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  1. #1
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    Emco F3 mill conversion X Axis

    I thought I'd start another thread for the X Axis conversion part of this project.

    Last night I removed the chip collection trays and cleaned all the loose chips lodged underneath. Next up I removed the sliding curtains that shield the X Axis ways and lead screw from debris. This enabled me to access the adjustment nut that compresses the bronze split nut that runs on the lead screw. I'd noticed quite a bit of backlash in the X axis so tightened this up to see how much backlash could be removed and whether I could use the existing 3mm pitch Acme leadscrew, or if a new screw and nut was required.

    The best adjustment I could get still had about 0.06mm of backlash - if I tightened the nut any more the friction was excessive, and most likely would lead to excessive wear on the screw and nut.
    So further disassembly is required to see how a replacement screw and nut can be fitted.

  2. #2
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    Re: Emco F3 mill conversion X Axis

    The Emco F3 has a removable table that is secured in two T slots that run along the face of the X Axis carriage. This allows the table to be removed and larger items fixed directly to the carriage for machining.

    So I loosened the four bolts that hold the table to the X axis carriage and set that aside, this is approx 30kg. I then removed the existing X Axis drive motor and the glass scales for the DRO.

    The handwheel at the right end of carriage has two cap screws holding the bearing so I removed these, removed the nut securing the handwheel and removed the assembly.

    Because the existing screw and nut have to be replaced, I need to remove the X Axis carriage. I carefully moved this to the end of the travel and dismounted it. This is a large lump of cast iron, 660mm long and approx 50kg, and has a gib adjuster at each end. I made sure to catch the spring and follower for each gib.

    With the table and carriage out of the way I could tap out the existing screw and nut assembly and takes some measurements to see what can be fitted.

    Photos and options for automation to follow later.

  3. #3
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    Re: Emco F3 mill conversion X Axis

    Here's a photo of the existing ballscrew and nut and threaded retainer/adjuster collar.
    Attachment 405042

    This is a photo of the mount for the carriage, show the ways and the 25mm bore for the leadscrew/nut. Note the nice factory installed oil grooves. Quality Austrian engineering here.
    Attachment 405092

    This bore through the carriage is enlarged at the end for the nut to 33mm diameter and approx 58mm deep. There is an internal thread to engage with the retention collar.. The casting slides up and down the Z Axis to provide the third axis of travel. The two dome fasteners provide quick release for the sliding curtains.
    Attachment 405094

    The final photo shows a front on view of the Z carriage/X mount.
    Click image for larger version. 

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  4. #4
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    Re: Emco F3 mill conversion X Axis

    Options for replacing the leadscrew with a ballscrew fall into several categories:
    - Mount a ballnut to replace the existing ACME nut and support the ends of the ballscrew at each end of the X axis carriage. The fixed end will be on the left where the existing motor is (replaced with a stepper) and the supported end will be where the handwheel was (no longer required). This closely follows the existing mechanical setup but the limitation will be the size of the ballnut that can be fitted within the existing 33mm bore (from initial investigation a 16mm ballscrew)
    - As above but get the ballnut recess enlarged to take a larger screw. Initial research shows 36mm is required for a 20mm ballscrew. This requires more disassembly of the mill and external machining.
    - Mount a 20mm ballnut externally at one end of the bore. This will restrict X axis travel by the length of the nut but does not require any further machining.
    - Mount the fixed end of the ballscrew using the existing recess for the acme nut, fabricate a bracket to fasten the ballnut to the carriage and drive the supported end. This will require a support structure and will stick out from the side of the machine even when the table is at the opposite end of travel.
    - As per option 2 but leave the non driven end of the ballscrew unsupported. I'll need to check that the critical speed of the ballscrew is not exceeded.

    C7 20mm ballscrews with 5mm pitch require a 36mm diam x 32mm deep recess in the bore.

  5. #5
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    Re: Emco F3 mill conversion X Axis

    The existing folding curtains that cover and protect the screw and X axis ways, concertina as the carriage moves from side to side. When fully collapsed they are approx 28mm thick. Although the X carriage and table are 660mm long, and the mount is 300, there is only 300mm travel in the X direction due to the curtains. As I will need to fabricate new carriage ends (with the motor support at the left and a blanked off plate at the right) I can alter the design so the fully compressed curtain does not restrict the travel. This way I can increase the X axis travel to 350+ mm. Another nice bonus.

    Time to do some design work tonight.

  6. #6
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    Re: Emco F3 mill conversion X Axis

    So, a classic chicken and egg situation. I need a working mill to bore out the carriage mount for the new ballscrew. But the piece I need to machine is part of the mill :devious:

    I could either send it out for machining, or I could make a temporary worktable that clamps to the z axis ways and secures the work piece, and use the boring head to make the required modification.

  7. #7
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    Re: Emco F3 mill conversion X Axis

    So a couple of photos while I'm pondering that earlier question:
    1. waiting for a quote from a local machine shop vs
    2. reassembling the machine, building a temporary fixture, disassembling the machine, machining the part, and reassembling the machine, and having a beer because I've earned it

    The first photo shows the shielding curtain for the X axis from the visible (exterior) side.
    Attachment 405118

    The second shows the other side of the curtain and how the pleats hook into the dovetail of the ways
    Click image for larger version. 

