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Thread: Slow Speed or High(er) Speed Grinder??

  1. #1
    Join Date
    May 2009
    Location
    Philadelphia, PA
    Posts
    96

    Slow Speed or High(er) Speed Grinder??

    Hi friends,

    So after years of flat-grinding on a granite plate and hack-sawing long bolts shorter only to have to file their ends, I think I'm ready to finally "break down" and buy myself a bench grinder. I have nothing against power tools, rather, just the space they take up ( my shop is exactly one half of our 12x20 garage).

    As a hobbyist (mostly) hand tool wood worker and a home owner, I'm really looking for something that's multi-use tool here. I don't imagine I'd be using this tool every day but nevertheless, but I've fallen DEEP into Analysis Paralysis all the same, especially when it comes down to the grinder's speed. Yes, I will grind the bevels on my chisels/plane blades (will I hollow grind EVERYTHING, probably not). I'm not a wood turner or carver (and I don't know that I ever really plan to be). But I also can't imagine I won't sharpen my lawnmower blade this way, too. Recently I had to grind (sand) a flat edge on a bunch of washers and that SUCKED by hand, so I know I'll be doing that kind of work, too.

    I've gone back & forth literally a dozen times between "Get the slow speed; a little more time on some projects doesn't matter next to not frying your plane blades," and "Screw it, get the 3450 speed; you can learn to grind tools safely and then still lean into roughing off material if/when you have to." I've read that variable speed grinders can eventually wear their motors out in a way dedicated speeds tend to not (or, at least, not as quickly). Any observed truth to this?

    I know wheel material matters, in terms of what task I'm doing (white aluminum oxide for sharpening woodworking tools vs silicon carbide). I do eventually hope to upgrade one wheel to CBN for my sharpening but that'll have to wait for funds (should that affect my decision at all?).

    Any advice or suggestions would be well-received and appreciated. Thanks!!
    Please Pick One of the Following:

    Built Correctly & Within Budget / Within Budget & Done Quickly / Done Quickly & Built Correctly

  2. #2
    Join Date
    Nov 2017
    Location
    Winston Salem, NC
    Posts
    78
    I'll take option 1 from your sig: Built Correctly and Within Budget. I have the Rikon 8" 1600 speed grinder, and have a few different wheels for it. I know there is a philosophy about "get the wheel balanced, and never remove it again...", but I don't see that as a dealbreaker - since I would rather spend money on 3 additional (better) wheels and have the ability to grind/sharpen/whatever I want given a few extra minutes. Not that there's anything wrong with the wheels that came with the grinder . . . they will do the job for many applications (80 grit and 120 grit if memory serves).

  3. #3
    Join Date
    Feb 2004
    Location
    Perth, Australia
    Posts
    6,274
    The speed of grinding a blade on a half-speed bench grinder (1450 rpm in Oz) is not much off a full-speed bench grinder (2900 rpm in Oz). However, the drop in surface speed does reduce the heat enough to recommend the half-speed, in my opinion. The half-speed bench grinder is a completely different animal to a slow speed grinder, such as a Tormek (120 rpm). Speed of cutting steel is more to do with the wheel used, with a coarse vitreous wheel around 36 grit preferred, if you go down that route. A 180 grit CBN runs cooler than this, and can be as fast because it does not load up, as the vitreous wheel will do, and you can grind for longer without the blade heating up.

    The full speed grinder is best used by turners, who are more likely to use HSS, which is unaffected by the heat generated.

    Regards from Perth

    Derek

  4. #4
    Join Date
    Feb 2014
    Location
    Lake Gaston, Henrico, NC
    Posts
    3,564
    I have a fast one. Get a slow (half speed) one.

  5. #5
    I have a full-speed 6" grinder, and it is much faster than I would like for grinding chisels and plane blades, with a Norton 3x 80 grit wheel on it. I wish it were slower so I had more control over the process. I don't grind other tools on it, but I find it hard to imagine that you would find a half-speed grinder too slow for sharpening a lawnmower blade. I think it would take under a minute for me to sharpen a lawnmower blade, so even at half speed, it's still a small amount of time. I'd definitely trade that minute for having more control when grinding precision hand tools.

  6. #6
    Join Date
    Dec 2016
    Location
    South West Ontario
    Posts
    796
    A generic water cooled slow speed grinder is inexpensive and works just fine. A CBN wheel is even better if you have the budget.
    ​You can do a lot with very little! You can do a little more with a lot!

