View Full Version : Getting a blank perfectly flat for profiling

05-26-2010, 10:21 PM
I have a piece of spring steel from a ford truck that I've annealed with a fair amount of success and now I'm trying to get it completely flat so I can lay out my profile. It initially had a fairly good curve which I got mostly rid of when I annealed.


Is this just a time consuming event when doing by hand, or am I doing something wrong?

I have a 4x36 grinder/sander from harbor freight. This is a thick piece of steel, a bit more than 1/2 " when I started. I've got the one side ground down to within a 1/16" of being absolutely flat but I still have high spots when I check with a flat edge.

I started with a 40 grit and then switched to an 80 when I got within about an 1/8"

What I've been doing at this point is running a felt-tip marker over the high spots, grinding the marked spot off and re-checking with the flat edge. But it's taking a very long time doing it this way.

Am I just being impatient? Or is there a quicker method of checking and getting it flat? Presumably this needs to be as flat and as true as I can get it before profiling, right?

Thanks for any responses.

05-27-2010, 09:13 AM
On a 4x36, it will take a LONG time to get a piece of steel like that flat.

Something that came to mind when you mentioned it was a spring.... one of the reasons that I stopped using old vehicle springs years ago was because they always seem to retain a "memory"....which means that your gona spend a lot of time and effort getting it flat, and all too often when you heat treat a blade made from a spring, it's going to warp in the direction of the arch the material originally had. No matter what I did, I could never defeat that, and so I decided from that point on to use new barstock. I still occasionally get a warp, but now I can always track it to something I've done wrong...and not the material.

05-27-2010, 09:46 AM
Maybe mark the low spots with your felt tip and don't switch from your 40gr until you think it's flat and the low spots grind the same as the high spots. I thinks Ed's right, 1/2" is a really thick chunk and you're not sure if it'll behave like a knife steel. If you start with a bar that's the thickness you want, you can go right to profiling. There will probably be many other steps to concentrate or mess up on.

Good luck with it, Craig

05-27-2010, 10:41 PM
Thanks for the information.

I'm half-way there plus I've got a lot more of this stuff so I'm going to at least give it a try. I'll just keep working on it until I get it the way I want it.

I didn't realize that leaf springs would 'spring back' as it were. I'll watch for it and experiment a bit before I get to far on.

05-29-2010, 06:19 AM
honestly just a guess here maybe you can normalize a time ore to just to lose stress and memory let us know how it turns out good luck

05-30-2010, 02:08 PM
What I've done in the past, is to pound it as flat as possible while it's hot, and then use a side grinder to remove the high spots.

All of the springs I've come across have been way too thick for a blade, so you have a lot of room to work. I have a stockpile of 1/4" springs that usually end up at under 3/16ths by the time I get them straightened, flattened, and ground to remove small rust pits. That's a lot of grinding to do with a belt.

Brush it with an angle-grinder, though, and you can take off a lot of metal quickly.

In the end, though, it just isn't worth it. The money you save on "free" leaf springs is quickly ate up by the worn belts and messed up blanks.

05-30-2010, 06:06 PM
You guys are right. "free" leaf springs are a pain.

I've set that aside for the moment and bought a piece of flat steel for now. I may come back to the leaf spring steel later.

Right now I will admit to being a bit impatient. This is my first knife from scratch and I'd like to see some results.

With the flat I've already profiled and am in the process of grinding the edge now. Much quicker :)