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  1. #1
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    PM-932m CNC Conversion

    Introduction

    I placed an order with Precision Matthews for a lathe and a mill a week ago, originally the order was:

    • PM-1030V Lathe
    • PM-30M Mill


    The lathe was backordered, so a week later I reconsidered my choice of the mill and decided to go bigger and heavier for just a bit more money.

    So, I changed the mill order to be the PM-932m with the Power Down Feed and cast iron stand.

    Both the lathe and the mill will be here in December, and that is when I will start planning to convert the PM-932m to CNC.


    Wishlist

    Here's what I'd like to do to the mill:

    • Convert the leadscrews to ballscrews.
    • Start the CNC electronics with simple steppers, upgrade to full AC servos later.
    • Change the R8 Spindle to an NT30 spindle such as the one from Charter Oaks Automation.
    • Epoxy Granite All the Things
    • Convert the motion from dovetail ways to linear rails.
    • Replace the spindle head with a Chinese belt-driven BT30 spindle, rated for 10,000 RPM / 12,000 RPM Max.
    • Replace the 1.1kw/1.5hp AC motor with a 1.5/2.2kw AC Spindle Servo, rated for 6000 RPM, 8000 RPM Max.
    • Belt drive the spindle with the servo with a 2:1 overdrive.
    • Add a BT30 carousel ATC


    Initial Designs

    Thanks to KCJ for sharing his excellent CAD models, it's helped me get a much better idea and a quicker head start on designing the upgrade.

    KCJ's models:
    https://github.com/KurtJacobson/RF45...r/CAD%20Models


    So the initial design for the BT30 spindle and 1.5kw AC spindle servo was based on taking a giant block of cast iron and making an entire head out of it.

    Assuming I get the mill converted to CNC first, it should be able to mill its own replacement head.

    Attachment 430566

    Attachment 430568


    Initial Parts List

    Ball Screw Kit:
    TBD, have to find a matching kit for an RF-45/PM-45/ZX45/etc.

    Steppers / Servos:
    TBD, prefer to start with less expensive plain steppers just to get things moving.

    BT30 Spindle:
    Plenty of inexpensive 6000 RPM BT30 spindles listed on AliExpress, but here's one example rated for 10,000 RPM with a 12,000 RPM maximum:
    high speed ATC BT30 automaitc spindle for cnc machine / cutting machine 12000rpm

    AC Spindle Servo
    Found a AC Spindle Servo that comes in 1.5kW or 2.2kW sizes that fit within a 150x150mm square frame, complete with servo, driver, and brake resistor - and single-phase 220V compatible.

    How do these torque ratings compare to the stock AC motor? I don't know yet..




    ATC




    All comments and suggestions are welcome, this will most likely be a multi-year build.


    I am located in Atlanta, GA, if anybody else has a large mill and is willing to help, let me know!

  2. #2
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    Re: PM-932m CNC Conversion

    Steppers / Servos:

    I think for the motors for motion, I'll pick closed-loop hybrid steppers like these from Lichuan:




    With the AliExpress Sale starting on November 11th, I can get three of these beefy closed loop steppers for just under $600 with shipping.

    Toroid Transformers add to the cost, one per stepper driver.


    AC servos are also available, but they start at around $200 and the torque ratings are different...


    Control Electronics

    I will probably go with the Mesa US PCIe Stepper Kit, and run LinuxCNC.

  3. #3
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    Re: PM-932m CNC Conversion

    Also possible alternative for the Z-axis stepper, a closed loop stepper with a brake:

    https://www.omc-stepperonline.com/cl...tic-brake.html

  4. #4
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    Re: PM-932m CNC Conversion

    Might choose the Leadshine versions, their documentation seems to be better (it exists):

    Leadshine CS-M234120 (without Brake) for the X/Y axis.
    Leadshine CS-M234120B (with Brake) for the Z-axis.

    Stepper Driver CS-D808

  5. #5
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    Re: PM-932m CNC Conversion

    Ball Screw Kit:
    linearmotionbearings2008 on eBay has this kit:
    X Y & Z ball screws kit 772mm/397mm/602mm for ENCO RF45 CLONE CNC conversion


    If the pictures look familiar, they're from KCJ:
    https://www.cnczone.com/forums/rf-45...ml#post1991518

    But these are sold with double-ballnuts instead of two separate ball nuts.

  6. #6
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    Re: PM-932m CNC Conversion

    Playing with the idea of mounting Hiwin QR-series heavy-duty rails on the axises (axii?).

    The QR Series uses rollers instead of ball bearings, so they're for super heavy duty motion.

    These are the 30mm wide models, with flanged carriages.


