Need Tips regarding surface grinding

L

Laredian

Joined
May 27, 2013
Messages
199
Greetings,

I need some advice regarding surface grinding.

I have a good friend who offered to surface grind a few blades for me. He has access to a big surface grinder with a stone wheel at work.

Now to give some context: my surface grinding up until now consisted of a lot of hand sanding on a granite surface plate with sandpaper. I was able to do it, but man was it always a pain in the butt.

So my question is this: how diligent are you to make sure your steel is as straight as possible before your surface grind it?

I am asking because my understanding is that, if you slap a piece of steel that has a slight bend to it on a magnetic table of a surface grinder, the magnetic table will just straighten the piece out when you turn it on. Then your surface grind and get your stock nice and flat and parallel and then if you take the piece off the table again the bend is still there. (Please correct me if my assumption on this is not correct!)

Also I would be grateful for any good tips and tricks you use to straighten your steel, especially how you deal with a twist in your stock.

Note: this is all talking PRE-heat treat!

Best regards
 
Either straighten it before you grind it or shim it on the magnet. It doesn't need 100% contact to resist flexing to the magnet but the closer the better.

I'm actually standing next to a grinder right now doing just this. I straightened 30 blades in about 20 minutes with a hammer.

20180325_154608.jpg
 
I hope you dont mind me asking, but how exactly did you straighten them with a hammer? Did you do it on your anvil? Did you use a wooden stump? Did you hit the inside of the bend with the peen or the outside of the bend with the flat side of your hammer?
 
These haven't been heat treated yet, so, I set them on a flat surface to see where which side is concave. Then I put the concave side down on 2 pieces of wood like a bridge. Then smack the convex side in the middle and set it back on the flat surface. I use a soft faced hammer so I don't ding them up. You get pretty good at it, and it doesn't need to be perfect. In reality you can't begin to approximate perfect without surface grinding. The thinner the material the closer you need to be, as it will suck down to the magnet easier.

There's a point of diminishing returns or pedantic effort. If these knives come off the grinder with a .003" bow, does it matter? Not really. You're not going to see it, and it's not going to impact scale fit up. But if you want it perfect you really have to shim and grind post heat treat.

I do air hardening stuff like this: Profile - Straighten - Grind both sides parallel - Grind bevels - Heat treat - surface grind flats to finished size. Having 2 parallel sides, even if they're not flat means the best possible contact area in your quench plates and that they'll likely come out of them as flat or flatter than they went in.
 
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