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  1. #21
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    Default Re: Emco F3 mill conversion

    Grabbed a quick photo this morning. Welds are functional rather than pretty.

    Emco F3 mill conversion-imag1785-jpg



  2. #22
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    Default Re: Emco F3 mill conversion

    After a bit of measuring and figuring out how to mount the pulley, I decided to turn the shaft down to 12mm to match the pulley. This provides a shoulder between the 12mm pulley diameter and the 15mm bearing diameter so provides lateral location for the pulley. The pulley will be secured with the 2 grub screws onto flats on the shaft along with a 3mm cap screw.
    The ballscrew pulley is from SDP/SI, part number A 6A55M050NF1512, and is a GT2 5mm pitch, 15mm wide 50 tooth aluminium no-flange pulley.

    I removed the ballscrew from the mill and mounted it between centres in my lathe to turn the end of the shaft. This was sized to provide an interference fit to the pulley.



  3. #23
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    Default Re: Emco F3 mill conversion

    There is approx 1.5mm clearance between the endplate and the pulley. The pulley surface itself is 20mm wide for the 15mm wide belt so there should be no problem with the belt rubbing on the end plate.

    Emco F3 mill conversion-imag1790-jpg



  4. #24
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    Default Re: Emco F3 mill conversion

    The 25 tooth motor pulley arrived from SDP/SI today I'll see how I get on cutting a 5mm keyway this weekend. I plan to use the Lathe to cut the keyway



  5. #25
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    Default Re: Emco F3 mill conversion

    I enlarged the bore in the pulley yesterday, by mounting the pulley in the lathe in a 4 jaw chuck and dialling it in to get it centred. I then drilled it out - first to 13mm - and used an undersize 14mm drill, followed by a 14mm reamer to get it to be a friction fit onto the motor shaft.



  6. #26
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    Default Re: Emco F3 mill conversion

    Today I cut a keyway in the pulley to fit the 5mm key on the motor shaft. I started using the lathe method and finished in the vise.
    Emco F3 mill conversion-imaf1799-jpg
    The keyway is a little deep at the end of the pulley but the key is a nice firm fit, and the pulley is located onto the shaft with two grub screws.

    Next job is to buy some M8 bolts tomorrow and cut the spacers between the motor plate and the ballscrew endplate. I will use 20mm hex bar and bore the centres through to fit the M8 bolts.



  7. #27
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    Default Re: Emco F3 mill conversion

    I'm waiting for some steel and bolts to arrive to finish the mechanical part of the Y axis. So in the meantime I will install Arduino for Linux on my laptop. Prior to full CNC, I plan to control the Y axis manually using two buttons (forward and back) and a potentiometer to control speed. This will send pulse and dir commands to the stepper driver.

    Example 5 from the this page shows the Arduino sketch required. I will need to add limit switches as well.



  8. #28
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    Default Re: Emco F3 mill conversion

    The 20mm dia rod that I need to make the stand offs between the ball-screw end plate and the motor mount plate arrived on Friday. I've made 4x stand offs and fitted the drive belt. Photos to follow tomorrow.



  9. #29
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    Default Re: Emco F3 mill conversion

    I purchased the bolts I needed to finish the Y Axis conversion. This included longer M8 bolts to replace those holding the ballnut to the moving carriage, and stainless mushroom style socket screws that hold the sheet metal panels, and M6 bolts to secure the motor to the motor mounting plate.

    Yesterday I cut 4 spacers from 20mm round bar, on the lathe. I centre drilled them to 8mm so the fastening bolts pass through.

    Here is a photo of the motor with the belt installed - you can see the belt running over the 50T ballscrew pulley.
    Emco F3 mill conversion-imag1842-2-jpg

    Here is a photo showing the mill from the back with the motor installed.

    Attached Thumbnails Attached Thumbnails Emco F3 mill conversion-imag1843-2-jpg  


  10. #30
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    Default Re: Emco F3 mill conversion

    The motor is from Steppers Online and is a closed loop stepper with 4.5Nm torque in a Nema34 frame. This came as a kit with a matching driver.



  11. #31
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    Default Re: Emco F3 mill conversion

    So I got busy with a soldering iron yesterday. I mounted 5 switches and a potentiometer into a plastic case and soldered on flying leads for the arduino. There are two sets of switches: one for fwd/reverse for the Y Axis (and one for fwd/reverse for a future X Axis control) and a stop button laid out in a "+" formation. The potentiometer is the speed controller.

    Tonight I will program the Arduino and mount it in the box and connect to the stepper driver. There are 4 signal wires (2x GND plus direction and pulse) to connect between the arduino/switchbox and the driver.
    In addition, there are 4 motor winding wires and 6 motor feedback wires to connect between the motor and the driver. I will use my 60V 5A bench power supply to provide a temporary power supply for the stepper/driver.

    Fingers crossed I might have some motion in the Y Axis tonight



  12. #32
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    Default Re: Emco F3 mill conversion

    So I connected the motor feedback wires to the driver last night. This cable from the motor was terminated in a 3 row DB15 male connector, much like an old style VGA connector. As the cable is way too short (approx 300mm), I cut off the VGA connector and directly terminated the wires into the 6 way phoenix style connector. I'll need to source some 6 core shielded cable for a longer permanent connection but this works at the moment.

