Grinder for sharpening gouges etc

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Sachakins

The most wasted of days is one without woodwork
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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
 
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.
 
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
 
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.
 
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.
 
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.
 
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