Tuesday, January 31, 2017

More on the Hand Crank Grinder

I've been playing with the new (to me) grinder.  It's clear that it will take some practice to be able to use it well.  Fortunately I have a really crappy set of chisels and some old plane irons to mess with.

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
Here's a closer picture.  I'm pressing down (not too hard) on the tool rest with the thumb and using my first finger as a fence against the lower edge of the tool rest.
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.
Working the treadle while holding the tool 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.
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.
That's my shoe stepping down on the treadle
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.
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?


  1. I usually wear my everyday glasses, but they have shatter proof lens, anti scratch etc. Still i sometimes wear safety gogles over them...mostly when dealing with metals.
    As for the dust mask, i will admit i dont do it often enough, but it does create fine particulate metallic dust, probably a wise idea.

    Stance? You have to be mindfull of a broken grinding wheel could fly off chunks, but i do not think it would be as bad as with powered grinders which usually operate at 3450 Ripems.... Easily, mostly preventable by ring testing your wheel and or having a good look at it before use. Accidents can still happens, but being aware of dangers is a big once of prevention.

    I like your thread mill test ideas, interesting.....

    Bob, with Rudy still on my lap. i may have to disturb him to get more coffee :-)

    1. Had to search for "ring testing a grinding wheel". Great tip! I'll make sure mine is ringing properly before using again.

  2. You need a pintel at the bottom of the treadle where your foot is. Hard to describe but it will allow the top hole to move past the apex and go around again. Same thing was used on treadle spinning wheels. Bob Easton used something like that on his treadle lathe with a flywheel.

    1. "Pintel" is a new one for me too. Searched Bob Easton's site, but didn't come up with anything. Won't worry about it, though, unless I actually look more into building a treadle lathe.