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  1. #21
    With a short a travel required on the Z axis I followed some advice on here and virtually did away with the gantry sides and mounted rails on top of a pair of 6x2" box sections which resulted in a very solid gantry with little effort.
    http://www.mycncuk.com/attachment.ph...7&d=1461873328

  2. #22
    updated Z Axis
    Click image for larger version. 

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  3. #23
    Quote Originally Posted by lucan07 View Post
    With a short a travel required on the Z axis I followed some advice on here and virtually did away with the gantry sides and mounted rails on top of a pair of 6x2" box sections which resulted in a very solid gantry with little effort.
    http://www.mycncuk.com/attachment.ph...7&d=1461873328
    ok, will check that.. i was drawing while you post that :)

    Its your machine? Looks an strong and nice design because dont weld anyhing, wich is the post? is your machine?
    Last edited by samsagaz; 07-06-2016 at 07:31 PM.

  4. #24
    Quote Originally Posted by samsagaz View Post
    updated Z Axis
    Click image for larger version. 

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    Can you see the red rail blocks how are you going to drill the mounting holes they appear to be in the edge of the steel
    ..Clive
    The more you know, The better you know, How little you know

  5. #25
    Samgaz:

    Channel isn't very stiff and certainly not flat. Welding in braces etc will cause heat and twist etc. So unless you intend machining the Gantry flat and true then I'd suggets you look at better materials that won't need stiffening by welding.

    Your Z axis idea with Channel is disaster waiting to bite you. Like Clive mentions the practical side of bolting etc means it won't work but again Channel just isn't flat enough or good enough. Z axis IS THE MOST IMPORTANT part of the machine.

    25mm ballscrews are too large for machine this size and will actually lower the performance and increase the costs in ways you haven't realised yet.
    The extra interia of the Screw and Ballnut means you'll need motors with higher torque. This will mean using Nema 34 Motors.
    Nema 34 motors spin much slower than smaller nema 23 motors for the same amount of voltage. So this means you need higher voltage to get the same or similar RPM.
    In practise this means using drives which offer much higher voltage capabilty. While 60-70Vdc will be fine for nema 23 it will cripple performance of nema 34 and the Larger the motor size the worse it will get. So often larger Nema 34 Motors use drives that run at mains voltage levels.

    If you try to run tham at same voltage would nema 23 then your RPM will be so slow the machine is crippled.

    NorgMonster: This also applies to you and it's the only comment for you I'm making on this thread so start your own if haven't already.

    It's common mistake that Bigger is better and offers upgradabilty. It DOESNT. What it does is Cost more and lowers performance.
    Nema 23 motor matched with correct size and Pitch ballscrew run with correct voltage on decent quality drive will run rings around and cost much less than Nema 34 motor running on wrong voltage and connected to large ballscrew.

    In your case Norgmonster with R&P then you'll probably need nema 34 motors because of the much lower efficiency of R&P. But again if you don't correctly size and match components then peformance will suffer and money will be wasted.
    R&P machine requires careful thought towards pinion size and Reduction ratio used along with Motor/Drive/voltage selection.

    Both of you are going about this all wrong and you will Both end up wasting money, time and probably resutling in less than great machine unless you STOP buying without knowing what's required and Design the machine before starting. Fag packet drawings while ok for some things just make this CNC building a disater waiting to happen unless you have plenty of experience which you two clearly don't.!!

    Stop, take Step back look and learn then design. Then look again before buying any thing.!! . . . If in doubt ask.!!

  6. #26
    Yes i understand you, i can move a 10mm to the center each rail and can drill it without problem. Z Axis UPN are 21cm width, so have some space to drill the holes.

    Quote Originally Posted by Clive S View Post
    Can you see the red rail blocks how are you going to drill the mounting holes they appear to be in the edge of the steel

  7. #27
    Quote Originally Posted by samsagaz View Post
    ok, will check that.. i was drawing while you post that :)

    Its your machine? Looks an strong and nice design because dont weld anyhing, wich is the post? is your machine?
    It did turn out a strong build and have been happy with rigidity and weight so far a few things I would change if starting again, hindsights a wonderful thing, but as I have no previous experience in any sort of metal work apart from bolting some lightweight frames together a lot of the changes would be things learned during the build.
    http://www.mycncuk.com/threads/9678-...-Framed-Router

  8. #28
    Quote Originally Posted by JAZZCNC View Post
    Samgaz:

    Channel isn't very stiff and certainly not flat. Welding in braces etc will cause heat and twist etc. So unless you intend machining the Gantry flat and true then I'd suggets you look at better materials that won't need stiffening by welding.

