New RBG came today - questions? Eric??!!

Discussion in 'Lawn Mowing' started by Mr.Ziffel, Feb 15, 2001.

  1. Mr.Ziffel

    Mr.Ziffel LawnSite Senior Member
    Posts: 291

    My RBG2181P came this morning and I set the angle to match the factory grind of a new Dixie Chopper hi-lift blade which is what my dealer sold me to go on my new LazerZ! What I noticed is that the blade rocked when I moved it farthest away from the grinding wheel, so I drilled a couple of holes in a piece of 2" angle iron and bolted it to the front of the machine to extend the flat table area. This helped, but the outside end of the underside of the blade [farthest end away from the center hole] is not as flat as the rest of the blade, apparently because of the lifting 'wing' where the blade was bent.

    Now I have a lot of experience grinding woodworking tools and even have a special low-speed, water cooled machine [Tormek] for my chisels, etc. and I believe the specialized machine is best which is why I bought the RBG [and because of ERic's recommendation of course]. I had my blades ground at the local Coast to Coast once 2 years ago and they did such a crappy job I just have done it myself with a side grinder, but with the new Exmark I've decided to put sharp blades on every 4-6 hours. The first thing I do when I grind a chisel or plane blade is flatten the back, then grind the bevel [sloping part]. The bevel is ground so it is uniform over the entire surface of the angle and then ground finer and finer, then stropped so you can't see any grinding scratches. Of course a lawnmower blade won't be ground to this degree but I believe the bevel should be uniformly ground which doesn't seem possible at this point unless I completely regrind the blade by flattening the back and basically starting over. Questions:

    Eric could you post a picture closeup of one of your sharpened blades? Am I correct in grinding at a 45 degree angle to the wheel, thus having most of the cutting done by the inside edge of the wheel? That's the only way I can get the last part of the grind to match the factory bevel without regrinding closer to the center hole. Am I being too anal about this or is this the way you do it? Thanks for any help. Will
     
  2. Eric ELM

    Eric ELM Husband, Father, Friend, Angel
    Posts: 4,831

    When I got my grinder, I set the angle to a brand new blade also. What I found was that when you sharpen a blade with this grinder, it actually puts a very slight dip in the pitched part of the blade you are grinding due to the fact that the wheel is round. When you use a right angle grinder to do this, I actually had a slight hump instead of a dip, until I got a big 10" Milwaukee grinder. I'm sure when they grind the blades originally, they use a huge grinding wheel to prevent this dip. Anyway, I found that after a few times of sharpening the blades, you get them all the same and then it takes nothing to sharpen them. I set the angle of the grinder so it had to take some out of the angle of the blade before it started sharpening the cutting edge.

    Sharpening all your old blades will take some time getting them to all be the same angle of pitch. I got discouraged at first doing them all and thought; this is taking to long to sharpen them. I knew there were several other happy owners on Lawnsite using this grinder, so I just kept using it until now I wouldnÂ’t use anything else. What I did was if a blade I had sharpened with my hand grinders was at to steep of an angle, I took the big Milwaukee and took a lot of the top part of the angle off with it so it wouldn't take so long on the RBG. I also extended my table out to have more space to hold the blade flat. On a blade that has some twist to it, I hold the very end flat to the table and push it through, slide it back from the wheel and feed it through from the front again. It only takes about 3 or 4 swipes to sharpen them, once you have them all the same angle.

    You don't have to have them at a polished smooth finish. I feel the rougher the wheel, it gives it a more serrated affect and the blades cut even better. If the wheel gets too smooth and loaded up, it won't sharpen as fast, so I use the diamond to dress the wheel which helps a lot in the way it grinds the steel. I hope this helps and there are a lot of other guys on the forum that uses this same machine, so I hope they all post all their tips.
     
  3. cantoo

    cantoo LawnSite Silver Member
    Posts: 2,910

    Eric or anyone else, would the factory use a grinder on the blades or would they use a milling machine? A milling machine would makes the angle flat not hollow like a round grinder.
     
  4. TLS

    TLS LawnSite Fanatic
    Posts: 7,937

    Mr Ziffel,

    If I am reading your post correctly, you are describing the last 3" of blade would actually cut grass lower than the inner portion,....right? If you lay your blade on a flat table, the only things touching the table are the very tips of the blade. The rest is raised up, right? This is the way all Dixie blades are. Why? Who knows. They are difficult to sharpen, however like Eric said, after a few sharpenings, they will grind to the way they follow the table of your grinder. As for the approach angle, I go straight on at 90 degrees to the stone, this way it uses all the stone to cut. Did you get some sort of diamond dresser? You WILL need one, as all wheels will load up, regardless of type.

