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  1. #1
    Join Date
    Feb 2020
    Location
    Albury
    Age
    55
    Posts
    87

    Default BF20LV CNC conversion

    Finally made the first metal cuts under full CNC control.
    IMG_6122.jpg
    The machine is a stock standard Optimum BF20LV purchased from H&F earlier this year.
    Retrofitted with stepper motors, linear encoders and a Raspberry Pi running LinuxCNC.
    IMG_6123.jpg
    Note that this conversion uses the standard ACME lead screws.
    Whilst the X+Y screws are OK, the Z axis screw leaves a lot to be desired.
    Backlash on X is 0.4mm and 0.2mm on Y-axis, however, the linear encoders are mounted directly onto the table so the control can compensate.

    Overall I am pleased with the outcome.
    But I have ordered ball screws to overcome the limitations of ACME screws and backlash.

  2. #2
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    824

    Default

    TheApprentice,
    Congratulations on your first cuts, mine was only a few months ago - it is a great feeling.

    The use of a Raspeberry Pi is interesting.
    I am running LinuxCNC on an old desktop tower with Debian Wheezy, out of support but works fine.
    As this system is so old, I feel it prudent to have a fall-back option.
    Can you provide links to the sources and processes used ?

    Keep going,
    Keep well,
    John.

  3. #3
    Join Date
    Feb 2020
    Location
    Albury
    Age
    55
    Posts
    87

    Default

    Quote Originally Posted by electrosteam View Post
    Can you provide links to the sources and processes used ?
    Hi John,
    for the Raspberry Pi I used JT's instructions located here.
    Another set of instructions is here.
    Somewhere on the LinuxCNC forum I saw a reference to a downloadable image for the Pi ... maybe from andypugh?

    I've used Mesa's 7C81 card which connects to the Pi via SPI interface so you'll have no timing issues.
    I found the SPI interface a better solution for the Pi than the popular Mesa 7i76E Ethernet based card since the SPI is closer to the hardware core and isn't required for any other purpose.
    The stepper drives and encoders are connected via Mesa 7i85S card.

    A few more links with photos:
    Pi + Mesa 7C81
    Mesa 7i85S
    Siemens Digital IO modules

    Config files are on GitHub

    If you need any further information drop me an email on helioz2000 AT gmail DOT com
    Last edited by TheApprentice; 14th May 2020 at 11:18 PM. Reason: added detail

  4. #4
    Join Date
    Jun 2020
    Location
    Geelong
    Posts
    21

    Default

    Any further progress on this? They are a great little mill. Im interested to know how you went with the ballscrew conversion.

    I converted mine about 5 years ago and had some success but ended up mothballing the project.

    I used steppers with gecko G203V drivers, no feedbacks, and a USS Smooth stepper motion controller. I only had a laptop at the time, with no ethernet port, so I used the USB motion controller and Mach III on the laptop. I used the standard lead screws with backlash compensation and had it all running but there were a few issues.

    The USB control was buggy as hell. You just never knew when it was going to drop out mid cycle. This was the most disappointing aspect of the machine. Of course I could get another computer and then another ESS ethernet smooth stepper but that was more than I could afford at the time.
    When it wasn't dropping out it cut really well, but the leadscrews where definitely limiting its performance. climb milling while cutting a curve in a pocket was its biggest weakness. the table would move and leave a definite step in the part.

    overall it was a fun project but I didn't particularly need it for anything. I just wanted to learn a bit and have a play.

    Cheers, Rowdy

  5. #5
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,774

    Default

    Hi Rowdy, Guys,

    I have the Chinese clone of the Optimum BF20LV, and found that the anti backlash adjusting screws were rattling about in the cavity under the machine.

    How did you go about adjusting the leadscrew nut to minimise the backlash. I adjusted mine when I took the table off, not much adjustment between tight and loose. I found that the nut got tighter then looser in different places on the leadscrew as you moved the nut from one end of the leadscrew to the other, as if the leadscrew wasn’t uniform along its length.

    At best I have two hand wheel divisions of backlash at the moment.
    Best Regards:
    Baron J.

  6. #6
    Join Date
    Jun 2020
    Location
    Geelong
    Posts
    21

    Default

    Hi Baron,

    Im afraid that is probably pretty normal on these machines. I think i had the same problem as yourself, where i couldnt get it just right. Thats the reason people upgrade these to ballscrew for cnc. Its just something you have to compensate for in your operation.

    two hand wheel divisions, i think they are .02mm divisions by memory. So .04mm, thats not bad on a manual machine. Another thing i like to do is use long travel dial indicators when im trying to get something dead nuts. Thats what i do on my Machines so i don't have to think in imperial units or count the handwheels at all lol

    rowdy

  7. #7
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,774

    Default

    Hi Rowdy,

    Thank you for your post ! Yes you are right the hand wheels are 0.02 mm/div !

    I decided to get and fit a DRO, and whilst I was at it sort out some other issues as well. So it turned into a fairly extensive maintenance project. However the work improved the machine considerably so in that respect I'm quite pleased with it.

    I did a write up in the general section:

    https://metalworkforums.com/f65/t206308-dro-instalation

    Thanks about using "Ball Screws" ! That might be something to consider for later !
    Best Regards:
    Baron J.

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