    Anyway it was successful. I can now drive the Y Axis backwards and forwards and control the speed.

    Next up is making mounts for the limit switches and fitting these to the mill and the associated mods to the software.



  13. #33
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    Default Re: Emco F3 mill conversion

    And a small video - if the link works
    https://photos.app.goo.gl/Zd4qtr3n6CbXQztF6



  14. #34
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    Default Re: Emco F3 mill conversion

    So a little more diagnostic and exploratory work tonight.
    With the power supply set to 60VDC I measured 800mA current for traversal of the mill head at 900mm/min. That is when it is not cutting, so more measurements over the weekend to see the current draw when cutting.

    Also the driver unit is marked for setting the 4 DIP switches to set the step resolution.
    Emco F3 mill conversion-screenshot-2018-10-25-22-38-42-a

    However the documentation supplied with the driver is different
    Emco F3 mill conversion-screenshot-2018-10-25-22-40-03-a

    It looks like somebody forgot about zeroes when writing up the doc.

    Also the default setting is not 200 steps per revolution, from the time I measured for traversing 200mm it seemed closer to 400 steps/rev.

    The formula for steps per second is:
    speed (mm/min) / leadscrew pitch (mm) * steps per revolution / seconds per minute

    In this case I have chosen 800 steps per revolution so this becomes
    900 (mm/min) / 4(mm) * 800 (steps/rev) / 60 (secs/min) *2(gearing ratio)
    = 6,000 steps per second

    The Arduino Uno CPU is not capable of driving much above this speed.



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    Default Re: Emco F3 mill conversion

    So I made a limit switch cam and mounted it on the ballscrew adapter today. I also mounted the two limit switches onto the frame. The limit switches are snap action NC micro switches - part #854-1966 from RS Components.
    Still to do is the wiring up of the limit switches to the Arduino and altering the sketch code to ensure the stepper stops when the limit switch opens. Two digital inputs will be required so the motor can still reverse.
    More photos tomorrow.



  16. #36
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    Default Re: Emco F3 mill conversion

    Photo of limit switches and cam
    Emco F3 mill conversion-imag1860-2-jpg



  17. #37
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    Default Re: Emco F3 mill conversion

    Very interesting, thanks for sharing!



  18. #38
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    Default Re: Emco F3 mill conversion

    Just bringing this thread back to life ... I will remake the ball screw / motor bracket using slightly larger angle (50x50x5mm) and simplify the transmission by coupling the motor directly to the floating end of the ballscrew with an oldham coupler.
    But not quite yet

    Having fun with my Emco F3 and Super 11 CD


  19. #39
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    Default Re: Emco F3 mill conversion

    So, I've been rethinking this part of the design and how to simplify/improve it.

    I've got another idea in mind, partly inspired by this photo of a dismantled F3 CNC mill.
    Emco F3 mill conversion-15246474042014490384219182242996-jpg
    In the picture, the large rectangular casting at the top is the moving Y carriage, containing the 4 speed gearbox, spindle, and the spindle motor (attached where the drive belt comes out the side), and showing the acme screw nut in a casting bolted to the rear of the carriage.
    The casting underneath is the main Z axis column of the machine (moving knee design), the fixed end of the acme screw is retained in a recess by back to back 7302B bearings retained by a large flat 42mm diameter nut. The recess also contains a bevel gear that meshes with the Y axis handwheel (that will no longer be required).

    My revised design would replace the acme nut on the carriage with a plate holding the fixed bearing end of a ball screw, and attach the stepper in line via 4 stand offs and couple the shafts with an oldham coupler.
    The ballnut would attach to to the main column via a new attachment plate, and drill out the closed end of the recess to allow the 20mm ballscrew to travel into the recess in the column. Cast iron and a 25mm hole saw ?
    The mounting of the ballnut would need to be spaced off the chassis so the length of the free end of the ballscrew can be accommodated i.e the allowable Y axis travel (~220mm) needs to fit into the column. The current ballnut is 40mm long behind it's flange, so allowing a for a little clearance, that requires ~270mm of free space between the mounting bracket and the inside front face of the column.

    The advantages are that the stepper motor is no longer cantilevered out at the end of the machine's travel and shielding should be easier to fabricate.
    Downsides would be the end of the screw is unsupported, although it is a short screw so unlikely to have issues with whiplash. Also the limit switches will need to be mounted elsewhere than in the current design.

    Anyway that's enough musing - just good to capture the thinking here, which I'll revisit after I've got the other parts of the project working.

    Having fun with my Emco F3 and Super 11 CD


  20. #40
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    Default Re: Emco F3 mill conversion

    So a rough sketch to check that this is even physically possible i.e. will the ballscrew fit in the hollow casting that is the main column ?
    Initial measurements show this has a top thickness of approx 35mm, and the centre of the acme screw is about 50mm from the top. Retaining the existing centre line would mean there is 5mm clearance between the ball screw and the inner surface of the top part of the casting.
    The length of the recess is approx 240mm, so this will fit the amount of the ballscrew travel (220mm) plus a small extension (5mm)

    Here's the sketch, as a vertical section front-to-back, showing the clearances and initial layouts of the various components.
    Emco F3 mill conversion-screenshot-2022-01-22-14-15-02-a

    Having fun with my Emco F3 and Super 11 CD


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Emco F3 mill conversion

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