Measuring blade symmetry

timos-

timos-

Knifemaker / Craftsman / Service Provider
Joined
Oct 22, 2012
Messages
2,164
I have been using verniers and comparing measurements one either side of the blade for height of grinds. Then just eying up the edge along the length. I find myself wondering what more accurate tools or setups are out there. What do all the blade smith Pros use?
 
The center line of the edge is scribed, so that's not a big deal. I also measure from the edge to the grind line and also make sure the end of the grind line at the tip meets the spine equally on both sides. The hardest part to make sure you get symetrical is the grind where the spine starts to taper. As far as that goes you can only eyeball it. It'd be neat if someone has a way to actually measure that.
 
I've wondered about how to do some of these comparisons myself and I'm baffled by how one might go about measuring a hollow grind on a knife made by someone else. What I mean is that I'd like to know what size wheel was used for a particular hollow grind.

Are there gauges in bigger sizes? 6" - 14" for example? I'm not sure how I'd do a Google search for these.

Ohh well

Syn
 
If I were to figure out the diameter of a hollow grind Id probably make some perfect circles in some cardboard and use that as a gauge. Or you could use a drawing program to make an arc segment/block print it 1:1 scale then glue it on something...you could definitely guesstimate it. The difficult part would be measuring any variance in the hollow grind.
 
Aside from where the grinds come to the edge of the profile, are you able to even see both grinds at the same time? No, so as long as they are close to the same height you will be good to go.

As far as measuring where the grinds meet the spine, try laying a straight edge on the blade and use feeler guages between straight edge and blade.


-Xander
 
When handed a blade or knife to critique or examine, I first sight down the spine from the handle end, and then from the tip. Next sight straight down on the spine. Flip it over and do the same for the edge.

1) Sighting down the blade from the tip will show if the grinds are even.
2) Pay close attention to the plunge lines and the curvature of any radius there. Looking straight down on them will show if they line up.
3) The look straight down on the spine will show if the distal taper is sufficient and even.
4) The edge on view, as well as sighting down the edge will show any ripple, wave, or off center edge.
5) The tip on view of the spine will tell if any clip/swedge problems exist.
6) Examining the handle the same way will show if it is even or not.

These simple visual checks will spot any irregularities far greater than a measurement can. The human eye can spot differences in a few thousandths of and inch....and when comparing things, a tiny difference will look huge.
 
I agree, the eye will tell you.

A white or at least plain background will help you se the difference.

I do a lot of chisel ground blades but this helps with heat treat and other things too. I have a granite surface plate to check for flatness and they eye is always right.
 
Take a blade, make a mold. Make a casting.
Measure the casting's mid points along the blade, and cut the casting in half with a fine wire.
Take measurements, and enjoy.
 
If you are checking the blade by eye as suggested, use the computer screen (when it's on) as a background.. it shows very well
 
synthesist said:
I've wondered about how to do some of these comparisons myself and I'm baffled by how one might go about measuring a hollow grind on a knife made by someone else. What I mean is that I'd like to know what size wheel was used for a particular hollow grind.

Are there gauges in bigger sizes? 6" - 14" for example? I'm not sure how I'd do a Google search for these.

Ohh well

Syn
Click to expand...
A compass and some cardboard, wheels you already own, etc...
 
If you can gain access to use an optical comparator, you could measure any dimension you want. Most machine shops have them.
 
I found a solution to my hollow grind measuring dilemma in my old drafting equipment. A gadget called an Acu-Arc Ruler.









It will let you set it to arcs from 7" on up................. Works for me

Corey "synthesist" Gimbel
 
Hey Thanks for sharing that, too cool.
 
Glad you enjoyed that. It will do the job on hollows over 7". Under that I think I'm going to have to take a compass and some thin material i.e. cardboard, micarta, aluminum, plastic, whatever and make a set of measuring tools to assuage my curiosity.

Corey "synthesist" Gimbel
 
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