The ring test - is it affected by water?

Hi All,

This is my first post on this Forum. I am NOT a machinist; just a DIYer and tinkerer, so please be gentle if my questions are too basic or dumb

Anyways, I have just acquired an old, 6" bench grinder which I picked up at a yard sale. Having never used one, I tried to educate myself and have read articles and seen Youtube videos on the subject of bench grinders. It was certainly eye opening!

I would never have thought that a bench grinder could be dangerous (risk of grinding wheels exploding). The bench grinder as obtained was very dusty and filthy, so I decided to dismantle it and clean it. I took the grinding wheels off and performed the ring test and both wheels passed the test. Since they were very dusty and filthy, I decided to wash them. I just used soap and water and the wheels looked MUCH better after I was done. I dried the wheels with some rags and started putting the machine back together. Just before mounting the grinding wheels, I decided to do the ring test again and to my surprise, both wheels failed the test. I think it is because the wheels are water-logged. I did not mount the wheels and currently have them sitting vertically on a piece of cloth to drain the water. I have a couple of questions:

1. Is it safe to use a hair-dryer to dry out the wheels? (does heat expansion risk causing cracks?)
2. Is there any danger of the wheels exploding if mounted in their current (wet) state?

Thanks!

You are almost certainly correct that the water in the wheel pores is dampening the ring.

I wouldn't use a heat gun to dry the wheel out, even if I didn't know a definite reason why 800F air would damage the wheel. However, there's nothing wrong with using a fan, or a strong blast of air. A hair dryer is considerably less hot than a heat gun, but if it had a no-heat setting, I'd start with that.

Many grinders are operated with flood coolant. Some even deliberately feed the coolant through the porosity of the wheels, not just spray the coolant on them. When these machines start up, their wheels can be unbalanced until the loaded water is equalized, but wheel explosion is not considered a problem. Operators usually run the machines for a minute or two after turning off coolant to spin the vast majority of the coolant out of the wheels.

Having said that, bench grinder wheels of unknown age are not necessarily made to the same standard as modern surface grinder wheels. I would dry the wheels out for a day or two before firing up the grinder.

Dry the wheels until they ring
CarlBoyd

Lay them flat. Large grinding wheels are stored flat to prevent coolants from settling to one side and throwing the wheel out of balance. A small bench grinder wheel shouldn’t be too sensitive to this, but it’s still good practice.

Thank you all for your responses. They certainly make a lot of sense to me.

I now have the wheels laying flat on a piece of cloth. I will wait until they are completely dry before mounting them and firing up the grinder.

Couldn't you toss them on a cookie sheet in the oven as low as it would go? Wouldn't be hot enough to smoke any oil but would dry them out.

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Cole2534 said:

Couldn't you toss them on a cookie sheet in the oven as low as it would go? Wouldn't be hot enough to smoke any oil but would dry them out.

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And then don't try to solve problems that aren"t there. Things in a machine shop are not there to look pretty. They are there to work.
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