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What is sharp vs dull (scientifically)

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Forum topic by Desert_Woodworker posted 04-23-2017 03:45 AM 680 views 0 times favorited 7 replies Add to Favorites Watch
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Desert_Woodworker

1281 posts in 1051 days


04-23-2017 03:45 AM

Topic tags/keywords: router tool bits resource router

This is from a review that was previously posted by me: I would like to here from others on this Forum “What is dull?”
Amana Tools – router bits
I purchased a combo starter set for my CNC, 3 years ago. My .25 spiral bit is to retire to drill or experimentation runs. I honestly recommend Amana tool bit.
How do I know exactly know if it is dull (please review the Charles Neil review on sharpening- http://lumberjocks.com/topics/178682) scroll down to the end and how CN sets me straight on what determines if the bit is dull; scientifically.
I use Amana and recommend them.

-- Desert_Woodworker


7 replies so far

View clin's profile

clin

751 posts in 833 days


#1 posted 04-23-2017 05:29 AM

It’s somewhat subjective. But I think it is when the tool no longer performs as needed. If you’re cutting something soft, dull is very different than cutting something hard.

With some materials, more dull is okay, others you need it really sharp to get through fast without burning, tear, etc.

It can be difficult to judge since dulling usually occurs slowly. Sometimes you just don’t realize how dull a tool is until you replace it and realize you’ve been fighting a dull tool longer than you should have.

Even if there was a method to grade sharpness on a scale from 0-10, sometimes a 5 is okay, sometimes not.

In the end, I think it comes down to experience with what you are doing.

-- Clin

View Redoak49's profile

Redoak49

2894 posts in 1825 days


#2 posted 04-23-2017 12:04 PM

There is an interesting article called “Experiments on Knife Sharpening” by John D. Verhoeven. You can find it with a Google search as I could not get a link pasted into this response.

It shows some great electron Microscope pictures of sharp and dull edges.

View MrRon's profile

MrRon

4492 posts in 3080 days


#3 posted 04-23-2017 06:08 PM

I don’t believe dullness and sharpness can be explained scientifically. If a knife slices through a piece of meat easily, then it is sharp; if it struggles to cut through, then it’s dull. This is more easily understood in the metal working trades. A sharp drill will produce nice spirals of chips, but if dull, the chips will be deformed and everything will heat up. All that can be said is; if it does the job, it’s sharp enough; if not then it’s dull. A wood chisel is another good example. If it digs into the wood, it’s sharp; if the chisel skates over the wood and jabs you in the hand, it’s dull. As soon as a tool stops doing what it is supposed to do when new is the time to declare it as dull.

View Desert_Woodworker's profile

Desert_Woodworker

1281 posts in 1051 days


#4 posted 04-23-2017 06:36 PM



I don t believe dullness and sharpness can be explained scientifically. If a knife slices through a piece of meat easily, then it is sharp; if it struggles to cut through, then it s dull. This is more easily understood in the metal working trades. A sharp drill will produce nice spirals of chips, but if dull, the chips will be deformed and everything will heat up. All that can be said is; if it does the job, it s sharp enough; if not then it s dull. A wood chisel is another good example. If it digs into the wood, it s sharp; if the chisel skates over the wood and jabs you in the hand, it s dull. As soon as a tool stops doing what it is supposed to do when new is the time to declare it as dull.

- MrRon


Excellent insight- thanks

-- Desert_Woodworker

View Aj2's profile

Aj2

1175 posts in 1634 days


#5 posted 04-23-2017 07:02 PM

Ive experienced a bevel down plane blade that makes nice shaving on walnut but will not shave arm hair.
In fact a edge that will shave arm hair sometimes fails quickly on wood.
I’m pretty sure this is the mystery we all argue about when it come to sharpening.
Good topic.

-- Aj

View BigYin's profile

BigYin

403 posts in 2253 days


#6 posted 04-23-2017 07:13 PM

easy .. when the ER doctor looks at the jagged wound produced by your tool and says “oh thats nasty”, its a fair bet the tool was blunt. However if the Doc says “thats a nice clean cut and will heal well and quickly” the offending tool was sharp.
D’ya wanna guess how I know this ??

-- ... Never Apologise For Being Right ...

View Jimintomahawak's profile

Jimintomahawak

57 posts in 312 days


#7 posted 04-23-2017 10:33 PM

Lol bigyin… sharpness can be measured but not easily in many cases. Shaving arm hair is sharp, but is that edge suitable for planing walnut? For router bits you can tell with a loupe 10-20x if you have wear on the edge. After .001-.003 cut quality will degrade and motor loads will increase. burning will start to show up as well. Now if you look at the edges 200-400X you will very easily see dull and sharp. You will also start seeing if the carbide is any good or not. Voids and poor grain structure. Search sharpness test on google and see some of the crazy tests. String with weight… won’t work on a router bit. The sharpest most effective edges come from good steel and proper grinding and honing. My pet peeve is finding out part was burned ( turned blue) during grinding then they rework it and you don’t know it. Edges that have had that issue won’t last long.

Sharpness is a fascinating discussion. Ahh Billions of razor blades and all of them razor sharp

-- Laziness drives creative thinking...

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