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  1. #1
    Join Date
    Aug 2019
    Sydney, Australia

    Default Lathe attachment for horizontal milling, or slot milling

    So, about a year ago I bought a little high-speed spindle motor/collet from eBay, to build a CNC cutter/mill. That never happened, but when a friend gave me a lathe as a project I thought about how I could use it on a lathe.

    1) Bolted to an old lathe's slide, as an accurate drill?
    That was with a Dremel style HSS burr, to remove broken bolts from a vice, that failed to "EzyOut."

    2) Bolted in a different way to an old lathe, as a tiny grinder?
    Another Dremel tool, cutting slits in a "new" vice jaw.

    3) In a lathe tool holder, as a weird horizontal mill?
    Step one, fabricate (or get someone to CNC) a bracket to fit your tool post..

    Step two, use toolpost height adjustment (or shims) to align to centre, as with any tool, and use it to mill, drill, slot, or grind anything in your chuck. Here I am milling radial slots in a face plate:
    I have a clamp and an inclinometer on the plate.

    Other possible uses?

    4) Turn it around, like a parting tool, and you can drill holes through the middle of a machined shaft for split pins etc.
    Same for cutting parallel slots.

    5) Fit a little grinding wheel, and you can (slowly) refinish hardened or carbide centres, polish collets, et c.

    6) Castellated nuts? No problem!
    Last edited by nigelpearson; 2nd Dec 2019 at 07:55 PM. Reason: added pic

  2. #2
    Join Date
    Sep 2008
    Riddells Creek, Vic.


    What speed did you run the spindle at to cut those slots in the faceplate Nigel?
    Did you start with a smaller cutter first?

  3. #3
    Join Date
    Aug 2019
    Sydney, Australia


    Techo1, the little spindle/mill motor is rated at 12,000rpm: but I'm only driving at 50v, so maybe 5,000rpm?

    The face plate is actually an old casting, that I think my Dad made. It already had some healthy slots made by casting cores - I was only cleaning them up. The flat side was down to 5.5mm in places, and the rear is over 9mm.

    I am using an old 2 flute HSS, 1/4" diameter. Started by plunging in at a few spots, but realised the cutter was OK to just plunge at one end, then slowly feed fore or aft with the cross slide.

    I decided to widen the slots to 8mm, to either use 8mm bolts, or 6mm t-slot nuts. So, align slot angle with inclinometer, roughly check against slide feed, wind cutter & motor up or down in tool post to cut either top or bottom edge, and mill.

    (although, being cast iron, grind is a more apt phrase - it is just fine gray dust everywhere!)

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