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"cnc" mill conversion (Van Norman #12)

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  • "cnc" mill conversion (Van Norman #12)

    CNC should be taken very "loosely". What I should actually call it is numerically controlled power feed.

    I'm putting this on an old van norman #12. The leadscrews are beat to heck (in the center, no adjustment left), so milling without jerking the table around is pretty unheard of. I'm going to pull the old screws out of the van norman and replace them with ballscrews (because that's what I have). With ballscrews, I'm not overly interested in keeping the movements manual, and since a lot of what I do is repetitive anyway, I might as well slap a couple surplus stepper motors that I have on there.

    Anyway, what I need to do is source the motor drive / coupling. I'm planning on using timing belts, but I'm having trouble deciding on the width and pitch of the belt. I figure the braintrusts on this list are much better en-jin-ears than I am, so that's what I'm asking for advisement with. I'd just go for 3/4, but the cost for the pulleys is outrageous...I'd LOVE to go smaller if it's feasible.

    And yes, I know the ignorance of converting a big huge clapped out manual machine to CNC, but it's either this or the scrap heap. I rarely use it, and when I do, I'm breaking endmills left and right, and ruining parts. If I'm going to go to the trouble of replacing the screws, I might as well get something that I allows one hand to hold my coffee and the other hand to scratch my ass while it's cutting away. (I do not intend to do high precision or 3D or for that matter, even 2D profiling very often). With that said, I don't want to go all the way to bicycle chain drive.

  • #2
    Why bother with pulleys?
    Drive it direct onto a 0.200" pitch screw with a 1,000 Oz / in motor thru an oldham coupling.

    Many machines were made with this configuration, I'm still using one as a daily drive.
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      My Bridgeport Boss 5 runs timing belts with a 1 to 1 pulley ratio. I'm running the original steppers with 203V Geckos. I'm getting 120IPM rapids on X & Y (Sigma motors), and 100 IPM on Z (Superior motor). The leadscrews are the original 0.200" pitch.

      -Mike

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      • #4
        My motors are 640 ozin I believe. Do you think the direct drive is still an option for the smaller motors?

        I am NOT concerned about speed. 120IPM would shake my garage!

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        • #5
          Gear it down 2 to 1 and get twice the resolution. Bridgeport did that with the Boss 6. If your motor are the newer square bodied type, you'll probably be fine.
          I'm pushing my original motors with a 70VDC 20A power supply, and so for it's been more than adequate.

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          • #6
            Thanks for the help.

            I figured out that I can get "sticks" of timing belt pulley from SPDSI and make my own flanges for about 1/2 the cost of buying the belts individually, and still have a lot left over for other projects. The other advantage is that if for some reason one belt isn't strong enough, I can double stack them this way and use two belts.

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