I have seen before on here (possibly by FYGT) a very good explanation of grind height and angles on the various thickness of blade ( this is 3 mm ) but I cant find it. Can anyone advise a good angle and height for a 3mm blade.
Grind height and angle are interrelated. For a given thickness, one can be worked out from the other using trig. Calculations based on right-angled triangles are done using SOH-CAH-TOA. For this, TOA can be used - TOA means "the tangent of the angle is equal to the opposite divided by the adjacent". The opposite is the length of the side of the imagined r/a triangle that is opposite the angle we want to find, and the adjacent is the length of the side that meets the angle we want to find. The opposite and adjacent are the two sides that have the right angle between them.
We know the opposite - it's half the thickness of the blade. What needs to be decided is whether we start with a grind height to get an angle, or start with an angle to get a grind height.
I'm not a knife maker, but I would have thought that it's desirable to have a certain amount of meat behind the cutting edge to make it less likely to chip, but not too much so that it can still cut and slice. If we assume an overall angle of 20°, the grind height can be calculated, but we need to transpose the formula (which, as 'TOA', is set up to find the angle from two known sides).
It starts with Tan = Opp / Adj
We know Opp (opposite) and we know Tan (tangent of angle), and we want Adj (grind height).
When transposed, it becomes Adj = Opp / Tan
We need the half angle to work with a r/a triangle, so our angle is 10°. The tangent of this is 0.176. To get the grind height, divide the half-thickness by the tangent...
1.5 / 0.176 = 8.5mm
On my woody copy, I get a grind height of about 8.4mm (measuring along the flat surface of the blade - not along the sloping part of the grind). It's 4mm thick, giving a half thickness of 2mm. To
find the angle on this knife...
Tan = Opp / Adj
Tan = 2 / 8.4
Tan = 0.238
To get the half angle, find the arctangent of 0.238, which my trusty calculator tells me is 13.39°. A full angle of very nearly 27°.
If you wanted to use that same angle on a 3mm blade (to get a similar amount of meat behind the edge), you'd do...
Adj = Opp / Tan
Adj = 1.5 / 0.238
Adj = 6.3mm