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  1. #1
    I am planning to build a router for wood, with occasional machining of some aluminium parts. I have plenty of time before I will be able to actually start building the machine, so I though it would be a good idea to start a thread to gather opinions and advise from more experienced CNC builders.

    The build is going to be based around the parts I already have at hand:

    • 2x 1400mm linear rails
    • 2x 800mm linear rails
    • 2x 350mm linear rails
    • 1x 1400mm ball screw
    • 2x 800mm ball screws
    • 1x 350mm ball screw
    • 2.2 kW water cooled spindle
    • 4x NEMA23 steppers


    All screws are 1605, the rails are 20 mm rectangular, 2 slider blocks per rail. X is going to be the longest axis. One reason is that I want 2 ball screws on Y axis, and the other is that this configuration better fits my planned workshop layout.

    Materials:

    • all steel
    • 80x4 square tubes for frame and gantry, smaller tubes for base (possibly filled with concrete or sand )
    • 4 - 5mm thick steel for plates, gussets, brackets and similar parts


    Goals and requirement:

    • simple power tools. Angle grinder, MIG welding machine, hand drill, possibly a very basic drill press. No machined parts
    • aiming for 0.1 mm precision across whole working area
    • fast axis movement would be nice, but precision is much higher priority
    • the design should include 4th (rotary) axis, although I will be building it only after the 3 axis machine is complete


    Given the precision goal, I need to provide means for aligning the rails. I am thinking about using set screws as shown in the pictures below

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    After the alignment is done, I can pour epoxy to permanently fix the rails (oh, how do I prevent leaks through holes in the tube?!). This will allow me to precisely align the rails in up-down direction, but I will have to tolerate any inconsistencies the rails may have in left-right direction. Also, X axis will need both rails mounted on the same plane (front of gantry) instead of mounting one in the front and one at the top. That is probably OK.

    I have also seen people pouring resin into interconnected channels built around rails supports, and then mounting the rails on top of resulting surface. Intuitively, set screws allow for more precise alignment, but maybe I am wrong.

    For me, the alignment approach is the fundamental decision I have to make before I start designing the machine, so that's it for now. Comments and advise are highly appreciated

  2. #2
    I'm no expert, but seems like you have grasped the basics of the challenge and are grappling with the details.

    Two minor points:
    - Wood machines need speed, and so more normally use 1610 ballscrews. You can do the maths, but might want to gear up between stepper and ballscrew.
    - As linear rails carry two spaced carriages wider than your ballscrew, typically ballscrews can be shorter than their rails.

    A major contributor here always stresses ' buy nothing till you have finalized your design' but guess you have those parts already.

    As to rail leveling, you are quite correct to focus on this as a key step to building an accurate machine. You will find plenty on this forum about epoxy leveling. If done right, it addresses both leveling the surface for the rails and getting them coplanar. Your adjustable screw approach is an alternative for leveling each rail, but seems a lot of work verses simply shimming the rail.

    Good luck with your planning
    Last edited by Andrewg; 15-02-2021 at 12:01 PM.

  3. #3
    Andrewg, thanks for your input!

    I got a good deal on the rails and ballscrews set. That's what I've got, and I have to work with that.

    I was planning on connecting the motors directly to ballscrews, but I will take your advise and order some pulleys and belts. If I later decide that I need more speed, I can change pulleys and possibly upgrade the motors.

  4. Good afternoon . A year ago I finished building my second cnc. Maybe something can come in handy
    Indulis Click image for larger version. 

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    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  5. If there is any interest in this design, I will be happy to share information or drawings .
    I have only a little trouble with the English language .
    At school we were learn only Russian.

    Indulis

  6. #6
    Looks like quite a rigid machine that you built there Indulis.

    How much have you used that 4th Axis and using what software?

  7. 4 Asis - DESC PROTO, 3asis - Aspire Click image for larger version. 

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  8. The Following User Says Thank You to indulisap For This Useful Post:



  9. #9
    Quote Originally Posted by indulisap View Post
    4 Asis - DESC PROTO, 3asis - Aspire Click image for larger version. 

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    Very nice work.You have a machine to be proud of.

  10. Click image for larger version. 

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ID:	29671I scrape the shavings to see the inside of the frame.
    I don't get chips on the floor under the workbench. Many constructions forget about it

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