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Thread: PM-932m CNC Conversion

  1. #21
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    Default Re: PM-932m CNC Conversion

    After some further discussion with JT @ Mesa US I've decided to go with the Mesa 7i76E as originally recommended (good call!).



  2. #22
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    Default Re: PM-932m CNC Conversion

    Glad you talked to one of the 2 vendors - I think you'll be very happy with that setup.
    As far as the PC goes - you may want to have it closer to the screen depending on where the electronics box ends up. Otherwise you have to run multiple long cables to your screen and other input devices (mouse & keyboard, pendant, etc). If you have the pc near the screen its just the cat5e cable back to the electronics box (and maybe the AC power for it). Also makes it easier to plug in USB sticks unless you plan that out in advance too.



  3. #23
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    Default Re: PM-932m CNC Conversion

    Quote Originally Posted by ninefinger View Post
    Glad you talked to one of the 2 vendors - I think you'll be very happy with that setup.
    As far as the PC goes - you may want to have it closer to the screen depending on where the electronics box ends up. Otherwise you have to run multiple long cables to your screen and other input devices (mouse & keyboard, pendant, etc). If you have the pc near the screen its just the cat5e cable back to the electronics box (and maybe the AC power for it). Also makes it easier to plug in USB sticks unless you plan that out in advance too.
    I will probably have the PC initially set up on its own cart, with the connection to the CNC control box being via the ethernet cable.


    I have an older Asrock C2750D4I Mini-ITX motherboard that I'm thinking of using as the PC's guts.

    Maybe with a Mini-ITX case that can be VESA mounted on a monitor arm...

    The motherboard is fanless, and has the benefit of having 2 x LAN ports - one for internet access, and the other for the CNC control.



  4. #24
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    Default Re: PM-932m CNC Conversion

    I also have one of these Supermicro X10SDV-TLN4F Mini-ITX boards that I modified with a copper finned heatsink...

    But this board is massive overkill...


    The other C2750 board may be fine, but I'm also concerned about the lack of USB ports (3 max), and I'd rather not have to do USB hubs...

    Maybe one of those J1900-style ultra compact PCs?



  5. #25
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    Default Re: PM-932m CNC Conversion

    Kind of looking at this J1900-based SFF PC, Qotom Q190S.

    Benefits:

    • Fanless
    • VESA Mount
    • 2 x LAN Ports - 1 for Internet, 1 for Mesa
    • 3 x USB 2.0 Ports
    • 1 x USB 3.0 Port
    • HDMI and VGA
    • RS-232 Serial
    • Quad-Core CPU, 2.0/2.4 Ghz, 8GB RAM, 64GB disk.



    $188 + $30 shipping from Qotom.



  6. #26
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    Default Re: PM-932m CNC Conversion

    I've figured out the size I will use for linear rails - 25mm Hiwin HG series, as they're easily available.

    A quick price check of Hiwin HG series, 2 sets of 25mm rails with 2 blocks per rail, from MotionConstrained.com:

    • X Axis HGH25CAZAC 520mm: $291
    • Y Axis HGH25CAZAC 820mm: $353
    • Z Axis HGH25CAZAC 700mm: $328



    I've also determined how to mount the rails to the Z axis:

    Precision ground steel bars from McMaster (thickness ground to +/- 0.025mm), one 3mm x 20mm bar as a datum reference, and two 10mm x 25mm bars as support for the rails.

    It's a combination of ideas I've borrowed from Youtube users CNC4XR7 and MetalMusings.

    CNC4XR7 had the idea for the datum bar with a PM-727, and MetalMusings had the idea for the double-stacked support bars.

    PM-932m CNC Conversion-pm-932m-v11-z-axis-linear-rails

    Last edited by gmoschini; 11-12-2019 at 09:29 PM.


  7. #27
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    Default Re: PM-932m CNC Conversion

    Hiwin HG vs RG Series

    I was able to get a price from MotionConstrained.com for a full set of Hiwin RG-series rails in the 20mm size for about $1100, a little bit more than the cost for the HG series.

    And still half the price of the RG series from the other vendor.


    So, let's take a look at the differences between the HG and RG rails.

    HG 25mm on the left, RG 25mm on the right.


    The HG series have fewer mounting holes, spaced further apart - allowing for some inaccuracies in tolerance when installing.

    The RG series have twice the number of mounting holes, and require a smaller tolerance / greater accuracy when installing.


    The RG series are much stiffer, with a higher dynamic load range.

    Hiwin HG description:

    The HG series linear guideways are designed with load capacity and rigidity higher than other similar products with circular-arc groove and structure optimization. It features equal load ratings in the radial, reverse radial and lateral directions, and self-aligning to absorb installation-error. Thus, the HG series linear guideways can achieve a long life with high speed, high accuracy and smooth linear motion.

    Hiwin RG description:

    The RG series features a roller as the rolling element instead of steel balls. The RG series is designed with a 45-degree angle of contact. Elastic deformation of the linear contact surface, during loading, is greatly reduced thereby offering greater rigidity and higher load capacities in all 4 load directions. The RG series linear guideway offers high performance for high-precision manufacturing and can achieve a longer service life than traditional ball bearing linear guideways.


    So with all else being equal, I'd probably go for the RG series in 25mm size if I can arrange it.

    PM-932m CNC Conversion-pm-932m-v3-hg-vs-rg-front

    PM-932m CNC Conversion-pm-932m-v3-hg-vs-rg-iso



  8. #28
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    Default Re: PM-932m CNC Conversion

    Hiwin RG Series rails on the X and Y axis.


