I have a wheel question

[Adam Pinson]

I intend to purchase a Woolverine like system (actually a handmade British made system) but will also need an 8" grinder, i was reading that the white Aluminium oxide wheels are good for this (can't afford a CBN)... I don't know which grit size will be best or even if there is a different or better material for this as there are so many types and choices online !! any advice would be great, thanks...

 

[Robbo3]

As you have already got your tools to the required shape the idea is to consistently remove as little metal as possible to get the cutting edge sharp. So a fine rather than coarse wheel. White is the norm but there are also red & blue aimed at wood turners.
Phil Irons, a pro turner, argues that an 8" wheel defeats the object of keeping the periferal speed down thus we should use 6" wheels on a normal speed grinder. Food for thought!

 

[Paul Hannaby]

A 6" wheel has a circumference of 28" and an 8" wheel has a circumference of 50" so the peripheral speed of the 8" wheel is almost double that of the 6" wheel for the same rpm. Putting the 8" wheel on a slow grinder will roughly halve it's speed and will bring it back down to where the 6" wheel on a high speed grinder is.
As a comparison, a 10" wheel on a whetstone grinder running at 120rpm will have a peripheral speed of 157 inches/second; a 6" wheel on a fast grinder will have a peripheral speed of 1413 inches/sec and an 8" wheel on a slow grinder will have a peripheral speed of 1214 inches/sec. All these sharpen the tool but the whetstone is significantly slower.

There are other factors to consider too -
The faster the wheel, the faster the removal of metal
The faster the wheel, the greater the amount of heat is generated.
The harder you press, the more heat is generated!
The longer you hold the tool against the wheel, the more heat is generated!
A newly dressed wheel will cut faster and cooler.
Not all wheels cut at the same rate. Generally the better wheels cut faster.

Much of the above is common sense but there are many factors other than speed that affect the outcome.

In answer to the original question, an AlOx wheel of 80-120 grit would be fine for general use.

 

[Inspector]

The advantage of the larger diameter wheel is the "hollow" the wheel scoops out is more gradual than with a small wheel. It is easier to turn with in some cases.

If you go to an industrial abrasives supplier and tell them about the steel in the tools you want to grind, they will give you the proper wheel. It most likely will be a light grey as that is what most industrial wheels are. The abrasive will still be aluminium oxide and the friability ( softness or hardness) of the wheel will be correct along with the proper grit. They will likely be less costly than the wheels sold by woodworking/turning sellers. Dress the wheel often to keep it cutting cool. If you see "glazing" (shiny flat looking areas) it is the sign of a dull wheel. Also NEVER sharpen alumimium, brass, copper or bronze (non-ferrous metas) on a bench grinder. They smear up the wheel causing excessive heat from friction. The resulting heat expanding the outer edge of the wheel causing it to fly apart.

Pete

 

[Adam Pinson]

As you have already got your tools to the required shape the idea is to consistently remove as little metal as possible to get the cutting edge sharp. So a fine rather than coarse wheel. White is the norm but there are also red & blue aimed at wood turners.
Phil Irons, a pro turner, argues that an 8" wheel defeats the object of keeping the periferal speed down thus we should use 6" wheels on a normal speed grinder. Food for thought!

That does seem to make sense... it would mean i don't have to purchase another grinder... thanks

 

[Adam Pinson]

A 6" wheel has a circumference of 28" and an 8" wheel has a circumference of 50" so the peripheral speed of the 8" wheel is almost double that of the 6" wheel for the same rpm. Putting the 8" wheel on a slow grinder will roughly halve it's speed and will bring it back down to where the 6" wheel on a high speed grinder is.
As a comparison, a 10" wheel on a whetstone grinder running at 120rpm will have a peripheral speed of 157 inches/second; a 6" wheel on a fast grinder will have a peripheral speed of 1413 inches/sec and an 8" wheel on a slow grinder will have a peripheral speed of 1214 inches/sec. All these sharpen the tool but the whetstone is significantly slower.

