Rippling and gouges on blade flats

Frank Hunter

Well-Known Member
After a few hours over several days searching I've decided to post up for some advice on this. How are you more experienced makers finishing the flats of your blades prior to installing pinned bolsters and hollow grinding? I can get a bright finish if I go through the grits, taking my time and getting all the scratches out and then buffing. However, I am having some nasty ripples and gouges that although smooth, look pretty nasty when you view at a low angle or from the end of the blade down the face of it. Usually takes some reflection of the overhead shop lights to show up really good. MS paint art included of the location and direction of these. Are you using a 9" or 12" disc, or drawing the blade across the 2" flat platen on your grinders? I'm using the latter method, and it seems any combination of speed and pressure still is causing some problems. I'm betting this is operator error but any advice would be welcome. Thanks!Rippling.jpg
 
Here are a couple of ideas. One is that you may be pausing as you move your blade across the platen and allowing the belt to cut into one area on the blade more. A problem that I have had was allowing the blade to ride up over a corner of the platen though that seemed to make a squiggly mark along the length of the blade. Possibly you're catching the edge of the platen by lifting the blade slightly at one end. Concentrate on bringing your blade down flat and then moving it at a constant speed from the plunge line to the tip.

Doug
 
Excellent. I reviewed several searches on the topic, and made a change. I removed the work rest to give me clearance to get right up on the machine. This also prevented the belt from driving the knife down against the rest and making it stick and drag as I draw it across. Now I'm getting absolutely shirt-dragging belly-up to the grinder and it feels like there is a lot less rocking the knife against the platen. This might be old hat to some but being self-taught I've never worked against the platen before without the rest, I should have been doing this the whole time. I hollow grind free hand and the hollows turn out fantastic, this feels pretty similiar. Thanks Doug, with a little practice I should be getting it down.
 
Frank,
Is your Platen flat? another thing to watch for is that you get a dish out or lines etc... Ground into the platen.

The rocking and chatter can be a symptom of this. Take off the Platen and regrind it flat on a 6 x 48 or other FLAT sanding machine you have. Take it to at least 220G or I prefer 400 Grit.

This should help you smooth things out!

Laurence

www.rhinoknives.com/
 
My instincts tell me that what your seeing it where the edge of the belt(s) are digging in. This is usually due to not being in a steady/stable grinding position, and putting uneven pressure on the blade, as well as slight pauses during the grinding pass.

The grinding passes should only be in one direction. The way I teach it is to stand with the heels of you hands resting against you body/belly. ARMS AND HANDS DO NOT MOVE DURING A GRINDING PASS. All movement is in your hips and knees, just kinda "sway". Start a grinding pass in the middle of the blade, allowing it to "find" the flat, with little or no pressure. Then move to the plunge, apply pressure, and using your hips/knees, make the grinding pass. There's a lot of little nuances along the way, but that's the basic principle. You never change hand positions during a grinding pass, and your hands MUST rest on your body/belly to remain stable. If you have to reach in any direction to grind, them your grinder isn't set at the proper height for you.
 
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one other pointer that may help is.

I always break & feather over the edges of a new belt before I grind anything with it. A piece of Crock stick, a old Coffee mug or even broken China helps do this, That way you are less likely to get those lines if your approach is not even and you contact with one side first or roll at all during your pass.

Laurence

www.rhinoknives.com/
 
All great replies. Thanks guys! Definitely working from the hips only now, and I did take off the platen and draw-file it using layout die until it was dead flat. Things are a *lot* better. I had changed several things at one time, including replacing the backing platen and kind of lost my way.
 
Great thread! The diagnosis and solutions here are much appreciated. My usual fix is to remove more steel on waterstones to eliminate the gouge. My fingers and my sanity will thank me for heeding the advice here.

-- Lee
 
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