    The Rails on the X axis (the table) have datum bar spacers that are offset - the fronts (right side) are 20mm, while the rears (left side) are 15mm.

    This is necessary because the dovetails are asymmetric, and there's less room on the back of the table.

    PM-932m CNC Conversion-pm-932m-v13-x-axis-linear-rails


    The Y axis rails are mounted similar, but these dovetails are symmetric so the spacers are the same.

    PM-932m CNC Conversion-pm-932m-v13-y-axis-iso-jpg

    PM-932m CNC Conversion-pm-932m-v13-y-axis-front-jpg


    The mounting arrangement of a thin datum bar and two 10mm riser bars leaves a gap in between the steel bars and the edge of the dovetail.

    I think I will probably fill that in with epoxy sand/gravel for some stability.



  9. #29
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    Default Re: PM-932m CNC Conversion

    The steel panel for the electronics box arrived.

    It's thicker and heavier than I expected.

    18" x 18"

    Sent from my Pixel 3 XL using Tapatalk



  10. #30
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    Default Re: PM-932m CNC Conversion

    This enclosure box is bigger than I was expecting!

    It has two pre-drilled holes on the cover panel.

    Sent from my Pixel 3 XL using Tapatalk



  11. #31
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    Default Re: PM-932m CNC Conversion

    Re-working the design to use RG 25mm rails, and also 25mm ballscrews.

    25mm ballscrews require a larger MBA20-F motor mount, and a special FKA20 bearing mount on the front, standard BF20 floating end.


    The motor mount is bolted to a 6" cast iron angle plate that's had one side cut down and will bolt on to the front of the base casting.


    The plate on top of the Y-axis blocks is 35mm thick, with a notch cut in on one side for clearing the motor mount, and with clearance channels cut underneath for the OFU2505 double-ballnut.


    The plate should be relatively easy to machine manually with just endmills and boring bars.

    PM-932m CNC Conversion-pm-932m-linear-rails-v6-base-side

    PM-932m CNC Conversion-pm-932m-linear-rails-v6-base-iso

    PM-932m CNC Conversion-pm-932m-linear-rails-v6-base-back

    PM-932m CNC Conversion-pm-932m-linear-rails-v6-base-front



  12. #32
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    Default Re: PM-932m CNC Conversion

    I once went down this rabbit hole as well. At the end of the day, what is the point of buying the RF-45 clone? The only parts you end up keeping are the four main castings, and they are all heavily modified. You may as well put the money from the RF-45 clone into a paying someone else to do the machining of home built versions of these four structural components. YOu obviously have the design skills to do this. Whether you do the frame in heavy square section steel like a Fadal, or epoxy granite is a personal taste.

    I ended up buying an existing CNC machine (Maho) with a dead controller, and retrofitting that.

    For example, for the price of a RF-45, you could get this german guys MAHO 400E for €1100 and pay for shipment to the states, have awesome ballscrews, hydraulic tool release, way oiler, a back gear spindle for torque, much better iron, and a fourth axis.
    Peters CNCECKE
    Mark

    Regards,
    Mark


  13. #33
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    Default Re: PM-932m CNC Conversion

    Something like that would be cool, I admit...

    But I think I would have trouble getting it through the doorway into the space in my basement, even if I was able to disassemble it.

    Sent from my Pixel 3 XL using Tapatalk



  14. #34
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    Default Re: PM-932m CNC Conversion

    Maybe a steel frame like a mini Fadal? Laser cut steel is very cheap these days.

    Regards,
    Mark


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    Default Re: PM-932m CNC Conversion

    Possibly.

    There is a video of a guy on YouTube that made his CNC mill out of epoxy granite castings, and even has the BT30 belt-driven spindle.

    Here it is:




    So, I might go down that route for a 2nd mill.


    Or go down the route of VMC style with vertical aluminum/steel plates as you mentioned.


    At this point this is all a thought experiment, and I may just use the PM-932 / RF-45 as is with the simplest conversion I can come up with, just to get started.

    Sent from my Pixel 3 XL using Tapatalk



  16. #36
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    Default Re: PM-932m CNC Conversion

    While I appreciate a robust build I tend to also dislike the "bigger is always better" approach as it is wasteful and not necessarily true.
    IMHO the 25mm ballscrews are way too big for this machines weight and power handling capacity. Using the Misumi calculation software its seems that even 15mm are suitable, and I didn't check smaller than that.
    I also checked against my own spreadsheet I used 15 years ago when building my machine and 16mm ballscrews are ok in it too.
    The most heavily loaded axis is Z and 20mm is fine for it, so you could just standardize at that size.
    You don't really benefit from going larger and just create new issues with spacing and fitment. Also for the Y axis and maybe Z axis you should do the calculations but you can likely run fixed at the one end and free at the other end for simplicity, you only really need to support the far end for long screws that may whip if spun too fast (i.e. for X axis)

    Last edited by ninefinger; 11-17-2019 at 03:10 PM.


  17. #37
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    Default Re: PM-932m CNC Conversion

    Thanks for that info.

    Do you have a link for the Misumi / Mitsumi calculation software?

    Sent from my Pixel 3 XL using Tapatalk



  18. #38
    Member ninefinger's Avatar
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    Default Re: PM-932m CNC Conversion

    https://us.misumi-ec.com/maker/misum.../choice06.html

    There are others too that are online - you need to know / assume a bunch of stuff (Mass, acceleration, max velocity, lengths) but shouldn't be too hard.



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