Materials suitable for coolant.

Hi everyone,

I've been machining some hefty pieces of cast iron recently and i am fully aware that with practically any drilling operation coolant will help, i'm not so sure about turning/milling..I just remember in the back of my mind somewhere there are some situations where oily coolants/lubricants actually hinder the cutting action rather than help.

For example, correct me if i'm wrong but i was always told brass is one material that doesn't need lubricant.

I was thinking along the logic of where the tool would tend to slip on a light cut rather than engage with the cutting face in an efficient manner?

I could just be going bonkers,

Michael W

I never use cutting fluid with cast iron

You need to get an engineers reference book. I have one from Cromwell tools, a give away, from some years ago. Inside these are all sorts of engineers cutting information, including speeds and feed and coolant requirements.

Things have changed some over the years with synthetic coolants and tool coatings. So try to use upto date references, not something that was said in the 50's.

At the end of the day the best way to learn is research, and find what suits your equipment. Remember that a lot of people may refer to industrial size machines which will produce very different results to a hobby size machine. Having said all that for most situations in hobby machining an aerosol cutting lubricant or non is all that is needed as the cuts are light and short.

Materials that chip rather than create ribbon-like swarf (e.g. cast iron and brass) don't rub on the tool in the same way and create a lot less friction and therefore less heat as well.

Neil

Michael,

My copy of "Metal Cutting" by Trent & Wright (fourth edition 2000) does indeed show a situation where the cutting fluid increased the wear on a tool cutting cast iron. I also like your take on the situation with brass - you probably don't want anything that will make the brass more "slippery".

My take on cutting fluids for turning is as follows: A water based fluid is best for cooling. This keeps the job cool and helps prevent distortion. It also helps keep the tool cool but may not make much difference at the actual cutting edge. The aforesaid may not be terribly relevant to the home workshop. I think the biggest problem in our workshops is a built up edge on the tool tip. Modern coatings on replaceable TC tools are largely overcoming this problem with steels and the highly polished tips available for aluminium are also very good. With HSS tools it is beneficial to have something in contact with the tip that interferes with the chemistry that allows the swarf to weld itself to the tool tip and for this the additives in a soluble oil or a straight oil probably help. This is especially important when cutting aluminium and its alloys, where paraffin (or WD40) seem to be beneficial. Cast iron has its own in-built lubrication with carbon flakes. The situation with milling is slightly different in that the best thing a cutting fluid does is to wash the the swarf from around the job. In theory a small amount of cutting fluid makes things worse but I have found that the occasional squirt of WD40 helps when milling aluminium, probably because it helps stop the swarf welding itself to the cutter tips. I've recently discovered the joy of using CT90 when drilling - makes a big difference, perhaps because it lubricates the passage of the swarf up the flutes.

All the above may be complete nonsense, but I offer it up for discussion

Rod

Cast Iron is the only metal I've heard of that should be machined 'dry'.

The main purpose of cutting lubricants is to keep tools sharp by removing heat, to improve finish and to discourage metal from sticking to the tool and blunting it. Flood cooling also flushes swarf away from the cutting edge which is a very good thing. I don't think slipping on a light cut would be a problem in the way that a scrape would be.

Water based coolants are recommended for steel, and light oils for everything else.

My needs are usually far less demanding than an industrial process. For light cuts I rarely bother with coolant at all. For medium work, parting and threading I splash bottled or aerosol CT90 about, perhaps paraffin on aluminium because it's cheaper. I flood cool heavy milling with neat cutting oil rather than an emulsion. This is because flood cooling is extremely messy and neat oil won't cause rust when it ends up somewhere precious!

One thing I learned the hard way is not to splash coolant on to carbide cutters. Thermal shock cracks them. Carbide is all or nothing: either run dry or flood generously.

I agree with HowardT about old recipes. Some of them grow bacteria and can badly infect cuts,. And they stink when they go off. His point about experimenting to find out what suits you and your equipment is also very well made.

Cheers,

Dave

In a hobby environment I question wether you would want to get into flood coolant. I remember when we used to clean machine systems out and the awful mess. As Dave said in his note they can go off and produce an awful smell as well as being a bio hazard. I have known instances of leaving a machine over the weekend to come back to hundreds of litres of rancid coolant. That required the expense of a tanker to dispose of it and a day cleaning everything out. Oh happy days!

Cheers all

Howard

I thank you all for your responses,

I guess i wasn't so kooky after all, there is some truth to it, I was taking a face mill cut with cast iron and my machine has a low gear mode and so has a hefty amount of grunt at full chat (450rpm) and it seemed to be doing ok and i'm standing there with a bottle of 3 in 1 thinking "should i, or shouldnt i?" to slather it on it. I do have a water soluble coolant system its on standby at the moment because i'm chasing leaks all over it.

I havent used it for ages and havent noticed any scum of sorts, only separation and grit on the surface.

I'm sure i probably dont need it most of the time but, its a personal choice i guess, i always turned steel with coolant at college so i feel like i want to do it. Being at that environment made me think alot about all the processes in machining and whether little things like this even matter, i couldnt help myself but wonder.

Michael W

I agree with the other comments regarding cast iron and liquid cooling. But the cutter does need some cooling and for big cuts I use compressed air from a duster nozzle to keep the cutter cool and to blow away the swarf. But CI dust is not healthy so do this at your own risk!

I agree. I don't use mine much and in my home workshop at least the money would have been better spent on almost anything else. Inexperience led me to expect that I was going to do much more heavy milling than is actually the case. DRO was a far better investment.

Regards,

Dave

A bad point about using coolant with cast iron is if the coolant hasnt got sufficient oil content in it and the wet swarf is left sitting on the bedways of the machine the whole lot can turn to rust and potentially ruin a machine if its left more than a few days , the machine shops ive worked in always machined it dry and i do the same in my own workshop.

regards Geoff