Carving Knife Blade

[Muddy Dog]

This question may have been asked before, please forgive me if it has.
I was thinking about making a carving knife from a saber saw blade that has never been used.
Can anyone give me some pointers?

[Brian T]

Hand work will take a lifetime. And, you are certain to wreck more than a few files. I go through chainsaw files on crooked knives, 1 file for every 2 knives. Forestry supply place sells in boxes of a dozen.

I now have a 6-speed grinder. Just touch, touch, touch, to never get hot enough to cook the steel.
Because the new edge is so thin, I do all the finishing work by hand still so I can't over heat it.

[Jamie Sharp]

I have a number of pointers on the blog on my website on how to make a carving. One thing I'll suggest is a good belt sander. Stones/sandpaper/files can work but take a very, very long time.

Also, being able to heat treat the blade after doing rough sanding to shape is immensely helpful. an oxygen bottle + propane bottle + regulators and torch will let you do basic small metal forging/heat treatment. Oxygen is like $200+ for the bottle, $40 to refill. regulators/torch/etc kits are like $300. Propane bottle is like $70 for a 20lb bbq size, you can even reuse your BBQ propane bottle if you got one.

A small forge is another option. Gives you a lot of options for shaping steel in the future too.

[Claude]

The saber saw blade might be too thick to make a good carving knife unless you are able to thin it down on a grinder or belt sander. Here is some data I have on my own knives that will show you. I prefer thin and flexible blades for most of my carving, but I do use a thicker Flexcut knife when I need a stiff blade that will not flex. This would generally be when I was scoring a stop cut. If you do use a grinder or belt sander, be extra careful to not allow the blade to overheat while grinding. A "normal" grinder or belt sander motor turns about around 3400 rpm. When I use my belt sander, I touch the blade to the moving belt for 3 seconds, then dunk it into a glass of water to cool it down. If the metal turns blue, you've overheated it and it must be either re-heat treated, or ground down until all the blue is gone. I lost 1/4 inch off the end of one of my Pfiel gouges because of this! (plus several hours to get the bevel back)...

Claude

Knife blade thickness.jpg

[Jamie Sharp]

Wow those are some thin blades. Most of my knives are made from 1/16" stock (0.0625") and even that is pretty springy on the longer blades.

What is the thickness at the spine of those blades?

[Claude]

Sorry about the delay, @Jamie - been busy and just now saw this. The "blade thickness" in my chart is measured at the back or spine of the blade. The blades are all flat-grind from cutting edge to spine, except the Flexcuts.

Claude

[Jamie Sharp]

Sorry about the delay, @Jamie - been busy and just now saw this. The "blade thickness" in my chart is measured at the back or spine of the blade. The blades are all flat-grind from cutting edge to spine, except the Flexcuts.

Claude

Wow. those are some sharp angles. Is there any secondary bevel on the blades?

How is the life between sharpening? and what wood are you using them on?

[pallin]

Consider what happens if you take the figures from Claude's chart and double the blade width. The bevel angle for a flat grind from edge to spine would be divided in half. A 3+ degree bevel on the Goodman and Helvie Med. might not be very durable. Sharpness is always a compromise between easy cuts and durability. Whittling only basswood is very forgiving on the factor of durability. Why would you want to work the whole surface of the blade every time you tune up the edge?

[Claude]

Wow. those are some sharp angles. Is there any secondary bevel on the blades?

How is the life between sharpening? and what wood are you using them on?

Interestingly, the Goodman blade lasts longest between stroppings, next best is the Helvie Med. Detail. I can usually carve at least a half hour between stroppings - I can feel the blade beginning to drag a bit, so I pause and give it about 15 strops per side then go back to carving. The shape of the Goodman blade (scimitar up-sweep makes nearly all the cuts into slicing cuts, which is why, I think, that the blade stays sharp - it's slicing the wood instead of "chiseling" it. I normally use basswood for my carvings, although I have done several in poplar and walnut. I usually stay with gouges on the harder woods. Oh - no secondary bevel - flat all the way edge to spine.

[Claude]

Consider what happens if you take the figures from Claude's chart and double the blade width. The bevel angle for a flat grind from edge to spine would be divided in half. A 3+ degree bevel on the Goodman and Helvie Med. might not be very durable. Sharpness is always a compromise between easy cuts and durability. Whittling only basswood is very forgiving on the factor of durability. Why would you want to work the whole surface of the blade every time you tune up the edge?

First, I would not like to carve with a blade any wider than 7mm - too difficult to make any sort of scoop or roll cut. If I did have to make a wider blade - maybe for chip carving (which I don't do), I could see going to 10mm width or even more for added blade stiffness, but I'd still keep the same included angle (6°-9°) so the blade would be thicker at the spine and therefore stiffer. The thinner blade makes it easier to cut the wood as the blade is not trying to push aside as much wood. Brian T. has posted on this several times.

Claude

[pallin]

Claude - You clearly have given a lot of thought to your knives. I was not criticizing your analysis, but trying to get beginners to think beyond simple concepts of bevel or width.

Phil

[Brian T]

Curiosity got the better of me. Just about every crooked knife I use has a bevel of 12 degrees, certainly no more than 15 degrees. I made them all that way if they began as something else.
Sat and measured the metal stock thickness on a variety of blades.

Just about every one of them was made from 1/16" thick metal. Hall farrier knives are 3/32".
One blade from Crescent Knife Works (marketed by Lee Valley) and a Kestrel 'C' blade are
also 3/32". That added stiffness does not change the delicacy of the shavings but I suppose for rough outs, you could cut heavier chips as they are the biggest blades that I use.

Old and worn down Hall farrier's knives are quite narrow, maybe 1/4" wide for part of the length.
New Hall blades are about 5/8" wide. The old ones can turn a much tighter radius that the wide new blades. But in carving, I'm not cutting like a farrier must be doing.

[Claude]

Claude - You clearly have given a lot of thought to your knives. I was not criticizing your analysis, but trying to get beginners to think beyond simple concepts of bevel or width.

Phil

I understand, and I didn't take it as criticism - I totally agree that understanding how a knife works, what helps (thick/thin/wide/narrow/etc.), is something that beginners will likely not know. Having worked as an engineer for nearly 40 years, I have a need to know "Why". So, when I switched knives while carving, and one worked much better than the other, I had to figure out "Why". It took me quite some time and experimenting to decide what worked best FOR ME while carving. It also helped that I belonged to a couple of carving clubs where I could try other carver's knives to see what I liked/didn't like about them. Finally took my digital calipers with me and started measuring some blades.

Claude