If I can only buy 1 CBN grinding wheel, is 180 grit aggressive enough?

[Frederick Skelly]

I'd like to use it for fixing nicks, reshaping primary bevels or establishing different primary bevels. Mostly A2 or O1 steel. Speed is important - don't want to take 20 mins to do it. Will be using it on a 6" high speed grinder. After using the CBN I will finish sharpening on my DMT''s.

I thought about 80 grit but was concerned I couldn't get the scratches out after grinding.

Any thoughts guys?

Thanks much,
Fred

[Tom M King]

I bought the 180 first, thinking I would add a coarser one later. I've never had the need to get any other one. To do what you want, which is about all I do with mine, will take about 3 seconds, not 20 minutes. Not sure which wheel for a 6" grinder though.

[Mike Cherry]

I agree with Tom. I have the 180 grit and cannot imagine a need for the 80. Maybe when I start turning I would need it. I faced the same question as you and I have a call to the guy at CBN. I think his name is Dave. He steered me towards the 180 and I couldn't be happier

[Kees Heiden]

This is a question I am interested in too. Say, I have an old woody iron with pitting near the edge. I grind it back, half a cm or so, and grind a new bevel. Would that be a doable job on the 180 CBN? I guess it would take a little longer then 3 seconds...

[Frederick Skelly]

Tom, Mike - thanks very much!

Kees - I'm just curious - half a cm is a lot of metal. Have you ever had to grind an iron back that far, or was your question more theoretical?

Fred

[Tom M King]

Kees, I think to remove that much metal you would need coolant with any kind of wheel. A CBN wheel doesn't heat up the piece anything like a friable wheel does, but I feel like part of that is because it cuts so fast that you don't need to hold it on for very long at all. It does put some heat in the piece, and I would think if it stayed on the grinder long enough it would build up too much.

[Kees Heiden]

Half a cm is a lot indeed, but I regularly grind them down almost that much. It's a lot quicker then trying to remove pitting like that on a lap. I've also ground back edges of blades, next steel project is going from a 54 to a 52 mm blade (somehow I am postponing that one...) That's a lot of steel too. It is no problem with a Norton 3X, 46 grit wheel, just a little dusty. Of course I cool the steel often in a bucket of water. It's been a long time since I overheated a blade.

I wonder if a CBN wheel is usable for work like that, and if 180 grit would be too slow.

[george wilson]

I can easily grind away MANY TIMES that amount on my Square Wheel belt grinder. When the cutting edge gets thin,I dip in water. I use 36 grit blue zirconia belts for big stock removal,finer belts for finishing,followed by hand polishing for a mirror finish. Much cooler grinding than a wheel because the belt is 72" long,and doesn't stay hot due to its length,plus the 36 grit is much more aggressive. Sometimes i "sharpen" used belts by dragging a single point diamond dresser across them at full speed. This works to some extent,but the belts are not as good as new,but good for some extra use,at least. Only works on coarse belts that are thickly coated enough to not have their cloth backing cut by the diamond.

I grind out whole knives with my belt grinder,starting from bar stock. These grinders are pretty expensive,but you can get a serviceable belt grinder from Grizzly. BE SURE to use a DEDICATED vacuum (NO WOOD DUST!!!!),right under the place where you do the grinding. That means right under the tool rest,or else the point where you grind freehand. You don't want to go breathing steel dust OR ceramic dust(EVEN WORSE!!) from the belt. It never goes away in your lungs. I have enough COPD already.

If you want significant stock removal,get a belt grinder and use the blue zirconia belts. You can buy the belts cheapest on Ebay.

However,1/2 cm. is not what I'd even consider a significant amount to grind,anyway. Just grind a few seconds and dip in water. The whole operation won't really take very long.

The 6" Bowie knife I made was completely ground on a belt grinder,as was the 8" amputating knife for the museum . Both were ground from 1/4" tool steel. I probably easily ground away at least 1/2 of the steel in the sawn out blank with the belt grinder. And,I used VERY TOUGH types of tool steel on each,because they were air hardening,the safest types of steel to use if you don't want distortion or cracking when you quench. These just harden in air without a quench. The amputating knife has a cross section that looks like a straight razor. A lot of steel was ground away.

Go buy a belt grinder. The Grizzly isn't any more expensive than a GOOD bench (wheel type) grinder(last time I checked). The difference between a belt SANDER and belt GRINDER is the belt grinder runs at least twice the speed of a belt sander. A belt grinder will burn wood,it is so fast. Plus,the belts are usually a lot narrower,like 2" wide,for example. The foot per minute surface speed for a belt grinder is on the order of 4200 sfpm or more. Can be twice that on really powerful industrial units.

[Patrick Chase]

This is a question I am interested in too. Say, I have an old woody iron with pitting near the edge. I grind it back, half a cm or so, and grind a new bevel. Would that be a doable job on the 180 CBN? I guess it would take a little longer then 3 seconds...

I have both 80 and 180 CBN wheels, and use them on a 1700 rpm grinder (the 1 hp Rikon).

You can certainly do everything you describe on the 180. The thing to keep in mind is that the 180 heats the workpiece at about the same rate as the 80, but removes material ~half as fast. If you impose grinding time limits between rests/quenches then everything will be fine. Also it's CBN, so the heating rates are relatively low to begin with.

[Patrick Chase]

I can easily grind away MANY TIMES that amount on my Square Wheel belt grinder. When the cutting edge gets thin,I dip in water. I use 36 grit blue zirconia belts for big stock removal,finer belts for finishing,followed by hand polishing for a mirror finish. Much cooler grinding than a wheel because the belt is 72" long,and doesn't stay hot due to its length,plus the 36 grit is much more aggressive. Sometimes i "sharpen" used belts by dragging a single point diamond dresser across them at full speed. This works to some extent,but the belts are not as good as new,but good for some extra use,at least. Only works on coarse belts that are thickly coated enough to not have their cloth backing cut by the diamond.

