You MUST use the platen to belt sand flat parts of a blade.

You can NOT get a flat grind properly without using the platen.

The platen is the flat metal plate behind the belt. (*See plate behind belt circled in blue.)



I don't own a Harbor Freight belt sander, but I assume "some" assembly may be required. Did you install/attach the platen? They are usually removeable on that type of sander.

For some things they can be in the way. I leave mine attached and sand above the platen for slack belt when I "Want" convex.

But, usually you can remove the platen for a large slack area.

* Try to make sure your platen is lined up as plumb as possible inline and perpendicular with the belt. Check tracking of belt.

Again, you should practice with a junk knife first. The biggest trick with the platen is the initial contact with blade to sandpaper/platen. You want to try to contact the flat part of the blade as perfectly flat as you can on one end and then move the blade across the belt/platen. I usually start near the handle and move towards the tip. I tend to reverse the process left to right vs. flipping the knife over. I stand on one side for one direction and on the other for the other direction. I don't know if there is a proper technique or not. I was not taught by a professional. I have just tinkered enough to hopefully feel what is working best.

The sandpaper belts grind more aggressively and not quite as smoothly when grinding against the platen. I would guess it will remove metal about twice as fast. So, you have to be a little more carefull.

If you contact the blade at an off angle, it can grind a bad mark on the blade very fast that can take a long time to fix and sometimes you have to take a lot of metal off to fix.

Since you have to try to keep the blade cool, you must contact the blade to the belt/platen many times in most efforts to get the pits out.

The areas up against the Res-C can be tricky too.

If your belts track to one side a little, I often have the sides of my belts cut into the Res-C a little. I have never had "Bad" damage to the Res-C, but you have to keep an eye on the belt.

I have to wear eye protection (and mask) and highly recommend it anyway. I have to see well. Make sure you have very good lighting at the contact of the belt and on the blade. Good lighting helps a LOT!


Here is another past link with some more Belt Grinder Info: Stripping the Coating


Hopefully, you didn't mess up the flats too much.

Good luck.

.