Blacksmithing: Plow Work
by James M. Drew, Minnesota, 1943
Wherever steel plows are used the smith will be called upon to sharpen dull plowshares and to apply new points. While these are not particularly difficult tasks they require painstaking care and some knowledge of the proper working of steel.
To sharpen plowshares without aid, the tool to use is a heavy hand hammer with a rounding face. With such a tool it is possible to draw the share out to a thin edge by pounding on the upper side, at the same time keeping the bottom straight by holding it level on the face of the anvil. Drawing the edge out thin has a tendency to crowd the point around too much “to land.” This tendency should be corrected from time to time as the drawing out process progresses, by holding the edge against a hardwood block and driving the point back to its proper position. Of course it would dull the edge to hold it against the anvil while doing this straightening.
During the whole process of sharpening the utmost care should be used to avoid burning the share. When the edge is drawn out much thinner than the rest of the share, it becomes hot so much more quickly than the thicker part that it is almost sure to be overheated unless the smith is very watchful. A light red heat is what is wanted. It is a good plan to have the fire rather long in shape and to hold the edge of the share out beyond the hottest part of the fire, especially after it is drawn out thin, so that it will not be in danger of burning before the thicker part back from the edge becomes hot enough to work.
Some plowshares are made from steel containing enough carbon to allow of being hardened like tool steel. Such shares, after being sharpened, should be heated to a dull red, care being used to see that all parts of the share are of an even heat, then plunged into cold water. The thick edge should go into the water first.
Shares made from mild plow steel containing too little carbon for self-hardening may be hardened on the surface – case hardened – by bringing to an even light red heat and sprinkling with prussiate of potash. The potash will melt and flow over the entire surface of the share which should then be plunged into water or brine.
Prussiate of potash is a dangerous poison. The smith when using it for case hardening should carefully avoid breathing any of the fumes which rise from it when heated. It goes without saying that it should be kept out of the reach of children.
After a plowshare has been sharpened a number of times it will usually be found that the point has become so short that it no longer serves its purpose and a new point must be welded on. The new point should be made of plow steel and not from any high carbon steel such as an old rasp or file, as the latter will cause too much trouble in welding, and may discourage the amateur smith. A suitable piece for a new point may usually be cut from the back or upper part of an old share which has not been worn too thin.
Plow steel, or any mild steel, may be easily sheared into any form by heating to just the right heat and shearing it over the edge of the anvil by the use of the set hammer as the upper blade, so to speak, of the shear. The particular heat at which it may be most easily cut is between black and red; that is, when it is just cooling from red heat to black. No one seems to be able to explain why this is true, but such is the fact.
The new piece to be welded to the point should be shaped. It is, of course, to be welded to the bottom of the share. In making the weld it will be necessary to use great care to have the parts reach the welding heat at the same time. To do this, it is well to heat slowly so as to give the larger part time to get to the welding heat before the small point becomes too hot. Borax and iron filings should be used as a flux, and the first part of the welding should be done in the fire. By this method it is easier and more certain to get the parts welded in the right position than by trying to place them together on the anvil after taking from the fire. When the two parts are at welding heat and still in the fire, the point should be placed in the proper position and a few taps given with a light hammer. This will cause the point to stick fast where it belongs, and the whole may then be taken out on the anvil and the weld finished with a heavier hammer.
If the throat of the old share is worn away, a piece of plow steel is shaped to be welded on the bottom of the throat.
If the old point is worn very short, a piece is shaped. It should be long enough to bend over and weld to the top side of the share. The part to be welded to the top of the share should be thinned down to a feather edge before bending.
To make a new share for the style of plow using what is known as a slip share, plow steel 9/16 by 3 inches in size should be used. A piece of this steel 9 inches in length will make two landsides if it is cut. The long edge of the short landside should be bent to fit the curve of the share, then it should be fitted to the plow so that the bottom edge will extend below the main landside about 3/16 of an inch, to allow for welding, which will narrow it up somewhat. The bolt hole should then be drilled and the short landside bolted to the plow, and the blank share put in place and marked. It should extend about 1/8 inch beyond the edge of the landside. The short landside and blank share should be clamped together by using a clamp and wedge. The whole is then to be unbolted from the plow, and a light weld taken at the point to hold it fast. The clamp is then to be moved down to the middle and a weld taken at the upper corner. This plan will avoid the creeping up out of shape which is sure to take place if the welding is followed up from the point as is sometimes done. The whole should then be welded solidly and the point turned down under and welded and trimmed to shape.
In a shop without power, a very effective tool for shaping plow points after welding may be made from an old horse rasp, fitted with a rather long iron handle. This is to be used while the steel is hot, and is to be followed with the file after the metal cools.
To make a tool which is somewhat handier than ordinary tongs for handling slip shares while sharpening them, the writer once took a piece of 5/8 – inch round iron 2 ½ feet long, welded the ends together and shaped it like a long link, with just enough space between the two sides to hold a plow bolt. Another rod of the same length was bent, and the ends welded to the ends of the link. With the share bolted to the link it was easy to handle, and the stiff link had a tendency also to keep the share from warping while it was heated and sharpened.
Trouble is often encountered in removing shares from plows because of rusted bolts which have a provoking way of turning when an attempt is made to screw off the nuts. Many tools have been invented to hold such bolts in place. One of the best simple tools of this kind consists of two pieces of 7/16 – inch round, mild steel united by a hinge joint. One piece has a bit of tool steel welded in its end. The other has an end bent like a hook. The steel end is sharpened and tempered like a small cold chisel. In use the bent end is hooked over the edge of the moldboard or share, and the chisel end placed against the head of the bolt. This gives a purchase that holds the bolt from turning. The writer once saw such a tool made from the braces of an old buggy top which was found in a scrap heap. The two braces were joined by their original hinge join, and all that was necessary to complete the tool was to finish the two ends as described above.