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  1. #1
    Hi, this is my first post on this site (other than new members intro ) and am not quite sure where to post!!!

    I have a very solid cnc router converted from a pcb drill router. the Z axis is very robust, using a vertical roller bearing slide on each side.

    As the machine was not intended for the input of various Z depths it does not have a Z leadscrew, but the axis servo drives a horizontal shaft with a crank and conrod arrangement to drive the Z slide (Ihope that makes sense).

    I intend to try to convert the Z axis to ballscrew. At present there is a 24mm hole from top to bottom of the Z slide which houses a spring to help lift the slide on the up stroke. I would like to fit a ball screw through the spring hole, but there is only about 2mm from the back ot the hole to the edge of the slide.

    The ideal solution would be to find a ballnut that would fit into the 24mm hole. I think it would be possible to to bore out the top 50mm of the slide to accomodate a nut up to 28mm diameter if the nut flanges did not exceed 28mm. I think it would also be possible to mount the ballscrew offcentre (within the 24mm hole) to permit a larger diameter screw if neccessary.

    As the Z stroke will only be about 50mm (total slide length is 205mm) would it be practical to use a fixed bearing at the bottom end (of the static section of the Z axis assembly), the ball nut fixed to the top of the slide, and do away with the top bearing (ie using the ball nut as the top bearing)? Would the Z axis with spindle be too heavy or would I need to incorporate a "helper" spring to lift the axis. Any thoughts would be much appreciated.
    Regards, Geoff.
    Last edited by GEOFFREY; 06-12-2012 at 06:41 PM. Reason: for clarification of the bottom bearing location

  2. #2
    Welcome to the site Geoff.

    Think it would be worth your while editing your post into paragraphs, as many folk (well me at least) may find it that difficult to follow that they the wouldn't be bothered to read it.


  3. #3
    Hi Andy,

    Thanks for your comments.

    I have just edited my post into paragraphs, Hope it helps.

    Regards, Geoff.

  4. #4
    That makes a world of difference Geoff! Sure someone will pop along to help as I'm afraid I don't have the correct know-how ... But can now follow your query.

    Sorry, I should probably have sent a PM instead of advising formatting by post.

    Maybe the mods can remove our few "formatting" posts from the thread to give better focus to your query?

  5. The Following User Says Thank You to WandrinAndy For This Useful Post:

  6. #5
    Geoff, anythings possible with a bit of imagination. I must admit I'm struggling to visualise exactly what you're they say a picture paints a thousand words, can you take some photos of your machine? Then I'm sure you'll get some of the old hands (figuratively speaking in some cases) chipping in :)


  7. #6
    Hi Neil, thanks for your reply. Trouble is I have not yet worked out how to post pictures!!! I'll get the wife to have a go.

    Regards, Geoff.

  8. #7
    this forum is acctually quite easy to post pictures to, there is a button above the quick reply box, it's the 3rd button after the smiley face, when you hover over it, is says insert picture, click it then you will see 2 tabs, one says from computer the other from URL, if you picture is stored on your computer click from computer, then select files, then search for the picture as you would, t's likely the picture is in my pictures, on on your camera if thats plugged in to your computer.

    then when you have found said picture, double click on the file name, and hen in next window click upload files and it will automatically place the picture at the end of your last piece of text
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	aauk.jpg 
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  9. #8
    Here's a rule of thumb:- A 1Nm motor on to a 5mm pitch ballscrew will lift one fat bloke off the floor.

    Assuming 1 fat bloke = 282 lbs

    Substitute a 0.5Nm motor or a 10mm pitch screw and you can only lift half a fat bloke. The maths is easy.

    Wide ball screws are used where you need long travel or massive power.

    You don't need either so a skinny ballscrew and dinky motor will be fine and dandy.

  10. #9
    Thanks Wilfy, willtake some pics tomorrow and ive it a try.Regards,Geoff.

  11. #10
    Thankyou Robin, I see what you mean, I don't suppose I need more than a fat mans leg.

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