Belt Sharpening Makes Knives Duller!

[Squilchuck]

I thought I found a perfect solution for fast and efficient knife sharpening in an older thread with links that described the use a 1x30 belt sander with various grit and leather belts. I bought a Harbor Freight 1x30 belt sander and the prescribed belts. I can get a nice polished edge, but nothing as sharp as with my diamond hones and hand strop. Certainly not razor sharp. Sometimes the edge is downright dull! The process does not seem like rocket science, so I am puzzled about what I am doing wrong?

Several things occur to me. Maybe the belt is too slack and my edge is too round? I sharpen just below the top wheel, and have tried other positions too. Maybe I keep pushing the wire edge back and forth and break it off? I tried grinding at less than a 20 degree angle too. The other thing is the belt on the HF sander is a bit concave from side to side (not flat) because of the concave wheels spinning the belt. Basically, the middle half of the belt gets used, and I have to be careful a the tip of the blade to not round it back when I hit that concavity.

Please help! I am about the chuck the thing and go back to the diamond hones.

[Grey Drakkon]

One thing that might be affecting it is if the belt is producing a lot of heat. That can anneal the metal a bit, making it dull (or at least let it lose its edge fast).

[TwinOaks]

I would have to say that improper belt sharpening dulls the knife, not belt sharpening in general. A 1x30 isn't much belt sander (I have one) and there isn't much room to work with, or on. If you take a look at some knifemaker's vids you'll likely see that many use a jig to maintain a specific angle. They also have a wider assortment of belt grits than most hardware stores carry in 1x30

. For example: the finest grit I have found locally is 120 for a 1x30 sander. That in itself will produce coarser results than most stones. Also consider that with only 30" of belt, you're loading up the belt or wearing it down pretty quickly. Either case means that your blade is creating more heat than it should. When I've use mine for sharpening, I work bare handed and anytime the blade feels warm, I cool it. I reprofiled two kitchen knives after my son clanged them together edge to edge (too much LOTR) and when I got done they needed only a few passes on a ceramic rod to be back in working order. I also used it to change the bevel angle on my head knife with similar results. Maybe the key to using the diminutive sander for sharpening is to work slowly and in small steps.

[Squilchuck]

Thanks. I am very careful to keep the blade cool. I use a light pressure and quick even pass of the blade across the belt, then touch for heat. I am using up to 1200 grit belts from Lee Valley.

[zuludog]

You could try asking on this forum

http://www.britishblades.com

[Gump]

When using a slack belt ,you must lay the blade almost flat against the belt. You are right that it is rounding over the fine edge and creating to much bevel angle. This is great for a butchers knife, going through soft meat that parts easily, but way to thick at the edge to cut dense leather easily.

[Squilchuck]

Thanks for the help. I'll keep working at it with your suggestions.

[TexasJack]

One of the curious things that happens when you are sharpening a knife is that you can get what is called a "wire edge". This is especially true if you sharpen with the blade in the same direction as the belt. A very thin strip of metal will form on the edge of the blade and will make it seem like it's very sharp, but if you use the blade the wire edge folds over and it's suddenly very dull. That edge can be removed with a leather strop.

I've never seen a 1x30 belt that goes slow enough to be worth anything for sharpening a blade. At best it can be used to form a new edge on a piece of steel. The belt goes too fast and doesn't present enough surface area. Knifemakers typically use a 72" belt and slow it down as much as possible.

Power tools are best at making things go badly very fast. Unless you abuse your knife blades - or let them go far too long before sharpening - you really don't need a grinder or belt for sharpening. Sharpening a knife by hand is one of those basic skills that everybody should have. If you don't have it, work on learning it.

[rawcustom]

You will be fighting a few issues with the HF belt sander. As others have mentioned sharpening on slack belt is tricky to not develop a rounded edge. A lot of guys still do this with the right angle and pressure, but no matter how you do it, you will get an elliptical convex edge, that I find far from ideal and tend to burden your next sharpening efforts. If you try to sharpen against a platen then you will have more heat (that belt sander is running at a high belt speed) plus you have to take into effect the belt movement, and true flatness of your platen. Even with a true flat platen you will have enough belt bounce to round and edge, especially if you grind edge up. Belt grinders are great for knocking down your primary bevel and I like them for power stropping. Use it to restore or add a bevel to a dull knife, then switch to hand sharpening. when you are all done it and it should be very sharp, a leather belt strop works well with a little CO. Just be sure you focus your pressure at the back of the sharpening bevel and that will lend just a small amount of stropping to the edge. Very easy to overdo things with power tools, and that belt sander is running fast enough and likely wild enough to make for a sharp learning curve. May want to practice on the axe and hatchet and garden tools first.

[rawcustom]

Also, in case it isn't obvious, always strop edge down.

[Squilchuck]

Thanks for all the advice.

[Trox]

I use a cheap belt sander with good result. I use 2 inch wide belt belts for wood, because thats the only ones available for it (180 and 80 grit). Remove any under belt support plate and let the belt be slack. Always sharpen against the belt movement of course and use a flat angle. I move the knife fast sideways, especially with a new belt. Start practicing with something cheap until you get the hang of it. The advantage with this system is of course that you can sharpen for a long time without the need of any cooling. I use it to form an edge, remove rust etc. The final sharpening is done on a fine ceramic stone before polishing. However, I know people that do their polishing on their belt sander too. It all depends of the grit of the belt. If you only have coarse belts like me, moving the knife fast sideways will make a finer result