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Broach cast iron dry... right?

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  • Broach cast iron dry... right?

    It feels like a stupid question, but do you broach cast iron dry (no cutting fluid)? It is a standard keyway broach in an arbor press.

  • #2
    Originally posted by Arthur.Marks
    It feels like a stupid question, but do you broach cast iron dry (no cutting fluid)? It is a standard keyway broach in an arbor press.
    I do. That doesn't mean that it's right, only that it worked for me.


    • #3
      Anything can be broached dry, but you will prolong the life of your cutter with the help of a coolant/lubricant.
      Amount of experience is in direct proportion to the value of broken equipment.


      • #4
        +1 with JF.

        But broaching is best done in incremental stages - as your arm and arbor press will soon show you.

        If the cut is "too heavy" and if the broach is relatively thin and is standing above the job far enough to form a "slender column" and if the arbor press is big enough (say 3 ton) it may not only be hard enough to push the job through the job but the broach may buckle and snap with no warning.

        Most metals are different enough to see/feel the varying "push" required to force the broach through the job - most steels are harder to broach than say brass or aluminium.

        Hasten slowly.


        • #5
          This poses the wider question, should all machining of cast iron be done dry? That's always what I was taught, and it machines just fine without cutting fluid. So do many materials for that matter. Hard brass springs to mind.

          How is cast iron machined in industry? Dry, or flooded in coolant?

          All of the gear, no idea...


          • #6

            you right for the majority of cases, but a broach is moving down a very tight fit (on the sides) and a jam or galling part way through is something I at least can do without - again.

            I'd probably prefer molybdenum disulphide or copper-based grease.

            A blunt broach is not a lot of help either.


            • #7
              once in a while---

              Occasionally I have noticed that if I happen inadvertantly to get a material which I am machining 'dry' ( eg Brass or cast iron)wet with coolant or oil in just one place then my tools seem to stop cutting and simply slide over just that place. This happens only when taking light cuts, annoyingly even when just looking for that " last thou". This has led me to either making sure the work is kept dry and clean, not so easy in a world full of oily model steam engines,or fully lubricated, whether really needed in theory or not. Have others ever met this little joker of a problem? Maybe If my machines were stronger or newer it wouldnt happen? Regards David Powell.


              • #8
                Like Russ says, its worked well dry for me. The cast iron will cut very well dry without hurting the cutting tool.....but I can see how the job mighgt benefit from a small squirt of cutting oil, if for no other reason than to reduce friction on the back and to lesser degree sides of the broach, but can say I've bothered when doing CI


                • #9
                  Thanks for the replies, guys. Yeah, the question came from my experience turning and milling cast iron. In the books it is usually, if not always, mentioned to cut cast iron dry. I can't remember exactly what happened now, but I have used cutting oil on cast iron in the distant past. All I can remember now is that it was not a good experience. It hasn't been done since in my shop. Broaching is such a low SFM operation that it made me wonder. Surprisingly, I don't believe I have ever needed to broach anything made of C-I before yesterday. You'd think I would have with all the cast iron pulleys with keyways out there, but I guess not. With steel I copiously coat the work and broach in a tapping fluid which is meant for low speed, high pressure. That works a treat. It just made me wonder if there were any drawbacks/advantages in this instance. Cast basically crumbles into dust... so you've actually had this kind of "swarf" jam your broach, oldtiffie?


                  • #10
                    Both Hassay-Savage and Dumont recommend broaching cast iron DRY. However, the both suggest adding a lubricant between the shim and the broach.

                    For instance, scroll down to the engineering section:

                    In industry, cast iron is broached dry with a moly or other EP lubricant between any guide surfaces/shims.

                    If OT was having problems with chip buildup, it wasn't for lack of lubricant. Cast iron doesn't "gall". The high carbon content acts as a dry lubricant and, as you noted, tends to "crumble".

                    I've broached many keyways in cast iron pulleys, steel pulley and aluminum pulleys. The only ones that are a pain are the aluminum and that was because I didn't have the proper lubricant to prevent the gummy aluminum from galling. I've never had a broach fail and I was doing it with an air-over hydraulic press - no "feel".

                    Chip build up is far more likely to be a problem with oil. You've probably noticed how cast iron chips turn into goopy mess if you add oil - imagine that sticking to your broach! They do make specialized lubricants for machining cast iron and in BIG broaches, I expect a flood coolant with an EP additive would be prudent. It's thin enough to wash the chips away but leaves a film of lubricant behind. (I'm talking about those big two story broaches and etc). For home shop broaching operations, dry is the way to go.
                    Last edited by Fasttrack; 04-20-2012, 01:10 PM.


                    • #11
                      Fasttrack, that was very definitive especially with the references. Thanks!


                      • #12
                        When I worked at Vickers, we machined tons of cast iron every week. Lubricant was used in all operations.


                        • #13
                          From what I've read.....

                          Typically cast iron is not lubricated because the graphite that is in it already provides the lubrication......that said lubrication for tool cooling is a different issue.
                          Allans Rule: Anything worth doing is going to be a pain in the butt.


                          • #14
                            I've always been told to machine Cast Iron dry.
                            The high Graphite content of Cast iron provides enough 'lube' for all cutting operations.
                            Also, as I learned the hard way, Cast Iron will quickly turn coolant rancid.
                            Cast + Coolant = Yuck!
                            I believe that the Machinery's Handbook recommends cutting dry as well.