Looking For Mathematical Method For Determining Angle -

R

rlinger

Joined
Mar 29, 2002
Messages
4,591
Math experts:

Suppose a 1.09 inch wide blade that is 0.182 inch thick and you want to bevel it flat 1/3 the blade width (a Scandi grind). What mathematical (Trig I suppose) formula would you use to determine the bevel angle? This is a blade I am grinding tonight and I have already roughly determined the angle with angle blocks and just plain judgement at the grinder but it would be so much faster if I could learn or remember the math for it instead.

Thanks.

RL
 
Roger you need ,of course, trig tables or a calculator with tangent functions.... Tangent of total angle = 2 x ( 1/2 t / B x w ) ..... t = thickness of blade [in this case .182" ] , B=fraction of blade to be beveled [ in this case 1/3 ], and w =blade width [ in this case 1.09" ].......Tan A =2(.091/.3597).....Tan A = .5059....A = 26.83 degrees.
 
Thank you Mete. I knew you would know. I guess the best way to do it is just by experience at the grinder but I'm still working on that part.

RL
 
I hate to say so but I don't use the math often enough to remember how to do angles but I can still find my Machinists' Handbook. Look under "Sine Bar Table" and you will find more than you ever wanted to know about angles.
Good luck
 
Can anyone validate my reasoning?

If the formula given previously is for a single bevel on a single side of a blade, my reasoning leads me to conclude that for a single bevel on BOTH sides (converging in the middle) the equation would be:

a= atan (2((1/4t)/(bw)) where a=the angle ground on each side

Is this correct? I believe that I've verified it using the law of sines, but I've never used the formula given previously, and it's been a long time since trigonometry class ;-)

Thanks for any help.
Redwolf
 
If you want the easy way just draw a right triangle with the height being the length from edge to top of desired bevel and the width being from the center of the edge to the thickness at the top of the bevel, then just measure the angle you drew.
 
Oww! Oww! My head hurts! If my eyeball ever go to he** I'm in deep trouble. Tess could probably answer this though, she's a math genius.
:D
 
Uh Rodger....not to be a stick in the mud but after you find the correct angle, how are you going to free hand it to the exact angle or as Tom said....

Grind it to the line! :D
 
Sounds like somebodies tilting their plaaatennnn.... I'm gonna tell! LOL Or it's a Higgy-jig or sumpin!
 
No, actually I adjust the platen to perpendicular with the earth. I grind free hand but adjust the grind according to what the angle finder tells me and go from there.

RL
 
Just joking, Roger! How you grind is your business, regardless. Your results speak for themselves...... you've done very well in a relatively short time, and many are impressed.
 
Fitzo, I was trying to figure out a reliable way to grind the Scandi bevels at a precise width. Since then I have learned a little more experience grinding them helps more than doing calculations. Still got lots to learn about them. I'm grinding 5 Scandi blades tonight. Four down and one to go. :)

RL
 
Grinding blades is certainly one of those skills that can be defined as a "practice skill", like playing a musical instrument. Without constant practice, even the best lose some measure of fine control.

Hope the blades all made you smile.... :)
 
Roger or anyone,

This is gonna sound a little stupid but I've never held a scandi in my hands and after seeing a few pics of Bushcraft knives, I'm a little confused.

Is a scandi grind one bevel on one side (sorta like a chisel), or is it a single bevel on each side?

When reading about them, I always interpreted the grind as being a single bevel on a single side, leaving the other side totally flat and unground.

Also, wouldn't that make them non-ambidextrous, and if so, which side of the blade should be ground for a right-hander?

Finally, I've come to the conclusion through field use that I prefer flat grinds to hollow. I used to make hollow ground knives, but I got out of it for a few years and in the interim sold my Burr King.

I'm looking into getting back into knife making, but this time doing flat ground blades exclusively.

I've heard many people suggest that a disc grinder is better for doing flat grinds.

With that in mind, what machine should I look at? Would a combo (disc/smaller belt) grinder be a good start?

All opinions welcome

Thanks for any info.
Redwolf
 
Scandinavian grind is NOT a chisel grind. It is ground on both sides and is flat ,not hollow ground or convex ground. It does not have a secondary bevel. When you sharpen it you sharpen the whole bevel.I got my first one direct from Norway when I was just a little kid. The scandinavians have been using it successfully for hundreds of years. I've been using them all my life and they are very practical.
 
I answered the grind height/angle question on another forum a couple of months ago. Chest puffed up, "me man, me make complex trigonometric calculation" - then someone came along and pointed out that if your grind height is 2x the stock thickness, you have an included angle of 30 degrees. I was so deflated I didn't even remember to point out that it was only 28.072 degrees (to 3 dec places).

Sigh...

:D

For amusement, here are the stock thicknesses, grind heights and blade depths of 3 scandi grind knives I have to hand - all in mm, sorry -

2.5, 6.5, 17.4 - Brusletto
3.3, 10.2, 19.0 - Kellam
4.0, 8.4, 26.4 - UK custom maker

No "one true angle" amongst them.

HTH

Peter
 
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