 shape tang/grip area
Step 7 cut off knife from bar.
Step 8 refine the end of the grip/tang
Dealing with Medium and High carbon steels.
When making a knife a high or medium carbon steel is needed. When working with these steels the higher the carbon content and the higher the alloying content the more sensitive the steel will be to being worked with in the correct temperature ranges. Some of these alloys can be red hard (a temperature range that the steel is to hard to work) or red short (a temperature range that the steel is prone to cracking of crumbling) generally these problems are more common in high alloy steels, simple high carbon steels tend less to these problems but will develop large grain size if overheated Large grain size weakens the steel, and is detrimental to the cutting ability of the finished knife.
The way to avoid damaging the steel you are working with is to know what alloy you are working with. Look that alloy up on line, or in one of the many reference books. Find out what that alloy is prone to, (if it is red short or red hard) what the hardening and temper ranges are. (you will need this info later) with any of these alloys there are a few things that should be done. First Do not soak the steel in the forge, second do not heat the steel to a higher temperature than is necessary to work it, and third as you forge closer to finished shape work at progressively cooler temperatures. Finally normalize the steel before finishing the knife (filing grinding etc) to normalize, heat the steel to critical temp, this temp can be found by using a magnet to find the curire point,(the point that heated steel turns nonmagnetic) critical temp is a few hundred deg. Higher than the curie point. Heat to critical and let cool in still air to about 400 deg F, this is around the temp that the steel with return to magnetic., do this three times ( or cycles) this will reduce the grain size break down any carbides that might have formed, and soften the steel making the grinding/filing easier.
In the USA carbon Steel alloys are graded using two main systems, the first is a numeric based system (SAE, AISI) in this system there are 4 or 5 digits that determine the alloy, the first two determine the alloy content and the last two or three the carbon content. The number deturining carbon content are called points, 100 points equals 1 percent by weight of carbon so 1050 steel would be a simple carbon steel (10=simple carbon steel) with .50% carbon content. The minimum carbon content to make a serviceable knife is about 45 points (.45%) and the maximum is around 1%.
The second grading system is the letter number system of tool steels, theses are specialty alloys that were developed for a purpose so with in one set of steels (D series is developed to produce dies and molds for example) there can be a total change of alloys with similar fished properties. Some of the more common steels in this system are O1,W1,W2 ,L6,S7 and D2. Most of these steels can make vary good knives but can also be very difficult to work.
Forging the shape
Begin by deburring the end of the bar, easing the edges is sufficient. Now take a forging heat on the point of the bar,( a forging heat is a bright orange heat) set the end of the bar on the far edge of the anvil and hammer the top corner back into the bar. Every other heat forge the thickness back in line with the parent bar by rotating 90DEG and hammering the flats (work both sides of the flats)
Forging in the point in this way avoids fish mouth. ( the end of the bar folding over it’s self forming a crack) when working with off size stock forging a point as you would in square stock by forging in for both sides will lead to fish mouth. As the center of the bar will not move as fast as the out side. Once the bar has been taken to a point begin refining the shape of the profile into the perform of the blade shape. Take care as you forge in the shape that the flats do not get wider than the parent bar and that the bar stays flat.
Once the shape is forged in taper the thickness (distal taper) the point of the blade should be about 1/8”or a little under, and taper to the parent bar thickness at the hilt side of the blade. To taper the blade take a forging heat, and forge the point down to about 1/8” then work back toward the hilt tapering the flats, re forge the profile as needed.
Forging in the grip
Begin by establishing the length of the blade, remember that the blade will lengthen as you forge in the bevels. take a high forging heat ( bright orange- yellow) and set down the beginning of the grip over the horn of the anvil. To forge in the indent set the blade over the horn and hammer straight down over the horn, is the blow is to the far side of the horn, the blade will bend down the near up. Once the indent is forged down to about 1/3”-1/2” begin forging the rest of the grip to shape, do this by shaping the grip over the anvil face, draw a taper from the indent to the end of the grip. Greater width can be achieved by lightly beveling the edges of the grip. A second method to forge the end of the grip/tang in is using the far edge of the anvil, to do this hang the blade section off the far edge and then hammer with a half faced blow (so that on half the hammers face is on the anvil one half off. The edge of the anvil needs to be slightly rounded however. If not it can forma stressriser and cause a crack to form.
