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CNC, setup/run times

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  • CNC, setup/run times

    Boy, does this subject fit in the "General" catagory...
    I have a couple of widget designs. I have done a pre-production run (8 units) on one of them in my 'manual' shop. I'm hoping to produce them in a number between 100 and 1,000.
    When does CNC become valuable? 20 units? How does multiple clamping figure into this?
    Any books or sources?

  • #2

    If there a fair bit of work to do them, CNC can save enormous time and produce better fit and finish.

    Rather than buying a machine you could sub it out (get a non-disclosure agreement if it is your invention). If demand warrants it, you can always buy your own mill later.
    Great (at least we "think" it is) ideas sometimes just spin their wheels and suck money from your wallet - timing is bad, or market is not ready for it, or distributors are so greedy you can't make money.

    It is a tough decision, but one you have to face yourself. Sometimes it is better to be behind on orders than to be overstocked...



    • #3
      Set up time varies shop to shop.
      I used to use standardized tooling.
      Most frequently used tools were in the magazine waiting to be called up at all times.
      I left a few positions for special tools.
      If you have your vices pre-set, you set your parts, set tool lengths and you're in biz. Run that way cnc can compete with the bridgeport on short runs, except on an hourly cost basis.
      Many shops start each job with tool #1. All tools need to be set up for each job.
      What a pain in the butt.
      I arn't no expert but on many 1-4 pc runs I could have the parts done on a bridgeport before the cnc was setup.
      Of course they would clean my clock on longer runs.
      Can't really answer your quiry, depends on the shop. Maybe 10 or so pieces depending on complexity.

      [This message has been edited by kap pullen (edited 12-21-2001).]


      • #4
        What sort of quantities makes the CNC economical?
        Lets say a part needs milling on one surface, rotation in the vice and milling on another surface; how's that handled?
        What about drilling and tapping on a third surface?
        Thanks, Kap. This is the sort of info I need.
        Ron LaDow


        • #5
          For milling two sides on steel? I'd find a blanchard grinding shop where they can grind twenty,or fifty, or 100 parts at a time.
          Aluminum flycuts like butter on a bridgeport.
          The ponderingjunkman was looking for work.
          A hustler with a bridgeport can drill and tap pretty quick in operations. Here's where a tapping head makes you money.
          A machining center with dual fixtures is hard to beat. Load one while the other is running.
          Just a couple of ideas.

          Merry xmas


          • #6

            You have to consider several things.
            1. Complexity
            2. Amount of material to be removed
            3. Tolerances
            4. Number of tools needed
            5. Number of parts in a production run
            6. Skill of operator

            These are just a few of the criteria that come into play. You cannot just base the decision to go cnc on the number of parts. There are many shops who run one of a kind on cnc equipment and many shops who still produce large numbers on old conventional machines. I do both in my shop we run 20 pump housings a vertical machining center and 2000 aluminum castings on a Bridgeport, all depends on the economics of the situation. I have the same guy running both machines and get two for one.

            The multiple sided machining can be done by simply stopping the program and flipping the part in the vise or by using a machine with more than three axis motion. VMC,s come as three axis machines x,y,z, just like your BP only the computer controls the motion. To rotate the part it is necessary to add another axis of motion usually genericaly refered to as a 4th axis. This fourth axis can be in the form of a rotating table, or a rotating device similar to an indexing head. Some machines allow for full 4 axis simultaneous control and some allow for only 3 axis simultaneous control all depends on your needs and wallet. You can go on to 5 axis control and more if you want all it takes is money.

            I run my own shop and do this everyday if you pass along more info on your project I will be glad to give all the input you can stand and maybe more.

            sorry for rambling