Before we dive in again, a word of caution regarding belt sanders since they are the main tool* used in this section. Obviously they can remove material quickly, and this is especially true of finger tips and other body parts. So as most people can figure out, safety glasses and gloves are a must. What is not necessarily so obvious is the need for a respirator. A decent respirator may cost $25-$35 but the amount of grinding grit and steel dust it will stop from going into your lung is well worth it!
*Don’t have a belt sander? No problem; you can achieve the same results with a file and lot of elbow grease and I’ll be talking about filing techniques too. Although there are a few ways to remove metal from the blank to finish the blade, if you are working totally by hand the first rule is actually to “move it, not remove it”. Every minute you forge the blade hot will save you at least three minutes if you were to do it by cold filing. So, take the time to make sure the blade is symmetrical, straight, and free of hammer marks. This can take some practice particularly if you’ve also decided to start the edge bevels by hammering.
Once the spear blank is complete, find the center line by measuring the width at any 3 given points and dividing the measurement of each one of those points in half, then connect the dots. This centerline will not only show you how symmetrical you’ve made the point and whether the socket is inline but will be the “grind-to” line for the ridge peak. (Fig 11)
When grinding I typically do the bulk of my work with an ultra-coarse 40 grit, finish with 120 grit, and start my “polishing phase” with 220 or 360 grit. A fair portion of what grit to start with and how big to jump between grits is personal preference so try some variations to see what you like.
Next, clean up any symmetry issues along the edges and make sure the thickness is even near the tip and the transition to the socket. It’s very common for these areas to become thicker during the tapering and this will throw things off later. Just like the peak, the edge centerline is marked. (Fig 12) Now it’s time to start grinding the main bevel.
The bevel is ground “edge up” against the direction of the belt with the goal of grinding to the center of the cutting edge then grinding to the peak. A “steep” angle of grind is used on the first pass. The steep angle means a manageable amount of material is removed while at the same time getting you to the edge centerline quickly.(Fig 13) This needs to be done on all four faces (Fig 14) until the edge is approx 1/32” thick. (Fig 15)
Another bevel cut is then started, though this one is at a shallower angle than the first. By working in this fashion each successive bevel cut will remove a reasonable amount of material, get a step closer towards the peak centerline, and maintain the edge. (Fig 16) This process is nearly identical if you’re working with a file and not a belt sander. The biggest difference is that because the spearhead will be held in a vice the file angle is changed instead of the spearhead.
Another difference is the use of a technique known as “draw filing” to file cut the bevels. This process will greatly even the smoothness of the bevel face and speed up the cut. Draw filing involves using the file a lot like a draw knife. The file is held 35-45deg to the bevel, moved along the entire spear edge while at the same time pushing so it uses it full cutting surface. With a sharp file and practiced hand it is possible for the file to cut so effectively that it will remove little ribbons of steel on each pass.
On all remaining bevel cuts you can tell whether they are complete by looking for a shadow or gap between the edge and the belt. (Fig 17) Once the gap disappears you’ve completed that cut and it matches the bevel. The next bevel cut can begin. (Fig 18)
This process of making multiple bevel cuts continues until you’ve nearly reached the peak centerline. Remember this is your rough shaping and so you don’t want to go all the way to the peak or edge centerline; that will be accomplished with the next two grit levels.
Once the rough bevel cutting is complete, swap the belt to something finer (I switch from 40 grit down to 120 grit.) Simply match the bevel and work evenly on all faces until the ridge centerlines and edge centerlines meet themselves. If you wish you can now swap up to an even higher grit (220 or 360) and polish the spear. As long as you make sure to work in the same plane as the bevel, you’ll end up with a nice defined ridge peak, and razor sharp edge. (Fig 19)
Fig 11 - The spear blank is marked with a centerline and symmetry is assessed.
Fig 13 - The first steep bevel cut has been completed to the edge centerline along the entire length of the blade.
Fig 15 - Both first bevel cuts are complete and come within 1/32" of forming a sharp edge. (The edge will naturally sharpen as successively finer grits are used).
Fig 17 - As the second (and successive) bevel cuts are made a shadow/gap appears between the edge and the belt in areas where the new cut is not completed
Fig 19 - After multiple successive passes all bevel cuts are complete and this is fully functional spearhead. The only additional option is to continue on the current bevel angle with successively finer grits of sand paper to polish it.
Fig 12 - The tip has been ground symmetrical and to 90% of it's final shape
Fig 14 - The backside of the first cut is also completed. It is at the same angle (and therefore width) as the first and nearly meets at the edge centerline.
Fig 16 - The second bevel cut has been started. Notice it is shallower, comes closer to the peak centerline, but yet maintains the position of the edge centerline.
Fig 18 - Once the new bevel cut is complete to the edge centerline the shadow dissapears. Paying close attention to this indicator will ensure that the bevel remains smooth and even.