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Optimizing a milling operation

  1. Nov 22, 2011 #1
    Kind of off the wall question but here it goes:

    I am trying to figure if my set up for a CNC machine is one that will work and what feed rate I should use to cut 2024 AL. Right now ( as per the free mount I got with the kit ) I am using a dremel 300 with a 1/8 in tungsten carbide bit from dremel. The dremel was not happy and sounded horrid (I have done proper milling before so I am positive it was not a good noise).

    My thoughts were that I should either get a different bit (one that is an actual end mill) or just not use the dremel and get something with some more horsepower. But in order to do that I need a "framework" of equations or a resource that will point me in the right direction.

    I remember I took a class some time back that had a way of using a combination of the taylor tool life equation and some other related manufacturing equations to figure out the optimal speed feed and horsepower for milling (and turning) operations. I have lost the book for that course though and my google searches have been unsuccessful.

    Things I know are involved and would like the relationships between:

    Chip load
    number of flutes
    material removal rate
    cutter dia
    RPM
    HP
    Hardness
    machine-ability rating
    and feed rate



    Thanks so much
     
  2. jcsd
  3. Nov 22, 2011 #2
    1) this is not a physics question
    2) do you have values (off a manual or anythiing) for recommended tooth load, RPM, or surface speed? If yes, you can easily calculate everything else.
     
  4. Nov 22, 2011 #3
    I would debate you on your assertion that this is not a physics question.

    I did eventually find some somewhat arbitrarily recommended values for the chip load. The dremel only puts out about 138 watts and has a range of 5000-35000 RPM but again that's not helpful. Yes you could easily figure out how much material could be removed but the question becomes is it effective and optimal i.e whats cost to the cutter and heat.

    Anyway,

    There should be a way of calculating the power needed in a cutter to remove a material at a certain rate while also accounting for the thermal component of the operation. Which I would assume involves the material properties of the work piece i.e modulus of elasticity, brinelle hardness etc.
     
  5. Nov 22, 2011 #4
    Someone makes a kit to turn a dremel into a CNC? It seems absurd, because a dremel isn't made to take side loads like that. The average drill press isn't made to handle milling side loads, and a drill press is vastly sturdier than a dremel.
     
  6. Nov 22, 2011 #5
    Agreed

    The dremel truly made for wood working and small DIY and is not made for this it was more of a free gag.

    The way the tool attaches to the gantry however, you can bolt on something far more beefy including a 3 HP dedicated router you or can use a "normal" spindle.

    But before I spend money on new tools etc. it would be really nice to be able to say given X material this is the power, feed rate and cutter that would be best suited for the operation so the original question still stands.
     
  7. Nov 22, 2011 #6
  8. Nov 23, 2011 #7
    There's something called "specific cutting energy" that gives the work required to remove a certain volume of material, and knowing your removal rate you can use this to determine the power required by the machine, and knowing your cutting speeds, the force also.

    But it is BS since it matters what type of chips you are making. In engineering they assume this "specific cutting energy" to be a constant, but engineering=bs so I wouldn't trust any of that.
     
  9. Nov 23, 2011 #8
    A dremel does not have properly preloaded bearings and you will destroy it by trying to mill. You have likely damaged the bearings already.

    A three flute 1/8th endmill in aluminium could safely cut at around 60IPM at 15-20,000RPM and as fast as 200IPM at 30,000RPM given proper geometry, engagement, chip evacuation, cooling etc. You would need less than 1/2HP to cut with a 1/8" endmill.

    This is really not a physics question since there are far too many factors to come up with a meaningful answer. Even the fancy software just looks up your end-mill in a manufacturer provided database of tested feeds and speeds and de-rates according to your machine specs. I would recommend no more than 8000RPM and 12IPM until you know what you are doing. In general, you should change the RPM and IPM proportionally because if you go too slow the cutter will rub instead of "peeling" off metal and will heat up extremely fast.

    Go to cnczone and look around. If you want something that can cut well with small bits look into a water cooled chinese spindle. They have a 2.2KW model that shreds aluminium, wood, composites, plastic etc.

    Routers tend to have high runout which will cause problems milling metal with small bits but a decent router would do an okay job with a 1/8" bit.
     
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