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  1. #11
    Hi Michael,


    You should be able to zip them and then upload them. For example . . .
    Attached Files Attached Files
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #12
    Quote Originally Posted by m.marino View Post
    Build is going well and looking at adding a rotary table as a fourth axis. Anyone got experience in converting one from manual to CNC? If so what motor is most likely best to do this with. Looking at either a 4" or 6" diameter table. Any and all input would be seriously appreciated. Also looking at converting to ball-screws for all axis' as well and thinking that 12mm would do my well for that.
    I just started writing a reply to this then realised that I'm a bit too late. Nevermind I'll say a little anyway...

    I converted a 6" vertex rotary table to use as a 4th axis. It was easy enough to machine a bit of 3" aluminium bar to fit on where the handle/dial used to and hold the stepper. It's very sturdy, however the 90:1 ratio makes it a bit slow to turn. I think the stepper has worn the worm drive prematurely since the backlash has increased a lot from new.

    A while ago I started making a faster 4th axis which I've posted about elsewhere in the forum. That's using tapered roller bearings and will be driven by a stepper via a belt, so will be faster and also strong.

  3. #13
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    Quote Originally Posted by Jonathan View Post
    I converted a 6" vertex rotary table to use as a 4th axis. It was easy enough to machine a bit of 3" aluminium bar to fit on where the handle/dial used to and hold the stepper. It's very sturdy, however the 90:1 ratio makes it a bit slow to turn. I think the stepper has worn the worm drive prematurely since the backlash has increased a lot from new.
    In standard form, vertex rotabs have the worm/handle on an eccentric so you can engage/disenage the worm and also adjust backlash...

  4. #14
    Quote Originally Posted by m_c View Post
    In standard form, vertex rotabs have the worm/handle on an eccentric so you can engage/disenage the worm and also adjust backlash...
    Yes, the way I converted mine means it still does...however I've tried that and I think the worm gear might be too far gone for that to help.

  5. #15
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    Quote Originally Posted by Jonathan View Post
    Yes, the way I converted mine means it still does...however I've tried that and I think the worm gear might be too far gone for that to help.
    Take it apart and check it. The worm wheel is just cast iron bolted onto the underside, which i discovered after removing several teeth while machining a bit 1/2" thick steel into a 12" round :-/
    Someday, once I've got the mill converted, I'll get it converted into a 4th axis.

  6. m_c,

    I am in Edinburgh. You are more than welcome to contact me and come over to look at the shop.


    Michael

  7. Well been getting some good cutting going (enough to require maintenance duty on the machine beyond normal clean up after a days work) and looking to do some upgrade work on the Wee Beastie.

    Looking for input on the best method for upgrading to Ballscrews and also raising the Z axis while keeping the rigidity up (if not increasing it). I am looking at either Alli' plate or extrusions and would like input there on the Y/Z axis unit (going to raising to 100-125 mm travel to allow the addition of an A-axis to the unit [already have the unit]).

    On the Ballscrew front what I am interested in information wise is input on how best to convert the unit I have (a Merchant Dice TR model) to Ballscrews. I have been looking at Zap and a few others and would like in put on the best method for setting up the bearings for the ballscrews and if it would be wise/possible to upgrade to 20mm ballscrew from the 16mm trapezoid screw that is currently there (this is on the X axis, on the Y and Z I plan to upgrade to increase rigidity a bit).

    Still cutting and business is improving so things going well. Hope everyone else is having a great day and take care.

    Michael

  8. #18
    Quote Originally Posted by m.marino View Post
    Looking for input on ... raising the Z axis while keeping the rigidity up (if not increasing it). I am looking at either Alli' plate or extrusions and would like input there on the Y/Z axis unit (going to raising to 100-125 mm travel to allow the addition of an A-axis to the unit [already have the unit]).
    Just make it as strong as you can. Extrusion is great if you can afford it. Plate is the worst solution in terms of bending for the gantry sides. Aluminum or steel channel or box section will be much stronger with forces parellel to the Y axis for the same mass. Irving posted an excellent spreadsheet about it somewhere...

    I would be inclined to increase the distance between the bearings on the X axis. This will of course loose travel but it may be neccarcy to keep it rigid.

    You could consider just simply raising the Y/Z axis to fit the A axis and leaving the Z axis with the same travel. That way you will only have the bending of taller gantry sides to worry about. When you don't want to use the A axis drop it down again. The slots in the aluminium extrusion make this easy to do and you could put a block of aluminum on either gantry side at the current height to locate the gantry so you don't have to get it level every time.

    Quote Originally Posted by m.marino View Post
    I have been looking at Zap and a few others and would like in put on the best method for setting up the bearings for the ballscrews and if it would be wise/possible to upgrade to 20mm ballscrew from the 16mm trapezoid screw that is currently there (this is on the X axis, on the Y and Z I plan to upgrade to increase rigidity a bit).
    The eBay seller linearmotionbearings2008 is much much cheaper than Zap. They will cut the screws to length and machine them. I've ordered a few times from them and not had any problems.

    The diameter of the ballscrew required depends on the length, and end fixity. I would put a double row angular contact bearing (or a pair of single row) at one end and a standard deep groove bearing at the other. The best way is to have angular contact bearings at both ends, however the critical speed of a 16mm screw, 400mm long (just guessing the size, correct me if I'm wrong) with the above bearings is around 10,000rpm - so plenty! I'm using a 550mm (ish) 16mm ballscrew on my Z-axis and it happily went at 10,000mm/min - it's limited by the motor torque.

    Since the critical speed for a 16mm ballscrew is so high there's not really much point using a 20mm screw. You're not going to exceed the load ratings of the 16mm either. Also if you had a 20mm screw the inertia is much greater (the effect is proportional to the diameter of the screw to the power 4), so your acceleration will suffer. The same is true with changing from 12mm to 16mm screws, however ballscrews are much more efficient than trapezoidal screws so you'll end up fine. Thinking about it it's not really an issue since the screws you have currently are 3mm pitch (I think?), which will have to turn faster than a 5mm pitch ballscrew ... so etc... (I think I've written enough!)
    Last edited by Jonathan; 08-06-2011 at 12:27 PM.

  9. Thanks Jonathan,

    Definitely some things to think on and thanks for the additional resource.

    Michael

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