Forging in the bevels
Starting at the grip side of the blade. Begin forging in the bevels, to do this angle the cutting edge side of the blade on the anvil and strike at this same angle, strike as near to the edge as possible and once a bevel is established shallow out the angles and begin working higher up on the blade to shift the bevel up the side of the blade until it reaches the spine of the blade.
Because the edge is expanding in length as it is forged thinner, the blade will curve away from the edge. Correct this at the end of each heat, when the blade is still in the reds by setting the spine of the knife on the anvil and firmly hammering the edge back to straight .As the bevels are forged in be sure to work both sides evenly. Flip the blade over and work the other side keeping the same angle used on the first. It is best to work both sides in the same heat, but if this proves difficult a workable option is to alternate side to side from one heat to the next. As the bevels are forged in concentrate on keeping the edge centered the bevels of an even thickness . forge the bevels down until the edge is about thickness of a quarter.
Cutting to length
Cut the grip to length to free the knife from the bar. This can be done with a hardie on the anvil hot, or with a chop saw /hacksaw cold. Once cut to length reforge the end , then normalize the blade and grip three times. Once cool any holes in the grip can be drilled at this time. If much Machine work is needed (hole drilled filed details etc) annealing can be warinted. To anneal, you can heat and cool at a very slow rate by leaving the blade in wood ashs or vermiculite. A second method is to spheriodize. This can be done from a normalised state but works better if the blade is quickly hardened first for steels with chrome or other carbide formers. To spheriodize heat to a very dull red (about 1200degF) and hold for a few min if possible and then air cool.
Grinding and finishing.
Begin by profiling the blade using a worn 30-60 grit belt. Grind back the shape and even out the lines of the knife. Leave the tight radius on the inside of the grip to be filed in later. After grinding to shape run the spine and edge lengthwise on the grinder to make the grinder marks run the long way. Any grinding marks running across the width of the edge or spine runs the risk of cracking in hardening.
Now begin grinding the bevels using a fresh 40-60 grit belt. With the edge up grind the bevels , set the angle with the first pass and stick to it, you can adjust the angle by adding pressure to one side or the other, as you grind. Grind along the flat from the base of the blade to the tip. Cool the blade in water as soon as it is to hot to touch. Grind one bevel down to clean metal then begin grinding the reverse side. Keep the same angle from side to side and from pass to pass. Grind the flats down until the edge is centered straight and about the thickness of a dime.
Now move to the 8” wheel and switch to a 120 grit belt, re grind the flats with the finer grit belt so that the grinding marks run the length of the blade. I prefer a swept grind, if the design calls for a hard plunge cut. Use the 120 grit belt to grind the flats on the flat platen, clean up the plunge cuts with a chainsaw file is necessary. Shifting the belt so that it tracks slightly off the edge of the platen can help in setting the plunge cuts , I would advise going up another grit to 220 grit to avoid the possibility of cracking.
If a small wheel attachment is available for the grinder then it can be used to shape and polish the inside corners on the grip of the knife. If a small wheel attachment is not available, then these areas will need to be filed to shape.
To file place the knife in the vice so that it is griped close to the area to be filed. Use a round file (3/8” ¾”” in size) to shape the radius near the blade. Roll the file strokes over to smooth and round the thickness. Use a half round file to blend this area with the rest of the grip. And round off the thickness. Remember that A file only cuts on the forward stroke, so apply a small amount of pressure when pushing the file away from you, and release the pressure when you draw the file back. Just a small amount of pressure is all that is necessary, just enough to get the file to “bite” any more is a waste of energy and will just make the file cut slower and wear out faster.
Basic heat treating for knife making is a three step process, it is the heat treating that is the most important part of making a knife. It is heat treating that turns a Knife shaped object into a knife. The steps are step one normalizing, step two hardening, step three tempering.