    Hope this is what you were refferring to .

     
  5. John DiMartino

    John DiMartino LawnSite Silver Member
    Posts: 2,555

    I think the factory mills them,I can see the rough mill marks in mine.I am going to make a grinder with 7"handheld grinder,and an old scoring tile cutter,mount the grinder to the tile cutters slides,and mount it all on a bence,set up a clamp for the blade,once the right angle is determined,you just set it there and leave it.This may not work,just an idea,and I have some junk parts laying around,when i get some free time ill try it.
     
  6. TLS

    TLS LawnSite Fanatic
    Posts: 7,937

    I pretty sure they mill them (kind of rough) and THEN bend in the lift wing. This is what I think causes the bend we are referring to. The new Exmark blades I have are straight, Old JD blades were straight, 1968 Cub Cadet blades were straight, but the Dixies are slightly tweaked.



     
  7. Mr.Ziffel

    Mr.Ziffel LawnSite Senior Member
    Posts: 291

    Thanks for all of the replies.

    Dixie, yes the DC blades have a bit of a 'tweak' in them--they also have a longer cutting surface than the Exmark factory blade. I took a 10" mill bastard file to the back side of the new blade and that gave me a much better surface to slide along the table. Also, I went to the 90 degree grind to use the whole surface of the wheel.

    Yes, I have several wheel dressers from my other sharpening experience. I did not get the one from RBG as it is a 'point dresser' and is very expensive, although I use one on my Tormek chisel sharpener. I don't recommend that anyone use a 'star dresser' which is found with regular bench grinders as they will chew the wheel up. The cheapest wheel dresser I've found is a broken saw blade from a concrete cutting machine. If you know someone who is in the trade, ask them if they've kept any old, broken blades. One segment of the broken blade works great.

    It looks to me like they use a milling machine on new blades. I have finished several blades now and man, are they sharp--I mean really shave your arm, slice paper sharp. We're in the middle of a cold spell so the grass has slowed down, but it makes me realize that I still haven't used really sharp blades on my new Z yet, so I'm looking forward to the next time. Like Eric said, it takes a while to get them shaped right but now that I've got a couple I can see that I won't have to do as much next time. Thanks again for the answers. Will
     
  8. TLS

    TLS LawnSite Fanatic
    Posts: 7,937

    Mr Ziffel,

    You WILL want to get the dedicated diamond wheel dresser. I have one for my Brandelien Fireball Jr. and it made a world of difference. It makes the grinding wheel BITE real good. It corrects any abnormal stone wear and trues the stone. Its good for those initial big grinds when you need it most. Think mine cost close to $100 for the diamond dresser. Money well spent. Also consider a Magna-Matic blade balancer (not cheap either) but VERY accurate! I mean V E R Y accurate!!!

    Happy sharpening, and how do your forearms look? Black with grit!!

     
  9. Mr.Ziffel

    Mr.Ziffel LawnSite Senior Member
    Posts: 291

    Dixie, I DO have a wheel dresser--it's a segment of broken concrete cutting saw--just loaded with diamonds; dresses and trues the wheel perfectly and it cost $00.00. It was free from a broken saw blade.

    Also, I have NO grit on me and didn't even need a dust mask, although of course I wear safety goggles. Instead of standing in front of the wheel and having the sparks and grit thrown at me, I'm standing at the end of the machine and everything is thrown to the side. On this machine it seems to give me a lot more control, I can see the 'cut' perfectly as the machine grinds and keep free of all the crud. I'm liking it.

    I also made Eric's ball-bearing balancer--quite an ordeal to find the correct size bearings, but I got'em. However, either my blades are coming out very even or it's no better than the nail on the wall or the little stepped-cone on a point thingy I'm comparing it against. They all show the blades to be the same when I compare them. If I start hearing an imbalance on the mower I'll look into the $165 magna-matic--anyone seen it cheaper? Will
     
  10. Ricky

    Ricky LawnSite Member
    Posts: 154

    I have a question for those that use the RBG blade grinder. I understand that the grinder has a switch that you can have the wheel to turn in either direction. My question is which direction have you found that works the best, with the wheel turning into the edge of the blade to the back or the wheel turning from the back to the edge.
     

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