The main issue with using this grinder is holding the chisel or iron in one hand while cranking with the other hand.
|Cranking with the right, holding blade with the left|
|Hand position for holding a chisel|
This tool rest is not exactly rigid. So when I move the blade to the left where the tool rest has less support, it flexes more and I can end up grinding too deeply if I'm not careful.
Another issue is where to set the tool rest so that I grind in the center of the bevel. If it is not set just right, you will grind too far forward or too far back on the bevel.
|Front of bevel is too far off the wheel|
|Now back of bevel is way off the wheel|
|This looks to be just about right|
I can change the location of where the wheel contacts the bevel by nudging the tool rest forward or backward. Just a millimeter or two can make a big difference.
I wanted to take the guess work out of this, so I made a stick with a 25° bevel on one end. The lines I've drawn are perpendicular to the bevel. The left line represents the back of the bevel on a tool. The right line is 5/32" forward of the first line. Most of my plane blades are about 5/64" thick. For a 30° bevel, the total length of the bevel would be twice the iron thickness, or 5/32".
|Try to set the tool rest so that the wheel touches the center between the two lines|
This would be different for chisels because they have thicker blades. Later I drew another line on this stick that would help me set up for chisels. It was about 5/16" from the leftmost line because the chisels I looked at were about 5/32" thick just behind the bevel.
While researching this, I found a great article online by Bruce Wedlock that discussed the geometry involved in setting up the tool rest, including making a jig to help out. He even sent me some info on how the geometry was worked out.
Unfortunately, my tool rest is too wimpy to worry about being so precise. For me, the bottom line is this. Set up the tool rest with the wood block above to get close. Then mark the bevel with ink.
|Bevel marked with red Sharpie|
Grinding lightly (can use your right hand to slowly turn the wheel, rather than turn the crank) to see where the wheel is contacting the bevel. Note that on this chisel, the bevel is WAY too long from previous poorly executed sharpening.
|Grind marks a little too far back|
Adjust the tool rest by bumping it forward a tiny bit.
|The new grind marks are better located|
When satisfied, grind away. But be careful not to overheat the tip. Gotta keep water handy and dip it in there frequently.
|Grind until a millimeter or less of the tip is still red|
Then it's off to the sharpening stones and a strop to get a nice sharp chisel.
Here's another example. For this plane iron, the bevel was too long and I marked the extent of where I thought the bevel should end with a red line. I wanted to grind midway between the tip and the red line. My first attempt (before adding the red line) was too far back.
|First grinding was too far back|
|After adding the line and nudging the tool rest forward I got the grind centered between tip and red line|
I thought about how much better this would be if I could use two hands. I tried a couple things that ultimately didn't work out, but it was fun trying. First, I rigged up a "treadle" to see if I could keep the wheel spinning with my right foot while holding the tool being ground with two hands.
The treadle was simple - the vertical part was a board with a hole in it that fit over the handle of the grinder.
|Working the treadle while holding the tool with two hands|
|Grinder handle is taped to prevent damage|
This was attached to a foot board with a loose bridle joint pinned with a dowel.
|Lower part of treadle|
In use, I would step on the lower part to get the handle cranking. But I'd have to pick my leg up before the momentum of the grinder arm would pick the treadle back up. If I wasn't fast enough, I would stop the grinder quickly, which would loosen the reverse-thread nut that tightens the wheel.
At one point I even tried to rig up some bungee cords to lift the treadle and thereby lift the grinder handle on the up-stroke.
|That's my shoe stepping down on the treadle|
|The bungee cord setup|
I think with enough practice this might have worked. But in the end, I dumped the treadle idea and I'll just practice grinding one-handed. I have to realize that grinding does not need to be a precision operation. I just need to get close so I can sharpen easier on the stones. On a bright note, I learned a little about making a treadle - might be useful someday with a lathe idea I've had for a while.
BTW, adding the hollow grind has made it MUCH easier and faster to sharpen my chisels and plane irons. The amount of metal you need to remove during sharpening is far less. I learned sharpening from Paul Sellers' videos and he sharpens to a convex bevel. I guess time will tell if I miss any features of the convex bevel.
I've a question for anybody reading who cares to comment. What safety precautions should one take when using a hand grinder? I normally wear glasses when I work, but are goggles recommended? Where to stand or where not to stand when grinding? Breathing protection? Other things?