40 vs 70 durometer

[amcardon]

Tried doing a search for this and didn't really find an answer... Anyway, I'm putting together my list of items to build a grinder and was curious about duro ratings for contact wheels, mainly why would you pick 70 over 40 or vice versa? I see that most all are 70 but I ned to get a 4" wheel and was wondering which would be most appropriate. Are there specific applications for each?
Thanks for the help!

 

[AcridSaint]

70 durometer is harder and will be better for removing stock. 40 is crazy soft and I have a feeling that you'll deform the wheel with pressure, giving inconsistent grinds. Might be useful for some limited applications, but 70 is more versatile.

 

[Ed Caffrey]

+1
70 durometer is the standard for most contact wheels. The best way I can describe 40 durometer is like a hard sponge rubber.....it deforms very easy, and is super easy to tear up.

 

[JMJones]

I have a 4 inch 40 duro wheel and love it. It can be used to go perpendicular to the typical grinding scratches and reduces the work of hand sanding dramatically. I would not use it with a work rest like a typical contact wheel to profile. It feels pretty soft if the hand but there is not really that much give when it is spinning at high speed with a belt on it.