How much will forging bevels change the blade width?

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Tin.Man

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Sep 5, 2010
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Has anyone every done the research or found a link that could give rough estimates to forging.

Two examples, how wide of a blade can be made with certain size round stock? Along the lines of without a press or power hammer? Thinking in the 3/8, 1/2, and 5/8 diameters for now.

Second, say I start with .25 thick 1” wide bar stock that has the necessary tip and preform already forged in, as I forge my bevels in what is a reasonable expectation of how wide I can expect my blade to get again using hand hammers and anvil no press or power hammer.

appreciate the help all, I’m stuck in an apartment for another 2 months so I’m already trying to plan ahead.
 
It's just geometry, calculating volumes taking into account loss due to scale.

Don't forget to curve the blade downward before forging the bevels in.
 
While there is no simple exact formula, figure that you can easily double the width. With skill, you can triple it. Your .25X1" size is a good size for this.

Round stock will fool you. You can make an entire good size blade from a 3" piece of 1" round stock.. I find 3/4" round to be hand forging friendly.. Work it as a continuous bevel as well as lengthening it. By doing both at the same time, the banana curve is much less.
 
These are very approximate:

For the round rod example, let's assume you are keeping the length equal and only increasing the width.
As such, we are just calculating how a circle gets turned into a rectangle while retaining it's area (minus material loss).

Area of circle : A=π r²
Area of rectangle: A = l w

Assume also a loss of material from decarb as 5% = 0.05. (adjust as you see fit)

π r² * ( 1 - 0.05 ) = w l

Set your parameters and make algebra do the work. Obviously, your target thickness impacts how wide the blade gets.

So if you had a 0.5" round (0.25" radius) that you wanted to be a 0.125" thick rectangular stock:
π 0.25² * ( 1 - 0.05 ) = w * 0.125
w = 1.4915

This reinforces the statement "with skill you can triple it"

An exact formula for bevels would get weird, I expect. As mentioned, the bevels will both widen the blade and lengthen one side of it.
Also consider the final edge thickness you will forge to. A more talentend smith will go for thinner. Less talented needs wiggle room for lack-of-straightness, more decarb, etc.
So even if you calculated for the resultant trapezoid cross section, it would need to account for which directions the material moved to.

That said I'd expect that a 1/8" thick blade will get 10% wider. A 1/4" blade might get 20% wider. These numbers can be safely ignored in favor of any experience you gain.
 
Even approximate I really appreciate it. I know it is going to be a big it depends but still nice to have a plan.
 
I don’t have any exact measurements, but here’s a picture of a knife a forged from 1/4” x 1” flat bar. It should give you an idea of how wide the bevels scan be drawn out. I left the spine fairly thick on this knife, and could have easily made the blade much thinner and wider.

JEOG1nV.jpg
 
One tip for forging out bevels:
Work to make the bevels smooth as you draw them out somewhat gently. A new smith tends to wail away and draw them down. This will lead to scale being forged into the blade as well as a very irregular surface with deep dents. Upon reaching your desired shape you may end up reducing the thickness by as much as half to get rid of these defects. Bu using a hammer with a smooth dressed surface and controlled overlapping blows you can draw down the bevels with much less distortion. Brushing the billet with a steel wire brush after every heat and before the next one will keep scale inclusions down a lot. Hammer control where the hammer flat strikes the blade surface evenly (not on the hammer face corner/edge) is very important. The right weight, shape, and handle length are what controls this.

Using good hammer control and the right hammer, I have watched Sam Salvati forge a blade to nearly finished by hammer alone. A few passes on the grinder and it was ready for HT.
 
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