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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > Scrapheap Challenge, cost-effective alu/steel CNC mill
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  1. #61
    Join Date
    Nov 2013
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    5408

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi,
    try searching for a 'rotary coupling' or 'rotary union'.

    'Sensibly priced' is highly subjective.

    Craig

  2. #62
    Join Date
    Oct 2024
    Posts
    25

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi Craig, I could be mistaken but I don't think the cylinder needs to be able to rotate with the shaft necessarily? Basically the drawbar has a cutout in the spindle shaft where the stock setup passes a pin and a sleeve that needs to be pressed down to release the drawbar. The sleeve and pin would need to rotate with the shaft but as long as said release mechanism has a spring return or something with clearance that "stays out of the way" while the spindle is at >0 rpm, it doesn't necessarily have to rotate with the shaft I think? Not a lot of room either way, since there would need to be a flexible coupling of some sort at the top of that shaft in the picture to connect to the servo output shaft.

  3. #63
    Join Date
    Nov 2013
    Posts
    5408

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi,
    most empathically the cylinder does not rotate, its not even close to balanced. The cylinder must remain stationary, and yes the piston must retract so that the actuator shaft (of the piston) does not bear down
    on the drawbar while the spindle is operating.


    My new spindle has a double acting piston, or actually three pistons in series if the truth be known. When the cylinder is active the pistons bear down on the drawbar to release the tool. When the cylinder is inactive
    the pneumatics are such that the pistons withdraw and thereby leave a mm or two clearance between the shaft and the drawbar.

    I your case with a direct coupled servo either the shaft of the servo needs be hollow that the ATC piston actuator shaft can pass through the centre of the servo, OR, the ATC cylinder must have a bore though the centre.
    Neither sound likely to be available.

    The only other way I can think of is to have two cylinders parallel but symetrically displaced from the centre line of the spindle with the drive passing through the center of a yoke between the two cylinders. The yoke would bear down on the
    draw bar.

    Craig

  4. #64
    Join Date
    Oct 2024
    Posts
    25

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Yeah, doubt hollow servo motors are a thing. Hollow/through bore pneumatic cylinders are actually a thing, although many options are too bulky and/or expensive. Mack Corp in the US makes some that would at least roughly fit the bill (see attachment). Main issue is that they seem to be a fairly bespoke part so probably won't find one with the right dimensions second hand on ebay. Did also arrive at the plan B of somehow pushing down from two sides.

  5. #65
    Join Date
    Oct 2024
    Posts
    25

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Bit of a plot twist, I was procrastinating pretty hard on the frame design. Then my eyes fell on an old shaper for sale and one thing led to another...

    I only plan to use the base and the main frame of the shaper. As a bonus there are already some rough X Y Z reference surfaces, although there is a decent amount of wear in places of course.
    Attached Thumbnails Attached Thumbnails varnamo_before.jpg   varnamo_after.jpg  

  6. #66
    Join Date
    Nov 2013
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    5408

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi,
    its bloody hard to beat old cast iron like that. Its as tough as hell, stable and rigid.

    I would not concern yourself with the wear in the beds, what the bet it is only half-a-thou or so anyway. Get your machine working and then maybe consider scraping the ways flat.
    To make it perfect paint it pink with little flowers on it!

    Craig

  7. #67
    Join Date
    Oct 2024
    Posts
    25

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Some drafting of a Mori CMX inspired design. The corner posts are just for guesstimating an enclosure footprint.
    Attached Thumbnails Attached Thumbnails Varnamo_drafting_1.PNG  

  8. #68
    Join Date
    Nov 2013
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    5408

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi,
    looks good, could only improve by being pink!

    Craig

  9. #69
    Join Date
    Jul 2018
    Posts
    6841

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi ook - Its looking good but be careful with the webs on the bed, they can vibrate. If you can do FEA have a look at modal analysis this will identify vibration modes. Peter
    Attached Thumbnails Attached Thumbnails webs.jpg  

  10. #70
    Join Date
    Oct 2024
    Posts
    25

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Quote Originally Posted by peteeng View Post
    Hi ook - Its looking good but be careful with the webs on the bed, they can vibrate. If you can do FEA have a look at modal analysis this will identify vibration modes. Peter
    Hi Pete, I ended up taking a shortcut on the mill table, a big cast iron right angle milling fixture came up on Facebook Marketplace and I couldn't resist it. Dimensions aren't perfect for what I want (about 600x240mm work area, 300mm height on the mounting surface) but it should save me a lot of work making something similar out of plate steel.

  11. #71
    Join Date
    Nov 2013
    Posts
    5408

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Hi,
    no matter whether it's made of steel or cast iron, the Tee-slots are the key to versatile work holding.

    Many people end up with a flat table but no real way to attach vises or workpieces except maybe a network of threaded holes....'useless as tits on a bull'.

    Craig

  12. #72
    Join Date
    May 2025
    Posts
    1

    Re: Scrapheap Challenge, cost-effective alu/steel CNC mill

    Matara UK have a lot of blogs that are informational that i find really helpful. they specialise in Linear motion and pneumatics. I recommend you have a look - https://www.matara.com/

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