    Your Z axis idea with Channel is disaster waiting to bite you. Like Clive mentions the practical side of bolting etc means it won't work but again Channel just isn't flat enough or good enough. Z axis IS THE MOST IMPORTANT part of the machine.

    25mm ballscrews are too large for machine this size and will actually lower the performance and increase the costs in ways you haven't realised yet.
    The extra interia of the Screw and Ballnut means you'll need motors with higher torque. This will mean using Nema 34 Motors.
    Nema 34 motors spin much slower than smaller nema 23 motors for the same amount of voltage. So this means you need higher voltage to get the same or similar RPM.
    In practise this means using drives which offer much higher voltage capabilty. While 60-70Vdc will be fine for nema 23 it will cripple performance of nema 34 and the Larger the motor size the worse it will get. So often larger Nema 34 Motors use drives that run at mains voltage levels.

    If you try to run tham at same voltage would nema 23 then your RPM will be so slow the machine is crippled.

    NorgMonster: This also applies to you and it's the only comment for you I'm making on this thread so start your own if haven't already.

    It's common mistake that Bigger is better and offers upgradabilty. It DOESNT. What it does is Cost more and lowers performance.
    Nema 23 motor matched with correct size and Pitch ballscrew run with correct voltage on decent quality drive will run rings around and cost much less than Nema 34 motor running on wrong voltage and connected to large ballscrew.

    In your case Norgmonster with R&P then you'll probably need nema 34 motors because of the much lower efficiency of R&P. But again if you don't correctly size and match components then peformance will suffer and money will be wasted.
    R&P machine requires careful thought towards pinion size and Reduction ratio used along with Motor/Drive/voltage selection.

    Both of you are going about this all wrong and you will Both end up wasting money, time and probably resutling in less than great machine unless you STOP buying without knowing what's required and Design the machine before starting. Fag packet drawings while ok for some things just make this CNC building a disater waiting to happen unless you have plenty of experience which you two clearly don't.!!

    Stop, take Step back look and learn then design. Then look again before buying any thing.!! . . . If in doubt ask.!!
    Thanks for take time to write so much! Really appreciate your words/help.

    I Already have nema 23 motors and drivers :/ im 99% sure that they support some high voltaje. I already made the mistake that purchase a lot of stuff a few years ago, will try to make it better now and follow your advices before waste more money :/

    Maybe copy the design from other guys?

    I really want to use some of the pieces that already have, but if not possible is OK, i want an stiff machine, dont want tooo much precision, but of course if more precise better.

  9. #29
    Samsagas
    Do as instructed by jazz, take some time to read the build logs all the way through, then read them again. the forum contains priceless knowledge you just have ingest it.
    Good luck
    Mike

  10. #30
    Quote Originally Posted by samsagaz View Post
    I Already have nema 23 motors and drivers :/ im 99% sure that they support some high voltaje. I already made the mistake that purchase a lot of stuff a few years ago, will try to make it better now and follow your advices before waste more money :/
    I'd doubt they'll be more than 80Vdc drives. Which means Max voltage you'll be able to run motors is 70-75Vdc and that's not enough for large nema 34 motor. Your motors are nema 23 which for 25mm ballscrew are not strong enough. I'd also wager if bought from Ebay/china they are high inductance motors which lowers performance.


    Quote Originally Posted by samsagaz View Post
    i want an stiff machine, dont want tooo much precision, but of course if more precise better.
    Well if you want real stiffness and precision then dispite what's been said by Lucan07 then I suggest you forget using round rail and buy some profiled linear rails. It's ok for router but when comes to stiffness and precision it sucks compared to Profiled rails and don't let anyone tell you different.
    Last edited by JAZZCNC; 07-06-2016 at 08:18 PM.

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