Step one normalizing
heat the blade to a orange heat and let cool to still air down to a black heat, do this three times . this will remove any stresses built up by grinding, reduce the grain size, and leave the steel in the best condition to be hardened. alternately a low temp stress relief can also be used heating to around 1200 deg and slow cooling to around 500 deg or so.
Hardening is heating the blade to critical temp.(the temp. at with all carbon is in solution with the iron) and quenching it (in most cases in oil.) this will force the steel into it’s hardest state. Critical temp varies from alloy to alloy (usually between 1450-1550 DEG F) to find critical, heat the steel and check it with a magnet, the temp at which it looses magnetism is called the curie point,(around1414 deg) about 50-100deg above this point is critical. In practice quenching from the point that the steel looses magnetism is close enough. judging the temp by color is affected by ambient light so even if when using a steel you are familiar with it is a good Idea to check the temp using a magnet. Heat the blade to this point and quench the blade in oil, quench the blade, edge down or tip first in oil, do not angle the blade when entering the quench or the blade will warp. For most steels vegetable or peanut oil works fine and is non toxic, motor oil can also be used,(fresh not used) as can transmission fluid. For a more consistent quench and when working with faster hardening steels a commercial quenchant like Parks-50 should be used. Quench the blade until all color is gone from the blade then let cool to room temperature. Check the edge using a file to be sure the blade hardened, if the file “skates “ then proceed to tempering. If the file “bites” the blade didn’t harden, reheat to a slightly higher temp and requench then check again. If the blade still isn’t hardening the edge may have decarburized, lightly grind the blade and check again if it is still not hard the steel you are using may not have enough carbon to harden.
Step three Tempering.
Tempering is heating the steel to 150-1000 deg F. This will take away the brittleness along with some of the hardness in the steel. The tempering temps will vary depending on the alloy used , size and type of knife being made. For the most part a temper of 300-450 Deg F for an hour is common. Hardness in steel is measured using the Rockwell C scale (RC) this scale ranges from RC30 (unhardened steel) to about RC70 for a med sized knife (6-8” blade) a hardness of around RC58-60 is about right a smaller knife can be harder (RC58-62) and a larger knife should be a bit softer.(RC52-58) For a bit greater performance three cycles of temper can be done, the first 50 deg below the finished temper. For a temper of 350 start with one hour at 300, let cool then one hour at 325 let cool and a final temper of 350 for an hour.
Temper ranges for common blade steels
Steel AS Hard 300 Deg 400Deg 500deg
1050 RC59 RC55 RC52 RC48
1075 RC64 RC62 RC59 RC58
5160 RC62 RC59 RC56 RC54
O1 RC64 RC62 RC60 RC58
W1 Rc65 RC63 Rc61 RC59
(Temper ranges found online from various manufactures websites)
After heat treating lightly regrind the blade using a 120grit belt (remember to keep the blade cool) then move to the 220 grit belt and then the 400 grit. (or begin hand sanding at any point)
Begin hand sanding starting with one grit lower than the last grit used on the grinder. Sand at an angle to the last grit until and even surface is achieved with no lines left from the last grit, then move on to the next grit. Again at an angle to the last grit sand until all mark of the last grit are removed. The last grit used should run length wise on the blade for the best finish.
For a brighter finish, the blade can be polished using a buffing wheel. Charge the wheel with emery and buff the blade. Clean the emery off with acetone and buff with green chrome.
A word of warning here the buffer is a very dangerous tool , do not present an edge to the wheel or it will catch on the wheel and be thrown. Knife makers have been seriously injured when a blade they were buffing caught and was thrown at them.
There are many different wraps that work well for a knife handle, and many materials that work well for wrapping. Para cord, leather lacing and silk cord all work well.
When planning some styles of wrap is a good idea to drill a hole in the end of the handle to secure the end of the wrap in.
