Geek Out! Has Anyone Analyzed Labor Time Increase As Function of Blade Thickness?

redsquid2

redsquid2

Rockabilly Interim Pardon Viscount
Knifemaker / Craftsman / Service Provider
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Aug 31, 2011
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Take a given thickness of stock for stock removal, say 1/8".

Take a given stock removal method.

Take a given grind, say "flat," because there are no radii to consider.

Take a given length, from plunge line to tip.

Make it a straight edge, and make the tip just squared off, rather than any kind of pointy. That will simplify things.

Now take all those given specs, and just change the thickness, and compare time spent on stock removal. The results could no doubt be guestimated, just using math.

Being an amateur knifemaker, and having done most of my grinding with files, I make my knives as thin as they need to be, in order to fulfill their intended purpose.

These musings also partly spring from my involvement in lightweight and ultralight backpacking. For 3 days on the trail, I will typically start out with 27 pounds, which includes 3 quarts of water, and all necessary food and fuel. When it comes to outdoor gear, I think in terms of usefulness-per-ounce. My trail knife is a Buck Vantage Small. My shelter is silicone-treated nylon. But lightweight gear is a topic for another forum. I just give these examples to flesh out my philosophy a bit.

I am bored because I am sitting at home sick today. Ate some bad seafood last night, so I am sitting here drinking tea and thinking about stuff.
 
I have some 3/16 and 1/4 in my shop, I can't put a number on it but it'll be a while before I resort to grinding those down while there is still 1/8 around :P
 
Kris and zcd:

Sometimes I think about making a 3/16" hard use knife, but I'm not that ambitious.

I think Bob Loveless used a thicker stock. It looks cool, but it is more work than I want to tackle.
 
I don't have the numbers all crunched out, but I can definitely say there is more than one reason why probably 80% of stock-removal handmade knives have 5" or shorter blades and are less than 3/16" thick... and one of those reasons is profitability.
 
I'm starting to make my own knives and am starting with 1/4" thick 3V. However, my buddy (he and I are going in together on this project) bought some 3/16" CPM REX M4.

All I can say is that it took him more time to work the thinner M4 stock than it took me to work the 3V stock. I guess he got a flat stock piece where the rollers had "forged" the M4. We both cut the rough blanks out with a band saw. But on his first attempt on the M4, he found a hard spot that folded the band saw teeth, twice.

So what I'm trying to say is that the size of the stock is not the only thing to think about. Initial hardness of the raw stock, properties of the steel you're working, etc, can play into the amount of time that is put into the knife.

I don't care that much, we just drink a lot of beer and cut steel in the garage, so it works out in the end.

Thanks,
Tom
 
redsquid2 said:
Kris and zcd:

Sometimes I think about making a 3/16" hard use knife, but I'm not that ambitious.

I think Bob Loveless used a thicker stock. It looks cool, but it is more work than I want to tackle.
Click to expand...

Can you imagine how many belts the Miller Bros go through at 0.323" thick??
 
You could figure out the amount of steel to remove a given volume of steel and use that as a base to estimate times.
Example 1" wide blade 4" long, 1/8" Full Flat grind. We'll consider straight edge with square tip)
The volume of steel removed to leave the spine 1/8" and file to a sharp point (though you'd not go that low before HT) would be, for a symetrical wedge of this nature, half the volume of the rectangle (1x4x0.125)/2 = 0.25 cubic inches of metal to grind both sides.
If it takes you say 90min to file that blade (strictly grind time) then you can grind away 0.167 cubic inches of steel an hour.
So the same blade in 3/16", (1x4x0.187)/2 = 0.374, 0.374/0.167 = 2.24 hours
So adding 1/16" of thickness would add roughly an hour to your grind time for that same blade profile in the same steel.
Just for fun.... 1/4" 2" wide 9" long blade, (2x10x.25)/2 = 2.25/0.167 = 13.47 hours!
 
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FullyTorque said:
You could figure out the amount of steel to remove a given volume of steel and use that as a base to estimate times.
Click to expand...

Volume of steel. Exactly. Probably not worth the time for me to calculate stuff like that, but it might be useful information for a newbie who wants to make a 9" bowie out of 1/4" stock.
 
I don't think it's a silly question, it's just hard to pin down.

redsquid2 said:
Volume of steel. Exactly. Probably not worth the time for me to calculate stuff like that, but it might be useful information for a newbie who wants to make a 9" bowie out of 1/4" stock.
Click to expand...

Right, that (or measuring by weight) will get you in the ballpark. There are still other factors involved that muddy the waters a bit and prevent a simple, straightforward equation, such as the fact that it's faster to grind a cubic inch (or quarter ounce) off the edge of a thin 1/16" bar, than to grind it off the 2" wide face of a 1/4" bar.

It's hard to even keep track of the total time accurately, because (at least for me) when you get to really hogging steel, there's going to be breaks required just to let the thing cool down. No matter how often you dunk it, heat's going to build up throughout the bar when you're peeling off big showers of metal with a 36 or 50 grit belt.

Even on small blades I usually work on 2 or 3 at a time just so I can keep rotating through them... grinding on #2 and #3 while #1 cools off, etc.

There's also the waste factor... grinding big blades turns a whole lot of perfectly good steel into useless dust mixed with belt-grit. That gets expensive.

To rephrase my earlier statement, there's a reason 80% of 9" x 1/4" bowies are forged, not ground. ;)
 
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Don't forget to factor in decreasing grinding efficiency as your belts wear, or as your arms tire if filing by hand.
 
No doubt this is important in mass production ..but when making a few knives even a few dozen I just charge a little more for thicker stock...i double my cost of abrasives with 1/4" over 1/8". Ive got a 16" OAL 1/4" thick 5160 that has worn in a fresh blaze and worn out an old one. Ive got a sickness I like to break everything down into numbers so questions like yours appeal to me. I do agree with frank though it is foolishness:)
 
I like Frank a lot, but as I understand, he mostly makes gent's folders. That's not particularly relevant to this convo.

Y'all might be surprised how many people contact me and others for quotes on large, thick, handmade fixed blades made from high-alloy steels, and want to know exactly why they cost so much.

You might also be surprised by how many knives like that actually sell and put food on knifemakers' tables. It's a tough "market niche" for certain, but it does exist. Those folks paid my mortgage last month, and they will next month, too.
 
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Thickness is nothing compared to width. Try making 3 inch wide chef knives or 5 inch wide cleavers, The amount of surface area that now needs to be finished is a lot more labor than hogging off a bit of thickness.
 
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