Stress Risers from Perpendicular Grinds and Polish

Ausbrooks

Ausbrooks

KNIFE MAKER
I have read some that leaving grind or polish lines on a bevel perpendicular to length of blade actually builds significant stress risers into a blade. Aside from the all the other characteristics of a blade that make it resistant to breakage - HT and temper, steel type, plunge angle and design, handle design, thickness, filework, etc. I was wondering if anyone had knowledge and or experience to share on this either way. I typically polish all my hollow grinds perpendicular to length and wondered if this is really an issue and I need to change my cross grindin' ways. Seems that it is not so much of an issue but I am curious if others think this is taboo as some guys in the mags think - Thx
 
Ausbrooks said:
I have read some that leaving grind or polish lines on a bevel perpendicular to length of blade actually builds significant stress risers into a blade. Aside from the all the other characteristics of a blade that make it resistant to breakage - HT and temper, steel type, plunge angle and design, handle design, thickness, filework, etc. I was wondering if anyone had knowledge and or experience to share on this either way. I typically polish all my hollow grinds perpendicular to length and wondered if this is really an issue and I need to change my cross grindin' ways. Seems that it is not so much of an issue but I am curious if others think this is taboo as some guys in the mags think - Thx
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My experience with this is limited but I can say that the late Mr. Bob Loveless stressed the point of sanding down all of your blades entirely to at least 220 Grit and counter sinking your handle pin holes, etc and having sufficient
normalizing steps done before Heat treatment to reduce the chances of stress risers forming and even breaking during Heat Treatment.

I don't think your sanding direction would have any bearing on this??

Laurence

www.rhinoknives.com
 
I agree Laurence that sanding direction should not have much, if any, affect on creating stress risers. Per Mr. Loveless's thinking, if initial pre-heat treat grind was very coarse, and final grind was coarse as well I can Maybe see some being generated but if I am polishing down to 800 grit I don't see this an issue, unless I'm missing something.
 
I too have read that grinding at right angles to the long axis of the blade (the way 99.9%+ of the people grind) will cause stress risers but I'm not buying it even though the person who claimed this was a very well known and highly skilled maker. I think that things like the courseness of the grind and sharp corners would more important along with proper stress relief before quenching.

Doug
 
Doug I agree - Seems that proper HT and temper are what make a truly durable blade- not drinking the koolaid.
 
The only time I have seen this be a concern is when brine quenching 1095 or W2. I do sand all my blades from tang to tip to at least 220 grit ,before quench. It has reduced stress cracks dureing quench. I couldn't see it as an issue after heat-treat. ( Just a note 99% of my knives are 1095 or W2).
 
I think the blade profile sanding can be a problem also. I take it down to 400 grit to make sure. Also if you make a guard lug cut out to seat the guard , it should not be square corner but an arch on a full tang knife.
 
When seeking the ultimate high endurance performance blade if you practice testing a representative sample of your knives to destruction, you will find that high performance is not the result of any single event, but develops one step at a time. Some variables will increase performance dramatically, others contribute in less dramatic results, but each has its contribution to make.

You will only know when you develop blade performance testing methods that are sophisticated enough to reveal the contribution of each event.

In my experience I have found that final polishing the blade from tang to tip will increase lateral strength in two ways.

First: you will be able to see any scratches that run from spine to edge that you may not see when all grinding and polishing is done in the same direction these scratches are potential stress raisers, that can be significant during hardening and in the finished blade.

Second: if you put a torque wrench on your blade and measure the lateral strength you will find a small but significant increase in lateral strength.

You only know when you test blades made my you in your shop using your methods and your steel of choice. What works for one may not work for another.

When you seek advice, you will learn more about the value of advice offered if you ask those giving advice how they test their blades. This is probably the most significant question makers or clients can ask.
 
Ed, thanks for your expertise on this. It is very interesting that you have actually been able to detect an increase in lateral strenght when torque testing a tang to tip polished blade.
So for one thing it sounds like I need to develop a standard test for my blades, whether I tang to tip polish or not, to communicate to a knowlegeable customer why my blades are really made to a performance standard, even if I develop my own standard, especially when I do my own HT and cryo.
When you said you used a torque wrench to test lateral strength, did you mean you would test by twisting the end of the blade or are you pulling sideways on the end or tip in a side bending action that would simulate the bend of knife if it was used as a pry bar? The subject of testing a knife has been discussed since dawn of time but I would sure like to know what an "industry standard" is for a knife test that could be performed with common tools....vise and a large hammer would do it...
 
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The one industrial standard that seems to be used the most by production knife Mfg's is of course a Rockwell hardness tester.
Granted it is limited and shows only one measure of hardness but it's one thing we can do that doesn't involve destruction and gives a common number that can be aimed for during heat treatment.

I am all for testing to destruction when it will give important information but there is always things that can be learned from shall we say? Less destructive testing and examination.

I am interested in learning more about a impact or the Charpy test. I give the ability of a knife to take impact much more credence than the bending test I have seen a few VG-10 disciples tout.

Anyone have some more tests we could do with and without destruction?

Laurence

www.rhinoknives.com
 
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