Belt Grinder sharpening technique questions

V

vrex

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Oct 30, 2002
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Hopefully the belt grinder sharpening experts can give me some pointers on sharpening khukuris.
I have a 1"x42" belt grinder/sander 1/4 hp motor 1725rpm (from Lee Valley).
I've been using it for about a year now with pretty good results (regular knives). The belts I first started with were the blue zirconia 40,80 & 120 grits, a 15 micron silicon carbide and a leather honing belt with the compound.
I don't know why I got the 40 and 80 grits, I don't even use those for axes or lawn mower blades.

Any way I think I've put some decent edges on my WWII and 12" AK with the 120x/15mc/ and leather belt, but I thought the 120X was taking a bit too much off to start with so I picked up some new aluminum oxide 3M belts today 180X(80mc),320X(40mc),500X(20mc)
So thats what I have to work with.

Is 180X okay to start with? Then progress through each one until final honing?

Also I don't use the platen, I sharpen in the slack area area of the belt below the top pulley. I hold the egde facing up and the belt direction running from bottom to top (running off the the edge)

Any suggestions or links would be appreciated.

Thanks,
Chuck
 
Sharpen on the slack area. Sharpen edge up. Buy the best belts you can lay your hands on, and use them like they're free.
 
I started out using a 100 grit belt on my sander. it took off way to much steel... Now I'm using a 220 or 320 (Wish I could remember which) grit belt and love it. Not only does it work good at sharpening, but I can also slowly reprofile an edge. :) Doesn't get the knife as hot as fast either.

I almost always sharpen with the edge down, belt moving from spine to edge. Am a little uncomfortable sharpening with the edge up.. Unless it's a small knife. Most always sharpen on the slack part of the belt. Unless I'm doing some extra grinding on the tip of the knife. Ala Swamp Rat Penatrator tips.. or sharpening the clip point on my Becker BK-9.. Blade is awesome with a choil, convex edge and sharpened clip.

Once I found the right angle to hold my knives at, I was able to get some really good edges on my Khukuris and pretty quick too. Sure beets sharpening with a stone. Still have a lot to learn and it's a lot of fun doing it! :D Good luck!

Heber
 
I sharpen mine with the edge facing into the belt; i.e. with the edge is facing upward and the belt running top to bottom.
 
Sounds like the same technique I use. I normally try to use the finest grit that will get the job done to avoid taking off too much steel or overheating the edge.
 
A dumb question. Do you move the blade side to side against the belt or do you do one section at a time?

Thx

Ice
 
Not a dumb question at all. I try to keep the blade continuously moving as I grind.
 
I start at the cho end and work towards the tip in a smooth continuous motion.
Do one side then the other.
I still need more practice at the tip.
Take care not to round the tip off.
 
I sharpen edge down, edge trailing. That's the proper way to say it, btw - "edge leading" or "edge trailing".

Edge leading is dangerous on a slack belt - especially at the higher grits. You can slice through the belt pretty easily.

The way I look at it.....it's like stropping at 180 grit all the way up to 10,000 grit (compound on leather)....I use the same motion throughout.
 
I never thought about cutting the belt.

I was always more worried about seeing what I was working on.

Wow, could you really cut something covered in rotating carbide? I dont want to find out.
 
Jebadiah_Smith said:
I never thought about cutting the belt.

I was always more worried about seeing what I was working on.

Wow, could you really cut something covered in rotating carbide? I dont want to find out.
Click to expand...

I think edge up is okay (safe) so long as the belt rotating direction is "edge trailing" as described by Dan. I feel I can see a bit better this way myself. Definately some risk if you are leading with the edge.

Dan, does the sharpening CD you are working on cover belt sander sharpening or just "hand" sharpening.

Thanks for the info guys.
 
it has belt sanding on it....so does the old one.


Wow, could you really cut something covered in rotating carbide? I
Click to expand...

Can, and Have done it. ;)


A belt coming apart at 1750 rpm and hitting you in the face (or, conversely, a knife catching and being thrown) is an eye opener for sure. Talk about blood racing throughout your body instantaneously.....

For most makers (myself included)...when it happens, it happens so fast...after the initial shock, you immediately start checking for body parts...make sure everything's still attached.

And then after the adrenalin wears off......you'll find out where it got ya....


Example:

Belt delaminated on me once at high speed, came around and hit me in the head. I went into immediate fight-or-flight mode....100% adrenalin....checkin' fingers, toes, etc. You could've hit me with a baseball bat and I wouldn't have felt it...

10 minutes later...I notice my leg is bleeding...."Now why would my leg start bleeding?"....couldn't figure it out...but sure enough, I had a nice gash from the knife hitting my leg before it hit the ground - an event that to this day, I do not remember happening.

;)


Be careful with your tools, guys.
 
I've had the 3M Gold Belts break apart on me several times. I think the problem was that my platen was overheating and causing the glue or whatever that holds the belt together to weaken. The belts were also pretty old and on their last legs. I need one of those things that goes on the platen and prevents heat buildup.

When they break, it really is pretty scary.
 
I've only had one belt delaminate on me. Faceshield and apron saved the day.
 
What Dan and the others said; one of the belt sanders at MWKK04 had a belt break on me. I suddenly became REALLY glad I was so careful about wearing my safety glasses that day, since it hit me right across the eye. I normally wear glasses anyway, so my eye probably would have been OK, but if that belt had scratched my $150 lenses as opposed to my Army-issued ones, I would have been a little :mad:. As Dan said, it was an instant adrenaline rush. I didn't drop the khuk; instead I just turned off the sander and looked over everything to make sure all my pieces were where they were supposed to be. Not fun.
 
Edge down, edge trailing for me. Only use one belt - #120 (I think, don't hold me to that) that came with it; I do all the other grits by hand. I've done my entire collection and several pieces owned by other people...one close call (a karda almost got away from me) but no real drama yet.

A parting belt is probably my greatest fear with that sander. I really hate getting smacked in the face by high speed objects.
 
One of the things Dan shared with us at the MWKK was how to maintain the correct angle/engagement by *listening* to the belt...there is a particular "swish" noise made when the ideal relationship is established and it would be easy to do it with your eyes closed (not recommended!).

Dan can explain it better...Dan?
 
I use 800 grit belts, but unless the edge is dull, or needs reprofiling I hardly ever use the belt sander. My strop with some 600 - 800 grit strip of paper laid across it and say 8 or 10 passes on each side is usually enough. I tend to take too much steel off with the sander. :eek:

However I'd love to have a 30" leather belt for my sander. Anybody know a source??
 
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