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  8. #8
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    Re: Emco F3 mill conversion X Axis

    I decided to mount the new 2005 ballscrew using a variation of option 2 above. The left hand end of the X axis carriage will need a new plate fabricated to hold the BK15 bearing mount, the NEMA34 motor, and the way cover. The 25mm bore running through the Z carriage/ X mount will be enlarged at the left end to 36mm diam for a depth of approx 42mm to house the ballnut. The right end of this bore is unmodified from the original in case anybody ever wants to revert this to a manual machine.
    The right end of the screw is unsupported. I ordered a 500mm screw but will cut it slightly shorter as the max travel is 360mm with another 60mm for the fixed end.

    The screw has been ordered and was shipped within 6 hours .
    Next up is removing the part from the mill and getting a local machine shop to make the modification.

  9. #9
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    Re: Emco F3 mill conversion X Axis

    After calling several local machine shops it seems that most are very busy (6 week lead times) or don't want one-off jobbing work. The best I could do was to drop it off at shop that is not located very conveniently to see if someone would do it in their lunch break.
    So back to plan A, which is to fabricate a fixture so I can mill part of the mill - on the mill.
    More tomorrow - with photos

  10. #10
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    Re: Emco F3 mill conversion X Axis

    My approach was to build 2 temporary fixtures to clamp to the Z Axis dovetail ways. These are used to locate and support the mill part that needs machining. The key challenge is how to clamp to the dovetail ways securely without damaging them but securely enough so the machining operation is stable and the workpiece is securely held.

    After a bit of doodling this is what I came up with
    Attachment 405368

    A scrap of approx 18mm diameter round bar has a flat machined onto one side. This will rest against the angled part of the dovetail. To form the support 2 pieces of 12mm thick flat bar will clamp across the dovetail. They have a groove milled near to one end and the rounded side of the bar rests in the groove. A 16mm threaded rod is used to pull the support pieces together across the dovetail. The clamping forces ensures the support pieces are pulled to the base of the dovetail thus aligning them, and providing enough friction to keep the fixture in place.

  11. #11
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    Re: Emco F3 mill conversion X Axis

    Here's some photos of fitting the two fixture brackets to the Z axis dovetail.

    This is the lower fixture that the part will rest on, with the angle plate to provide support and the correct spacing from the reference face of the Z Axis
    Attachment 405370Attachment 405372

    This is the upper fixture to provide support for milling
    Attachment 405374

    The table and X Axis dovetail / Z Axis carriage was removed after these parts were mounted.

  12. #12
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    Re: Emco F3 mill conversion X Axis

    Here's the part to be machined mounted and positioned correctly on the fixture brackets. I had to carefully align it in the X Axis direction, but could use the mills head to get the Y Axis dialed in.
    Attachment 405376

    Here are two side views showing how the fixture brackets work to hold and align the work piece.
    Attachment 405378Attachment 405380

    And a final one showing the boring head ready to go.
    Attachment 405382

    That's the 25mm existing bore in the last photo. The quill has 45mm of travel but the boring bar I'm using is limited to 36mm of depth. That's more than enough for the ballnut (approx 32mm required).

    And about 45 minutes later ... here's the bore enlarged to 36.05mm
    Click image for larger version. 

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  13. #13
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    Re: Emco F3 mill conversion X Axis

    I'll post some photos of the brackets once I have finished the milling (still have the holes for the 4x M6 ballnut mounting screws to drill).

  14. #14
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    Re: Emco F3 mill conversion X Axis

    Found a good online bolt circle diameter calculator at the Theoretical Machinist website. Here's the x,y offsets for the 6 mounting holes (holes 3&7 not required)
    Attachment 405444

  15. #15
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    Re: Emco F3 mill conversion X Axis

    The stepper motor and driver arrived yesterday. This is from Steppers Online and is a NEMA34 size closed loop motor/driver rated at 8.5Nm holding torque.
    I measured the hole layouts for the existing X axis carriage endplates and have plotted those into QCAD.
    Next up is designing the replacement endplates (left end has the motor mount, right end is blank) and detail design for the ballscrew bearing support / motor mount.

  16. #16
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    Re: Emco F3 mill conversion X Axis

    While I've got the Z Axis carriage dismounted from the machine I will replace the bracket that holds the ball joint at the top of the Z Axis gas strut. This was offset as I just used existing holes and the angle bracket supplied with the strut. The centre of the lower mount is 40mm from the left of the column, and 75mm from the reference face. As the ball joint bolt has a 15mm offset from the centre of the strut, the mounting point needs to be X=40 and Y=60mm.
    I can either use the existing holes in the carriage and fabricate a new bracket, or use the existing bracket and drill new holes.

  17. #17
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    Re: Emco F3 mill conversion X Axis

    The ballscrew arrived today. Here's a photo of the ballnut/ballscrew sitting inside the milled recess. Holes for mounting screws yet to be drilled.
    Attachment 405862

  18. #18
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    Re: Emco F3 mill conversion X Axis

    Here's a couple of photos showing how the clamps that gripped the dovetail ways work.
    This one from the outside of the clamp
    Attachment 406132
    And this one from the front/inside of the clamp
    Attachment 406134
    The round bars were the cutters from an old pasta cutter that I had dismantled - thinking the steel would be handy one day

  19. #19
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    Re: Emco F3 mill conversion X Axis

    Started reassembly of the mill. Here's the Z carriage remounted, showing the tapped M6 holes for the X axis ballnut.
    Attachment 406242

  20. #20
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    Re: Emco F3 mill conversion X Axis

    I've got the mill back together but have run out of project time for this year, with family coming from overseas for Xmas I need to move onto some domestic projects. Watch out for updates in 2019

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