    I got the idea from CNC4RX7 on YouTube, who's doing something similar with a PM-727.

    He has his ballscrew inside the column, I'm thinking of moving the ballscrew forward and filling the column with epoxy granite.

    Attachment 430668

    Attachment 430670

  7. #7
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    Re: PM-932m CNC Conversion

    Linear Rails

    I think I'll go with Hiwin genuine HG series rails, from motionconstrained.com:

    Z Axis: 2 x HGH20CAZAC rails with normal blocks, 20mm rails 760mm long. $288
    X Axis: 2 x HGH20CAZAC rails with normal blocks, 20mm rails 820mm long. $299
    Y Axis: 2 x HGH20CAZAC rails with normal blocks, 20mm rails 520mm long. $245

    Total: $832


    The rails are longer than the dovetail slots, so I'll have to support the ends for some overtravel.

  8. #8
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    Re: PM-932m CNC Conversion

    Hybrid Closed-Loop Steppers

    Prices from Leadshine USA (leadshine.com):

    2 x $148: Leadshine CS-M234120 (without Brake) for the X/Y axis.
    1 x $208: Leadshine CS-M234120B (with Brake) for the Z-axis.

    3 x $129: Stepper Driver CS-D808

    So total cost: $891

  9. #9
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    Re: PM-932m CNC Conversion

    Hiwin RG Series Rails

    I am also getting quotes for the Hiwin RG Series rails, which use angled rollers instead of ball bearings.

    RGH20CA2R520ZAHII: $671

    2 x RGH20 rails, Heavy Load, Standard Block, Medium Preload, Precision H, 2 blocks per rail, 520mm long.


    RGH20CA2R760ZAHII: $718

    2 x RGH20 rails, Heavy Load, Standard Block, Medium Preload, Precision H, 2 blocks per rail, 760mm long.


    RGH20CA2R820ZAHII: $741

    2 x RGH20 rails, Heavy Load, Standard Block, Medium Preload, Precision H, 2 blocks per rail, 820mm long.


    Total: $2282


    This quote was from Braas Automation, brassco.com.

    What's interesting about these prices is that the rails are cheap - but the bearing blocks are $132 each!

  10. #10
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    Re: PM-932m CNC Conversion

    I'm looking at the TBI Motion store for Ball Screws:

    https://www.aliexpress.com/store/1797664


    They have some double-nut C3 or C5 grade ballscrews in 2005 series that are interesting:

    https://www.aliexpress.com/item/32942915298.html


    The manufacturer's page has info and drawings/cad:
    https://www.tbimotion.com.tw/en/page...e-catalog.html

    https://www.tbimotion.com.tw/en/download/index.html

  11. #11
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    Re: PM-932m CNC Conversion

    X-Axis Ballscrew

    Came up with a simpler mount for the X-axis ballscrew and motor mount, allowing for a full length ball screw and more travel.

    The parts are designed based on off-the-shelf components:

    • MBA15-F Nema 34 Motor Mount
    • FK15-F Fixed End Flanged Bearing Block
    • FF15 Floating End Flanged Bearing Block
    • MGD-20 Ballnut Mounting Block, modified with 6mm cut off from the bottom and the top.


    The only custom parts are the 15mm thick plates on each end of the table which serve as the mounting points for the ballscrew assembly.

    The Ballscrew is looking to be a 2005 series (20mm, 5mm lead), with a DFU/OFU double-ball nut.

    The saddle will need some minor pocket machining to fit the MGD-20 mounting block, I could probably even bolt it down to my tiny X2-series mill to do that.


    Attachment 430798

    Attachment 430800

    Click image for larger version. 

Name:	PM-932m v23 - X Axis OFU Double Ball Nut.jpg 
Views:	0 
Size:	75.7 KB 
ID:	430802

  12. #12
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    Re: PM-932m CNC Conversion

    AC Servos

    Decided to splurge and go for DMM AC Servos and DYN4 drives:

    • 86M-DHT 0.75 kW AC Servo on X
    • 86M-DHT 0.75 kW AC Servo on Y
    • 86M-DHT 0.75 kW AC Servo with Brake on Z
    • 3 x DYN4 AC Servo Drives


    Cost: $1643


    The DYN4 AC Servo drives have the benefit that they can run directly off of single-phase 110/220V AC, so a DC power supply or an AC toroidal transformer isn't required.


    For controlling hardware, I'm going to with the Mesa electronics 7I77 6-Axis Servo control board, and either a PCI/PCIe 5i25 or 6i25 card and LinuxCNC.

    5i25-7i77 PCI Kit
    6825-7i77 PCIe Kit

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