knife shrinkage???

M

matlocc

Joined
Jan 29, 2016
Messages
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I am very new to this and have probably made about five knives. I seem to have a problem after cutting out a blank, when grinding my knives seem to shrink down quite a bit. Is there any secret to not over grinding? Usually (no pun here) the length goes down by a half to an inch. Any help?
 
Do you mean that you grind so far that you grind to an edge and past that, losing material by the edge?

You just need to keep a close eye on where your grind is going and adjust the angle as needed. Go slow.
 
Don't grind your knives in a cold swimming pool :D

In all seriousness I'm not sure what you're asking. Do you have photos? Steel won't shrink 1/2" to 1" without you grinding that amount off.
 
I think what the OP is saying, during the grinding process he winds up grinding off more than planned making the blade shorter than desired. Simple over grinding to remove uh-ohs that happen. The cure is practice, and more practice.
 
Shrinkage is an improper term here !
Typical use of growth or shrinkage in steels involve changes in crystal structure not mistakes in grinding !
 
That is what i have done. kept grinding to fix mistakes and ended up with a paring knife.
I made a angle iron jig but it seems freehand is the way to go. I am kind of frustrated. I dont have before and after pics but i will take em for the next one.
 
In all seriousness, and I'm definitely not an expert, but can share what many of the experts have shared with me to help me. I had always pushed really hard to grind as much off as fast as possible and as with most things when I try to go too fast because I'm impatient I make more mistakes, (I still have that problem with handles) so let the grinder do its job, slow it down. If you are still really having trouble maybe even slow down the grinder speed if you can or even go to a higher grit. But for me once I stopped pushing so hard my plunge lines got so much better and I was able to get the blade thickness much more even.
 
“Make a mark and don’t grind past it?”

I essence this ^^^.

When initially grinding bevels you should never apex the cutting edge, the cutting edge should maintain a flat about the thickness of a dime. You can scribe a center line to help and just to keep you conscious of where it is. Same for the extreme tip if you are having problems. Stop grinding just short of the tip don’t grind through it, and finish it there later. Mark where you want your grinds to be and only grind there.
 
3fifty7 said:
When initially grinding bevels you should never apex the cutting edge, the cutting edge should maintain a flat about the thickness of a dime. You can scribe a center line to help and just to keep you conscious of where it is. Same for the extreme tip if you are having problems. Stop grinding just short of the tip don’t grind through it, and finish it there later. Mark where you want your grinds to be and only grind there.
Click to expand...

^This...

What kind of grinder you using? I have a cheapo 1x30 belt grinder, and if the belt tension isn't set tight against the platen, it's easy to grind extra off the edge. Grind edge up so you can see what's happening. Also, always check your work. Do a pass or two and check if you're actually removing metal where you wanted to remove metal.
 
I know this sounds flippant, but cut outside the line and approach the line gently after rough shaping. Switching to a higher grit belt reduced the amount taken.

Larry
Tinkerer
 
when you are pulling the knife along the belt, you have to lighten the pressure when you come to the tip. otherwise the metal sands away faster simply because there is less of it there.
 
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