I need grinder speed help

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DAVE DEMATTEO

Joined
Nov 30, 2021
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17
I'm just getting started in knifemaking and have a 2x42 grinder that only has one fixed speed. I find that when grinding bevels, even when quenching after each pass, my blade gets very hot, blackening the point. Can anyone tell me if I can insert a speed reducer. I found one on amazon for under $20 but not sure if will work.
 
What grit are you trying to grind with? Would probably be better to grind with 60-120 ceramics and hand sand to final finish. How much time is “one pass” spending on the belt?
 
DAVE DEMATTEO said:
I'm just getting started in knifemaking and have a 2x42 grinder that only has one fixed speed. I find that when grinding bevels, even when quenching after each pass, my blade gets very hot, blackening the point. Can anyone tell me if I can insert a speed reducer. I found one on amazon for under $20 but not sure if will work.
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No

The speed controller is for universal motors with brushes.

The motor on your grinder is an induction motor.

You can use it. It will give some control on speed, but below a certain amount it will just be useless.
Since the controller reduces voltage it uses greater amperage to try to work.

Since the motor is moving slower, it's not getting the cooling from the slower turning fan.

Eventually it all overheats and smokes.



If you find a youtube video on $500 knife shop, they use step pulleys to slow it down.
Also - use new belts.

Try NEW finer grit belts like a four hundred grit.
They work more slowly and you have more time to learn how to grind.
 
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Daniel Carraher said:
What grit are you trying to grind with? Would probably be better to grind with 60-120 ceramics and hand sand to final finish. How much time is “one pass” spending on the belt?
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I'm grinding with the grits you mentioned, 60, 80, 120. By "one pass," I mean one pass across the blade (approx 5 seconds). I feel perhaps a slower speed will not heat up my blade as much as well as give me a little more control.
 
Sounds more like over use if belts. Dull belts burn steel.
Sharp belts and a lighter touch will solve your problem.
I also started on a 2 x48 .
 
The blade heating up is part of the physics of grinding. Lower speed will help, but you will still get some heat. As you learn to grind you will make faster passes and use less pressure. I have watched guys with screaming fast grinders make 1 second passes, dip in the slack pan under the belt, and make an immediate second pass. It wasn't a skill learned in a day, so it will take practice.
New belts is a must to keep heat down. I find a new 120 grit blue-zirconium belt about perfect for heat control grinding. 400 grit is fine for clean-up but will actually create more heat if trying to remove material.
Smooth passes - not too slow and not too much pressure. Three passes with light pressure will remove as much steel as one with high pressure .. but with more control.
Put some dish soap in the dip pan. A teaspoon in a gallon of water lowers the surface tension and makes the water a more efficient cooling agent.
 
Stacy E. Apelt - Bladesmith said:
Smooth passes - not too slow and not too much pressure. Three passes with light pressure will remove as much steel as one with high pressure .. but with more control.
Put some dish soap in the dip pan. A teaspoon in a gallon of water lowers the surface tension and makes the water a more efficient cooling agent.
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What is not to slow and not too much pressure everyone should find it themselves .
I can't explain in words how I do it , even if I make a video, will not help someone. You can't determine how much pressure I use by watching.
I am reading some posts on this topic which do not agree at all with my experience . How you heat steel so fast is not clear to me ? For example, at 30 or 40 meters per minute belt speed I can do at least three pass / and take off a lot of steel / and then I notice that the steel I am grinding has little heated up ? I'm talking about hardened M2 steel at 64 hrc .
 
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DAVE DEMATTEO said:
I'm just getting started in knifemaking and have a 2x42 grinder that only has one fixed speed. I find that when grinding bevels, even when quenching after each pass, my blade gets very hot, blackening the point. Can anyone tell me if I can insert a speed reducer. I found one on amazon for under $20 but not sure if will work.
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What is belt speed on your grinder and which grit belt you use. I hope you use ceramic belts not AO ? If you don t know belt speed ,give me RPM of motor and Dia. of drive wheel and I will calculate belt speed which is important which grit belt you can use on that speed? For example you can not use 400 grit on 4000 SFPM .........
 
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Natlek said:
What is belt speed on your grinder and which grit belt you use. I hope you use ceramic belts not AO ? If you don t know belt speed ,give me RPM of motor and Dia. of drive wheel and I will calculate belt speed which is important which grit belt you can use on that speed? For example you can not use 400 grit on 4000 SFPM .........
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My belt speed is 4480 FPM and I am using ceramic belts, grits, 60, 80, and 120 but would like to go higher after heat treat. How high a grit do you think I should go?
 
DAVE DEMATTEO said:
My belt speed is 4480 FPM and I am using ceramic belts, grits, 60, 80, and 120 but would like to go higher after heat treat. How high a grit do you think I should go?
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That is 22 m/s , good speed for heavy grinding with coarse belts like 40 ,60 and maybe 80 grit .You should be very careful when you use that 120 belt on that speed , bevels are already thin and it is easy to overheat edge and tip .As you go up with grits like 240 , 400 you need to slow down speed or increase pressure on steel so they cut steel not just rub/ if bevels get some kind of black mate colors , that is that grits don t cut they just rub on steel and make scratches / and will overheat steel fast . On coarse belts we have less grain per square inch , on fine belts we have many many times more and small grains on square inch and simple 40 grit belt and 400 grit belt can not work on same pressure and speed .I can t help you more with fine grit belts , higher i use is 100 grit ceramic and they work , I can even grind bevels from start on that belt BUT I use grinding jig and all my weight and with feet on the floor as if pushing a car to push on jig ................that is lot of pressure , I don think that anyone can do that free hand grinding .
 
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I use a 2x42. Grinding profiles, I use worn 60 grit ceramics. Grinding bevels I start with 36 grit ceramic, then 60 grit ceramic, then trizact A300 (80 grit), then I hand sand at 120. I have not tried an A165 yet (120 grit), but it will be on my next belt order. I would avoid anything finer than 120 grit, and at 120 you need to be fast and light. I have tried some high grit AO belts, but they just do not cut well on my hardened steel blanks.

I have ground some using only 60 grit, but they do get hot quick. You need to be cautious at the tip especially, and don't focus your effort there. Focus on the meat of the blade and only touch the tip on blending passes.
 
Natlek said:
I hope you mean forty grit ?
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No, Four hundred.

new sharp belts in fine grit, removes material slower teaches grinding results.
Avoids the horrible deep scratches from super coarse grits like thirty six grit.


Ed - Montana has been discussing somewhat the same thing. He's going directly from sixty to four hundred.
 
I find 400 grit will build heat if the surface isn't at least 120 grit. My physics tells me more grits per inch equals more friction.
I will have to look at the data from Montana.
 
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