Talking with one of the boys after church this week, a couple of interesting points came up about setting up a grinding machine.
First off let’s clarify what is grinding and how it differs to honing. Grinding tools is what you do to the edge of a tool that is damaged and requires re-profiling whereas honing is a light polish to maintain an edge. The set-up, which I have used for many years, is an ordinary everyday twin-wheel bench-grinder. Now these machines operate at far too high a speed and spin the wheels in the wrong direction. The reason the wheels are spinning the ‘wrong way’ is because they will catch the tool and drag it down, damaging the tool not fixing it! What you need is for the tool to ride on the wheel and so the first thing you need to do is to unbolt the base, turn it around, and bolt it back down: this reverses the direction the wheels travel in. As far as speed goes, I use a very light touch but you could probably just plug in a transformer.
Most importantly you MUST junk the wheels and replace them with medium or fine grinding wheels made specifically for tool-sharpening – I use a ruby wheel on one side for grinding and a rubber wheel on the other for honing- the rubber wheel is loaded with chrome polishing paste – the high speed of the wheel throws the paste off quickly but you use a tiny dab at a time – wear safety glasses and wash your face at the end – the reversed wheel direction throws all the waste product, including all the sparks, all over you if you put the tool you are grinding too low on the wheel. Try to use the sector as close to the top as you can.
It is perfectly acceptable to cut out an MDF wheel as a cheap alternative to a rubber wheel, as the glues in the MDF are actually course enough to act as a grinding medium but then the glues in MDF can be extremely toxic so this is a path I have never travelled.
I also removed the shrouds to give myself access to as much of the wheel as possible but this leaves the wheels without safety guards and you need to contrive a box of some sort to replace them – work safely the life you save will be your own.
Once the tool has been ground on the ruby wheel and honed on the rubber wheel, you can put the grinder away in the back of the cupboard; all tools properly sharpened need a gentle hone from then on and this is best done by hand – I use a slip-stone, dry (no oil, no water), which is classed as bad practice because the pores of the stone clog and make it glass-like, also the slurry raised on a wet stone is its own grinding paste. The glass-like surface on my slip stones is undoubtedly slower than a marginally more aggressive (wet) stone but it polishes a cutting edge beautifully none-the-less and sits in my pocket ready for use to touch-up an edge every time I pick up a new tool, as opposed to sitting in a mucky oil/water stone box that I may be less inclined to fetch. I am more inclined to regularly hone tools if the stone is in my pocket. Many of my students prefer a strop loaded with chrome polish on the bench or in the top of their tool box. Whatever your chosen method the important thing is to make certain you hone tools all the time so that the edge of every tool remains razor sharp and never dulls enough to require re-grinding.