How long do you use each belt in total? I'm asking because the one big advantage that conventional grinding wheels have is friability, wherein they sacrifice abrasive from the surface as it begins to dull. In the absence of your "diamond sharpening trick" a belt dulls exactly like a non-friable wheel of the same abrasive and grit. My own experience with belt grinders is that they work great at first but then start to run hot. I still use them for plenty of stuff though.

Also, bulk belt/wheel temp isn't an issue with either. If you quickly stop a grinding wheel after heavy work you'll notice that it's pretty cool, mostly likely due to the fact that it has high thermal mass and was spinning around really quickly in air. The heating we need to worry about is of the localized sort.

The 6" Bowie knife I made was completely ground on a belt grinder,as was the 8" amputating knife for the museum . Both were ground from 1/4" tool steel. I probably easily ground away at least 1/2 of the steel in the sawn out blank with the belt grinder. And,I used VERY TOUGH types of tool steel on each,because they were air hardening,the safest types of steel to use if you don't want distortion or cracking when you quench. These just harden in air without a quench. The amputating knife has a cross section that looks like a straight razor. A lot of steel was ground away.

Did you grind those out of annealed bars and then heat-treat, or did you actually shape them at full hardness? If the former then that isn't really relevant to Kees' question - Just about *any* grinding method is effective on annealed tool steel (annealed A2 is Rc 32 or so), and as a bonus you don't have to worry about de-tempering.

[george wilson]

What I wrote was exactly the correct information. I have spent hundreds of hours grinding. More like thousands of hours. No time now for more talk.

O.K.,I'm back. But for a short time.

The knives were ground from annealed tool steel,A2 and D2,then hardened.

It is EXTREMELY incorrect to say that "any grinding method" is as effective as any other on annealed tool steel. D2 steel has about 12% CHROME,which makes it hard to grind in any condition. Even on MILD STEEL,a belt grinder will grind circles around a bench grinder. I don't have the most powerful unit. Mine runs about 4200 SFPM. Some high powered units run more like 8000 sfpm. I have seen a high powered unit grind a 45º angle FROM THE SQUARE END OF THE ANGLE IRON in about 5 SECONDS. The angle iron was heavy gauge,with walls 1/4" thick. Try that on your bench grinder.

I have a Wilton Square wheel grinder,and I guarantee that it will remove steel many,many times faster than a wheel of ANY KIND.

You WILL NOT FIND any knife maker out there who uses a wheel type grinder. They all use belt grinders,unless they just cannot afford better. Go to youtube and find some knife makers grinding. Unless they are total amateurs,they will be using belt grinders,because they can't afford to work for .25 cents an hour.

Yes,belts cost money,but if you are working for a living,like I was doing as toolmaker,the cost of a belt or 2 is a LOT LESS than what your time is worth. I think I paid $2.50 per belt from Barbkat on Ebay. I can't tell you how long they last as I seldom used one till it was worn out at one sitting. But,I could spend several hours grinding on one blue belt. Brown aluminum oxide belts are cheaper,and do not last as long,or grind as cool.

Belts grind cooler,period. The belts are long,so each part of a belt stays in contact with the steel a much shorter time. This is not up for argument.

[Kees Heiden]

I can see a belt grinder in my future. But not now, little low on money at the moment. So no CBN wheel either. The question was mostly out of curiosity.

[george wilson]

Very sensible,Kees.

[paul cottingham]

I use a small Viel 42" belt grinder for sharpening (don't judge me George!) and I would never go back. If I had the money, I would buy a proper 72" 2" wide grinder in a heart beat. As it is, my budget will likely lead me to buying another 42" Viel rigged for stropping.

that being said, if I bought a CBN, it would be the finer one.

[george wilson]

Paul,if you find the little 1x42" belt grinder to be useful,you will think you have died and gone to Heaven when you get a 2"x72" high speed (4200SFPM) belt grinder. I really think the Grizzly model would be fine. The Wilton is made in Taiwan,and I think they are just riding the Wilton name a bit. i do like the Wilton's enclosed belt,though. Some dust does get carried past the dust collector nozzle. I'd made a plywood enclosure,at least. My dust collector "nozzle" is a 12" x 12" black plastic "scoop. We had a metal nozzle at work,but the plastic one shows no sign of melting,etc.. I put a coarse screen over the hole at the bottom of the scoop to catch whatever I might drop. Better than taking the hose loose.

The belt grinder at work got used so much,the black,wire enforced hose got full of holes. I got a high temperature SILICONE RUBBER hose with spiral wire in it. It never got holes in it. You'd have to get that from a rubber supply place.

You will get the benefit of an 8" wheel,plus the flat platen. On my Wilton,they also offer very small wheels,but they are easy to wear out the small bearings on. I also made a curved platen that clamps to the flat platen. It gives the effect of a much larger grinding wheel,like those of the 18th. and 19th. C.. The Bowie and the amputation knife were both hollow ground with the curved platen. The belt just runs right over it,no moving parts.

I also got tired of having to re machine the cast iron platen from grooves getting worn on it. I made a FULLY HARDENED A2 steel platen surface that has a countersunk flat head screw in each corner. Countersunk on both sides so I can turn it over. But,the fully hardened A2 platen has lasted many years by now. MUCH better than running on the soft cast iron platen. Really good grinders have a sheet of carbide,like those for contour grinding windows for cars. But,the carbide has to be custom made. Big bucks probably. A2 works fine. D2 would be even better. But,I used what I had on hand.