Hollow Grind question

peter nap

peter nap

Joined
Nov 27, 1999
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I built a new grinder yesterday. I really only wanted a powerful fast grinder to hog with but as usual I decided to get in over my head. I decided to make a few contact wheels so I could hollow grind. I've never tried it. I built a 10 inch wheel (Didn't have stock big enough to turn a 14 but maybe this week) It works great....

How do you figure where to start your hollow grind on the blade? I seem to start too close to the edge each time.:o
 
One of the cool things we learned at Tom Anderson's last summer was how to do reliable and straight hollow grinds. There's many methods I'm sure, but I like the way Tom does it for several reasons. First, you take a small square and mark off on the blade where the plunge will be and where the top of your grind will be. Do both sides so that they're even.

Next, Tom uses a 6-8" piece of HEAVY duty 3 inch angle iron, available at your local welding shop for a couple of bucks. He has it drilled to accept a bolt the size of the pivot pin. Bolt that sucker on to the outside edge of the angle and you have a nifty heatsinking grinding fixture. You will also have to drill a hole for a peg of some sort so that the piece won't rotate on you or you could clamp it somehow from the top.

This is the good part. Now you just lay that fixture on the workrest and drag it across against the contact wheel. It works incredibly well and the blade barely gets hot by the time you're done with it. Tom uses compressed air occasionally to cool it off and remove dust. It only takes a minute to flip it over and grind the other side. I tried it last week on a test blade and it took me about 45 minutes to get a really nice finished hollow grind. You will have to experiment to get the height of the grind according to the size of contact wheel.

http://www.realrates.com/pics/tom9.jpg
http://www.realrates.com/pics/tom10.jpg
 
Thanks Peter. I had already built a fixture except I built a sliding knife vice. It works well but it was the height of the grind I was thinking about. I thought someone may have come up with a trick to get it right without guess work. I was afraid it was going to be an try and test project though. Gotta work today so I guess it will have to wait until tonight.....Man does that thing take off some steel. Should cut my Grind time in half.:eek:
 
Peter, here's how I do it, your milage will vary:
I scribe two lines for the width of the blade. I'll grind the edge with a worn belt (edge down) down 45degrees or so to nearly the width I am going for to stop from shaving off the grit. Then I'll switch to a sharp belt and start just above the bevel (edge up) and cut a groove in. I follow the curve of the blade all the way to the tip instead of straight across. After I've established a groove, I'll start torquing the blade down (twisting it against the wheel), putting pressure on the bottom of the groove to push the hollow grind down, toward the spine, removing very little at the top edge of the groove. The curve of the blade requires a little extra attention to remove the 'fat' part of the hollow grind.
 
Thanks tmickley, I think I gott the idea. Instead of trying to get the wheel to work out you roll the grind to the edge. Makes sense.
I haven't taken yet Ripper. I will soon. It's not very pretty but I had a 1.5 HP motor and a few other things just begging to get put together.:D
 
Peter,

Take a look at Rob Frink's website www.beaumontmetalworks.com
He has some detailed instructions there, to do exactly the calculations you are asking for. Just click on: "How to determine the contact wheel size for the desired hollow grind."
 
Peter, what are you making your contact wheels out of and what are are you using for the tire part?? Thanks. Michael
 
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