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Neubie 101: When to use cutting fluid?

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  • Neubie 101: When to use cutting fluid?

    Total neubie question here:

    I was making some t-nuts for my mini-mill. I held the stock in a vise and used a 4 blade end mill to cut them. I started with a higher RPM than I should have and the oil smoked off as I cut. (I guess this is why everyone recommends newbs get cheap end mills to learn with.) I eventually realized that I could get a really nice cut if I removed the .038 I needed to cut using a slow speed on the cutter followed by a .002 cut in the other direction using a high speed. Along the way I stopped using cutting fluid (forgot about it) and everything still worked fine with the finish cut looking real nice.

    When do I use oil? Where do I put it? Do I keep adding more as the cut proceeds?


  • #2
    i recomend a kool-mist system. no more splatter line on yout walls and you.


    • #3
      When using HHS drills or mills the chips shouldn't be turning color. If it turns brown or (yikes) blue slow down or use coolant.
      The optimum speed would be as fast as you can go just up to but not turning brown. There is of course formulas and charts but this works nice. It only applies to cutting mild steel.
      Super Dave


      • #4
        Time for a confession here.
        I (novice) almost never use cutting fluid, except for tapping and thread cutting w/the lathe. When I do use it I can't tell that it makes a dime's worth of difference, other than making a bigger mess to clean up. But I'll admit that I do tend to cut on the slow side of the rpm range. I also don't push it very aggressively on the feed and depth of cuts either.
        Lynn (Huntsville, AL)


        • #5
          I'm a kinda middle-bee. Not a pro but been at it for many years at home.

          As I understand it, there are three reasons for using cutting fluids, AKA coolants. Notice, it's primarily a coolant that has lubricating properties, not vice-versa.

          1. To improve tool life. The cutting action creates heat. Intense heat at the cutting edge. Heat destroys tools. It can cause tool steel to loose it's temper and therefore wear very rapidly.

          The cutting fluid removes the heat by boiling/vaporizing. It takes heat to vaporize it and that heat is removed from the tool and workpiece, thereby cooling them.

          2. To prevent the work ftom becomming work hardened. Tbis sounds like the opposite effect as number one but it happens. The work is usually softer than the tool and it can be easily hardened by the heat of cutting. This makes the next pass more difficult.

          3. Better surface finish. This is probably tied in with the heat removal thing. The thing is, many metals will have a better finish when cut with a cutting fluid. I find this to be especially true with aluminum but it works with others as well.

          All of the above is associated with heat. Some people also use a cold air blast when cutting.

          As for how much, I generally keep it wet. This can usually be accomplished with a drop or two every few seconds, depending on the size of the cut and tool. Smoke is normal with an oil type coolant and you should apply more when or before it quits.

          I generally tend to use slower, less aggerssive cuts. As I said, I am not in a commercial shop where there is pressure to turn out as many parts as possible in a given time. I still have cutters I purchased 20 or 30 years ago and they are still sharp.

          Paul A.
          Paul A.
          SE Texas

          Make it fit.
          You can't win and there is a penalty for trying!


          • #6
            Paul's about got it, I think. My primary motivation for using coolant is increased tool life. Depending on the material, I find it also (sometimes) makes a difference in the surface finish. It can also help keep aluminum from welding to the cutting edge.

            I've got a mist coolant system, but you can slather on cutting oil with a brush or squirt it with an oiler and it works fine...just somewhat more messy.
            Try to make a living, not a killing. -- Utah Phillips
            Don't believe everything you know. -- Bumper sticker
            Everybody is ignorant, only on different subjects. -- Will Rogers
            There are lots of people who mistake their imagination for their memory. - Josh Billings
            Law of Logical Argument - Anything is possible if you don't know what you are talking about.
            Don't own anything you have to feed or paint. - Hood River Blackie


            • #7
              I'm with Paul. If you look in the catalogs you will find the overwhelming majority of cutting fluids referred to as either just coolant or lubricoolant. Cooling is the main job, lubrication is second. But, the lubrication does matter. Think about how long your hacksaw blade will last cutting steel without oil of some kind.
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              • #8
                I absolutely agree with the theoretical reasoning behind the coolant argument. And it could well be (probably is) true that I'm sacrificing some tool life by cutting dry, but it hasn't been to the extent that it's been obvious.
                Now I do lube the hand hacksaw where it definitly seems to make a difference in ease of sawing. I also lube the power h/v bandsaw, if cutting pretty substantial material.
                Most of my endmills are carbide, and I've been told they need either constant coolant or NONE at all.
                Maybe it's my imagination (tho I think not), but I seem to notice a distinctly better finish on most stuff (steel) that I do when cutting dry, especially on the lathe (and that's w/HSS), except maybe threads.

                I will concede that I've been the victim of the work hardening at times when cutting pretty aggressively.
                Lynn (Huntsville, AL)


                • #9
                  I do get better finishes on drill rod when turning on the lathe, it seams to help wash away the swarf. I use a drop or 2 of tap magic.


                  • #10
                    Always use cutting fluid when cutting with HSS....I still love Tap-Magic..good stuff, and it smells good too...



                    • #11
                      I appreciate everyone's advise here. Great thread. Thanks!



                      • #12
                        Another consideration for me is the material you are cutting. The other day I was cutting soft unalloyed aluminum. I have to confess that I broke two 3/8" end mills and a Kwik Switch adapter that held a Jacobs chuck. It snapped at the taper that holds the chuck. The problem is the gummy aluminum sticking to cutting edges and filling up the flutes. My big Bridgeport is so strong it is sometimes scary because it doesn't grunt or bog down it just breaks things if you aren't on top of it. I have a mist coolant system but it was missing some parts so I built my own. I need to get this right though, and especially for the soft stuff. I really appreciate all the information you experienced machinists can add to this subject. I like the results from kerosene when I apply with a brush. I would like to use this in my spraymist system but I don't want fumes or fire hazard. I was thinking about mineral oil. I've also been looking at commercial products.




                        • #13
                          Is anyone here using a cold air system OR know of anyone that is? I wonder "exactly" what sort of compressor you would need?



                          • #14
                            Smokedady, I have been looking at the coolair system myself and wondering if anyone is using it. I think I will start a new thead for it.

                            Pics of shop and some projects