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OX CNC Router

Discussion in 'CNC Mills/Routers' started by Chefson, Feb 5, 2017.

  1. Chefson

    Chefson Well-Known
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    Chefson published a new build:

    Read more about this build...
     
  2. Jamie Charleston

    Jamie Charleston Well-Known
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    Hello,
    Where did you find the stl files? I am looking for those myself. Thank you.
     
  3. snokid

    snokid Master
    Staff Member Moderator Builder

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  4. Chefson

    Chefson Well-Known
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    Thanks for the answer snokid. this is where I found them.
     
  5. Jamie Charleston

    Jamie Charleston Well-Known
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    thanks, they are helping me with my prototyping my hybrid system. I have 9 ft y axis beams.
     
  6. TonyTheToolGuy

    TonyTheToolGuy Well-Known
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    As a mechanical engineer, I highly recommend that you attach some open build extrusions or something similar to the exterior of your vertical plates to stiffen them.
    Even your 5mm side plates will flex notably, and since you already have your Y-stepper hanging off the side of the plate, its clearance requirements afford you significant useable width to play with. YOU SHOULD USE IT, all the width you can.
    The side plates could be "boxed" to maximize their stiffness/weight, but just bolting on a vertical extrusion to the exterior surface as in the photo below would do wonders in limiting X-deflection and vibrations. Placing some acrylic double stick tape between the side plates and the surfaces of the extrusions/beams/"angle irons"/"whatever you use" along with some hard fasteners (bolts) would be very effective at transferring the stiffening forces.

    If you put two verticals like the one in the photo (they don't need to be parallel) and then put some sheet material multiply attached to the outside of those, you would have a boxed vertical side plate with extreme stiffness for its mass. You could think of it as a torsion box, and it would transfer all of the X-axis's motion more effectively into the base of your side rails and your table. Right now, your side plates will act sort of like spring levers due to their thinness which makes them lack flexural rigidity.

    The engineering concept behind the stiffness of things comes from what is called the area moment of inertia and it is a cubed function, so if a stiffening member is located twice as far and is still connected by some material like the thin section of an I-beam to transfer some shear stress, then the stiffness is 2 cubed, or 8 times. Three times the distance equals 27 times the stiffness, 3x3x3. This is why I-beams, bicycle tubes, airplane wings, empty Coke cans, and foam cored sheet laminated panels are so amazingly stiff for their mass.
     
    dvma likes this.
  7. Chefson

    Chefson Well-Known
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    Thanks for the interest !

    I'll probably give it a try the next time I'll be in a "mechanical phase" for the project.

    At the moment I'm running my first real milling tests (MDF, plywood, hardwood) and I have to solve a dimensionnal accuracy problem. I'm sure it's not my software configuration (triple checked !).

    I rather suspect too much flexibility in my build. The Z axis is tall (maybe too much for the hardware)

    I've already planned to add a 4th set of wheels on the Z-axis. The next change will be based on your advice. I'm not sure to have enough stock of v-slot profile but i'm sure that iI have some L shaped aluminium profile.

    Thanks.
     
  8. TonyTheToolGuy

    TonyTheToolGuy Well-Known
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    It may be tedious, but building boxed side plates would be your stiffest for-the-weight solution. For a boxed side plate, sandwiching vertical (or nearly vertical considering you might want to follow the angle on the leading edge of your plates) aluminum bar stock would be very effective.
    Just buy some Al bar that is wide enough to reach beyond the motor and thick enough to drill and tap and accomodate a screw or bolt (or drill clean through and use a long bolt and nut to go through the outer plate, the bar, and your existing inner plate).
    I would use three bars, one on either side of the stepper and one--with a bend in it--following the leading edge of your existing side plate. Leaving the top and bottom open would suffer no strength penalty and would allow "heat tower" cooling of your stepper, likely more effectively than your current open-air design due to the "heat-rising" smokestack effect inducing air flow. On that note, the bars on either side of the stepper would need some space between them and the stepper to afford vertical air flow.
    You would be very pleased with how this would look since it would give your side plates some substance!
    I suspect the bar stock will be less pricey than extrusions too.
     
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  9. TonyTheToolGuy

    TonyTheToolGuy Well-Known
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    You may want to double up your X-axis beam too. It could be just an aluminum plate bolted to the unused side of the beam/extrusion.
    A tube is the stiffest in all bending directions for its weight and more resistant to twisting than any other shape, so you may want to attach a tube/pipe to the unused side of your X-axis. You would likely need to drill through the diameter of the tube every few inches and use a bolt longer than that diameter to just bolt/clamp the tube/pipe to the t-slot extrusion nuts. Simple, effective, and improved stiffness and twisting resistance.
    Take a look at electrical metallic tubing at a home center for a very cheap solution, thin steel but stiff. Buy the largest diameter that will fit your x-axis and drill and bolt.
    There would be not real need to attach this extra member to your endplates. If you could easily, great, but it would not be critical to the stiffening task.

    A box section tube with the same wall thickness and width/diameter/size as a similarly sized round tube is about 25% more torsionally stiff (resistant to twisting) and about 30% stiffer in bending. The square wins the competition when size is the criteria, but for its mass, the round tube is a bit better.
     
    #9 TonyTheToolGuy, May 24, 2017
    Last edited: May 24, 2017
  10. stargeezer

    stargeezer Veteran
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    I'm sure others will have some very good suggestions to increase the Z accuracy, but what I'd consider is making the X axis carriage wider and as has been pointed out, 5mm is a bit on the thin size for the Y plates. I started with 6.25mm plates, but I'm now up to 1/2" (around 13mm) and I'm very happy with the results. For most people it might be overkill, but I do make some deep cuts that require extra clearance under the router and the rigidity gained by the thicker plates cuts down on my sanding time.

    I haven't widened my X plates yet, but it's next up on my change list. BTW changing to screws over belts was the best change of all. If you make that change, I'd suggest stepping up to NEMA 34 steppers if possible. If you do use the NEMA 23 motors you have now, you will need to gear them down with a belt drive like you can find in the parts store. A 50% reduction should work (this is just a guess) a 20 tooth pulley on the stepper and 30 tooth on the screw.

    Thanks for sharing your work with us too. I love the bar stool. Do you make the base to, or is it a purchased part?
     
  11. Chefson

    Chefson Well-Known
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    "I just found the base abandonned on the street..."
     
  12. stargeezer

    stargeezer Veteran
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    :) That's my favorite way to find "parts". Awesome job.
     
  13. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Contest Winner! Builder

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    Got to say! 1) Immense respect for bootstrapping your machine using 3D printed plates, to mill parts to upgrade itself. Thats what this is all about man! 2) that chair looks awesome! I want one! The paint job really made it pop! 3) All round awesomeness. #teamopenbuilds salutes!
     
    #13 Peter Van Der Walt, Jul 20, 2017
    Last edited: Jul 31, 2017
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  14. nitrosurf

    nitrosurf New
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    Salut Chefson ! Je suis novice dans le domaine du CNC et j'ai du mal à trouver des info en francais. Je vois que tu as reussi à faire l'openbuild ox. Pourrais tu me dire combien elle t'a couté et où as tu acheté les pieces. J'ai cru comprendre qu'il y avait des pieces en aluminium découpé suivant un modele précis. Je cherche une cnc pour menuiserie amateur.
    En attendant ta réponse...
    vincent
     

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