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Cutting Cst Iron

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  • Cutting Cst Iron

    I've done some minor milling and turning on cast iron for repairs and such but that is all. I'm starting work on the castings for a minor tool kit and would appreciate some direction. I've read that I should start with cuts heavy enough to get under the top casting layers but am unsure about what depth that might be in a casting which is 2" x 2" by 6" long. What might be a good starting depth-of-cut range? Should I be using carbide or HHS for the first cuts?

    Following the initial cuts I'm expecting to continue with light cuts at the recommended sfm until I get to the recommended dimension. Would carbide or HHS be best for secondary cuts? My understanding is that no lubricant is the best approach for cast iron. This is what I can think of to ask and would appreciate any other tips and recommendations..

  • #2
    The type cutter is going to be more involved with the machine that your using. Basically, it depends more on the RPM of the machine. With carbide requiring a higher rpm compaired to HSS. Now castiron tends to come off in little bits, it doesnt make a chip like you would expect to see with steel or aluminum. This tends to make it a little rougher on the cutters and HSS would be my choice unless you have a machine that is very ridgid with a high rpm spindle. Smaller machines are not normally very ridgid and I have broke carbide cutters when cutting cast iron because of it ( even though I had a high rpm range).

    I am not sure what kinda tooling kits your talking about, but unless they have been heat treated they want have a hard outer skin, or atleast nothing hard enough to need extra care. Pick a bit that is designed for cast iron, check there recamended feeds/speeds, and you should be good. Use the most ridgid setup you can when milling, like locking the axis that is not being used to help eliminate any vibrations.

    Now really to help anymore than just these small suggestion it would help if you supplied pics of your parts you will be working on, and a discription of the machine you willl use.

    BTW I am sure there are others with more expeirance than me so it would be good to get inputs from others that will chime in late.



    • #3
      Get your feeds and speed right and you are good. I milled off about 5 lbs from a follow rest I bought off fleabay to fit my larger lathe and then had a couple of 3/4" x 1" blocks to square for another project. First block went fine, got greedy on the second block and tried more feed and this is what happens when you get too much deflection:



      • #4
        You soon discover that whether using carbide or HSS, the cast iron dulls tools quite rapidly compared to other materials. Don't know your machine or capabilities, but I would go at it with carbide inserts and about 100 m/min surface speed. Feed according to your insert or it won't cut properly.
        Amount of experience is in direct proportion to the value of broken equipment.


        • #5
          Yes cast iron can be brutal at times to HSS. I would try at least 0.050"-0.100" if your lathe can handle it. 2X deeper for the mill.
          If lathing I would use one of the 'junky' C2 brazed lathe bits to cut through all the scale and down to a place where you can rough it in then use a good HSS or carbide insert tool (with appropriate grade). You may have to feed heavy to get under the skin first. Back gear can be your friend if you don't have the HP.
          If milling, see how bad the scale/skin is on HSS. If it chews it up or laughs at it you have some issues. The biggest issue is getting below the skin (unless it is Durabar then it is great from the beginning). Carbide insert mill or solid insert may be your best bet if you have problems with the skin. Either that or grind it off but that is a total mess. Do not use lubrications when cutting, you will end up with quite a mess. Cast iron cast leave a great finish if worked properly.
          I used C2 brazed bit on my MLA Loop Collet Chuck years ago to get through the skin then used my good inserts after it was roughed.

          And all put together and well used
          Last edited by mc_n_g; 03-07-2013, 11:46 PM. Reason: forgot to mention something


          • #6
            Carbide for me, in the noodlelathe. Back gears engaged, low RPMs, and cut as deep as I can. Chips were coming off so hot they were extremely uncomfortable when they landed on me. I eventually had to keep a rag over my carriage-hand.