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The S.R. "Steve" Johnson Forum Specialized knife making tips, technique and training for "ultra precision" design work enthusiasts.

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  #1  
Old 10-23-2019, 09:22 AM
s mcfall s mcfall is offline
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radius on hollow grinding

how do you get the nice radius on your grindlines? radius the contact wheel or hang the belt off the side of contact wheel? and roughing belts better than other (more flexable)?

thanks for any answers!
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Old 10-24-2019, 03:48 PM
jimmontg jimmontg is offline
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I use a radius wheel.

Most knife makers who do a hollow grind on their knives use, typically an eight inch or ten inch wheel. They practice until they get good at it or use a jig like I do. I mostly do flat grinds, but that's just me. Some knives are best served with a flat grind like kitchen or filet knives. I hope that helps.
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Old 10-25-2019, 09:10 AM
s mcfall s mcfall is offline
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not the radius i was talking about :-) the radius on the ricasso where the plunge cut starts.

sorry about the confusion.

Last edited by s mcfall; 10-25-2019 at 09:22 AM.
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Old 10-25-2019, 05:30 PM
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Steve M Steve M is offline
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I use a 60 grit belt and hang it over the edge between 1/16"- 1/8" with the grinder running slow/medium speed. And as Steve says in the DVD you use it like a sculpting tool freehand and gently nibble away at it. Use a rest for stability.
I don"t think putting a radius on the corner of the contact wheel would be an advantage; I would imagine that would make it difficult to keep crisp grind lines and make it impossible to sweep your grinds due to a portion of the belt being unsupported right where you need it.
And don't forget practice - lots of it.
best wishes
Steve M
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Old 10-25-2019, 11:44 PM
jimmontg jimmontg is offline
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I can't add much to what Steve M said

Except to agree with him about putting a radius on the edge of you grinding wheel, you don't want to do that. If you want your plunge cut to be radiused hang the belt about an 1/8 inch off the edge of the wheel by adjusting your belt off center with your belt alignment knob or screw and use a flex belt. My grinders have a screw on one and a knob on the other to adjust my belts.
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Old 10-26-2019, 09:50 PM
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I don't shift the belt at all. I feather-wash it across so that it arcs. I do a typical plunge 1/2 up and then feather the cut up to the spline. Over the years of the doing various cuts the edge of the wheel contacting the steel it has developed a slight radius but not significant to have much of a change in how the belt is on the contact wheel.
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Old 11-02-2019, 02:46 PM
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I plunge with a stiff course belt at 60g and establish my desired pre-ht bevels. Then, go to J-Flex belts for progressive grits with an 1/8" over the edge if the plunge needs refining. My favorite hollow is done on my 12" wheel.


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Old 11-04-2019, 08:20 PM
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Brett Schaller Brett Schaller is offline
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I rounded the edge of a contact wheel once and did not like the results.

As others have said, track the belt off about 1/8". Sometimes this will give you the nice radius you're after automatically - sometimes it won't. If it doesn't, sculpt the radius in by pulling the knife away from the wheel as you back into the ricasso area. Depending on how steady my hands are that day, I may or may not support my hand - not the blade - on the tool rest. I drop the rest way below the wheel for this.


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Old 11-04-2019, 08:34 PM
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Andrew Garrett Andrew Garrett is offline
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For inspiration, look at the grinds of Dave Darpnian. You can see some of his work at kansasknives.org.
Dave matches his bevel to ricasso junction with the shape of his tip. It's very cool!


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Old 02-05-2020, 10:06 AM
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I've tried rounding the corner of the wheel and can't recommend that, for my own use, though, with use, the edge will round off, somewhat, by itself. Just run the belt over the edge 1/2-3/16" and let the curve happen, as you get to the end fo the grind and gently push into the edge of the belt. You need to pay attention to what is happening, check it often, practice a lot. If the belt edge is too soft, it'll not work, but if it's too stiff,it doesn't want to make that curve, either, it'll cut a sharp corner. You may have to go with a used belt, until you get the ability to "carve" that curve. Again, try any method you feel comfortable with and PRACTICE.


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Old 03-15-2020, 02:10 PM
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Quote:
Originally Posted by Steve View Post
I've tried rounding the corner of the wheel and can't recommend that, for my own use, though, with use, the edge will round off, somewhat, by itself. Just run the belt over the edge 1/2-3/16" and let the curve happen, as you get to the end fo the grind and gently push into the edge of the belt. You need to pay attention to what is happening, check it often, practice a lot. If the belt edge is too soft, it'll not work, but if it's too stiff,it doesn't want to make that curve, either, it'll cut a sharp corner. You may have to go with a used belt, until you get the ability to "carve" that curve. Again, try any method you feel comfortable with and PRACTICE.
Good to see you posting.


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