bench grinder

Discussion in 'Starting a Lawn Care Business' started by Jaybrown, Mar 20, 2013.

  1. Magna-Matic

    Magna-Matic Sponsor
    Posts: 826

    Hello All,

    Jaybrown asked if there was an advantage/disadvantage between a 6" and 8" diameter wheel.

    SPEED
    The advantage to having a larger diameter grinding wheel is that it increases the SURFACE FEET PER MINUTE of the grinder. This can increase the speed that it will grind, depending on what you are grinding. Now it is not JUST the wheel diameter, but also the MOTOR RPM that affects the surface feet per minute. When you read the SFPM definition you will understand that not every type of metal can be ground at the same SFPM.

    Here is a link defining SURFACE FEET PER MINUTE
    http://en.wikipedia.org/wiki/Surface_feet_per_minute


    BENCH GRINDERS AND OTHERS LIKE THEM
    Generally speaking most all bench grinders and bench grinder style sharpeners run at 1725 RPM. A 1725 RPM motor is a less expensive motor, and by using this motor to increase the surface feet per minute the grinder manufacturer needs to use a larger diameter grinding wheel to get the SFPM higher. This requires a more expensive grinding wheel. So they have made the machine cheaper to build and passing along a more expensive grinding wheels cost to the consumer. I am speaking generally here – please understand that a standard bench grinder is designed to sharpen tool bits, chisels, etc steel that is usually 60 ROCKWELL or higher, for this application a very hard grinding wheel at 1725 rpm will produce a better SFPM for that application.

    All lawnmower blades are generally between 20-40 ROCKWELL – now the SFPM of the bench grinder is too slow with a grinding wheel that is too hard – this causes burning, glazing, dressing, chatter, slow grinding speed etc. MAGNA-MATIC runs 3450 RPM with 7” diameter wheels, and the grinding wheels we use are properly matched to at our SFPM to remove steel from a lawnmower blade very quickly without burning it, or glazing the grinding wheel.


    WHEEL LIFE
    As Kelly’s Landscaping mentioned - having a larger will provide a longer overall grinding wheel life, however at a substantial cost. One of the reasons we use 7” diameter wheels is they are a size that the scale of economy provides the best grinding wheel for the dollar size. When you start getting up at 8” to 14” the wheels get far more expensive.


    BEVEL/ANGLE/HOLLOW GRIND
    Windflower mentioned how it will change the look of the angle. A larger diameter wheel will create less of a “hollow grind” (where the surface of the cutting edge angle looks concave). This is true only when the wheel is new, as the wheel reduces in diameter it will make the same surface as any other wheel at that same diameter. The diameter of the wheel does not change the ANGLE / BEVEL, that is controlled by the sharpener (if you use MAGNA-MATIC) or it is controlled by the operator’s hands and how steady he/she can be.

    OUT-OF-ROUND / WHEEL CHATTER
    Remember the larger the wheel the more violent the vibration can be when a grinding wheel becomes “out-of-round” due to non-rigid work-piece holding – the vibratory condition of a 10” or 14” wheel rumbling a grinder can be more dangerous than a smaller wheel.

    It is for all of these design considerations and engineering why MAGNA-MATIC sharpeners are designed so much differently than all the others out there, and why our sharpeners are faster, more quiet, do not vibrate, sharpen a blade in 1-2 minutes, don’t require wheel dressing, don’t burn the blade, maintain consistent cutting edge angles, can dial-in specific cutting edge angles, etc.

    ANGLE GRINDERS
    All of the same concerns mentioned above also apply, but with an even larger problem - total inconsistency of cutting edge angle. When an angle is changed every time a lawnmower blade is serviced this removes far more steel from the blade than is necessary to sharpen it. If you would sharpen the lawnmower blade consistently at the same angle the lawnmower blade would have a longer useful life, it would provide a better quality cut on the lawn, you would use less of the abrasive “grinding wheel/flap disc”, and it would take less time.

    Sorry for making such a long post, but there is a lot of information to consider with the question that was asked. Here is a link to some additional education info if anyone is interested http://www.magna-matic.com/educational-info.html

    Thank you,
     
  2. Banksy

    Banksy LawnSite Member
    Posts: 190

    If you take your time with a less abrasive flap disc, you can do just as good of a job with it. It works great for me. Plus, it doesn't grab the blade and my hands don't have to touch it. Assuming we all wear leather gloves.
    Posted via Mobile Device
     
  3. Jaybrown

    Jaybrown LawnSite Bronze Member
    Posts: 1,160

    Wow thanks. I ended up buy an angle grinder Seems to real work well
     
  4. Slimreynolds

    Slimreynolds LawnSite Member
    Posts: 96

    what grit do you use?
     
  5. CQ_DX

    CQ_DX LawnSite Member
    from MA
    Posts: 67

    I disagree - completely. A right angle grinder will NEVER do "just as good of a job". If you did an A-B comparison, you'd understand.

    Magna-Matic tools WON'T grab the blade - bench grinders will.

    Not sure what is meant by "my hands don't have to touch it". I wear gloves when cleaning with the MAG-12008 and different gloves when sharpening with the 8000. I also have gloves on while balancing. I also have gloves on when removing/installing blades.

    Most who use a right angle grinder sharpen the blades while mounted - and then don't balance them. That's a huge mistake.

    A tool "works great for me" is a common message - by those who have yet to experience something better. Same with comments made by people who say "balancing is not necessary" - they simply don't know any better or they simply don't care. You'll never change a stubborn mind.

    I've used just about every tool and technique out there and am always looking for something better - the 8000 Magna-Matic is the best I have ever used. If there were something better, I'd do as before and sell it to a LSC and move on.

    Bottom Line - sorry, but after trying other products and techniques, the only thing a right angle grinder brings to the table is it's the wrong tool for the job. Easy & fast? Maybe. But "just as good of a job" - laughable!
     
  6. cpllawncare

    cpllawncare LawnSite Silver Member
    Posts: 2,659

    I would love to be able to afford the magna matic but it's just not in the budget this year, so I guess the bench grinder will have to suffice for now, I agree the proper tool for the job is the right way to go but there's always the budget to consider.
     
  7. Chineau

    Chineau LawnSite Member
    Posts: 35

    Thank you to the folks from Mag-matic sharpeners for the explanation about grinder theory. Now a quick word from the safety dept. prior to starting my little business I worked at a mine and for the last couple of years was a foreman, each morning lining up crews for work I was tasked with delivering a safety message. One that stands out is a conversation about a young man who was a t.q welder he was using a 4 inch angle grinder and the disc broke apart one of those pieces hit him in the throat cut an artery and he died. Safety glasses as a minimum and face shield preferred.
    Grinders are a useful tool, but used improperly can hurt or kill you quick.
     
  8. Banksy

    Banksy LawnSite Member
    Posts: 190

    I can't justify the purchase of the Magna tool you suggest, but it looks awesome. I remove my blades, clamp them in the vice (ie, not having to touch them comment), and go slow while holding a steady angle with the flap disc. It doesn't take much to have them sharp again. And then I put them on a blade balancer before reinstalling them.

    So, ya it works just fine for me.
     
    Last edited: May 23, 2013

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