Belt Sander Sharpening Question

B

BladesB4Firearms

Joined
Oct 13, 2013
Messages
182
I use a 1x30 belt sander for my knife sharpening, because I prefer the nicely polished convex edge it gives me. I have however, run into a small problem. (NOTE: I have removed the back plate because it is just too annoying to work around in some of my larger blades) The edges I'm making are a bit too obtuse for my personal preference, even though I sharpen on an extremely shallow angle. (5-10 degrees) Could this be because I'm pushing down too hard and causing the belt to flex excessively? The terminating inclusive angle is about 50 degrees, while I prefer 30 inclusive. Any advice or answers to this will be greatly appreciated.
 
You should be able to adjust the tightness of the belt. On my harbor freight there's a little knob toward the back. It adjusts tracking and tension.
 
Something is not computing here. If you were holding at a 5-10⁰ angle and pushing hard enough to end up with a 25⁰ angle, you would be touching...and grinding... the spine side of the blade. How are you measuring this 5-10⁰ angle? Just a "guesstimate"...or 5-10⁰ to the curvature of the belt? Not the same as 5-10⁰ to absolute vertical. Come to think of it, how are you measuring the finished angle of a CONVEX edge?
 
As far as the 5-10 degree mark its eyeballing from years of hand sharpening on stones. The way to measure the terminating angle of a convex edge is to take a straight index card and slide the edge along it, increasing the angle until the edge catches. (Similar to a thumbnail test of sharpness) Also, there is the occasion where the spine will ever so slightly kiss the belt. The belts I'm using are not the 3M Trizact with the stiff backing, just simple (paper thin) aluminum oxide grinding belts in 320, 500, 1000, and 1200 grit, finishing with a leather belt loaded with green compound. Thanks for all the input. I just tried my hand at it again with my Rajah II using much less pressure and the edge came out exactly as I wanted it to. Problem solved. Thanks guys :thumbup:
 
The best way to use your belts you have is with "light" pressure. Go slow and let the belt do the grinding. Too much pressure will end in wrong angles desired, and possibly the overheating of the blade. Sharpening with a rotating grinder type machine needs light pressure and an easy touch. Using them is like cooking Bar-B-Q, it is not done until it is done. You can't hurry either one. :)

Blessings,

Omar
 
Thanks for the tips :) I've only been using a belt sander for a couple weeks and all of this was very informative :thumbup:
 
Light pressure and use a belt cleaning bar (if you aren't familiar with them they are basically a big eraser). Light pressure will slow heat buildup, slow belt wear, and give a more controlled edge. The belt cleaner will remove metal buildup from the belt, allowing it to cut better and it somehow greatly extends the life of the belt.

You may also want to look at some higher grit belts for your sander. I know you can easily get belts up to like 6k for very little. I would just recommend staying away from the checker pattern belts. Those things have been nothing but crap for me.
 
I get it as close to the geometry that I want using a heavy low grit zirc belt, then follow the progression until I start having the same issue.

This is going to sound nuts, and you have to be extremely careful, but with the high grit belts I take the index finger from my off hand and lightly apply pressure to the back of the belt as it's running. With smaller blades I can still keep my thumb from the same hand guiding the blade.

You *can* burn yourself if you're not careful, but I've only gotten warm.

I especially use this method while regrinding a flat ground blade to narrow the stock.

One thing you could try is to put a little tape on your finger, but you'd probably still have to be careful not to touch the grit at the sides of the belt.
 
Last edited:
Where can I find a belt cleaning bar? I have a lot of trouble with metal building in my 1200 grit belt. I also plan on getting belts up to 12000 grit and a separate leather belt to put jeweler's rogue on for use after the belt loaded with green compound.
 
Harbor Freight $6 or 7 I believe.

IMAG1790_zpsd43b0205.jpg
 
Strigamort said:
I
This is going to sound nuts, and you have to be extremely careful, but with the high grit belts I take the index finger from my off hand and lightly apply pressure to the back of the belt as it's running
Click to expand...

I guess you haven't seen Ken Schwartz's video of his insanely great belt grinder setup? It's variable speed and reversible, plus vertical or horizontal orientation. He shows a technique where he controls the speed, plus on/off with two foot pedals, and he uses his hand, in a leather glove, to apply pressure from the back side of the running belt to selectively grind down the sides of a blade. It is extremely impressive!

[video=youtube;XSF3VF9aIp0]http://www.youtube.com/watch?v=XSF3VF9aIp0[/video]
At about the 15:50 mark he talks about what he's going to do and then shows it.

Some day when I grow up, I'd like to have a grinder like that! :) :)

Brian.
 
By the way, my second or third time using it, I was sharpening a Spyderco Tenacious and wasn't careful, so the 500 grit paper thin belt let my finger know it was there by digging into it deep. Most painful and worst paper cut I've ever had.
 
You must log in or register to reply here.
Back
Top