Thread: Norton Blu Max and 3X grinder wheels

Originally Posted by derekcohen

What experiences have you of the Norton Blu Max and the 3X grinding wheels?

The Blu Max is only sold by Timbercon, as far as I am aware. No grit rating is provided, only that it provides cooler grinding.

After some skepticism exhibited by me in this thread (https://www.woodworkforums.com/archiv...p/t-42253.html) I bought a Blu Max but have never used it. It has a 46/60 grit rating whereas the 3X has a 46/100 grit rating. The mixed grit rating is apparently why they are serious stock removers. I do believe they are both cool grinders, a serious improvement over the grey wheels and a significant improvement over the white.

Originally Posted by derekcohen

The 3X is highly regarded, it appears, in the USA but I have not found a supplier here in Oz. Where can one find one?

Just before I bought my BluMax I shopped around and made a contact in a ToolMart store who chased down and enquired about getting a 3X wheel in for me. The Owner of the Norton 3X is Saint-Gobain Abrasives. The WA Saint-Gobain agent would only bring them into Australia if I bought 5 or 6 wheels and from memory the 6" ones were $82 each and I never got the price of the 8". They were also only 25 mm wide whereas the BluMax is 40mm wide. This is ridiculous considering the 6" are only US$35 in the states

Originally Posted by derekcohen

Lastly, what differenes are there in speed comparing 6" and 8" high speed grinders? ... speed on the circumference of the wheel, that is. And what would occur in this regard if an 8" wheel were used on a 6" machine?

I posted so info on that a couple of days ago. If both 6" and 8" have the same RPM the 8" will have a 33% higher surface speed provided your grinder engine is up for it otherwise it will slow down. You can also overload and overheat a small grinder by putting to large a wheel on it.

Hello,

Never tried out those particular ones, but recently after introducing that new breed of aluminas being more of sharp cornered type (and maintaining the sharpness instead of oversmoothening), there has been real improvement in applying multimodal particle size distributions in grinder wheel roughing stones.

I suppose that this new type of abrasive particle provides this way a shortcut to overcome some difficulties in the binder design and concentration in the wheel, despite of the actual binding method. The wear mechanisms would favor this way an overcrushed particle to be torn out of the surface before smoothing too much and therefore causing too much contact friction instead of cutting.

8", as 6", is designed to work according to the rotational speed provided by a bench grinder, that is the typical 1750...3950 rpm. Normally, I believe, the typical max speed limit for these wheels is set at 35 m/s for abrasive surface. More parameters lie within the applied surface pressure between the wheel and the workpiece.

For a 6" grinder, I would think the most stress would be initially laid on axle bearings, possibly shortening their life. I would not believe this would become a real problem because Norton is reputed for well balanced stones at least in the upper end of the line. This is indeed not granted with them cheapos, where for example density differences in the wheel may be quite surprising.

25% of increase in wheel radius will cause an increase of momentum and decrease torque and therefore make an effect in heat build-up in motor coils. Under extreme conditions, this may cause trouble if the motor revs suddenly decrease let's say 10...20% and after release it has to accelerate back to unloaded speed. But, the heavier stone will also operate as flywheel and I would guess that short contact periods of the bevels against the stone would meet the grinder there.

But, it would be so that a grinder aimed for big wheels would work safe and sound, so to speak (this was just a disclaimer, I do not want to give a bad advice but only discuss about it. I would personally try it out, but can't really recommend it to anyone ).

kippis,

sumu

Originally Posted by sumu

25% of increase in wheel radius

Just querying your math.

Going from 6 to 8" inches is a 33% increase in the diameter of the 6" wheel.

A 25% increase in the diameter of a 6" wheel would be 1.5" added to 6" would make it 7.5"

Going from 8 to 6" inches is a 25% decrease in the diameter of the 8" wheel.

Just going for the smallest common denominator for precise fractions.

4/4 for 8" and 3/4 for 6". I would compare momentum difference by these ratios. Could be 8/8 and 6/8, too.

But I may be wrong, of course.

kippis,

sumu

Originally Posted by sumu

Just going for the smallest common denominator for precise fractions.