There are other factors to consider too -
The faster the wheel, the faster the removal of metal
The faster the wheel, the greater the amount of heat is generated.
The harder you press, the more heat is generated!
The longer you hold the tool against the wheel, the more heat is generated!
A newly dressed wheel will cut faster and cooler.
Not all wheels cut at the same rate. Generally the better wheels cut faster.

Much of the above is common sense but there are many factors other than speed that affect the outcome.

In answer to the original question, an AlOx wheel of 80-120 grit would be fine for general use.

cheers Paul, very scientific

 

[Adam Pinson]

The advantage of the larger diameter wheel is the "hollow" the wheel scoops out is more gradual than with a small wheel. It is easier to turn with in some cases.

If you go to an industrial abrasives supplier and tell them about the steel in the tools you want to grind, they will give you the proper wheel. It most likely will be a light grey as that is what most industrial wheels are. The abrasive will still be aluminium oxide and the friability ( softness or hardness) of the wheel will be correct along with the proper grit. They will likely be less costly than the wheels sold by woodworking/turning sellers. Dress the wheel often to keep it cutting cool. If you see "glazing" (shiny flat looking areas) it is the sign of a dull wheel. Also NEVER sharpen alumimium, brass, copper or bronze (non-ferrous metas) on a bench grinder. They smear up the wheel causing excessive heat from friction. The resulting heat expanding the outer edge of the wheel causing it to fly apart.

Pete

Great advice Pete, i have heard people talking about the 'hollowing' shape difference on an 8" wheel yes... cheers

 

[Max Power]

cheers Paul, very scientific

Actually very wrong though. Circumference is 3.142 times diameter, so a 6" wheel is actually a little over 18" in circumference not 28" and an 8" a little over 24"

 

[Phil Pascoe]

All the wheels at our club were six inch worn down to about four inches, They weren't changed as they were preferred by many experienced turners specifically BECAUSE of the more hollow grind. For the same reason many refused to use a Pro Edge.

 

[Phil Pascoe]

A 6" wheel has a circumference of 28" and an 8" wheel has a circumference of 50" ...

Yes, a bit of weird maths there.

 

[Adam Pinson]

Actually very wrong though. Circumference is 3.142 times diameter, so a 6" wheel is actually a little over 18" in circumference not 28" and an 8" a little over 24"

All I really need to know is if my 6" grinder is sufficient, if all I have to do is buy a new wheel that would be ideal.

 

[Phil Pascoe]

I use Sorby jigs with a 6" wheel, it's fine.

 

[Adam Pinson]

I use Sorby jigs with a 6" wheel, it's fine.

What kind of wheel do you use ?

 

[Paul Hannaby]

Ye

A 6" wheel has a circumference of 28" and an 8" wheel has a circumference of 50" ...

Yes, a bit of weird maths there.

Yes, very weird! I think I got my formulas mixed up there but the principle still applies.

 

[Phil Pascoe]

What kind of wheel do you use ?

I have a wide Creusen fine white wheel that was with the grinder when I bought it second hand and I've just repaced a cheap pink wheel that I put on it with a decent coarse white wheel.

 

[Adam Pinson]

I have a wide Creusen fine white wheel that was with the grinder when I bought it second hand and I've just repaced a cheap pink wheel that I put on it with a decent coarse white wheel.

Thanks, I'm having trouble finding a wider wheel ! Is 25mm wide enough for gouges, sorry about all the questions...

 

[Robbo3]

Thanks, I'm having trouble finding a wider wheel ! Is 25mm wide enough for gouges?

Yes. IIRC 3/4" (19mm) used to be the norm. Even if you find a wider one, the shaft might not be long enough for it to fit or you might have to run it without the side guard on the grinder. Not recommended.

 

[Nautilus21]

I thought circumference was 2x pi x r making it 37.7 and 50 respectively? So the difference is not nearly as big as imagined

 

[Lard]

I thought circumference was 2x pi x r making it 37.7 and 50 respectively? So the difference is not nearly as big as imagined

You’re mixing up your ’R’s’ with your ‘D’s’

 

[Phil Pascoe]

Pi x d is more usual.