# Belt sanders are awesome



## mhpr262 (Dec 20, 2014)

My first ever belt sander arrived yesterday, and holy crap, what a fantastic tool that is. Actually it is just a cheap hobby machine, but it does work.

I am not much into the fancy blades, I mostly collect the utilitarian workhorses you would find in commercial kitchens (Wüsthof, F. Dick) and have bought quite a number of those and some no-name knives on ebay. Some of them turned out to be real crap, with the blade behind the bevel so thick that you easily split firewood into kindling with them using a wooden mallet.

I had stashed most of those knives in a dusty drawer in my basement, but with the belt sander I was able to give two of them an almost professional looking new finish on the bladeface and thin them down to a convex cross section so that the final, cutting bevel at 22° ist just half a millimeter or so wide. All this done by somebody who had never attempted to thin a knife or operated a belt sander before (and whose craftsman skills are pretty mediocre at best). I am really pleased with this thing. 

For what it's worth it is this baby here:

http://www.amazon.de/gp/product/B002CZPNP8/?tag=skimlinks_replacement-20


One of the knives is this one:
http://www.ebay.de/itm/Profi-Kochme...hen_Genießen_Küchenmesser&hash=item20f2710536

(the price is ridiculous, I got mine for 10 with free shipping. For that price it is a good knife to experiment with)


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## Bill13 (Dec 20, 2014)

It never happened if there are no pictures of some finished knives.


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## XooMG (Dec 20, 2014)

I agree; even cheap belt sanders can be extremely useful tools if one is looking to fix the bigger issues.

One of my only regrets about living in a quiet urban apartment is that I can't set up any real equipment anymore. It would make things so much easier. I haven't found any decent belt grinders that run quietly and can be set up in a small space.


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## mhpr262 (Dec 20, 2014)

Bill13 said:


> It never happened if there are no pictures of some finished knives.






















The matte spots and marks you see on the bladefaces is just some discoloration left after trying them out and washing them. They would probably vanish if I put some oil on the steel, but why bother.

The top knife also had a super ugly concave spot in the spine where it curves down towards the tip, that was ground out literally within seconds, now the curve is perfectly smooth and convex.

The ugly spot near the handle of the serrated knife is a hollow spot that the belt sander can't reach. It was the knife of an acquaintance who tried to thin it himself, by means of an angle grinder and left huge semi circular scratches all over the bladefaces. those were removed in just a minute or three. Pretty amazing. the finish you see here is just the 100 grit belt it came with, I'm thinking about buying something finer. Is there a recommended grit for surface finishing purposes?


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## samuraistuart (Dec 20, 2014)

I'm sure you are aware of this....but using a belt sander to sharpen a knife you must be careful not to overheat the edge. This will ruin the temper at the edge apex. As a matter of fact, studies from a few sources show that ANY powered sharpening WILL over temper an edge at those last few microns, unless it is cooled during sharpening. I have noticed this for quite some time, doing powered sharpening, be it wheels or belt sanders. I quit using powered devices after reading the studies. Roman Landes being one. I will not even use stones dry.....always with lube of some sort.


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## mhpr262 (Dec 20, 2014)

I know, I stopped a good bit before the edge. I just took off the shoulder between bevel and bladeface to keep the temper intact. I do that last bit with waterstones. I also hold the blade with bare hands, that helps keep you aware of the temperature (the blade can become VERY hot VERY quickly, ouch )


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## rick_english (Dec 20, 2014)

Nice work. I tried putting some blades on my 1x42, with less-than-satisfactory results. I think the wider belt really helps.


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## LKH9 (Dec 20, 2014)

> the finish you see here is just the 100 grit belt it came with, I'm thinking about buying something finer. Is there a recommended grit for surface finishing purposes?



Is it possible to make your own belt for loading metal compound on? For a better mirror finish.

I will suggest that you put a block of sponge soaked in water at your side for cooling the blade down from time to time. Just touch the hot blade onto the wet sponge. (once saw an electrician doing that to a drill bit when drilling through a thick piece of steel, with a cup of water instead. He knows about steel temper, professional guy)


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## psfred (Dec 20, 2014)

220 grit will give a nicer finish, but be aware that the finer the grit and the higher the working pressure, the more heat is generated. A fine grit belt will heat the knife much more that a coarse one because there are many more particles in contact with the steel at the same time.

Also remember that a belt sander will cut very quickly -- the hobby 4 x 36 ones are generally fairly slow, but some models really fly that belt around, and you can chew out divots very quickly.

Peter


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## mhpr262 (Dec 21, 2014)

Thanks for the tip about finer grits generating more heat. I hadn't thought about that, even the 80 grit I have on right now is at the limit for working with bare hands. 

I'm thinking about buying an additional speed controller that is plugged into a wall outlet. Does anybody know what kind of motor belt sanders like this normally use? The data sheet of the controller says it works with nearly all asynchroneous motors ... no idea what kind of motor my belt sander has.


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## mhpr262 (Dec 21, 2014)

I have just finished another knife that had been lying around - a crappy "JUSTINUS" santoku (this one: http://www.xxxlshop.de/kuechen-esse...M_31_v1.opid&gclid=COvTouCy18ICFefMtAodbx4A7Q) and thinned it down. I have also found out that the belt sander has a portion of its length where the belt is unsupported and where the belt "gives" when you press a knife against it. That way you can give the blades a smooth convex grind. I treid that with the other two knives too, but by constantly wiggling them back and forth between two angles while moving their length across the belt. It worked but didn't look so good at a close inspection. I may have to redo them with my new method.
The knife cuts pretty well now, no comparison to before.


