Building a blade grinder

Discussion in 'Mechanic and Repair' started by riches139, Oct 13, 2004.

  1. riches139

    riches139 LawnSite Senior Member
    Posts: 369

    I have my design layed out for a blade grinder I wish to build.

    My question is should I use a motor with 1725rpm or 3450rpm?
    I see both advertised on other grinders.

    I don't want to burn the metal. :angry:
     
  2. fixer67

    fixer67 LawnSite Silver Member
    Posts: 2,100

    What will the grind stone be rated at? You do not want a stone to come apart in your face it could ruin your whole day. And what size will the stone be? The bigger the stone the faster the surface speed will be at a given RPM.
     
  3. riches139

    riches139 LawnSite Senior Member
    Posts: 369

    I realize that a smaller wheel will have a lower surface speed,
    but I may need a 8" wheel for clearance.
    I haven't checked on the rating yet, but I'm sure they make wheels compatable for both rpm ranges.

    I guess my question is, will the 1725rpm motor be sufficient for the task using the same size wheel and rating?

    Never owned a grinder before, so I don't want to invest in a new motor that won't do the job.

    Thanks Fixer
     
  4. fixer67

    fixer67 LawnSite Silver Member
    Posts: 2,100

    I checked our grinder at work today and it is rated at 3450 RPMs and has a 7" wheel and I have not had a problem with burning blades. You can sharpen mower blades free hand on just about any bench mounted grinder. In fact that is what we use at work. With all the funny shaped blades out now days the fancy high dollar blade machine is up on a shelf in back of the shop collecting dust. It was just too much of a PITA to try and set it up for every blade sharpen because no two were alike. And you had to have a mounting jig for every blade shape. It was more like cutting keys than sharping blades. A blade sharpening machine would be OK if all or most of the blades were the same type and shape I guess but I fine a bench grinder works just fine. I have even used a side grinder when some one else was using the bench grinder. By the way our bench grinder is not mounted on a bench. It is mounted on a pedestal (post) which makes it easier to use without the other end of what you are grinding hitting any thing. When you get your grinder built you should post some pictures of it. Have fun and good luck.
     
  5. UNISCAPER

    UNISCAPER LawnSite Bronze Member
    Posts: 1,426

    If you are going to the trouble of making a blade grinder, go a step firther. Look in the equipment, machinery trader for an old Bridgeport milling machine. Set the table for the angle you want, shave the dings off the blade. Takes about 10 seconds a side, you make even cuts, so balancing is nearly unnecessary, and you can put the shavings into a can, run them to the recycler and get Christams party money. We had $350.00 in ours when we were mowing alot and sold it for $500.00 when we moved. It was the best investment we ever made.
     
  6. riches139

    riches139 LawnSite Senior Member
    Posts: 369

    I guess mine will work somewhat similar.

    I will use a machinist cross slide vice to move blade back and forth, side to side.
    Motor and wheel will be mounted 30 degrees to the horizontal plane.
    Initial height adjustment will be with new wheel, as wheel wears thin shims can be added under blade to increase height.I can also use an adjustable motor mount to change height, but will increase cost.

    Blades for my M60 Tank and walk behind are virtually straight, so I intend to end up with a "factory" quality grind.
     
  7. The Doctor

    The Doctor LawnSite Member
    from Troy,AL
    Posts: 10

    Take a look at the RBG blade grinders and make one just like that. Use an 8'' premium ceramic wheel (about $50 each but they work fast and last!!!) and a 3450 rpm motor. The best grinder I've ever had.
     
  8. burnandreturn

    burnandreturn LawnSite Senior Member
    Male, from Germany
    Posts: 303

    One question, Why do you want to keep the blade edge straight? Much too much grinding with no improvement in cutting. As the blade wears, the tip gets the most wear. Grinding the blade edge straight to match the tip width is not required. The reason I say this is because I have built a couple of blade grinders and one of them was set up to do as you say. Took forever to sharpen with no appreciable cutting quality. The machinist's vise moves slowly and you MIGHT have trouble not over heating your blade. Typically a machinist will have a cooling agent running over the stock being machined.

    I sharpened blades on a lathe. Took forever and it was the same principle as what you are talking about. Then I converted a big radial arm saw, again the same principal, the stone would slide back an forth on the edge of the blade and it took forever to sharpen.

    My best sharpener is a belt sander I built form scratch with an adjustable blade rest. I use a 36 grit belt two inches wide and 72 inches long. 1 hp motor at 3475. One minute a blade. I have a wire brush mounted on the belt sander also too facilitate cleaning the build-up of before sharpening. Total cost was somewhere around $250.00 and it will sharpen any type of blade and is useful for many other things. I have used all the commercial blade grinders and the belt sander is much better, IN MY OPINION!
     
  9. The Doctor

    The Doctor LawnSite Member
    from Troy,AL
    Posts: 10

    Have you tried the Wall grinders? If so, what size rock and how many rpms. The one I have has an 8'' rock with a 3450 rpm motor. It's the fastest thing I've seen yet. How fast do your belts wear out and how much are they to replace. I would think the belt would be shot or severely slow down on cutting after about three of four blades. One thing a belt cannot do is put a hollow ground edge on the blade. This helps tremendously on keeping the edge sharp and reducing the need for sharpening. Depending on how bad the edge is crooked, I also straighten out the edge to make it take less time to sharpen the blade. Even though the edge is thicker after straightening, it still takes less time to sharpen a straight edge than a crooked one.
     
  10. burnandreturn

    burnandreturn LawnSite Senior Member
    Male, from Germany
    Posts: 303

    No problem with the belt's wearing out very fast. Many more than three or four blades. I buy the belts in bulk and I think they are around $2.50 apiece.

    As to the hollow ground edge. If I wanted to hollow grind the blade I could, utilizing one of the small bearings on the triangle of the path of the belt.

    I quess I mis-spoke when I said "I've used them all". I haven't tried the Walls. My apologies!
     

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