4/4 for 8" and 3/4 for 6". I would compare momentum difference by these ratios. Could be 8/8 and 6/8, too.

But I may be wrong, of course.

kippis,

sumu

That is incorrect, its an increase of "2" over the original of "6" or 2/6 = 33%

My students have this problem of what I call reverse maths all the time.
I say to them something like. heres $600000: now I'll give you 30% more OR $800000 - take your pick? Quite a few go for 30% more because they think that going from $600000 to $800000 is only 25% whereas its 33%. 30% of $600000 is $180000.

Same as going from 1 to 1.5 - that's a 50% increase, a lot of people think its a 33% increase. whats confusing is going from 1.5 to 1 is a 33% decrease.

numerators and denominators confuse lots of people. Like a lot of things, it all depends on where you start. If you start at 6 then 8 is an increase of 33% (6x(1 +.33) = 8), if you start at 8, then 6 is a decrease of 25% (8 x (1 - .25) = 6).

It's not every lawyer who can do that....

Originally Posted by jmk89

numerators and denominators confuse lots of people. Like a lot of things, it all depends on where you start. If you start at 6 then 8 is an increase of 33% (6x(1 +.33) = 8), if you start at 8, then 6 is a decrease of 25% (8 x (1 - .25) = 6).

It's not every lawyer who can do that....

I'm disappointed JK - I expected more of a detailed debate from a lawyer.

What's important is the velocity of the outer edge of a 6" (150 mm) wheel doing 3000 rpm is 23.6 m/s while for an 8" wheel its 31.4 m/s

Derek, I have found the Blue Max wheel to be unsuited for the uses I have put it to. Specifically, grinding the D2 blades I found that it glazed very quickly and needed dressing 4-5 times more than a standard Norton white wheel. It was cooler, but not really when I consider how much material was being removed compared to the white wheel.

Having said the above, my experience may well be because I did not select the abrasive for the task but used what I had.

If you are thinking of grinding your D2 blade then I'd suggest a zirconia belt on your linisher and pass on the grinder.

What material are you going to grind? That may well determine which wheel is best, even the size.

Hi Derek,

I've got an 8-inch Norton 3X wheel on my grinder. My wheel is 60 grit and 1-inch wide. I bought the wheel from Tools for Working Wood in the USA. I can't remember what shipping cost me and I included other stuff in the order so the shipping wasn't specific to the wheel anyway.

I haven't used the wheel a lot yet but what experience I have with it suggests it runs a lot cooler than the 80 grit white wheel I was using before obtaining the 3X.

My 8-inch Abbott & Ashby grinder runs at 2850 RPM according to the sticker on the front. Converting to metric, my 8-inch wheel is 200mm in diameter (roughly). The circumference is therefore 2πr = 2 x π x 100 = 628.32mm. At 2850 RPM this equates to a tool tip grinding against 628.32 x 2850 = 1790712mm of wheel surface in 1 minute. This represents a circumferencial speed of 1790712 / 60 = 29845mm/sec or 29.8m/sec.

OK, forget the 6">8" conversion. I want cooler, not hotter.

Also forget the 3X and Blu-Max - the 3X is not cost effective and the Blu-Max is not better than the white Norton wheel I have.

I want a 46 grit wheel. This will run cooler than the 60 grit I have at present (80 is too fine).

What I really want is a 10" wheel! NOW we are talking!! Why? Because I can switch between the grinder and the Tormek (which has a 10" wheel).

I will have to make my own grinder. I have a spare 3/4 hp motor which came off my bandsaw (when I upgraded to 1 1/2 hp). This runs at 1400 rpm. Perfect! Better slower than faster.

I need a mandrel. Carba-tec sell these. What size is necessary (not necessarily best - no point in overkill, but also no point in saving a couple of dollars and spoiling the whole thing)? Are these available elsewhere? Cheaper?

And I need a 10" Nortion wheel (1" wide would be nice) with a suitable hole or bushing to fit. And a belt to connect (V or link - where can you buy the linked type)? Where can one buy a wheel this size?

What do you think?

