Grinder for sharpening gouges etc

[Sachakins]

Hi,
About to pull the trigger on new grinder + CBN wheel, but checking CBN wheel prices, there's a massive price difference between 6" and 8" wheels.

On all the YouTube turner's I watch, it's mainly 8" grinders they use.

I currently have an 8" triton and Wolverine type jig.

Is there a specific reason to go for 8" over 6" that you know of.
Cheers

 

[Lazurus]

Less of a hollow grind on the bevels

 

[Richard_C]

Like lazarus says,. Price difference explained by the material used to make one, its proportional to the square of the diameter so an 8 inch needs 1.7x as much 'stuff' as a 6 inch.

 

[TRITON]

Bit of a reduction on axminster 6" grinder with twin white stones.
Not a huge amount off, but 27 quid is 27 quid.
https://www.axminstertools.com/axminster-craft-ac150bg-150mm-bench-grinder-105242
Edit: Sorry, just looking at your post again. Are you meaning a whet stone or a bench grinder ?.

 

[Sachakins]

Bit of a reduction on axminster 6" grinder with twin white stones.
Not a huge amount off, but 27 quid is 27 quid.
https://www.axminstertools.com/axminster-craft-ac150bg-150mm-bench-grinder-105242
Edit: Sorry, just looking at your post again. Are you meaning a whet stone or a bench grinder ?.

Bench grinder, thanks but 250w unlikely to take cbn wheel weights.

 

[Inspector]

Generally you would want a 1hp/750w or so grinder for a pair of 8" steel CBN wheels. There are aluminium CBN wheels out there that could be driven by a smaller grinder. I don't know whether or not they have the same or a shorter lifespan.

Pete

 

[Robbo3]

Phil Irons maintains that an 8" grinder is no benefit as they generally run at the same RPM as a 6" grinder which makes the peripheral speed too fast.
Phil Irons - Phil Irons Woodturning works of art, from Vases, Hollow Form Vessels, Urns and Writing Instruments

 

[Phil Pascoe]

One pro turner at the club used a ProEdge because he didn't want a hollow grind, the other used a well worn 6"wheel because it gave a more pronounced hollow grind. It depends what you prefer. The club wasn't short of money, but used only 6" grinders.

 

[Stigmorgan]

I have an Axminster Craft 8inch bench grinder, 25mm rough wheel on the left and a 50mm fine wheel on the right that can be changed over to CBN, I picked mine up at a show where Axminster where offering a huge discount, I get a pretty good edge from the 50mm white wheel but do plan to change to CBN when it needs replacing, if money wasn't an issue I would probably have gone with the Robert Sorby Pro-edge machine but it has a pretty price tag that I couldn't justify.

 

[Sachakins]

That was my thought too.

 

[gregmcateer]

Might be useful:

https://t-jtools.co.uk/diamond-and-cbn-wheels/cbn-wheel-150mm-x-40mm/

 

[Sideways]

Before buying either, check carefully that the wheel and grinder will work together. I bought an axminster 8" x 40mm wheel which needed bushes to reduce the bore to match different grinder spindles. The wheel plus flanges were so wide that almost no grinder had a spindle long enough to mount it. Axy admitted that they were clearing those wheels because they didn't sell a grinder that would use it and had no idea which grinder would !
Eventually, I matched it up with Records latest 8" made in China grinder which is sold as UNsuitable for CBN wheels, and I just spin the wheel by hand before switching on to take the edge off the startup current surge.
A CBN wheel needs precision bushes and tight tolerances because there's so much weight that a little slop will cause noticeable vibration. Properly centred, they are great.

Like for like, an 8" wheel has 33% more surface area than a 6" so it'll last longer as well as making a less hollow grind.

Oh, and a little googling to find recommended speeds for dry grinding with electroplated CBN wheels gave me this :
"These wheels require speeds of approximately 30 m/s for dry conditions and 60 m/s when run wet."
https://www.aerodefensetech.com/com...e/adt/supplements/amm/features/articles/38226
A 200mm dia wheel on a 3000 rpm grinder has a surface speed of 31.4m/S at no load. So just about right.
I'm not convinced by the comment attributed to Mr Irons.