Why mark the bevel height?

Outdoor Gear Dad

Outdoor Gear Dad

Joined
Jun 1, 2019
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211
So for context, I am new to knife making. Only been doing it for 11 months and I’m trying to learn as much as possible. I see some guys scribing the bevel height on their blade before they grind. Why do they do this? I guess if you are grinding at the same angle on each side to the centerline, in theory, shouldn’t the bevel height be the same on each side?

what am I missing?
 
As you approach your center line and it start to get very hard to read, the scribe line can show you where you might have less material by the bevel being slightly off in comparison to the line. It's easier to read in my opinion (i do want an optivisor though to help track the center line).
 
Even with jigs and work rests, it's easy to put a little too much pressure on one side of the platen or the other, and consequently be slightly off on how even or parallel your grinds end up. Scribing the lines just gives you one more visual reference to help keep things in check. If this is something you don't struggle with as a new maker, I'm envious!
 
Drew Riley said:
Even with jigs and work rests, it's easy to put a little too much pressure on one side of the platen or the other, and consequently be slightly off on how even or parallel your grinds end up. Scribing the lines just gives you one more visual reference to help keep things in check. If this is something you don't struggle with as a new maker, I'm envious!
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Oh I struggle! Trust me. So what’s the math formula for knowing how high to scribe based on your blade thickness and angle?
 
Outdoor Gear Dad said:
But how high do you know to mark the bevel height? My math was never great.
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I started out trying to do that math ... and (after discussion with people here) mostly came to the conclusion that the math should be tossed ... and just go with what "looks good" on the blade. I still mostly do full flat grind - as I really stink at keeping that grind line (shinogi) straight on anything but a pretty steep bevel....
 
Outdoor Gear Dad said:
Oh I struggle! Trust me. So what’s the math formula for knowing how high to scribe based on your blade thickness and angle?
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I'm a little rusty on my SOHCAHTOA forumulas, but here's a quick calculator: https://www.wedgek.com/a-angle-calculator.aspx

Personally, I most often just free hand things with the use of a work rest. I'll start with a shallow angle and gradually walk my grind down to the bevel line, or if I'm doing a full flat, walk it down to the spine. If I'm using a grinding jig, I'm more/less just doing the same thing while keeping an guy on my edge center lines. Start shallow, and adjust the angle of the platen and/or jig until you are just touching both lines.
 
I don't get the whole "I need to know the exact angle im grinding at" thing.

Just walk your grind up from the edge till you like the way it looks, or matches your drawing, then make the other side match.

Do your weak side first, then match the other side with your strong side. Easy!

Well maybe not easy, but much easier than trying to stick to some angle that you may have done the math wrong on...
 
A.McPherson said:
I don't get the whole "I need to know the exact angle im grinding at" thing.

Just walk your grind up from the edge till you like the way it looks, or matches your drawing, then make the other side match.

Do your weak side first, then match the other side with your strong side. Easy!

Well maybe not easy, but much easier than trying to stick to some angle that you may have done the math wrong on...
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If you are drawing your design and working it out on paper first, it helps to know what angle range you might be in.

Think of all the first knife designs you have seen with 1/4" stock and 1/4 high bevels.
 
There's all kinds of online calculators but the formula is simply:

(1/2 blade thickness) / tan(desired angle)

Example. You want to make a scandi ground knife from stock that is .12" thick and you want a bevel that 11 degrees on each side (22 degrees inclusive).

0.06" x tan(11) = 0.309".

You can easily increase or decrease the angle to get the desired height. Increasing the angle makes a shorter bevel ie 90 has no bevel height at all.

This is the formula to use pre grinding. If everything was ground precise and perfect and you measured the width of the bevel it would be slightly longer because that's the hypotenuse but the height would be correct.

I hope this makes sense. There are other ways to calculate it but that's a pretty simple formula and you only need the one.
 
Instead of working out the angles etc and marking one grind line I sometimes mark a few lines at different heights. You can then use these as a guide and they don't need to be in exactly the right place.

If you are a beginner you can mark lines at intervals all the way up to your final grind and use them in sequence to practice getting your grinds straight and even.
 
Mike Read said:
Instead of working out the angles etc and marking one grind line I sometimes mark a few lines at different heights. You can then use these as a guide and they don't need to be in exactly the right place.

If you are a beginner you can mark lines at intervals all the way up to your final grind and use them in sequence to practice getting your grinds straight and even.
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Love that. Thanks for the tip
 
Outdoor Gear Dad said:
So for context, I am new to knife making. Only been doing it for 11 months and I’m trying to learn as much as possible. I see some guys scribing the bevel height on their blade before they grind. Why do they do this? I guess if you are grinding at the same angle on each side to the centerline, in theory, shouldn’t the bevel height be the same on each side?

what am I missing?
Click to expand...
If you are controlling the grinding angle then you are correct; there is no need to scribe the bevel height. The height should still be measured to make sure they match.
Happy Grinding, Fred
 
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