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Thread: Is It Possible to Slow Down a Grinder's Speed?

  1. #16
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    Quote Originally Posted by bob blakeborough View Post
    Well circumference of an 8 inch and 6 inch wheel is pretty easy to figure out, and RPM's make the rest pretty simple. A mile has 5240 feet, so if my math is remotely accurate, the 6 inch wheel is turning at around 62mph (or 100KMH approx)while the 8 inch wheel is turning at about 41.5mph (67KMH approx). That is a fairly substantial difference I would think but as to the effect it has on an edged tool, I am not sure.
    Exactly. People have used high speed 6" grinders and slow speed 8" grinders successfully for years. I think these are perfectly manageable speed for grinding steels used for woodworking tools. However, I see "high speed 6" is about the same speed as slow speed 8"" quite often, but they are not and I think such difference (33% speed difference) should be clearly advised so that the person who are considering on buying a grinder can make informed choice there. I'm not saying one is better than the other, but I think at least information should be clear and reasonably accurate.
    Last edited by Sam Takeuchi; 01-23-2013 at 12:56 PM. Reason: Fixed derp

  2. #17
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    Quote Originally Posted by Sam Takeuchi View Post
    Exactly. People have used high speed 6" grinders and slow speed 8" grinders successfully for years. I think these are perfectly manageable speed for grinding steels used for woodworking tools. However, I see "high speed 6" is about the same speed as slow speed 8"" quite often, but they are not and I think such difference (67% speed difference) should be clearly advised so that the person who are considering on buying a grinder can make informed choice there. I'm not saying one is better than the other, but I think at least information should be clear and reasonably accurate.
    33% difference but the point is the same... It is definitely different, but both obviously still work...

  3. #18
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    Quote Originally Posted by bob blakeborough View Post
    33% difference but the point is the same... It is definitely different, but both obviously still work...
    Ha! I was mindlessly looking at the opposite side of the number. I didn't even realize that!

  4. #19
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    I couldn't tell exactly which kind of motor the Jet grinder has, but I'm pretty sure it's not a universal motor. Split phase, probably.
    Is it possibly a DC motor? When those are series wound they have decent torque at the lower speeds. A former co-worker of mine repairs exercise equipment and found me a tread mill with a good motor and controller for my lathe. Just another project on the to do list.

    Most of this is off my plate since my shop doesn't have a wheel grinder. My father's pedestal grinder was a 6" at 3450 rpm and he could sharpen drill bits or edges with an old grey wheel. The wheel was a lot smaller last time I recall seeing it.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  5. #20
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    You all have given me excellent information. I think that I will go ahead and get the Jet 6" grinder and just cool off the chisels and planes continually. I am initially planning to hollow ground the back of my plane irons. I will go ahead and get the white friable wheels to help keep the temperature down.

  6. #21
    I have a General 8" slow speed grinder, and just recently changed the wheels that came with it to a pair of the cooler running white wheels that LV sell.
    I wish I had done it years ago.
    The small tools that I was grinding before, needed to be dipped in cold water quite often, and now, the same tools did not even need to be dipped once.

    My guess is that you will see benefits from these white wheels on a 6" grinder too.
    Definition of an expert: Someone more than 50 miles from home with a briefcase.

  7. #22
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    iI just dip the chisel in water and quench it the instant the water starts to boil off. This is every 2 seconds when the edge is getting thin. NO NEED for slow speed grinders. If you want a cooler grinder that cuts faster,get a belt grinder. I use my Wilton Square Wheel grinder all the time. Grizzly puts out a decent belt grinder for MUCH less. It has no guards,but you could make some plywood ones to keep the dust down. I keep a large scoop with 4" hose right under mine,with a DEDICATED dust collector. Don't mmix wood dust with steel sparks. Right behind the dust bag I have a 2nd. shuttered wall fan to get any dust that comes through the bag.

  8. #23
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    All good points, but if it makes you feel better, go buy yourself a slow speed. I had an 8" WC and it served me very well.

    Sold, after I found a used Baldor in great shape.
    Where did I put that tape measure...

  9. #24
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    I guess that depends on what you mean by slow speed grinders. Like you described mine is a 3 phase variable frequency drive set up that goes from 0 - 120htz. I grind at about 8 - 10htz and it makes a world of difference. I can grind with my eyes closed, literally, by simply listening to the sound and the feel given off by the tool as to whether I'm grinding in the hollow bevel or not. At those sorts of speeds it's harder to burn a tool than not - you only need to quench if you get heavy handed. And! what no one can believe till I show them it's actually much quicker to grind at such low speeds - about 40% faster. I think it has to the metal being able to absorb and pull the heat away much faster, speed as a function of heat buildup and being able to remove larger amounts of material at slow speeds... Over all it's by far the best way to grind bar none. Probably the biggest benefit is at such speeds you can take your time and carefully grind some extremely complex shapes without EVER worrying about burning or over grinding the tool. YMMV
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  10. #25
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    I can't remember who said it other than it was a well known woodturner, but, "everyone has access to a slow-speed grinder; just use the 'off' button. "

    I think if you use this method, it might be prudent to keep an extra power switch on hand... on off on off on off...

  11. #26
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    Every grinder manual I've seen (yeah, I read the papers that come with even the most basic of tools) cautions against turning the power on and off rapidly, particularly if the wheel hasn't come to a stop yet. I guess it could eventually loosen the grinder wheel. I don't know if that's actually true or not, but I try to abide by it.

    Found the PDF of my manual - here's what mine says, at least:

    DO NOT TURN THE MOTOR SWITCH ON AND
    OFF RAPIDLY. This could cause the wheel to
    loosen and create a hazard. Should this ever
    occur, stand clear and allow the wheel to come to
    a complete stop. Disconnect your grinder from the
    power supply and retighten the wheel nut securely.
    Last edited by Joshua Pierce; 01-25-2013 at 9:47 AM.
    " Be willing to make mistakes in your basements, garages, apartments and palaces. I have made many. Your first attempts may be poor. They will not be futile. " - M.S. Bickford, Mouldings In Practice

  12. #27
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    Probably mostly over uses the switch,wearing it out. Especially with these cheap Asian grinders which we mostly have,I'd be careful about over use of the switch. My old 1964 Craftsmans are still working fine. I like the old flat front motors,especially for grinding tools like draw knives. The motor doesn't get in the way. At the time,we considered these grinders cheaply made (still are,compared to GOOD old ones!). They even have real glass windows in their guards(don't scratch up so easily). How things have gone down hill!!
    Last edited by george wilson; 01-25-2013 at 10:11 AM.

  13. #28
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    Both my grinders are 8" one slow, one high speed. I actually prefer the high speed one for grinding chisels and irons. I have found if you can pretty much grind without quenching unless you get heavy handed. For quenching (when I do get heavy handed) I use a water-soluble cutting oil concentrate from Grizzly.

  14. #29
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    Why would you do that? Water is a more effective quench.

  15. #30
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    Quote Originally Posted by bob blakeborough View Post
    A mile has 5240 feet...

    5,280 ft., no?

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