cleaning plunge lines - post heat treat

Barry Clodfelter

Barry Clodfelter

Knifemaker / Craftsman / Service Provider
Joined
May 29, 2007
Messages
578
I am wondering what your process is for cleaning up your plunge lines after you heat treat. The last few knives I have made I haven't gone back to the grinder after heat treating I have soaked them in vinegar for a half hour or so to loosen up the black then hand sand. The problem I'm having is getting the plunge lines as clean and smooth as the ricasso and blade. some of you guys have a seemless transition from the plunge line into the blade and I wonder what your method is?
 
What I do is wrap sandpaper around a machined piece of perfectly square stock, get the majority of the gunk and then work it gently from there with finer grits until I like it. Sometimes you can go from the ricasso towards the tip in one motion and get it fine tuned as well.

Only working off 2 hours sleep, so let me know if that doesn't make sense... :o

Charlie
 
I use a granite plate with the edge rounded off, wrap abrasive paper over it, then cover the surface of the abrasive with masking tape except for the rounded edge (the tape lets you work just the plunge area instead of the whole bevel) . Then place a file guide on the blade just behind the plunges, and use the file guide as a fence along the edge of the granite plate to lap the plunges down. I do this before HT and again afterwards if necessary, it is much easier before. It can take from a few minutes to an hour depending on how badly the plunges are butchered on the grinder, but gives more even and consistent results than any other method I have tried. Cheap sandpaper will really get your goat with this method, buy good stuff.
 
To sand into sharp plunges, I use a micarta stick with a square edge, wrap 280 grit around it to start with, and just dig in there with the edge. If a platen edge can put it in there, a square edge block should be able to get it out.

A milder plunge is easier to sand into, if you can pull it off.
 
Salem what do you mean by a milder plunge?

I might should have mentioned how I cut my plunge lines to start with. I use a file guide and a 1/8" round file to get out the majority of my plunge cuts then the belt sander finishes up after I bring down the blade to match. So I have rounded plunge lines.
 
Work smarter, not harder. Get everything smooth and clean (no deep scratches) before heat-treat and life will be much easier.
 
Thanks James! I do get everything smooth and clean before ht. I take them usually up to 400 grit with a nice even finish pre-heat treat. The problem is getting the plunges cleaned up post ht without going back to the grinder. It seems I have to up and down the plunge line to get all the black out then getting the scratch pattern to match the blade is where I am failing.
 
By mild I meant more of a swept type plunge, such as this- or even a shallower radius.

IMG_6094.JPG


If you are cutting them in with a file, I'd say the radius of your sanding block edge plus the thickness of the paper needs to be less than your 1/8" file, or you won't get into the scratches at the bottom. Even wrapping paper around the original file will make the circumference larger enough to frustrate.

So yeah, a square or very lightly rounded off edged block should work pretty well.
 
A buffer with a felt wheel works pretty well.
Should you want to hand sand later, you can.
 
I also always go back to the grinder after heat treat, but before I do I clean up the plunges of any oxides with a round diamond needle file, then when I get to the Trizact gators, it cleans up nicely.
 
Salem Straub said:
If you are cutting them in with a file, I'd say the radius of your sanding block edge plus the thickness of the paper needs to be less than your 1/8" file, or you won't get into the scratches at the bottom. Even wrapping paper around the original file will make the circumference larger enough to frustrate.
Click to expand...

I think this might be the problem. Next time I will cut the plunges with the file the wrap paper around it and take a little more while it is still soft. Hopefully this will give me enough room after HT to hit the bottom and have the scratch pattern flow like the one in your pic. Or maybe I'll use a larger round file then go back with the paper wrapped 1/8" after HT.

Great site Salem! Thanks for taking the time to put up all the great info!
 
You bet, hope it helps. I think you are on the right track there.

+1 on going back to the grinder after HT, though.
 
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