The Low Spark of High Speed Grinders


Being lazy, I like to use a grinder to prep cutting edges. Works great until I try to grind off that last little bit. Being somewhat inept, I invariably burn a corner. So I tried this: turn off the grinder! And it works pretty good. I have a 6″ Baldor, an awesome grinder, it spins forever when turned off, so I let it get up to speed, turn it off and grind away for a few seconds, check the edge and repeat. Not more burns when chasing the edge.

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11 Responses to The Low Spark of High Speed Grinders

  1. Jay says:

    This requires a video. Demands it actually. I’ve been wondering how some guys get the grind right down to the edge.

    • Zander K says:

      Sorry, I don’t have any way to make videos.
      Personally, I shouldn’t be grinding all the way to the edge, hollow grinding down to 1/32″ or so makes it easy to finish on a stone. But I do it anyway and this trick allows me to treat my grinder as a slow speed or hand cranked grinder for that last little bit: it is slowing down as I grind and isn’t spinning long enough to burn (well, I was able to burn a corner this morning but I was sorta trying to).

      I think the guys who can do it are good (one trick is to start in the middle and zoom off the end) and/or use a slow speed grinder, a “friable” grinding wheel (Norton 3X), or water cooled wheel (such as a Tormek).

      Another reason for me not to grind to the edge is, with some of the old bench plane irons I’m working with right now, it seems that grinding to the edge causes the edge to crumble in use. I have no idea what is going on but I’ve repeated it several times.

      • Jay says:

        Eh, your camera probably has a video function. You could post it to YouTube and Give a link even if your blog server doesn’t allow videos. But it’s easier for me to suggest it than for you to do it.

        I suspect your crumbly edges could be the effect of tree sap left on the iron for decades. Some of the saws I recondition have crumbly teeth until you get past the oxidation and into the good stuff; some still have bits of sawdust gummed up on the teeth and smell unmistakably of pine when I sharpen them. Leaving sappy sawdust on saw teeth or a plane iron must be like leaving these edges in turpentine for years. Old paperback books from the 1950s turn brown and crumble from the acid in the paper; a coffin smoother from 1850 with grunk on the tip of the iron is bound to be brittle.

      • Zander K says:

        >your camera probably has a video function. Nope, no such luck, my DSLR is pre video. No camera phone either. I have posted animations to YouTube and inserted links in web pages so that isn’t an issue.

        Interesting ideas about sap, that would not have occurred to me but I don’t think sap is contributor, I squared the edge before regrinding the bevel and I think it was one brand of blade (which I have now forgotten or it was unmarked, may have been a hole at the top Stanley) but after using a stone to redo the bevel it has been fine. I did more grinding today with no issues on a (I think) Sargent blade.

  2. Jay says:

    One thing you may want to take a look at is something like this.

    I snagged one but haven’t hooked it up to my grinder yet. Seems potentially useful for a number of things beyond sharpening chisels and plane irons. While I’m quite comfortable honing on oilstones by hand, i.e., without some sort of guide, grinders give me a case of the fantods. There appear to me to be many bloodcurdling ways to “become one” with your work when it comes to bench grinders! Mostly I use mine to steel brush rust off of crappy old tools I pick up. Does a great job.

    • Zander K says:

      That looks pretty nice, thanks for the pointer! I have attachments & jigs for grinding blades, where I have problems is not controlling heat and getting a consistent, even grind. I haven’t seen (or didn’t know what I was looking at) jigs for a nice square & consistent hollow grind. Using the mill seems like overkill & hot. I too have a knotted wire wheel on one side of the grinder (quite aggressive and can remove quite a bit of steel if I lean on it) and a plain wire wheel on the buffer. Luckily, when I mess up, the grinder just yanks stuff out my hands, sucks it into the chute and stalls. Taking skin off with the grinding/wire wheel does really hurt the next day. I’ve finally taught myself “grinder means gloves” and keep a pair next to it.

      • Jay says:

        “Luckily, when I mess up, the grinder just yanks stuff out my hands, sucks it into the chute and stalls.” Been there. Burnt up the relay on the split phase motor and still looking for a fix. One thing that is really handy for grinder debridement is a spring loaded hand vise that tightens with a wing nut, to hold on to smaller, odd-shaped pieces such as the nut from combo square.

        “Using the mill seems like overkill & hot.” plus you don’t want hot AlO2 dust sparks all over your slides. I finally found an old atlas horizontal, which will be quite the project.

      • Zander K says:

        I just ran across a video showing the process I’m trying to reproduce by turning off the grinder:

        I’ve looked at those vises and wondered what they were good for, now I know!

  3. Jay says:

    Yeah. I’ve been watching his blog for a while now with some bemusement. In a recent post he documented a ground-breaking discovery about how much better his paring chisels work when he followed Roy Underhill’s suggestion to grind them at around 20º instead of the 30º? 35º? 55º or whatever he was using. I’m reminded of Winston Churchill’s assessment of John Foster Dulles: “Dull, duller . . . “

  4. Steve Branam says:

    Thanks, Zander! And you too, Jay! Gotta learn somewhere, dumb mistakes and all.

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