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Thread: Lathe build

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  1. #1

    Lathe build

    Hi Folks,

    Have an idea to build a smallish but useful lathe for home use mainly doing the odd motorbike or garden equipment part and some slightly more complicated stuff like combustion chambers on single cylinder heads.
    Mostly aluminiums and plastics but would like to be able to to do steel when needed.
    Motivation is challenge/ learning and the cost of manual machine as not very many in circulation for less than £1500 here and i dont have the space or 3phase power for some of the older CNC offerings that are cheaper than manual machines.

    Came up with the following mainly based on availability of stuff i can get hold of for free/scrap value and welcome any input from those that have gone before.
    My background is manufacturing composites and some programming for waterjets and multiaxis ultrasonic machines.

    Construction - Mild steel and Alu )(
    300x900 x 20mm mild steel for bed, 2x rail risers cut out and welded/bolted - plate/risers and Headstock area milled flat to take rails.
    X and Z Axis will be 20mm Aluminium tooling plate. Possible to get more 20mm steel plate to prevent mixing materials/ expansion issues, more an issue on Z rather than X?
    Headstock and spindle will have to be sourced, hopefully from an old manual machine and modified to suit or made from scratch £££ (rather build headstock to suit a spindle).
    Welded 40mm x 5mm steel frame to bolt the bed to. This will be de-stressed and either milled or shimmed to keep the bed flat. Have lots of 40x5 at the min but i suspect larger/ rectangular might be better to stiffen the bed?
    Designed to take diameter upto 320mm, working length maximised (~500mm) with rails i have with option to add a manual tail stock.
    Initially will use single tool, ideally will build a mill waaayy down the line and make a tool changer.


    Motion
    I have an old computer that i have got linux CNC installed on and managed to get a used 2axis kit from ebay for £20 to play around with and i have motors spinning in the right directions.
    Only 1.8nm Nema 23s but will be ok to get going, likely run 2:1 to get some more torque and resolution.
    HIWIN 15mm linear rails and bearings, not the biggest and fiddly to work with but should take the loads expected. Used apparently but seem good as new.
    eBays finest 1605 ballscrew sets, 600mm and 250mm, Cheap and probably nasty but will get things moving and give scope to improve unless i can find quality used alternatives. Might be ok with incorporation of an encoder.
    Spindle drive, ideally a 3phase with VFD or a servo setup but it could be a treadmill or bench grinder motor with manual control to get going.

    Very much in the design stage any thoughts appreciated.

  2. #2
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    Join Date
    May 2016
    Posts
    260

    Re: Lathe build

    Quick thoughts from someone not expert in machine design...

    1. Skip the aluminum. It's not thermal expansion you need to worry about, it's stiffness.
    2. Get the tool holder as close to the X-axis rail/trucks as possible. As drawn it's cantilevered out there pretty far.
    3. Your base needs to be taller. Right now it's a noodle and will twist. It's doesn't have to be solid, but think of a 5-sided box vs. a flat board. The board will twist, but the box is significantly stiffer.
    4. There's no reason to put the Z-rails that close together. I see you're trying to get the cutting forces down between the Z-rails at an average diameter, but spread them apart as far as the base will allow.
    5. Make the Z-axis carriage longer. This will allow the Z-screw to be offset to the back (instead of centered down the carriage) without racking. You'll give up some Z-travel, but you've got heaps right now.
    6. Don't spend a ton more time on this design until you source a headstock. Everything will change once you find/buy the headstock and have to re-design the lathe around it.

    Consider converting a Hardinge HC or DV lathe. The whole thing is basically there, and there are plenty of commercial CNC conversions to copy.

    Even easier:

    https://www.ebay.co.uk/itm/Hardinge-...oAAOSwphJfMtmj

    Buy this thing and convert it. You'll spend less money on that than rails, screws, and a headstock from a dodgy source.

    Ditch the motor and electrical stuff and throw in a 3HP induction motor with a VFD.

    Don't even bother with rails - just bolt a stepper or servo to the leadscrew and cobble up something for X. If the ways are shot, you can always add rails and fabricate a carriage. It already has a turret you can (eventually) automate.

    Get it going and learn how to run a CNC lathe. Then you can build, convert, or buy something once you have a bit more lathe experience and know what you want or hate.

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