Quick question on grinding wheels

[devils4ever]

I have a newbie question here. I read in "The Home Machinist's Handbook" by Doug Briney that coarse wheels are better at rapid material removal on soft metals and fine wheels are better at fast removal of hard metals. This seems counter-intuitive. Is this correct?

I've been grinding my HSS lathe bits on the coarse wheel first to get the proper shape and finishing on the fine wheel. Am I doing this wrong?

I have a 36-grit gray wheel and a 120-grit white wheel. I bought these years ago (30+) for wood working so I'm not sure, but I think they are Aluminum Oxide.

 

[cbellanca]

I do not agree completely. Coarse grit wheels will remove metal faster, but will leave a rough finish. Hard or soft metal, fine grit will remove metal slower, but give a finer finish. I do just as you said I grind the profile first with course grit then finish with fine grit. At times I use a fine hand hone to produce a fine cutting edge for a super finish.

 

[SamI]

I would imagine that it’s more to do with the available space for removed metal to occupy during grinding. Soft metals such as aluminium would pack up and fill the voids in a fine wheel very quickly therefore a coarse wheel is used. With harder metals this is less of a concern therefore you can utilise the higher surface / contact area of the fine wheel to remove material quicker.

This is purely my speculation however. I only have one grinding wheel so I don’t need to worry myself with which one will be best for a given application!

 

[benmychree]

Coarse for roughing, fine for finishing, that said, coarse wheels can be used for finishing, typical for machine grinding, it all depends how the wheel is dressed.

 

[pdentrem]

This is a good read, may help demystify grit and bond.

Choosing The Right Grinding Wheel

Understanding grinding wheel fundamentals will help you choose the right wheel for the job.

www.mmsonline.com

Pierre

 

[devils4ever]

This is a good read, may help demystify grit and bond.

Choosing The Right Grinding Wheel

Understanding grinding wheel fundamentals will help you choose the right wheel for the job.

www.mmsonline.com

Interesting read especially the third paragraph in the "Tying It All Together" section. It seems to validate "The Home Machinist's Handbook" statement somewhat.