Water based coolant that won't cause quick rust? Or what to add to water?

[Grapevine]

I want to grind smooth the sides of some of my files to make them safe edges. I don't want the heat from grinding to ruin the temper so will need to dunk it into coolant every so often. I don't want to use oil based products since they'll leave residue and gunk up the teeth. Water on its own can make the file start to rust while I'm grinding.

Is there anything I can add to water to slow down the rust causing effect long enough to get through the grinding and then dry the file completely with a hair dryer? I think I read somewhere that a high pH can do it, but can't remember where or how effective. If so, would adding baking soda or ammonia do it, and in what ratio to water?

 

[Overmountain]

Try water-wetter. Get it at an auto parts store. It is specifically designed to enhance the cooling efficiency of water, as well as reduce the corrosive nature of water. And it is safe to dump down the drain. As far as changing the pH of the water, I would be guessing at how much to change it, but maybe someone who has tried this method and had it work will chime in.
When I grind, I dunk in plain water pretty liberally and have never had a rust problem (with simple carbon steel). Make it a quick dunk, and back to the grinder and usually it is dry enough to keep rolling. To get into the temper range with your grinding would be pretty aggressive anyway, and the heat in the steel should evaporate surface water almost immediately. For example, when doing long blades where I am removing a lot of material, I usually get into the grinder pretty good. At the end of my stroke, I dunk, sling, and right back on the belt. The heat in the blade usually has it steaming when it comes up from the water, and the last couple of drops are gone as soon as its on the belt again. I know everyone has a different method, but as long as it isn't absolutely surface boiling water, you aren't in danger of losing the hardness of the file.
Don't know what your time is worth to you, but I would say buy single edge files instead and then have both types...
Cheers.

 

[Carcara]

Washing soda, sodium carbonate added to the water is used by sword polishers to help with rusting prevention.

 

[Fred.Rowe]

Try Koolmist 77; water based machining coolant. The best product by far that I've found for tapping, drilling, sanding, grinding or any friction based technique. er
The mix is a quarter cup to a gallon of water. I buy it in 5 gal. containers but you can also get it in 1 gal size.

 

[Grapevine]

Thanks for the answers, guys. I'm going to test sodium carbonate first since it'll be cheaper than getting Koolmist.

Lucycustomknives, the thing I worry about using straight water is that the files have lots more surface area with the fine teeth than a knife blank. The knife blank's broad side gets grounded after the dunking, so the water would also get lifted off, while the file will have water sitting in its teeth grooves as the thin sides of it are being ground. Also files tend to be made from more easily rusting steels. Those things combined makes me wary. And I'm not sure on my chemistry here, but lots of small sessions of dunking the file into water then quick drying while heated on the grinder would add up to the equivalent time of one longer session of being wet with a longer drying...I think. Total time of exposure being the key? I don't know, but not something I want to risk since these are quality files that I've put effort into finding and they wouldn't be easily replaceable.

 

[Stacy E. Apelt - Bladesmith]

I use sodium carbonate or bi-carbonate for this when doing togi.

But, the worry of rust when grinding a blade or file is not worth bothering with putting anything but a few drops of dish soap in the dunk tub. The blade/file isn't what seems to rust before your eyes. It is the superfine powdered steel that gets suspended in the water spread across the blade. The water evaporates as the blade gets hot and the damp steel dust reacts with the oxygen in the air. This puts a coating of iron oxide on the blade. It will wipe off with a rag and some oil, or brush off with a wire brush. The steel of the blade/file itself is fine.

 

[Overmountain]

I didn't even think of the teeth retaining water... I know my wife does from time to time and its a problem, but not with my grinding. J/k. Never had occasion to grind a file though... my phase with that was mower blades not files... lol. (And yes I know you are doing it for a different purpose.)

I mentioned water wetter because it is cheap and easily available... One bottle treats a helluva lot of water. Royal purple has a similar product. Used to use it when I was racing because you would get fined by the facility for a spill of it contained anti-freeze or petroleum products...

I also put a couple of drops of dish soap in the dunk bucket, but I was told it would help with the skim that develops as I use WD40 like its free and it tends to skim up the surface holding little shavings and crap. Never thought about rust prevention, but I have always done it and never had a problem even in the recesses of my blades...