The frap wrap
Begin by cutting off twice what is needed to wrap the grip loosely. Now take one end of the cord and tape it in place along one side of the grip so that is runs from the blade to the butt of the handle. Now tape the other end of the cord, to the reverse of the handle so that is runs from the butt of the handle to the blade. Form a loop with the second end around the top of the handle. Now tightly wind the cord around the handle until you reach the butt of the handle. Form a second loop and pull the extra cord through using the taped end. Pull of both ends to tighten the wrap then use a razor knife to trim the extra cord (cut extra off one of two turns in for a cleaner finish that will not fray)
Prepare the handle by drilling a hole in the end. Then cut two and a half the amount it takes to loosely wrap the grip. Find the center of the cord and make a loop pull the loop tight over the blade side of the grip. Pass the two ends over each other and flip the knife over pull tight and repeat until end of grip. Be sure to pass the same side over the top each time. When you reach the butt of the knife pass the two ends through the hole and wrap one to each side of the hole then tie a knot. Pass the ends of the trough the hole and tie a second knot. trim and glue ends or leave long as a lanyard
The first edge on a newly finished knife can be cut in with the grinder to establish a secondary bevel.
On all knives with a secondary bevel (basically anything other than Japanese style work and razors), there are three types of edge: flat ground, convex, and concave (hollow ground edge), Most production knives have a flat ground edge of 15o to 25o. A flat ground edge can be easily re-sharpened and cuts well, Most custom knife makers use a convex edge of the same basic angle of 15-25. This type of edge is just as sharp as a flat edge, but it is stronger, and able to hold an edge longer. It is how ever slightly more difficult to re-sharpen with hand stones. The concave edge is a style that works well for some knives, such as meat cutting knives, that a steel will be used to sharpen but is of limited utility for an everyday knife as it is a relatively weak edge, will dull quickly and is impossible to re-sharpen with hand stones.
As said most custom knife makers use a convex edge, to set this type of edge the blade is ground on the slack belt of the grinder. ( I generally cut the edge with a 120 grit belt making sure to cool the edge frequently. ) Hold the knife edge down at a 10o angle, (as measured from the center line of the blade to the grinder) starting at the base of the blade press in slightly, and take one continuous pass along the whole edge. Cool the blade down and repeat these steps on the opposite side. Continue this process alternating sides until a burr (wire edge) develops all along the edge.
At this point move to a finer belt (220 grit) and continue alternating sides. Then, use 400 grit belt to re-polish the edge. After wards strop the edge on the buffer to remove the bur. The knife should be sharp. If the edge is not sharp after buffing, re-cut the edge at a slightly steeper angle and go through the steps again.
A second method of sharpening is to use water or oil stones, these have the advantage of conducting the heat away from the edge when cutting. Micrographs of edges have shown that even using a dry stone can anneal the edge for 1-2 microns and a belt ground edge at least 5-6 microns as a shaveing sharp edge is less than 1 micron this is less than ideal. A water or oil stone will not have this issue. I have found the best compermise of speed and performance, is to cut in the edge on the grinder, (normally I go to at least 120 grit) and then polish the edge using stones. The key to doing this is to keep a consistant angle of about 11deg and dont try and do to large a jump in grit get a verity of stones and more up in grit slowly rather than trying to do to much with just a higher grit. I use a hard strop to finish off the edge but a very fine stone of 4000grit or finer can also be used. I use a norton tristone set. Course med fine and then a very fine razor hone followed by the strop. For very damaged edges when resharpening, I use a dimond hone I find theses remove material very quickly and are a very good value but to not leave the highest quality finish.
The material being used as an abrasive will affect the cut and in turn the edge. Every material will cut differently this is due to the shape of the crystals diamond for example has approximately 90deg corners were garnet is 30deg this equates to a deeper or shallower “trough” left from a cut for a given grit size, so the quality of the finish from the same grit size in different abrasive can greatly effect how the edge performs.
Grinders, two wheel and three wheel styles
- Wayne Goddard
- $50 Knife Shop
- Wonder of Knife Making
- Jim Hrisoulas
- The Master Bladesmith
- The Complete Bladesmith
Machinery Handbook – (Pub.) Industrial Press