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  1. #1
    Hello,

    I'm designing a router to make molds, it is I need a lot of precision. (For this kind of work an error of 0.1 mm (0.0039 inches) is an huge error.)

    I did some research in terms of design and have something very much like the photo you posted yesterday ... JAZZ

    The router will have 1200 x 1500 (useful area 900x1200x350)

    I'm using tube 80x40x3, 2

    The CAD software I'm using is Solidworks.

    Would you, please, give me your opinion about the structure?

    Thanks.

    Sorry for my English ...

    -

    __________________
    Sincerely

    CarloSilva

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  2. #2
    For a CNC router it's not difficult to achieve +-0.05mm.

    Your Y and Z axis designs look good.

    I would increase the size of the triangular plates and add some to the other two sides. You could also use diagonal pieces of box section to reinforce the X-axis. If you can add a piece of box section across the back between the X-axis rails that will make it a lot stronger.

    What thickness are the gantry side plates? I'd reccomend 15-20mm aluminium. The X-axis ballnut mounts will be much stronger if you extend them down and mount the ballnut directly to the gantry side. The ballnut mounts are particularly important since any deflection in the ballnut mount directly leads to tool deflection and inaccuracy. You could also add a triangular support between the X-axis bearing block mounts and the gantry sides to help stop that joint bending.

    If you don't mind posting the solidworks model I can open it to have a better look.

    What ballscrews are you intending to use? For that size I would reccomend RM1610 on X and Y and RM1605 for Z with timing belts and pulleys on all of them.

  3. #3
    You will be hard pressed to achieve that accuracy on 10mm pitch screws and gearing down say 2:1 to get resolution will only be the same as running a 5mm pitch direct drive.

    Commercial routers use high lead screws because they are servo driven with at least a 2500 count encoder and running in quadrature that's a resolution of 10,000 pulses per rev
    John S -

  4. #4
    Yes I mentioned pulleys but forgot to say you should gear down 2:1.

    My machine easily obtains better than 0.1mm, often measure with the caliper and find it's within 0.01-0.02mm and that's on 1:1. Assuming the molds are out of wood you're surely not going to be able to measure much less than 0.1mm difference?

    I think using 10mm pitch screws is more versatile since you always have the option for higher feedrates than you could get with 5mm pitch should you need it, at the expense of worse resolution of course.

  5. #5
    Quote Originally Posted by Jonathan View Post
    I think using 10mm pitch screws is more versatile since you always have the option for higher feedrates than you could get with 5mm pitch should you need it, at the expense of worse resolution of course.
    Why does everyone assume you have to travel at warp speed, is it a dick slapping contest ?
    Anyway when you are cutting unless you are doing simple carcase routing where all moves are straight and long the home stepper driven machine can never accelerate to these insane speeds everyone is bandying about.

    Program a part to run at 2000 mm/min then watch the screen and read the actual feed-rates. No way does it get anywhere near this figure because it never get to speed before it has to perform the next line of code.

    Now I could understand 10mm pitch screws if you were on servo's and production work but personally I'd much prefer working more slowly and accurately and get the job done whist the machine is under control, not be boreline running away, especially for a beginner, after all this IS a hobby forum isn't it ?
    John S -

  6. #6
    I tend to mention 10mm pitch on this size machine as the machines I've seen in person with 5mm pitch screws don't seem to run as smoothly as mine or get as high acceleration.

    Quote Originally Posted by John S View Post
    Anyway when you are cutting unless you are doing simple carcase routing where all moves are straight and long the home stepper driven machine can never accelerate to these insane speeds everyone is bandying about.

    Program a part to run at 2000 mm/min then watch the screen and read the actual feed-rates. No way does it get anywhere near this figure because it never get to speed before it has to perform the next line of code.
    With the 3nm steppers on 70V and 10mm pitch my machine on the vast majority of jobs would get to 2000mm/min. I have the acceleration set to 1000mm/s^2 on X and more on Y. So to get from zero to 2000mm/min from zero takes:
    v^2=u^2+2as
    s=(v^2-u^2)/2a
    s=((2/60)^2)-0)/(2*1)
    s=0.000555...

    So for any linear move over 0.55mm it will get to 2m/min speed, or similarly it will maintain 2m/min for any arc above 1.1mm radius. When I cut woods I generally go at around 6m/min, been known to use 8m/min when roughing. High feedrates are especially good with MDF as you can maintain a big enough chipload to make chips, not dust which is bad for you, without lowering the spindle speed to the point where there is not enough power.

    I made the right size pulleys to run my machine on 2:1 for better resolution, but I've never needed to use them.
    Last edited by Jonathan; 05-04-2012 at 12:36 AM. Reason: Mental arithmatic breakdown

  7. #7
    Here we go again?????
    If the nagging gets really bad......Get a bigger shed:naughty:

  8. #8
    Quote Originally Posted by Jonathan View Post
    For a CNC router it's not difficult to achieve +-0.05mm.

    Your Y and Z axis designs look good.

    I would increase the size of the triangular plates and add some to the other two sides. You could also use diagonal pieces of box section to reinforce the X-axis. If you can add a piece of box section across the back between the X-axis rails that will make it a lot stronger.

    What thickness are the gantry side plates? I'd reccomend 15-20mm aluminium. The X-axis ballnut mounts will be much stronger if you extend them down and mount the ballnut directly to the gantry side. The ballnut mounts are particularly important since any deflection in the ballnut mount directly leads to tool deflection and inaccuracy. You could also add a triangular support between the X-axis bearing block mounts and the gantry sides to help stop that joint bending.

    If you don't mind posting the solidworks model I can open it to have a better look.

    What ballscrews are you intending to use? For that size I would reccomend RM1610 on X and Y and RM1605 for Z with timing belts and pulleys on all of them.
    where can I post the solidworks files???

  9. #9
    Quote Originally Posted by C.AlveSilva View Post
    where can I post the solidworks files???
    You should be able to attach them to a post using the advanced view. Same method you used for attaching the original pictures.

  10. #10
    Quote Originally Posted by Jonathan View Post
    You should be able to attach them to a post using the advanced view. Same method you used for attaching the original pictures.
    My Zip file. It's too big "5.76 MB" ...

    I sent an email with all the zip files, but in the meantime I made changes. Can I send again to your e-mail?

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