Hollow grinds

H

hellgap

Joined
Dec 17, 2008
Messages
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I havnt been here in a few weeks been tinkerin. Ide like you all to help me out. I have only really done about 7 or 8 hollow ground knives and need to know a few more things as to what in the world im doing right or wrong. So I will explain the best I can what im doing and if my order of doing is wrong or could be improved please let me know. I just ruined my first knife and want to know where i went wrong . I also feel my finish may be wrong as well as to how i complete the knife after heat treat. First i profile with 60 grit then go to 100 grit to remove scratches then mark my steel with a black permanent ink marker just for guiding. I then go back to 60 grit and work down the steel till i have no more imperfections in the piece of steel . I then put my 10 inch contact wheel on and 60 grit orange blaze belt and start hollow grinding fee hand i file the ricaso by hand previous to sanding. I keep a close eye on my thick ness and then work each side as even as i can then move to 100 grit then 220 then 320 ,400 and then drill my pin holes. Before I ship I buff shinny . I feel if i do 90 % before heat treat then I only have 10 % when i get them back after heat treat and do 500 grit finish with the handle sanding and buffing. Very rare if I have to go back to less than 320 grit after heat treat . I would like to know after heat treat should i even put the 10 inch wheel on to sand with 500 on the hollow ground area as ive usually ground it to the limits and is almost sharp when i send for heat and can sharpen easily with the paper wheel system. I could hand sand the scale off from heat treat on the hollow ground area in a few min rather than risking over grinding. Am I being over cautious. I think my problem with grinding through the last blade was the new blaze orange belts are more agressive than the other semi ceramic belt i was using .I am now also using the structured abrasive belts for finishing up to 1200 grit. LASTLY should i use my digital calipers . I am going by feel and I now know i have to ease up when using the orange belts. thanks kellyw
 
That's a lot of questions there. I'll try to talk about a couple.

I grind most of them 100% before HT and simply tumble them to remove the HT color and then use a scotchbrite belt to reapply the ground finish to the grinds. This is for most blades. I take most blades to .015-.025 before HT. There is no HT scale or decarb or this wouldn't work.

Thin blades (.010 and under) can get wavy in the edge during HT, so these I finish grind after HT from .015. I start with a 220 and finish with 400. Sometimes 600.

If you have calipers why aren't you measuring your edge thickness? I measure in several spots to be sure it is even (or specific thickness in specific areas) and then I'll preset them to something like .020 to see how far up they go into the grind. For example, a grind that measures .010 along the edge except .005 at the tip and .020 1/8" up into the grind is a very thin hollow grind and is good for a hunter's scalpel. A grind that measures .025 along the edge except .035 at the tip - and measures .060 1/8" up into the grind is a very stout hollow grind and would be good as a sharpened prybar etc.
 
Kelly this sounds much like the approach I use. I normally take the finish to about 320 before HT, and final finish after. I leave a bit more steel in the edge than you do. There might be some decarb, and you'll want to leave enough steel to remove that after HT. I know you're using stainless and may not have the decarb issues I face, but I think it makes sense to be cautious. Just my .02.
 
I cut, profile and drill before any grinding. I generally grind after heat treat. Use whatever belt progression you find works best for you, I learned with the same progression going from 80 - 120, 240, 320, 400, 600 and then however you want to final finish.
 
I noticed you did'nt mention scribing edge lines to grind to.This is an important step, as it will help keep things even. Also another little tip to save belts, After you scribe those lines take a used 60 grit belt and grind a 45 degree angle right up to the scribe lines on both sides. Then start your hollows with a fresh belt. The 45 will help keep from stripping all that fresh grit right off the belt before it starts doing any real work. You are right about doing 90% before heat treat. My method is a little more like what Nathan said closer to 100%.
 
I grind after heat treat as well I feel it gives me more control. I find if I'm not paying REALLY close attention I can take off too much with a 60 grit blaze.You might goto a 80 grit until y ou feel more comfortable about it.

I also second everything jbs said above about scribing lines.
 
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Thanks everyone I appreciate every bit of info. I only mark my layout with a permanent ink marker and have no scribe. I do have a expensive digital calipers and a good set of manual calipers and have only used them once. Reason is that i was unsure of the thickness really needed. Ide like to point out I was wrong and probably finish about 95 % before heat as usually there is little more than just take the scale off at 500 grit and buff . Thanks alot kellyw
 
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