Surface grinding and blade warp

REK Knives

REK Knives

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Knifemaker / Craftsman / Service Provider
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Apr 3, 2011
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Hey guys, I just got a folder blade back from ht (1095) and stuck it on my height gage on a granite plate and I have some decent warping. Not sure if this is normal as I was assured it would be straightened during ht, but it's about .012" of a bow in the middle.

So I stuck it on the surface grinder and ground both sides but the warp still seems to be there. I'm wondering if the magnetic chuck is bending the blade enough to straighten it during the grinding then it just bows right back when off of the chuck.

Any tips to get it perfectly flat, preferably not by hand?
 
.012" is a lot depending on how thick the blade is.

Yes the magnetic chuck will bend it down and you won't get it dead flat. Put a feeler gauge or some shim stock at the point you want to grind the most and it will force the warp up so you can surface grind it flat. Once you get one side flat the other side is easy.

Last resort is to soften it, bend straight and heat treat again...
 
If you have an electromagnetic chuck usually they're variable in magnetism, although that can get kind of hinky. Whenever I've had to take warp out of something by surface grinding, I have done it one of two ways. If the geometry of the part allows it to be held in a grinding vise, I prefer to do that. Most things do not, so I do it the way Mike described above with shims. Lay the concave side down and shim the apex of the warp so that when you press down on the center you do not feel or see any movement, you have a good 3 points of contact.

Grind the convex side flat, carefully, as your magnetic chuck is probably holding at no better than 50% as well as when you've laid a flat piece down on to it. Blocking up a shimmed blade with parallels that are thinner than the blade is a good idea.

Once the convex side is flat, you can put it directly on the magnet and grind the concave side flat.
 
Thanks guys, I was actually thinking about using shims, glad I wasn't too far off! Great advice above, thanks both of you!

It's 1/8" thick stock.
 
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