  7. #7
    Join Date
    Dec 2015
    Location
    Cincinnati, Ohio - north
    Posts
    67
    So, any comments about the variable speed grinders?

  8. #8
    Join Date
    Mar 2019
    Location
    Greeley, CO
    Posts
    21
    I have an old Craftsman 6" 3400rpm grinder. Even with white grinding wheels it's faster/hotter than I like for sharpening lathe chisels. I recently bought a Rikon 1800rpm 1/2hp grinder with white wheels and it's much better for lathe chisels. But I don't like wasting the white wheels for sharpening mower blades, grinding pipes burrs etc. So I'm resurrecting my old high speed 6" grinder (grey grinding wheel and brass brush wheel) for more mundane tasks and saving my 8" for precision tasks. HF has a 1800rpm 1/2hp on their catalog but it hasn't made it to the stores yet. Typical enabler answer; get both

    Another thought is the slow speed is better for CBN wheels. After a few more years I'll ditch the 8" white wheels and go with CBN but I need to use up the white wheels first.
    Last edited by Eric Danstrom; 05-11-2019 at 12:17 PM.

  9. #9
    Join Date
    Nov 2016
    Location
    Itapevi, SP - Brazil
    Posts
    362
    I have a slightly smaller shop than yours but I am mainly power tool user and a lover for hand tools.

    I went to an angle grinder when I was with similar thoughts than you because it is much more flexible. In the rare occasions I need to go to that aggressive sharpening procedure I use the grinder followed by my diamond plates. It works for me.

    Actually I am very glad as finally I am very comfortable to sharp my chisels free hand with my diamond plates and stropping them. It is easy and fast even for dent ones. It is very rare to need a grinder.

  10. #10
    Join Date
    Feb 2017
    Location
    Minnesota
    Posts
    216
    I've never sharpened a mower blade with anything other than a file.
    Do you really need a grinder to pull double duty for that task?

  11. #11
    Join Date
    Feb 2014
    Location
    Lake Gaston, Henrico, NC
    Posts
    3,564
    I use a 9" side grinder to sharpen mower blades, on everything from a push mower, to a 15' batwing. I have used a bench grinder, but would use such a coarse wheel for mower blades that I would have to keep one set up for just that purpose. The bushog, and batwing have their blades sharpened while on the machine (fabricated a door on the 7' rotary cutter just for that).

    Riding mower, and push mower blades get taken off with an air wrench, held with a foot on top on the corner of the low deck next to the tractor shed, and sharpened with the big side grinder. I like being able to see the top side of the bevel while I'm grinding it. There is a magnetic balancer mounted on the wall right beside where I do that grinding.

  12. #12
    Join Date
    May 2009
    Location
    Philadelphia, PA
    Posts
    96
    Thanks everyone. I honestly can't say why I've been so torn about what otherwise feels like it should be a fairly simple decision. I've used a file before on my lawnmower; it's takes longer than I'd like but it's fine. I guess I just thought, if I'm getting a tool for one thing, can I get it for other things, too. I sharpen my lawnmower ONCE a year, so yeah - I don't NEED a bench grinder for that.

    Osvaldo, if your shop is smaller than mine, I honestly don't know you get ANYTHING done; I sometimes feel like I can barely move in mine and I only have a bandsaw....!! Well done.

    Anyways, thanks all for your input. It is, as ALWAYS, super valuable.
    Please Pick One of the Following:

    Built Correctly & Within Budget / Within Budget & Done Quickly / Done Quickly & Built Correctly

  13. #13
    Join Date
    Jun 2017
    Location
    Raleigh, NC
    Posts
    167
    I just have a Delta 8" variable speed grinder from the BORG. Seems to work just fine after putting an aluminum oxide wheel on and larger washers to hold it.

  14. #14
    Join Date
    Jan 2007
    Location
    Michiana
    Posts
    1,191
    Quote Originally Posted by Steven Mikes View Post
    I just have a Delta 8" variable speed grinder from the BORG. Seems to work just fine after putting an aluminum oxide wheel on and larger washers to hold it.

    I did the same thing a few years ago. It works very well.

    12016227873_7c0db0c76f_b.jpg
    It's wood dust. Saw dust would suggest a problem.

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