Surface grinding - Coolant Queries

I have a J&S 540 surface grinder but little experience using it. There was some time ago an excellent post on grinding techniques that helped me form a couple of years of blundering about into a workable understanding. Coolant is often mentioned but seldom explained. When is it needed? Is it always an advantage and if you are using it how much and where is the best place to point it (at the wheel or the work).

Many thanks in advance.

David

I was trained as an apprentice in the early 70s on these wondrous machines, rarely used by hobby machinists as they have limited use for the footprint they take up in the workshop and the initial cost of them. The coolant should be aimed at the spot where the wheel meets the workpiece following the rotation of the wheel. This will help clear grindings and cool the workpiece, just enough pressure on the coolant to hit the spot is ample. An important thing to remember is to turn off the coolant before turning off the wheel or the coolant can be soaked into the wheel causing an imbalance and an angry sounding machine when started again until the coolant is expelled from the wheel. Just keep the cuts small, 0.001" max and finish with a repeat cut and it should look like a mirror on most steels. Have fun with it, I'm jealous

I used to do a lot of toolroom surface grinding. It was always done dry and a powerful vacuum dust extractor was used to minimise the considerable risk of inhaling grinding wheel and metal dust. Very large vertical and surface industrial grinders used soluble oil and washed through some sort of filtering system .It would not seem to be a good idea to use a coolant with a dust extractor. What a sticky mess would result! I would be careful to let the wheel spin dry after using any coolant due to imbalance on starting if the wheel has been stopped wet. Only small depth of cut can be applied when dry grinding, due to heating and job distortion, although I suppose the vacuum creates a cooling effect if it's strong enough. 0.002" is a very heavy cut on a dry grinder. Colin

David

My advise is based on experience in the industry from 25 years ago, things may have moved on since then so keep this in mind.

The coolant used for grinding back then was different from the coolant used for general machining. Whereas your average lathe and mill would use soluble oil and water mix, we used to refer to it as "mistic",  the grinding machines used a completely different coolant. Rather than the milky looking "mistic" this stuff was like water but with a slight colour - sometimes pink but mostly blue. I have no idea what the brand names were as the stuff was already pre-mixed by the time the grinder was topped up. Unlike certain mistics this stuff never went rancid so nasty niffs were not a problem.

Usage? Aim the coolant between the wheel and the job - flood it - but keep the wheel dressed and open to prevent burning of the job.

With just a few tenths of a thou to go - redress the wheel with a couple of slow passes with coolant running on the diamond. At this point, turn off the coolant flow and check the condition of the wheel surface by very lightly running a finger tip from side to side on the running wheel. The wheel should feel totally smooth. If gritty bits are felt then run the diamond across a couple times more until it DOES feel smooth.

Please note - this is how I used to do it for getting mirror finishes on hardened tooling. Sure, it might not apply to what YOU want to do but if I can offer the best advise I am able you can pick the bits out you want and chuck the rest away.

Whatever you do though, I cannot accept responsibility for lost digits/appendages.

Happy grinding

Rik

Edited By Rik Shaw on 06/12/2013 18:08:16

Edited By Rik Shaw on 06/12/2013 18:14:30

Rik Shaw is right on the money with his advice! That is how I did it for many years and wet grinding gives much better results if you have that option.

Tony

Many thanks for the replies. I am using ordinary soluble oil at the moment because I have it already but I'll maybe see if there is a more modern alternative that will be ok for sitting around in the grinder. I have just taken off the splash guard as it had numerous leaks. so this weekends task is to clean all the gunk off and replace it with new gunk then refit it. I also will look at a better delivery system as the tap that is fitted leaks like a strainer.

John I built a spray mist coolant system for my little CNC mill and had to abandon it due to the choking fumes. I really couldn't belive how bad ordinary coolant could be. You would need a powerful extraction system to cope with it. Having said that if you can get one to work I would be very interested to know how you do it.

Thanks again.

David

Standard water soluble coolant as used in the lathe will clog the grinding wheel and should not be used.

grinding coolant has one other major benefit other that keeping work cool, it contains the dust produced and is far healthier option for the lungs.

Alan

Hi There

We used special grinding coolant. As mentioned above it was about 100 to 1.

I believe it was green. We used it on a Jones and Shipman 540.

When you stop using the machine with coolant let the wheel continue running for about 30 minutes afterwards so that the coolant is expressed from the wheel or when you switch it on the following day the coolant may unbalance the wheel.

When grinding, we always relieved 3/4 of the wheel so we only ground on 1/4 of the width of the wheel.

If you have a combined steel/brass magnetic chuck, a silicon carbide (usually green grit) will give a far better finish than an Alundum wheel.

Also, from memory best results were obtained with an A 40 K 5 V or A 60 K 5 V Where, I think, A is aluminium oxide, 40 is the grit, K is the density 5 is the hardness and V is vitrified. K and 5 may be back to front, it was a very long while ago.

Anything finer like a 80 grit tended to burn the component as it was too fine.

regards David