I am interested in sandpaper sharpening. I read a few articles and tried a modified version of the procedure today with materials available in the shop. The articles recommended plate glass as a backer for the sandpaper because itís really flat, and I opted for MDF because it was readily available. The articles also gave specs on different quantities of varying grits of sandpaper, from 50 to 2000 grit, over as many as 8 steps. I found several grits available in the shop, but 120, 280, 500, 1000 and 2000 seemed to almost double each time over only 5 steps.
That progression of proper procedures produced mirror finishes, in less than 30 minutes, on the face and bevel of a $3, 1/2Ē chisel formerly reserved for scraping glue. However, Iím not sure how to make the best use of my time by skipping grits. After todayís experiment, my gut tells me to reserve 80, 150, 240 and 320 grits for grinding new, worn or damaged tools. I think 400, 800, 1200, 1500 and 2000 will hone a fine edge on a previously ground tool. If you have previous experience sharpening with sandpaper, please let me know the grit progression you follow. Any tips or advice are also appreciated.
From contributor A:
The grit you start with would depend on the coarseness or fineness of your grinding wheel. When I first bring a tool into the shop, whether it is a chisel, plane iron, spokeshave cutter, etc., I start flattening the back of the tool with a grit that makes sense for the condition of the back of the tool. For example, rust pits, way out of flat, or heavy machinistís mill marks equals a rough starting grit. I then polish the back through successive grits to a mirror finish.
After that, when regrinding the bevel after the tool gets dull again, I do not do much to the back again unless it has gotten scratched somehow. I use the finest grit that I used to polish the back to remove the wire edge created by honing the bevel. I use the glass and sand paper method and recommend that you go to a glass shop where they will give you free scraps of thick float glass. I use glass and paper for the backs, and my Arkansas stones for my bevels. Sand paper works fine for the bevels as well.
If I was sandpapering my bevels after grinding with a ruby colored wheel I would hone starting with 220 and then go 320, 400, and 600. Then itís up to you how fine you want to go.
Also, Iím not planning to use the grinding wheel at all because the sandpaper works so quickly. Instead, Iím going to use a honing guide to flatten the bevel a degree or two below the optimum cutting angle and only worry about defects near the cutting edge. Then, Iíll apply a micro bevel at the proper cutting angle.
I would advise you to learn to hone without a guide. Guides are an unnecessary step in an already lengthy process. Men honed chisels and plane irons and all manner of edge tools free hand for centuries before someone made a guide. I can assure you they got keen edges because unlike us, those hand tools were all they had.
Hereís a tip to learn to hone without a guide:
On whatever you are trying to hone, the thinner the steel is, the more difficult the job will be. So, start to learn with your largest chisel because it will have a thick blade. The thicker the blade is, the wider the bevel is, and the easier it is to feel when you are holding the bevel flat on the stone or sandpaper. If you like you can practice rubbing the bevel on a piece of glass with no sand paper and a little kerosene for lubrication.
When you learn to feel that you are holding it flat and not rocking it as you rub it to and fro, you no longer need a guide, and thatís one step eliminated from the process. Hold it with two hands and you will learn which of your fingers to put down near the bevel.
Some of my reluctance to grind is fear of burning. The grinding equipment is available at work, so expense is not the issue. Iíve also received some advice from our in-house sharpening guru that honing guides are unnecessary and hollow grinding on a wheel is the way to go. I see the support for that line of thinking in this post too. It initially appears that hollow grinding the bevel produces a slightly thinner, more flexible tip on the end of the chisel. Grinding the entire bevel two degrees below the optimum cutting angle, and adding a micro bevel at the appropriate cutting angle, intuitively seems to produce a more robust cutting tool.
The other item I can comment on at this point is micro bevels. They are a good thing to put on your edge because they make a tougher thicker edge that will last longer.You seem to think they can only be applied to a flat honed bevel. That is not the case. They can be added to the edge of a wheel ground bevel too.
The steps are:
1. Grind the tool to around 25 degrees.
2. Hone the bevel on whatever system you prefer.
3. Raise the tool slightly and hone in a micro bevel.