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  1. #11
    That's what we had in mind. But if we put a bit of pvc pipe inbetween the motor and the frame we can just use bolts from the motor into the tapped holes in the frame, which will give it a better structual strength too. Aswel as keeping the motor paralelle with the frame. Which i'm guessing is important to match the shaft from the NEMA to the leadscrews.

    And we have to just be able to use this machine in Uni so maybe some PCB engraving or something that is easy to setup with the software.

    Once that's done we will probably do a destruction test to see what it can ACTUALLY put up with because we're not aloud to sell it as we had the money for it on a grant :(. could have been beer money!! lol

  2. #12
    Quote Originally Posted by Jonathan View Post
    Definitely wasted your money, not possibly. I've mentioned it many times before on this forum, so I wont repeat myself but any machine made with MDF or unsupported rails, let alone both, will be exceptionally weak. Probably fine if you just want to cut PCBs but that's about it. Search on this forum for explanations...

    What do you want to make with the machine?
    Hmmm... I'm not too convinced. I see your point with un-supported rails etc.

    But (and this is where we're going to get a bit geeky with our engineering here lol) the rails are 350mm long and 16.0005mm diameter, we're guessing their toughened steel. Meaning the Transverse loading weight (which would actually have to be made by the machine it's self, unless you are putting something heavy on the machine) would have to be 96kilo's per 100mm to get a flex of <1mm. devided by the 350mm rail length would mean an actuall transverse loading of 27 kilo's from the part that moves back and forth (Y axis?) and even more on the side to side axis as it is only 300mm (32kg-<1mm)

    We couldnt find any stats on the density of the HDPE frame it's self that we have.
    But the way the machine is setup, from what we can see all the "shear" strength is taken by the rails.

    Given that the distance between the rails on the weakest part of the machine, the side to side (it's the weakest as the most energy is being put there when in motion and cutting) is 80mm, and the risen height from the bed (the place where the force is generated) is 100mm, theres a good ratio for ultimate strength.

    It hasn't been used yet, but a simple (by pushing it with an arm) the uniaxial compression from the top right of the machine on a 45 degree angle is pretty solid with no flex up until about 15 kilos.
    If i could remember the formular to workout what kind of force in kg that would be at the cutting edge then i would let you know.

    We only have to PCB engrave with it ayway, so by rights a machine made from cardboard would probably be strong enough lol.

  3. #13
    what about the affect of the cutter on the rails have you taken this into your equation ??
    plus the stop and start force of the x & Y axis.You have by the looks of it already made your mind up about this machine.

    but like Jonathan has already said you have wasted your money.

    James

  4. #14
    Quote Originally Posted by Jonathan View Post
    Definitely wasted your money, not possibly. I've mentioned it many times before on this forum, so I wont repeat myself but any machine made with MDF or unsupported rails, let alone both, will be exceptionally weak. Probably fine if you just want to cut PCBs but that's about it. Search on this forum for explanations...

    What do you want to make with the machine?
    Listen to him because he's absolutly correct. . . . . All you have there is poor fired wood and cheap metal to poke the fire with.!!

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