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## rick alen (Dec 22, 2014)

I doubt very much that it is synchronous. 0.5mm is still kinda thick, take it down a bit more with the 100 belt then go for 0.2 using the 220 belt and you really have a cutter there that will absolutely amaze you, despite the mediocre/crappy steel, given you know how to sharpen with a 10k+ stone. Then try bringing one of you paring knives down to .03, or close to it. You'll absolutely love it.


Rick


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## x737 (Dec 22, 2014)

samuraistuart said:


> I'm sure you are aware of this....but using a belt sander to sharpen a knife you must be careful not to overheat the edge. This will ruin the temper at the edge apex. As a matter of fact, studies from a few sources show that ANY powered sharpening WILL over temper an edge at those last few microns, unless it is cooled during sharpening. I have noticed this for quite some time, doing powered sharpening, be it wheels or belt sanders. I quit using powered devices after reading the studies. Roman Landes being one. I will not even use stones dry.....always with lube of some sort.


btw, what is the maximum temperature one can heat the knife to without ruining the HT? Is 100C (boiling water) hot enough?


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## XooMG (Dec 22, 2014)

x737 said:


> btw, what is the maximum temperature one can heat the knife to without ruining the HT? Is 100C (boiling water) hot enough?


Consider that a low temper may be 175-200C for extended periods (well over an hour). A brief exposure to boiling water is no big deal. Even when you see some discoloration to straw yellow, you're probably not significantly affecting temper, though extremely thin edges of course will heat up much faster and may reach much higher temperature than the thicker steel behind it. Still, if it's not going blue, it's not an extremely big deal.


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## Don Nguyen (Dec 23, 2014)

Generally around 400° F for most knives you'll see in the kitchen. The trickiest part is knowing which parts are hot or not. You may get the water sizzling in some parts of the blade, but if your edge was in contact with the belt that time you've probably blown the temper.


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## mhpr262 (Dec 23, 2014)

rick alen said:


> I doubt very much that it is synchronous.
> Rick



What do you mean by "synchronous"? Doesn't that usually describe two things that are happening the same way at exactly the same time? I don't quite see what that has to do with a blade edge?

BTW I don't even have a 10k+ stone, I just sharpen those cheapo knives on what I think is a silicium carbide combo stone (grey colour) with maybe 1000 or 1500 grit and finish with some passes over some medium fine polishing paste on a balsa strop. Makes it sharp enough to shave hairs with.

I will indeed have to get some higher grit belts though, I looked at the instruction manual and it seems my belt is not a 100 grit but just a 60 grit.


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## LKH9 (Dec 23, 2014)

2k silicon paper is enough to make a blade shave. I tried it on box-cutter blades at work, got to use anything I could get my hands on when I don't have my fine stone with me. After that 2k sandpaper, you can proceed to strop on metal compound.

I don't think boiling water can anneal a knife steel.


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## rick alen (Dec 24, 2014)

Don't worry about the synchronous thing, so long as you have an induction motor (no brushes) the controller you mentioned will work. A brush motor will need a different controller I believe.

Is that shaving hairs on your arm or your face? There is a difference. But easily shaving hair on your arms is adequate. In terms of mediocre stainless, your typical German grade, they simply cannot hold a fine polish anyway.


Rick


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## samuraistuart (Dec 24, 2014)

2000 grit paper to make a blade shave? I must be doing something right then. The hairs on my arm are gone after 220 grit. And boiling water is 212F...not even close to tempering temperatures. Typically starting around 350F.


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## mhpr262 (Dec 24, 2014)

I asked my brother, who is an electrical engineer, to take a look at the belt sander and he confirms that the motor is verly likely asynchroneous. He says I will likely be able to reduce the speed but will lose a good bit of torque in the process. That doesn't bother me too much, as the lower speed will only be needed after all the real thinning has been done, for finishing and removing the scratches form the rough 60 grit belt.


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## rick alen (Dec 24, 2014)

You can get controllers for induction motors that will preserve the torque, but they will cost a lot more than your sander.


Rick


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## LKH9 (Dec 24, 2014)

rick alen said:


> Don't worry about the synchronous thing, so long as you have an induction motor (no brushes) the controller you mentioned will work. A brush motor will need a different controller I believe.
> 
> Is that shaving hairs on your arm or your face? There is a difference. But easily shaving hair on your arms is adequate. In terms of mediocre stainless, your typical German grade, they simply cannot hold a fine polish anyway.
> 
> ...



By shaving I think most will mean shaving on arm hairs, comfortably and smoothly. 2k can shave a bit, but is very irritating. Shaving face needs far far higher grit, I don't have those 8k-10k stones, so I don't know, I tried honing and stropping my cheapo stainless straight razor and it still can't shave my face. Feels scary on finger test though. My arm hairs pop away on contact, but still not enough to shave a face safely.


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## mhpr262 (Dec 31, 2014)

So the speed controller arrived this morning and I tried it out on my belt sander. To put it bluntly, it doesn't work. It is possible to lower the RPM if you crank it down enough, but once they go down they keep falling until the sander comes to a standstill. If you crank the controller back up it will gather speed again until it is running at max RPMs. It is impossible to dial in a sort of equilibrium between max and zero RPMs. Just some info for anybody else's benefit who might be interested in this little experiment. I'm going to keep the controller though as I got it really cheap, something like 15$ with shipping, maybe I can use it for something else.


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## Bazzle (Jan 6, 2015)

Sometimes an edge with a small burr can shave and be confused with being sharp. I finish with a 2k grit for kitchen knives and add a leather stropping belt for some pocket knives. This will give a bit more shine on the edge. 2k should always shaves the arm with just the weight of the knife.


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