Microscopy in the workshop

[Sonic EscapeParticipant @sonicescape38234]

I’m curious what happens to grinding wheels on a microscopic level. Or how stones of different grit or hardness are influencing the cutting tools performance. And maybe other things. So I’ll add here what I think is interesting.

First an example of a common gray 150mm grinding wheel that was glazed after grinding a 10x10mm HSS blank. This is the first tool I made, and it works fine. But it ruined the wheel. Gray stones are useless for HSS. On the left is e picture on the unused side of the stone. The abrasive grains are clear. On the right is the working side.

Next is a 60 grit green stone. I used it many times to grind carbide blazed tools. It is very good. You can’t tell the difference between the side of the wheel (left) and the working end (right). I never had to dress this wheel. I used only once a dressing tool because it was out of round. And I didn’t had a proper truing tool. The trick with green stones is the weak bonding material. It wears out quickly and exposes new abrasive particles. So no chance of glazing. Interestingly they are recommended also for softer materials like aluminium or brass. I suppose they should work fine also for HSS but it would not be economically.

This is a pink fine grit wheel (120) with a closed structure. It is the latest member of my collection and I have high expectation from it. It needs an 12 to 20mm adapter. It should be fine for HRC above 60, so HSS, alloyed steels and so on. I would have preferred a lower hardness than L but that is what I found. The right picture is not pink because of the the bad white balance of my grocery store type microscope.

And last is my Aliexpress dressing tool. It has a few tiny diamonds embedded in that shiny metal

 

 

 

[Sonic EscapeParticipant @sonicescape38234]

I forgot to mention the first candidate in my wish list. This 250mm grinding wheel promises best performance for the hardest steels, up to HRC 67. And its binding material is H, so quite soft. That means no glazing. The problem is that I can’t find the maximum speed limit for it.

The second option would be this one. Also for hard steels. The 13mm width is perfect. Easier to dress than a wider one. And at 3700RPM max speed is should be safer.

 

 

 

[peak4Participant @peak4]

Tyrolit as a manufacturer, and Midland abrasives as a retailer are both reputable companies, and should be able to give advice regarding speeds, which may be quotes as either RPM or a peripheral speed recommendation, bering in mind the wheel structure and use.

There should be loads of info on Midland Abrasive, Norton, Master-Abrasive sites as well as compendium sites such as this

https://sites.google.com/site/lagadoacademy/machining—lathes-mills-etc/my-surface-grinder—2

 

Bill

[Martin KyteParticipant @martinkyte99762]

?

I am not a grinding wheel expert but grey wheels cut HSS fine. The issue is I think the bond and wheels come in a variety of harder and softer bonds so a softer bonded grey wheel would not have glazed so readily. Pink wheels I understand to be for stainless steels. Perhaps someone better qualified would comment.
regards Martin

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, Coventry Grinders can tell you what you need to know about different coloured wheels and their uses.

Regards Nick.

[Sonic EscapeParticipant @sonicescape38234]

I touched the dressing tool only a few seconds and the gray wheel is like new again. That tool is very effective!

This is my superficial understanding about grinding wheels. The gray ones have the weakest abrasive particles. Next are the white ones, then pink and ruby. There are also combinations and special types. And every color can have different bonding material strength. The harder the material you grind, the weakest should be the bonding.

[peak4Participant @peak4]

This is a pair of pages from an old PBR Abrasives catalogue, which tells you lots about markings and materials
At first glance I can’t see a more modern copy available for download, but the materials and nomenclature haven’t changed that much.

The Leading UK Suppliers Of All Types Of Abrasives & Grinding Wheels​

Bill

[peak4Participant @peak4]

And this is from a Master Abrasives brochure concerning speed, and effective hardness

https://www.master-abrasives.co.uk/abrasives/bonded/grinding-wheels.aspx

https://www.master-abrasives.co.uk/downloads/content/Master%20Abrasives%20Grinding%20Wheel%20brochure%20s.pdf

Bill

[old martParticipant @oldmart]

We have some nickel plated wheels that are diamond impregnated. They are metal, so are much safer than ordinary wheels which can explode. Not suitable for regular sharpening of steel tools because the diamond, being carbon will dissolve chemically into iron, but ok for occasional use. It excels for sharpening carbide which is tough even with green wheels.

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