Home Forum Show it off! Going fast

This topic contains 11 replies, has 1 voice, and was last updated by  Paul Kelly 3 years, 11 months ago.

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  • #2261

    Paul Kelly
    Participant

    Giving the mill at home a bit of a birthday. The X axis ballscrew always had a bit of slop in it and the main spindle only goes to about 2500RPM :
    [media=youtube]n6XOuQUBlHQ[/media]
    (it has oodles of torque though)

    If you want to use smaller cutters then you need to go faster. To that end, this turned up today:


    Yes, that’s 60,000 rpm!

    Pictures at 11.
    PK

    #2262

    parkview
    Participant

    That looks handy. Where did your source the motor from Paul? Do you have a link handy?

    http://www.swmakers.org/
    http://www.bdug.org.au/

    #2263

    Paul Kelly
    Participant
    #2264

    parkview
    Participant

    Nice one. Thanks.

    http://www.swmakers.org/
    http://www.bdug.org.au/

    #2267

    Paul Kelly
    Participant

    OK, so before I can start having fun with 60KRPM spindles, I owed the mill a little TLC.
    Now I’ve done a few mods to this mill. It started out looking like this:

    And pretty soon, looked like this:

    Too much to talk about there. Suffice it to say that a stock X3 is a piece of shit mill..

    After a fair bit of (ab)use, the X axis ballscrew was just flogged out which meant tool snapping backlash.
    On top of that, the way I had arranged the ballscrew was stupid in most respects…

    This pic shows that it looked really neat!


    The coupling between the stepper and the screw was under the table and the preloaded bearing was at the other end. This gives a neat looking install with minimum stick out, but means you have to align 3 axii (bearing, ballscrew nut, and stepper motor) in two dimensions, and the thing you really need to move to do this (the ballscrew nut mount) is unreachable when it’s assembled.
    The result was a bout 2mm of deflection at the motor end of the screw as the table moved to the left.

    Eventually, this took it’s toll on the coupling which failed.

    So this time I went for ‘clunky but simple’:


    A is the cover plate that clamps the double row angular contact bearing, the coupling is inside B and the dual shaft motor allows a hand wheel at C..
    In the background you can see the old motor with the broken coupling.

    The good things about this arrangement are:
    You can leave the other end of the screw unsupported.
    You only have to align one part the plate on the end of the table.

    Took me about 5 minutes to dial it in….

    Just got to wire it up now and we’ll be back to making swarf.

    #2270

    Creepyjoe
    Member

    Interesting setup, what work were you doing on the engine head, and what sort of thing are you doing with cutters small enough to warrant such a high speed spindle?

    #2271

    Paul Kelly
    Participant

    Creepyjoe, post: 3111, member: 674 wrote: Interesting setup, what work were you doing on the engine head

    We were installing dynamic pressure transducers to measure combustion pressures at high speed as part of a research project for a customer.

    and what sort of thing are you doing with cutters small enough to warrant such a high speed spindle?

    Its mostly about metal removal rates and sharp corners. If you think on the scale of something like an RC car (or model rocket in my case) then a 1/8″ diameter tool is medium sized. Running a cutter that sized at 2500RPM is going to:
    A: clog and break tools,
    B: require glacial feed rates.

    The big router can spin at 24KRPM, but it’s rack and pinion drive. I reckon it’s repeatable to about 100 microns, but that’s not far off your feed per tooth on a small cutter so breakages become common.

    I used to have a little router that had ballscrews and a 24K spindle, but it lacked rigidity and I had problems with tool deflection in metals.

    The other piece of the puzzle is that I’m starting to do more 3D work, this always means long jobs going back and forth with tiny step overs. Those parts that I brought to the last meetup took something ,like 3-4 hours each at 24KRPM. More speed ==more feed so we reduce the time to machine…

    PK

    #2273

    Creepyjoe
    Member

    Good stuff

    #2276

    Paul Kelly
    Participant

    So I finally made it home early enough to get the wiring done:
    [media=youtube]MvAbFORtBw0[/media]

    Now to make the mount for the new sub spindle!

    #2277

    Andrew-MOAMind
    Participant

    Looking great Paul. Shame it is probably a little too heavy to bring along to the next meetup.

    I have done some work recently with closed loop VFDs and I have been very impressed. We could easily control a basic 415 4 pole motor at sub 1 RPM. With the encoder mounted on the shaft it would simply bump up the current as the load changed. Completely absurd for regular use but it was an interesting result of having the encoder feedback to the VFD.

    What size are the stepper motors on your axes?

    #2280

    Paul Kelly
    Participant

    Andrew-MOAMind, post: 3118, member: 29 wrote:
    What size are the stepper motors on your axes?

    Just Medium torque (250ish oz.in) NEMA 23’s

    #2301

    Paul Kelly
    Participant

    So back to the topic.
    Next step: Rough machine a mount:

    Then get the bore spot on.

    For bonus points, spot what’s missing in these pics…

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