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Cutting fluid and mini-lathes

Cutting fluid is one of those mini-lathe related subjects which you can make as simple or as complicated as you like.

The purppose of cutting fluid when using a mini-lathe or micro-mill or mini-mill is twofold. Cutting materials on our machine tools creates heat. This heat can damage our tools, so we use cutting fluid to carry away some of this heat.

Cutting fluid also helps to lubricate the cutting tool when it is cutting metal on our mini-lathes. A typical beginners question, how can you lubricate a cutting tool? You don't want it to slde over the material, you want it to cut!

There is a simple test which helps demonstrate how useful a drop or two of cutting fluid can be. Take hold of a hand hacksaw and start cutting a metal bar. Your progress will be fairly slow, especially as you cut deeper into the bar. Now take the hacksaw out of the cut and put a few drops of oil on the blade. Any oil will do - automotive is probably fine. Now commence cutting again. Easier, isn;t it?

The cutting fluid helps carry away the heat, and reduces friction so that less heat is produced and the tool life is extended. Cutting fluid also helps carry swarf away from the tool during cutting.

Now, what cutting fluid should we be using on our mini-lathes? Well, as i said , you can make this complicated or simple. Complicated involves worrying about natural, semi-synthetic, synthetic, bacteria build up etc etc.

I prefer to keep it simple. The best cutting fluid on mini-lathes is normally kerosene. A simple source of kersosene is a can of the venerable WD-40. Admittedly if you are doing a huge amount of work, this can be expensive, but for my purposes a trade can of WD-40 is great. It has the advantage of being about to spray it on where you want it.

I normally spray WD-40 on taps before tapping, or spray it onto the part I am cutting on my mini-lathe. Normally this does fine for me. WD-40 is good when cutting aluminium, but if you are cutting steel, then some automotive engine oil is perhaps a better choice. I keep both by my mini-lathe.

I once tried an complicated emulsion of water and oil. Water is good because it evaporates, carrying away vast amounts of heat. However, as soon as it separated from the emulsion, it rusted the cast iron parts of my mini-lathe and micro-mill.

Some materials are best cut dry. Cast iron and brass cut better for me when they are dry. To be honest, for a quick job on the lathe in any metal, it is not compulsary to use a cutting fluid - but it does help get a better finish and prolong tool life if you do use it.

On my bandsaw i also spray on a bit of WD-40 during the cut. However, certainly haven't rigged up a pump and continous flow coolant system like some folks do. OK, if i was cutting all day every day, then maybe, but for a couple of cuts a week, it is not necessary.

Above all, do not fret and get worried about cutting fluid, it is just one small facet that makes up our great hobby. Don't sweat the details!

Latest cutting fluid news for mini-lathes...

Recently I have been told that WD40 is not such a good idea as a cutting fluid. I am not sure why, but I've heard suggestions that it contains chemicals which do not benefit the lathe.

It is also bloody expensive.

So, in an attempt to try something new, I purchased a gallon of paraffin greenhouse heater fuel from my loal B+Q. I now use this when cutting aluminium on the mini-lathe. I keep a cup of it near to the mini-lathe and apply it using a small paintbrush. Having a paintbrush to hand give another benefit: You are much less inclined to clear away bits of swarf with your finger if you are holding a paintbrush! As you all know, clearing away swarf and chips with your fingers will result in the mini-lathe clearing away parts of your fingers for you.

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