Regards from Perth

Derek

Thinking outside the box for a minute, you don't have to get a ten inch wheel and incur that expense. You could get a die grinding style bit with the same radius of the ten inch wheel or even use a DP mounted sanding spindle with the blade held side on. Just a thought.

Hello,

I have toyed with a thought to build a very similar kind large diameter medium speed (250 rpm...600 rpm) grinder equipped with water spray cooling, using either one of those old wet grinder stones or large bench grinder stone.

(Truing those old wet-grinding sandstones is not problematic at all, keep it rolling while truing it with an angle grinder and a stone grinding wheel, let it scratch the stone surface at high spots and proceed gradually until true. Makes lotsa dust, though.)

The water spray bottle cooling works very well with belt sander and a proper jig. The main motivation to build such would be there that the belt abrasive surface is not running as stable as with a solidbody stone, also the radius of hollow by a sander roller does not follow the Tormek stone diameter too well.

kippis,

sumu

Originally Posted by derekcohen

Also forget the 3X and Blu-Max - the 3X is not cost effective and the Blu-Max is not better than the white Norton wheel I have.

As I said, no personal experience but the Blu-Max is supposedly cooler than the white wheel.

Originally Posted by derekcohen

I want a 46 grit wheel. This will run cooler than the 60 grit I have at present (80 is too fine).

The mixed grit wheels like the Blu-Max and 3X are supposed to be the coolest.

Originally Posted by derekcohen

What I really want is a 10" wheel! NOW we are talking!! Why? Because I can switch between the grinder and the Tormek (which has a 10" wheel).

I will have to make my own grinder. I have a spare 3/4 hp motor which came off my bandsaw (when I upgraded to 1 1/2 hp). This runs at 1400 rpm. Perfect! Better slower than faster.

A 10" wheel at 1400 rpm is a surface velocity of 18 m/s but a 6" wheel at the same RPM is 11 m/s. To drive a 10" wheel you also really need around a 1.5HP motor.

Also slow RPM means it will take longer to cut. That's why they invented the 3X and Blu-Max. Run them at 3000 rpm and get a cool grind.

Originally Posted by derekcohen

I need a mandrel. Carba-tec sell these. What size is necessary (not necessarily best - no point in overkill, but also no point in saving a couple of dollars and spoiling the whole thing)? Are these available elsewhere? Cheaper?

And I need a 10" Nortion wheel (1" wide would be nice) with a suitable hole or bushing to fit. And a belt to connect (V or link - where can you buy the linked type)? Where can one buy a wheel this size?

Hare and Forbes Or Toolmart have 10" wheels.

Derek, You are more than welcome to play with my 46 grit white wheel and BluMax wheels while I am away in Melbourne if you wish - might help you make some decisions before you buy?

Hello BobL ,

Originally Posted by BobL

That is incorrect, its an increase of "2" over the original of "6" or 2/6 = 33%

My students have this problem of what I call reverse maths all the time.
I say to them something like. heres $600000: now I'll give you 30% more OR $800000 - take your pick?

As far as I managed to follow this part of the discussion, I think this was already commented above by jmk89?

I'd say even more fundamental starting point is to assume that if something is compared to something else, they both need to exist at the same time with all relevant parameters submitted for computations. Fractions with common denominators are good, they are both accurate values and by following the numerator, you can quickly pick up the relating ratios and pick up the preferred one, especially when starting to iterate something more complicated.

Same as going from 1 to 1.5 - that's a 50% increase, a lot of people think its a 33% increase. whats confusing is going from 1.5 to 1 is a 33% decrease.

I have heard another version of this, how different people see the request for "half bigger". To some people it is 50% bigger, to some others it is 100% bigger. The problem with this is that both impressions can be as correct, here being more depending on semantics than math. In this sense there is a good reason why percentages calculus is seldom used in actual computations for machine construction and such, usually seen only until when the final results are interpreted for the boss man .


Getting back to grinder wheels, the 35 m/s speed limit is kinda rule of thumb from manufacturers, covering these types of wheels. CBN and diamond wheels having metal matrix binder can usually be used with higher surface speeds.

kippis,

sumu