Finishing Large INSIDE Radius

Crag the Brewer

Crag the Brewer

I make Nice, boring knives
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A bit embarrassed about asking this, but I've made enough knives by now that I feel I Should have a better grasp of this....

How do you finish your Large sweeping Inside radius? Where my finger is pointing I like to have a gentle, radius where it leaves the handle, and enters the blade going to the point. On top/spine.
Idk how big it is, I'm guessing 10-20 feet in diameter, idk?
Funny, but small inside radius I'm good at finishing with files, and Dremel. It's the huge ones I get more visibly "wavey"



Currently I profile it just fine on my 2x72 belt running perpendicular. I'm good at that.

Then I clean it up running parallel on my belt, but I can only do so much on my metal platen wheels.
It's pretty rough. Would rubber contact wheels make much of a difference? (I have a small 3" one somewhere, but I really haven't used it much.)

So then I try cleaning them up and blend the profile with a diamond file. I try smoothing out the peaks and valleys, but it's kinda wavey. Slightly. Definitely not crisp.

I don't need for it to be perfect, as my knives aren't finished to the extreme. But I want to continue to step up my game. This has been bugging me.
 
I have a half-assed utility wheel I use that kinda helps if I pull it across continuously....idk how safe that wobbly thing is.


Does everyone use a large contact wheel for what I want?

I often think about getting a radius platen. That too could do it, maybe?
 
I'm thinking that's the best way..... Even with my crappy wheel, it worked ok.

And it's probably better than filing.
 
If I want the finish going the length of the blade the largest wheel possible, I have a 14” wheel that works really well or I jump over to a radius platen, I have one that mimics a 36” radius or 6 foot diameter that works really well for extremely shallow curves. Most of my knives I finish across the handle so I can just use the slack belt and get a uniform finish that way and it’s much simpler regardless of the shape of the handle.
 
I use an 8" rubber wheel, grinding at the bottom of the wheel parallel to the belt pulling the blade toward me. I usually start at the butt and grind toward the tip but pull off before I reach the point so I don't mistakenly round it off. Then at the end I'll start at the tip and work back toward the butt a couple of times to clean it up. I pull from one end to the other without stopping. Stopping and going mid blade will cause all kinds of bumps and valleys. The last pass from tip to butt I'll pull up on the knife right at the end so the wheel grinds slightly around the radius of the butt. This cleans up any choppiness that accumulates at that point from the multiple passes that started there. I don't go slow, keeping the pull at a steady rate. This is especially true on small wheels like 1 inchers. The slower you go on those small wheels the choppier the cuts, especially if the wheels aren't perfectly round. Steel or aluminum wheels are too hard. My profile pic actually shows me doing this at the factory.

Eric
 
I do it on an 8" wheel initially which can turn out wavy (you might get lucky with a soft touch).
Then I run a 120 grit EDM stone over it until it's nice and smooth. Then a 320 EDM stone, then up to whatever grit of paper I'm finishing at.
 
Way-Barney said:
A good sharp file, draw filing, is not to be sniffed at, couple of minutes, if that, tops.
Click to expand...
I do the same thing, as long as the steel has not yet been hardened. I do what I can on the flat platen with work rest, and then use a file to draw file the spine. Of course, constantly sighting down the spine under good light to make sure there are no waves, that it is one continuous curve.
 
I use the 6"rubber wheel on my combo platen to do that type of stuff. Start at one end and move it slowly at a steady speed. Starting, stopping, slowing down or speeding up will leave you with grooves and ripples like EA42 says. You can also try some F1 felt or S2-32 Felt on your platen and go across it perp to the belt. It will have some give/flex to it to help blend and follow the curve more than a hard platen will.
 
Maybe it is my understanding, but I think the OP want to make a concave plunge curving to the spine as shown where his finger is pointing in the photo. You can't do that on a flat platen or with a file. I use the edge of the contact wheel and turn the blade to form the concave plunge.
 

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Stacy E. Apelt - Bladesmith said:
Maybe it is my understanding, but I think the OP want to make a concave plunge curving to the spine as shown where his finger is pointing in the photo. You can't do that on a flat platen or with a file. I use the edge of the contact wheel and turn the blade to form the concave plunge.
Click to expand...
My understanding is that he's trying to smooth the spine.
 
Stacy E. Apelt - Bladesmith said:
Maybe it is my understanding, but I think the OP want to make a concave plunge curving to the spine as shown where his finger is pointing in the photo. You can't do that on a flat platen or with a file. I use the edge of the contact wheel and turn the blade to form the concave plunge.
Click to expand...

No, it's as simple as Just wanting a cleaner looking spine.
I did say I was embarrassed asking, and I Did know apparently the answer. I was just wondering if that's how everyone else was doing it...haha.

Once I get a bigger/better contact wheel, I'm sure it will get better.I

It's funny how knife making needs such obscure tooling, that I need to make sure I really Want it, cause I'm not going to use it for anything else.



*I'm thinking of changing this title to "All the questions as a knifemaker you were afraid to ask?". Haha.

I have quite a few....... :)
 
I used to use a contact wheel as well. However, ever since I begun working on a slack belt, I never looked back. Even passes across and there are no valleys on the spine. 400grit on the grinder and with 30 seconds of hand sanding, I can get a nice smooth 400grit finish running along the spine.
 
I use both a slack belt and a contact wheel. 120 grit on the slack belt perpendicular to the spine, 220 on the contact wheel, in line with the spine, using two separate grinders. Then 330 on the slack, perpendicular again. 400 on the contact wheel in line and finish with 600 grit on the contact wheel in line. Really takes longer to type than to do. The advantage of this system is it finishes all shapes and sizes of spines. The only place I don't use this is small finger grooves. There I use small wheels but anyhoo. As most know, I make a lot of custom sheaths for other folks knives too, A LOT. Finishing a spine is something that many makers struggle with. I know, I need the knife to make the sheath. BTW I use an 8" contact wheel for this. Lets me get to most areas, except as already mentioned.
 
I like doing slack belt grinding, but I haven't tried it on the spine...... I'll have to experiment some.
Thanks.
 
Crag the Brewer said:
I like doing slack belt grinding, but I haven't tried it on the spine...... I'll have to experiment some.
Thanks.
Click to expand...
Ya bet. I use that method described on both sides the spine (top of the blade and handle) and the bottom of the tang. I was using spine to cover both but strictly speaking they are not.
 
Crag, you are just referring to the plunge itself correct? Getting a large radius plunge?

Basically like this but less exaggerated and all the way up to the spine?
PXL_20231025_163537527.PORTRAIT.ORIGINAL~2.jpg
 
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