In article , Robin S.
wrote:
"Frank J Warner" wrote in message
...
I'm seeking advice about die polishing stones such as those found he
At work we use red 40g AlO stones for roughing. The ones we use are loosly
bound so they break down quickly (exposing new/sharp crystals quickly, and
conforming to the contours of the die) Mind out, we have to polish down
milled surfaces so you may not require such an aggressive stone.
Next is a 60g SiC stone, and then an 80g SiC stone. These are used to remove
the scratch marks from the 40g (and 60g). You'll always need a good
assortment of stones as you must completely remove the scratch marks from
the previous stone. This becomes very slow (and stoning is slow enough) when
you jump grits.
For semi-finishing, we use a 100g grey AlO stone. Once this is done, 220g,
320g, 400g and 600g sandpaper is used. While this series results in a
*smooth* surface, they aren't typically cosmetically smooth - you can still
see scratch marks.
For final polishing of draw surfaces (nearly mirror), we use while AlOx
stones, although I don't know what grit (320g comes to mind) as I have never
had to do the final polish on a draw die. This is slow, typically taking
more than two weeks for a couple of guys on two shifts.
As for technique, dies require consistant surfaces. Stoning in only one
direction will cause a surface, that should be flat, to become warped. We
call these low spots "holes" although they are only thousandths or
ten-thousandths of an inch deep. To prevent these holes, a crosshatch
pattern is used when possible (not usually possible on smaller rads) where a
surface is stoned at a certain angle, then the angle of motion is changed -
typically between 30º and 45º. This obviously gives a crosshatched pattern,
and a flat surface. Change directions consistantly. I typically give the
surface a healthy once-over in one direction, then change (this cycle may
need to be repeated tens of times).
Of course, use lube if the stone requires it. Oil stones don't come apart
easily so they load quickly and will stop cutting if used dry. Dry stones
can be tapped flatly on a surface to unload them, although good technique
should stop the loading. You should be able to feel it when the stone is
cutting as opposed to when it is rubbing (due to being loaded). You should
not be affriad to push reasonably hard.
Now, we polish surfaces that usually exceed 2 square metres so polishing
little knives will be slightly different.
The above is worth exactly what you paid for it. HTH.
Regards,
Robin
That's great info, Robin. Worth way more than I paid
I typically take my blades to 320 or 400 grit on the belt grinder, then
finish by hand. I often find myself going back a few grits with wet &
dry papers, to 180 or so, when I discover deep scratches that the belt
didn't get out. This often affects the character of my grind lines and
edges. And, rather than creating "holes," I get "hills," or flats that
should be perfectly flat but are actually slightly convex. I'm thinking
a set of stones from 150g up to about 600 would reduce some of these
problems.
The stones come in various sizes. Which do you prefer? I.e., 1/4" x
1/4", 1/4" x 1/2", etc.
They are used exclusively by hand? No holders, handles and so on? Are
die grinders a completely different thing?
Any light machine oil good for lube? Kerosene (the Engnath site
mentions that) okay? 3-in-1 oil? Tap-magic?
I appreciate the time you're taking with this.
-Frank
--
fwarner1-at-franksknives-dot-com
Here's some of my work:
http://www.franksknives.com/