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  1. #1
    Hello everyone. I am here completely new, but thinking of building a cnc for a while. I had built small router from mdf sheet and drawer slides, so now i want to go for more accuracy.. :)

    My aim is to build a machine with this working area: x1500 y1000 and z20 or 30. Not really sure about the Z. As I am now in a early designing stage all the advices are really apreciated. Main frame is going to be from 80/40 and 40/40 aluminium profiles. It will be used for wood cutting, plastic, mdf sheets and similar materials. Thinking about chinese 1605 ballscrews which I see are quite widely used, rails and blocks will be 15mm hiwin. Spindle is going to be water cooled 1.5kW or 2.2kW . Steppers nema 23.

    My big question for now is from which width should be used two ballscrews on the longest axis instead of one ballscrew in the middle? I am worried about it can start to wiggle a bit, which off course will affect accuracy. All the sizes of ballscrews, rails steppers and spindle are still considered, it is not my final decision. I found on internet a cnc with the same structure as I am thinking to build, so now you have rough vision what I am speaking about :) Thank you very much!!
    Click image for larger version. 

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  2. #2
    Hi and welcome to the forum!!

    for the size of machine you're looking to build then twin ballscrews are a must, at 1000mm wide cutting (at least 1300mm wide gantry) you'll get racking when cutting off centre with just one central ballscrew. For a 1500mm cutting area you'll need to look at the size of ballscrew you need to use as at this length you're right on the edge of ballscrew whip when cutting fast with 1610 ballscrews (what most people use as they give you the speed you need for plastics and wood) so will probably need to go up to 2010 (20mm diameter) ballscrews which will most probably need Nema34 steppers to overcome the inertia of the ballscrew.

    Have a look through the build logs in this section of the forum and inwardly digest all the information that's there, knock up a design and we'll all comment on it and help you
    Last edited by njhussey; 12-01-2016 at 11:07 AM. Reason: Spelling....
    Neil...

    Build log...here

  3. #3
    Thanks for the answer. What could be better to drive those two ballscrews with seperate motors, or put one motor in the middle and drive both screws with a belt? and if we run each screw with separate motor so this means we need adittional driver, or it will be enough one driver which has enough power to handle the current of both motors?

    Isiųsta naudojantis SM-G900F Tapatalk 4 Lt

  4. #4
    Quote Originally Posted by valdis034 View Post
    Thanks for the answer. What could be better to drive those two ballscrews with seperate motors, or put one motor in the middle and drive both screws with a belt? and if we run each screw with separate motor so this means we need adittional driver, or it will be enough one driver which has enough power to handle the current of both motors?

    Išsiųsta naudojantis SM-G900F Tapatalk 4 Lt
    Well that debate has been going on for a long time and both ways have there pro's & con's. If using one motor it normally needs to be bigger and generally a higher voltage on the drive. But you only need one homing switch on one side.

    Using two motors you will need two drives and two homing switches to make sure the gantry is square and good drives with stall detect in case one motor stalls and tries to rack the gantry.

    It is not a good idea to use one drive with two motors.

    Both systems if correctly done work fine.
    Last edited by Clive S; 13-01-2016 at 04:29 PM.
    ..Clive

  5. #5
    Welcome to the forum.

    My experience is 600mm is the maximum width for single central ballscrew. Even then you have to be mindful of hard cuts at the ends of the travel, but in general it's fine. Above that it is double ballscrew all the way (or drive from each side anyway).

    As Clive mentions single or double motors will work. Draw it out and take your pick. I like double motors as then you can buy lots of the same motor spec and driver and use them on every axis. Not a strong reason, but can make things simpler.

    Something to point out is that in post #1 the last picture (5-8.jpg) shows a better machine in the top corner with double ballscrew drive. This will cut wood and plastic well, but you can go a step further than this and remove the gantry sides (weak point) and raise the X axis rails up to meet the gantry cross beam. Use a series of legs to support the raised X axis connected back down to the bed and for not much extra effort you will have a much better machine.

    Good luck with the project . . .
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. #6
    Hi again. After a I while now i am going to put my free time into designing as much as possible. For now i have just several main extrusions with rails and blocks on them. Now want to start to count what exact lenght I need of extrusions, where to place rails and ballscrews, which is quite confusing to start with. I am considering if it is worth to buy custom made rails and ballscrews lenght to my exact dimensions, or it is cheaper to have a bit smaller work area than I wrote in my first post and to go with standard lenght which is 1500mm and 1000mm? I mean how expensive it can be to have those lenghts of rails and ballscrews at those dimensions, which could let me have exact 1500x1000 work area.

    Here is the picture how it looks at the moment.
    Click image for larger version. 

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    All the corners i am going to join with 90 degree L shape brackets. Do i Need the legs? If yes, then probably it would be nice idea to have a pair of legs in the middle yes?
    Thanks a lot! :)

  7. #7
    Lots of views no comments, ok probably i need to bring my design without initial questions. Thats what i will do :)

    Isiųsta naudojantis SM-G900F Tapatalk 4 Lt

  8. #8
    Hi, sorry didn't see this thread pop up again! You'll definitely need legs in the middle and you'll need cross bracing. Depending on what your bed is going to be made of you'll probably need more cross bed supports...
    Neil...

    Build log...here

  9. #9
    Yes Sorry I didn't see this thread at all.!!

    The machine design you are thinking to build is very similair to routers I build. I can tell you without doubt that you will need stronger than 80x45 to give the cutting area want at this length. 120 x 80 is what i'd use or at minimum 80 x 80.
    With correct profile you won't need middle leg and infact you can't have middle legs with this design because of the cross brace between gantry.

    The base will need at least one more support. Cross bracing isn't strictly required because the bed base forms part of the structure but it wouldn't hurt having some just to hold resonably square.
    Last edited by JAZZCNC; 08-02-2016 at 05:42 PM.

  10. #10
    I am not so used to this machine terminology, but cross bracing in my case are these aluminium extrusions which are joining longest (x) axis, yes?
    And if i understand right i cant have middle legs because that cross brace between gantry, but that aplies only for single ballscrew on x axis. I am going to have two ballscrews on x axis driven with belts by separate motors.
    The bed probably i will have several 4040 extrusions attached to the main frame, and on those extrusions i think should be good to have sacrificial plywood or mdf.

    Does that sound good?

    And sorry for my terminology, i promise i will get used to that! :)

    Isiųsta naudojantis SM-G900F Tapatalk 4 Lt

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