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  1. #21
    Still making some progress if a bit slow. I've now fettled the column dovetails (they weren't too bad really) and made the same mod to the gib screws as for the X and Y. It all works smoothly now.

    Checked the alignment of the spindle to the column:
    Click image for larger version. 

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    .. found the spindle is parallel to thee column within 2 thou over 8 in. However the head is skewed giving 20 thou variation in 8 in when measured as above. I'll have to separate the two head castings and re-align.

    Russell.

  2. #22
    Russell,
    That last picture, any chance of a shot of the column from the top looking down inside ?
    Mine has the original wet noodle tilting column, only a couple made this way before we designed the fixed column. Unfortunately my fixed column is in customs somewhere.

    Just wondering if the rack groove could be deepened ?
    John S -

  3. #23
    John,
    Picture from top of column:
    Click image for larger version. 

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    Yes the groove could be deepened by up to 10mm bringing the thickness to the same as the rest of the walls. This would enable the ballscrew to move back but the motor still won't clear the pulley on top unless a smaller one is used (I currently have 40T and 20T on the motor).

    BTW the column section on my file "z-axis plan.dxf", see my post about a week ago, is to scale.

    Hmm... it could just fit with a 30T pulley. Would there be any danger of the column distorting if that much is removed? I don't know how well the column has been stress relieved.

    Russell.
    Last edited by russell; 02-07-2012 at 08:30 PM.

  4. #24
    Quote Originally Posted by russell View Post

    Checked the alignment of the spindle to the column:
    . found the spindle is parallel to thee column within 2 thou over 8 in. However the head is skewed giving 20 thou variation in 8 in when measured as above. I'll have to separate the two head castings and re-align.

    Russell.
    Hi Russell
    Thanks for sharing your build, I'm enjoying following it!
    Have you had a chance to address the misalignment yet? I have the same problem but am living with it at the moment. Any experience you can pass on will be gratefully received!
    For powering the z axis I'm a bit embarrassed to admit that so far I've just bunged the motor on instead of the handwheel, there's at least 1.5mm of backlash through the rack and pinion, but the repeatability is pretty good, I just have the clearance plane in cambam set to 3mm.
    Looking forward to the next installment!
    Ian

  5. #25
    At least i will be able to see what I'm faced with, ARC reckon my column has landed at Leicester, need to pop down there anyway.
    However my build will take a while as I have commercial work in the way but I often get a few minutes to work things out.
    John S -

  6. #26
    Quote Originally Posted by ian823478 View Post
    Have you had a chance to address the misalignment yet? I have the same problem but am living with it at the moment. Any experience you can pass on will be gratefully received!
    Yes, not a real problem. I took the head off the column, loosened the four bolts that hold the two parts together but kept them tight enough so that the friction was enough for them not to slip in handling, then put it back on the column. Then tap the head with a hide hammer until the test bar showed no (or little) dial movement when moving the head along the column. It took half a dozen taps and tests to get it right. Took the head off, tightened the bolts and tested again. The misalignment is now just under 2 thou along 8 inches of Z movement.

    Russell.

  7. #27
    Quote Originally Posted by ian823478 View Post
    For powering the z axis I'm a bit embarrassed to admit that so far I've just bunged the motor on instead of the handwheel, there's at least 1.5mm of backlash through the rack and pinion, but the repeatability is pretty good, I just have the clearance plane in cambam set to 3mm.
    Yes, I've seen that done. It depends what you're using the machine for but I would be worried about cutting forces moving the head up and down. How well do you find it works? What material are you cutting?

    Russell.

  8. #28
    Quote Originally Posted by russell View Post
    Yes, I've seen that done. It depends what you're using the machine for but I would be worried about cutting forces moving the head up and down. How well do you find it works? What material are you cutting?

    Russell.
    Hi Russell. It seems to be accurate to at least 0.1mm as far as I can tell, probably nearer 0.05mm. I have a counterweight on the head and the gib reasonably tight.
    I mainly cut aluminium but had a play with some 304SS over the weekend. Here's a couple of pics (if I can work out how to upload them.......)
    Click image for larger version. 

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    Cutting the stainless was painfully slow (10mm/min 1mm DOC with a 2.5mm slot drill) but that was to prevent heat buildup (no coolant and just HSS bits). I've definitely got a lot to learn and loads of tools etc to save up for!
    I'm still on the original leadscrews/nuts and have the DIYCNC system 4 with 3.1Nm steppers driving direct. (I won't get the max from these motors cos the system4 only gives 3A while the motors can take 4A.) I'll probably change this to a 2:1 reduction even if I don't eventually move to ballscrews.
    I'm trying to convince myself I can make a bit of pocket money from it before spending much more!
    Cheers
    Ian

  9. #29
    Why didn't I think of it before?

    If I replace the 70T spindle drive belt with a 60T one the motor moves forwar by 25.5 mm giving enough room behind the motor for a much neater arrangement for driving the Z axis. I have to scrap the plastic belt cover and make a new motor mounting plate supported on pillars but that's no problem.

    Revised Z layout CAD file here ..still provisional of course. I've also changed the stepper motor drive belt from 65 to 75T to enable the motor to drop down behind the column.

    Russell.

  10. #30
    Time for another update:

    I've drilled and tapped the column for the ballnut mounting and also at the back to lower the electronics enclosure to make room for the stepper motor.

    Bolted the column in place and fitted the head to check the alignment of the column:
    Click image for larger version. 

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    The side to side alignment was good at less than 1thou over 8 in. However the front to back alignment was out by 5 thou over the width of the table. I corrected this by fitting shims ( a few layers of kitchen foil) at the front edge of the column mount. OK., I know I should have filed and scraped the mounting pads but fitting shims was easier.

    The end of the ballscrew was turned down and threaded M10 and a mounting plate made:
    Click image for larger version. 

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    I had originally intended to tap the head to take the ballscrew but decided it would be easier to make slight positional adjustments with the mounting plate. The plate is tapped to take the screw and a brass grubscrew was fitted to lock the screw to prevent rotation.

    I had originally intended to use an angular contact ball bearing in the ballnut assembly but couldn't find a suitable one so I used a normal bearing backed up with a needle roller thrust bearing like this:
    ballnut_assy.dfx The spacer is to ensure that the thrust from the thrust bearing is taken on the outer race of the ball bearing.
    Note also that I have threaded the end of the bush and made an adjusting collar (again with a grubscrew to lock it) to allow the preload on the thrust bearings to be adjusted. This isn't very well detailed on the drawing but can be seen in the picture of the parts:
    Click image for larger version. 

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    Finally the parts assembled:
    Click image for larger version. 

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    Just have to make the support now.

    All for now
    Russell.

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