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Rotary OX or C-Beam

Discussion in 'CNC Lathes' started by garagejob, Sep 2, 2015.

  1. garagejob

    garagejob New
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    So, I am a total noob. And because of this facts I probably dont have the terminology correct, AND I have a few questions about a build that I have in my head.

    What i am wanting to build (i think) is a rotary machine so that i can engrave an aluminum tube.

    I am not sure how to go about the build, so these are my thoughts. I was thinking also that this build could be the start of another build i have planned in my head for a standard cnc router. can you please tell me if my thinking is incorrect.

    I want to build a frame using something similar to the 80/20 line of beam.

    use some of Chris Laidlaws v-slot brackets http://www.ebay.com/itm/261855927419 to attach the rails to the frame.

    maybe some of Chris' tall ox plates to attach the gantry to the v-slot type rails. I will likely make the gantry stationary, with the router centered over the rotary axis.

    I am thinking that for this particular build i will need to use two rotary heads instead of one rotary head and a tailstock.

    now here are the questions i dont know how to ask properly so forgive me.

    using two rotary heads mounted face to face, can i connect the stepper motors so that they will work in sync but one obviously backwards? will this work using the cnc xpro controller as one of the rotary heads as a slave? or will i need to buy two cnc xpro controllers?

    on a similar note, could i use two c-beam linear actuators, one for either side of the gantry Y axis? and also use them as one of the slaves?

    I am sure that somewhere there is a setting to change the Y axis to be a rotary axis? if not i am thinking that i can set the Y axis to have the same dimensions as the outside diameter of the tube i intend to engrave?

    I havenet a clue how the limit switches or proximity switches work (ok i take that back, i know how a limit switch works, proximity switches cant be that much different). I am wondering how can the ZERO or home position be set and can it remain the exact same every single time? what is the repeat ability of such a machine? i have several tubes to engrave and would like them to be all as close to exact as possible.

    i was thinking that i will TRY to use sketchup, artcam (if i can figure it out) for the design, and mach3 for the control.

    i dont know what router i will use, i would like to use one with variable rpm if possible, but not necessary.

    i am under the impression that the slower the speed of direction, the more precise the cut? i will be using the smallest ball nose bit i can find for small engravings.

    sorry if this message seems scattered, it is late and i should have probably waited to post this.

    tell me where i am wrong, thanks in advance.

    -Garagejob
     
    #1 garagejob, Sep 2, 2015
    Last edited: Sep 2, 2015
  2. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

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    why do you think that? one properly made head will be more than powerful enough.
    yes of course you can connect one motor to go the other way (-:
    however, motors do work best when they have their own driver per motor, just do the reversing in software.
    rotary axis are named A , B or C, depending on what axis they are parallel to , X, Y or Z, in that order
    proximity switches are just switches that sense the proximity of a bit of metal. they are generally quite accurate in terms of how far away the metal will trigger them.

    you do not need limit or home switches to be accurately repeatable, YOU just have to spend the time to set up correctly (-:
    if you want to use a true rotary axis then have a look at Fusion360, combined CAD/CAM that can handle that, I don't know if Artcam can do it.

    to use SketchUcam, you will have to fake it by using the rotary axis as either X or Y and then setting the size of your engraving to the circumference of the tube.
    the rotary axis will need a lot of resolution, ie lots of steps per degree. this is because as the circumference increases, a 'step' of the motor becomes larger. somewhere on this forum is a post of mine that details the math behind this, please search for it.

    mechanically, you want either a harmonic drive, or a worm drive, for maximum rigidity and resolution. you can get away with a belt drive, but you will probably need 2 stage reduction, bringing with it some backlash and other issues requiring good precision engineering to ensure accuracy.

    high reduction means less speed though, you are correct in thinking that is the tradeoff. this can be reduced by using higher voltage to drive the steppers, higher voltage (within the drivers specs!) gives higher top speed.
     
    Mark Carew likes this.
  3. garagejob

    garagejob New
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    I didnt specify why I thought two rotary heads were needed. no it is not because of the power or torque, it is simply because of the size and shape of the parts i want to turn, i feel that a jawed chuck on either end would be a better solution than using a pointy tail stock, or making or buying adapters to use with the tail stock. was thinking more simplicity than necessity.

    so what you are saying is that the rotary axis in my design thought would be called the B axis? good to know.

    time is not a huge factor, i have been working on this idea in my head for more than a year now, just getting closer to pulling the trigger. i will look into those software offerings, i am not a CAD/CAM person so hopefully the learning curve is not too steep. I have been playing with sketchup for years just to put thoughts to a visual but i have never done anything is lots of detail of exacting specs, didnt seem to difficult to go the extra step for exacting measurements so i think i can figure that one out.

    i was thinking i could cheat like this. made since.

    will look for your thread detailing this. I had not considered that the decreasing circumfrence fact, needing more steps. toytally over looked that one. but in my case i think it is not important. mostly engraving very lightly on the surface some words and design and logo, nothing with depth (yet).

    i hate belts for this type of thing. but for the first build i will likely buy a cheap Chinese made belt driven rotary unit. after i get the hang of it i will upgrade later to a better more expensive head.

    SPEED is not an issue. i am not doing large production runs and if it takes all day to engrave one part, so be it. I just want to get the machine outta my head and on the work bench and working. as i see most of the posts and builds on here are the beginnings of more migger and better machines, i feel i will be in that same boat, this is the first, i already have another machine planned. it will likely spin out of control for me, as most things for me do.

    thanks for the info. off to the search pages and more reading.

    -garagejob
     

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