Thinning stock

Kevin McGovern

Kevin McGovern

Joined
Jul 31, 2015
Messages
3,118
So here is the blank for my KITH petty. This blank is longer than my platen. It is currently .178" thick. I think it should be thinner, maybe .11 or so. So the question is, do I need to thin it down, and if so, how?
69fd5d11072393163bbb24c6f39710dd.jpg
 
Last edited by a moderator:
Hey Kevin, that seems pretty darned thick for a petty IMHO. I use my platen to thin things down, but that is so think to start with I'd personally opt for thinner stock.

To thin long blades I start grinding vertically as normal, focusing on the tip for distal taper, but I then occasionally run a lengthwise grind to see where I might be high or low. It will be a real job to thin that down though, assuming a distal taper of maybe 3mm to 1.25 mm 2 inches from the tip.
 
Yeah, it's not ideal, but it's a special peice of steel. The fine gentleman who sent it to me orders his stuff thicker as he forges. I am stock removal only currently.
 
You might be better off with a piece that big to take it to a local machine shop and have them take it down to your desired thickness with a surface grinder. I know the machine shops around where I live don't charge much if anything at all for a small job like that.

Jeremy

Sent from my SM-N915V using Tapatalk
 
I use a lot of that size :)
I forge it down to widen the blade, and add some distal taper. Then I finish on the belt grinder.

On a petty or sujihiki, .18" is a bit thick, so a few pases on a 36 or 50 grit belt will be needed. I do this as I add the distal taper. Shoot for about .100" spine thickness above the heel, and a .06" spine at the center of the blade. About 1" from the tp it should be about .03".

On a single bevel blade, .18" isn't so bad as a starting point at the handle, as the upper part can be a bit heavier. On a yanagi-ba, I like the center of the blade to have a spine of .08-06.

I would suggest that you do the distal taper and basic blade shape to 400 grit, but leave the main bevels for after HT. At the very thinnest, I would suggest an edge of .040" pre-HT.



BTW, I changed "Thinking" to "Thinning" for you.
 
Stacy E. Apelt - Bladesmith said:
I use a lot of that size :)
I forge it down to widen the blade, and add some distal taper. Then I finish on the belt grinder.

On a petty or sujihiki, .18" is a bit thick, so a few pases on a 36 or 50 grit belt will be needed. I do this as I add the distal taper. Shoot for about .100" spine thickness above the heel, and a .06" spine at the center of the blade. About 1" from the tp it should be about .03".

On a single bevel blade, .18" isn't so bad as a starting point at the handle, as the upper part can be a bit heavier. On a yanagi-ba, I like the center of the blade to have a spine of .08-06.

I would suggest that you do the distal taper and basic blade shape to 400 grit, but leave the main bevels for after HT. At the very thinnest, I would suggest an edge of .040" pre-HT.



BTW, I changed "Thinking" to "Thinning" for you.
Click to expand...
So for a double grind like the picture below, should the distal taper be constant from heel to tip?
0897e2a2cdd8919925b55f1e0a097c6b.jpg
 
It is up to you, many of those pettys are less than .100 thick...so the distal taper may not start at the heel but in the last third of blade. I have used 1/8 stock for pettys and I start the taper at ferrule area. For .18 stock (deba type thickness) if it were me I would def start the taper at the heel.
 
On a blade like the one pictured, I taper to the spot where the bevel meets the spine ( about 1.5" back from the tip). At that point the spine is usually half to one third of the spine thickness above the heel.
 
Kevin, distal taper is a lot easier than you're thinking. You shouldn't need a machine shop to do that. As a matter of fact, it's probably going to take more time explaining it and setting up a machine shop to do it than you doing it on your grinder. You've done tapered tangs, do the distal taper in similar fashion.
 
Brock, no, I meant a symmetrical grind on both sides. I was grinding some paring knives last night and have a better idea of what I need to do on this one.
 
You must log in or register to reply here.
Back
Top