Grinding bevels with an angle iron jig

B

BoozeFighter

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Jul 6, 2015
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I have recently acquired a 1x30 grinder and have been attempting to grind bevels with it. I am using a jig I made out of some angle iron with a few bolts threaded into it to set the angle. The problem I am having is that the tip of the blade sits too low to make contact with the belt when I draw it across. The grind is nice and even right up until where the blade starts to curve, then because of the blade sitting lower on the face of the jig it makes no contact with the belt. What am I doing wrong? In every youtube video I watch of people using a similar jig, it looks like they are just working back and forth along the length of the blade.

Forgive me if this has come up before, I am painfully bad at using the search feature of the forum.
 
A sled is going to grind a straight line parallel to the bottom of the sled. If your not getting the tip, you just need to set the jig to a lesser angle and bring the grind above the tip of the knife. (see diagram).

grind.png
 
That makes sense. I was worried that with a steeper angle I would end removing not enough material and end up with too thick of a blade. I will try this, thank you.
 
Yeah, the trick is to find the right angle, so that you have an edge thickness of about .030 and the bevel extends to the grind height that you want.

grindh.png


Good luck!
 
As you approach the tip swing the handle back toward you so the to makes contact. Keep an eye on the thickness of the edge and keep it even. The tip will have a steeper grind this way. A 2 degree per side bevel might go up to 5 or 6, depending on how close to the spine your top is.
 
I did a chisel ground santoku at 5 degrees and the tip went up to about 7, but that's a santoku.
 
me2 said:
As you approach the tip swing the handle back toward you so the to makes contact. Keep an eye on the thickness of the edge and keep it even. The tip will have a steeper grind this way. A 2 degree per side bevel might go up to 5 or 6, depending on how close to the spine your top is.
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I had tried this approach, but I don't know if it is inconsistency on my part or just inexperience, but I have not been able to get anything to look even with the rest of the grind. I tried NC's method on a piece of mild steel i ground into a rough drop point shape and it was apparent immediately that this was the way to go. Now I just need to find the sweet spot for the blade height/thickness that I am working on.
 
Here's a grind angle chart that might help. Just keep in mind it will only get you in the ballpark to start, as it's about impossible to set your sled to the exact angle your going to need from the get go. Adjust the angle once you reach either the grind height you want, or the edge thickness, whichever you get to first.

Grind Angle Chart
 
Hope this makes sense. The grind angle is equal to the arctangent of the grind depth divided by the grind width. So then, say you've got stock that is 200 thousandths thick (0.2 inches) and you want to leave 40 thousandths on what will eventually be the edge. That would leave 160 thousandths that have to be ground down, a depth of 80 thousandths from each side. Lets go on to say that you want your grind width (bevel width) to be 1.2 inches. Now we have what we need to know. The grind angle must be arctangent (0.080 / 1.2). This results in an angle of 3.8 degrees. Most hand held calculators have trig functions, or you can easily find a trig function calculator online, or, if you have a smart phone, there are calculator apps available.

Edit: The arctangent function on a calculator is practically always the 2nd function of the tangent key.
 
Tony, I see the professor coming out here - good explanation and works like a champ.

Ken H>
 
Just can't help myself Ken. :D Being a novice knife maker, I'm just doing what I can to support knowledge base here. I'm glad you found it helpful.
 
TonyRV2 said:
Hope this makes sense. The grind angle is equal to the arctangent of the grind depth divided by the grind width. So then, say you've got stock that is 200 thousandths thick (0.2 inches) and you want to leave 40 thousandths on what will eventually be the edge. That would leave 160 thousandths that have to be ground down, a depth of 80 thousandths from each side. Lets go on to say that you want your grind width (bevel width) to be 1.2 inches. Now we have what we need to know. The grind angle must be arctangent (0.080 / 1.2). This results in an angle of 3.8 degrees. Most hand held calculators have trig functions, or you can easily find a trig function calculator online, or, if you have a smart phone, there are calculator apps available.

Edit: The arctangent function on a calculator is practically always the 2nd function of the tangent key.
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Hey Tony, I'm no math wiz, but something don't add up. If I use your formula and compare the answer to Mr. Penner's chart. I get two different answers. Your's being twice that of Mr. Penner's. Is your formula complete for the OP to use to set his jig?
 
NC Biker said:
Hey Tony, I'm no math wiz, but something don't add up. If I use your formula and compare the answer to Mr. Penner's chart. I get two different answers. Your's being twice that of Mr. Penner's. Is your formula complete for the OP to use to set his jig?
Click to expand...

Hey Chuck....the math is correct. The difference is because the author of the graph is not allowing for any retained edge thickness and is assuming that the edge is zero thousandths of an inch when ground. I verified this looking at a few of the graph entries. In his excel chart, he simply took the thickness of the blade and divided by two to come up with the amount of depth thats being ground down from each side. If your going to retain some edge thickness you have to first subtract that amount from the stock thickness before dividing by two in order to come up with the depth of the grind. Perhaps we're splitting hairs anyways. If we're grinding free hand of course we're lucky to be within a few degrees of ideal, but with proper preparation we manage to keep it close.
 
TonyRV2 said:
Hey Chuck....the math is correct. The difference is because the author of the graph is not allowing for any retained edge thickness and is assuming that the edge is zero thousandths of an inch when ground. I verified this looking at a few of the graph entries. In his excel chart, he simply took the thickness of the blade and divided by two to come up with the amount of depth thats being ground down from each side. If your going to retain some edge thickness you have to first subtract that amount from the stock thickness before dividing by two in order to come up with the depth of the grind. Perhaps we're splitting hairs anyways. If we're grinding free hand of course we're lucky to be within a few degrees of ideal, but with proper preparation we manage to keep it close.
Click to expand...

That makes sense. I grind freehand now a days, so I just grind from my marked edge to the spine, but if I ever find a need to go back to a sled, I'll certainly take advantage of your formula.

Thanks!
 
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