Best bonding and abrasive for bench grinder primary profiling

K

koduu

Joined
Feb 26, 2018
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Hello,
So I have just started knife making (so far 4 in pre heat treatment stage) Didn't have money for a belt grinder so I got a 70€ bench grinder (550W and 8 inch discs). Currently I am just practicing my hollow grinds with this and if the hobby sticks then i Will probably get some sort of a DIY large belt or Disck grinder solution. However, I have noticed something that kind of irks me.

Namely, the disc does not grind all that agressively or cool as I would like it to. Currently I have a 36 grit stone with an unknown bonding and abrasive. I was wondering what kind of stone material works best for knife steels. I will try to find a 24 or 16 grit stone, but specifically what material would give the coolest and most agressive cutting?
 
Welcome to shop Talk.
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Aggressive and coolest are opposite words when grinding.
Aggressive is with a coarser grit.
The way to grind cool is with a water spray or wet wheel. That won't be possible with your grinder.
The way to get the best grind with a bench grinder is with a large wheel ... that isn't possible with your grinder either.
Large Vitrified grinding wheels ( white ) are used by cutlery shops to grind blades for sharpening, but these aren't going to work at your grinder's speed.

Wheel TIPS:
For grinding steel you use an aluminum oxide wheel . These are usually light blue or white. They are the fastest and coolest for our tasks. Norton is probably the best maker of these. They should be available anywhere in the world.
The most important tool you need is a wheel dresser. There are the old type with hardened star wheels that re-surface the wheel, but most folks today use a diamond dresser. They are very cheap on ebay and paces like that. Dress the wheel regularly to "open up the pores" as the old machinists used to say. Once a wheel gets chewed up, it is hard to re-shape, but if dressed daily after each use, it can stay pretty square. If the wheel gets glazed in hard grinding, STOP and re-dress it.
Grind flat to the wheel surface. Don't use the corners to hog metal. It will ruin the wheel.
Go slow and take many smaller passes rather than a big one. It sounds silly, but this is faster to remove metal than bearing down and trying to take off larger amounts.

So, what to do when you don't have the money to get a big belt grinder? - use what you have to its best advantage. Use a medium grit stone ( wheel) to rough out the blade. Take smaller bites in multiple passes, slowly forming the shape. Have a dunk tub of water to cool the blade between passes. Once the basic shape is done, switching to a finer wheel and working the hollow smoother will refine the look. From there go to hand sanding with sandpaper and wooden backing blocks. You can shape a block with a rounded side to sand the hollow grinds smooth.

A used 1HP motor, a mandrel with a pulley mounted, and a 12" vitrified wheel can be made into a pretty good grinding stone for a reasonable price. Use a 3 step pulley setup that will slow the wheel to around 800RPM at full speed and have something like 400 and 200 on the lower range. You can bolt the mount together from 2" ( 50mm) thickness construction timbers. Ad a drip can or water supply hose and a valve and you have a pretty good wet grinder for knives. This setup was all there was for centuries ... and made millions of good knives. .
 
Thanks for the reply,

Location: Estonia, personally I was thinking of Russian, Luga Abrasive Plant discs, because they are cheap and already imported to my town.

The wheel dresser sounds like a good idea, Will definetly try that.

About the mandrel+pulley disc grinder, I was originally thinking on that already, but seeing the current cutting speed on discs, I am thinking that maybe it would make more sense to go straight to DIY belt grinder
 
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