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LR/BS CNC Router

Discussion in 'CNC Mills/Routers' started by Ptiwee, Apr 26, 2020.

  1. Ptiwee

    Ptiwee New
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    Ptiwee published a new build:

    Read more about this build...
     
  2. Joe Santarsiero

    Joe Santarsiero OB addict
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    Very nice. Will you be worried about the z-axis dropping when the motor is powered down?
    You could get more travel if you flipped the side the couplings are on, but it wouldn't look as clean.
    I think it would look better if the Y motors were off to the back of the machine. That's no big deal though.
     
  3. Ptiwee

    Ptiwee New
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    Does it happens with ballscrews ? Or is it related to weight ? I've been working with ACME screws on CNC and 3D printers and never faced this problem.

    I think this will require a second plate to fix the X-Axis rails to the V-Slots, am I wrong ?


    I put them on the front otherwise the Y-Axis will be outside of the frame, so I'll be losing some precious centimeters (I'm storing the machine in my appartement, small footprint is important to me).
     
  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    Yeah. Their friction is really low compared to ACME. ACME self lock. It is related to the weight it takes to overcome static friction.
    I'm not sure how the hobby scene is doing it, but there is usually a DC brake.
    You could just build it and put a wood block under the Z when the machine is off. :)

    I don't think it would. It looks pretty tight in there, but you might be able to get the screw encapsulation in the gantry arm and use the standoff plate to mount the motor to.

    Ohh. yep. I see can see that now. duh
     
  5. Ptiwee

    Ptiwee New
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    Thanks for your advice. Regarding the Z-Axis dropping, I added a little stand on the X plate where the Z-Axis can go resting outside of the work area.
    It allows me to implement a macro to go there, which should be more practical than the block.

    Stand-off.png
    Stand-off (2).png
     
  6. Joe Santarsiero

    Joe Santarsiero OB addict
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    That's a really nice idea if it does drop.
     
  7. Woodsmith

    Woodsmith New
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    Nice clean design, and just the design methodology I am interested in for building a machine too. With cheaper sources of profiled linear rails and ballscrews now available it makes sense to use the correct components to give a robust, low maintenance machine.

    It seems a little ironic to be using V- slot, (developed for wheel based linear motion) for mounting profile rails. Is there a reason to still use V-slot over T-slot?

    Only other observation is that whilst 1605 ballscrews seem common on metal cutting machines, 1610 seems more common for wood cutting ones (you want the greater speed)

    Please share more of the design and the thinking behind your decisions.

    Thanks
     
    #7 Woodsmith, May 1, 2020
    Last edited: May 1, 2020
  8. Yosmany325

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    Very nice work. I'm currently working in a design similar to this regarding the use of linear rails and ball screws. In my particular case, I don't have access neither to V-Slot nor T-Slots and I'm planning to use rectangular aluminum tube of 70x45x3mm. I will try to upload my ideas soon. Keep going and good luck.
     
  9. Ptiwee

    Ptiwee New
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    You're right, I'm using V-slots as they are easier for me to source (1 command on Ooznest and I can get all the components), actually any aluminium extrusion could do the job. T-slot should be even better as the contact surface with the rail will be larger.

    Indeed, once again SFU1605 are easier to find, but there is no constraint in the design not to switch to 1610.

    I will share the DXF for the plates as soon as I validate the design. I am now searching the right settings in order to cut the plates on my OX CNC.
     
  10. Ptiwee

    Ptiwee New
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    Hello, during the week I beefed up the design for more rigidity.

    MGN-15 rails have been replaced with HGR-15. The linear actuator have been reinforced with corner angles. They are now made of 1 20x80 V-Slot and 2 20x40 V-Slots. Aluminium plates have been thicken to 15mm. FK12/FF12 blocks have been replaced for BK12/BF12 which allows for bigger work area.

    I should order the material very soon. I think the first implementation will be made out of MDF to confirm that everything aligns properly. I may keep it like this for a while if it works properly ...
     
  11. Joe Santarsiero

    Joe Santarsiero OB addict
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    You're going to have very good alignment on the ball screw to stepper shafts. You could probably switch to solid couplings and tighten the motors after the ball screws have been installed. I've had those aluminum couplings twist up from too much torque and seen some break from fatigue.

    Run some math to spec out the right size carriages without over spending.
     
  12. Ptiwee

    Ptiwee New
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    That's definitely an easy and cheap update. Actually I put the flexible couplers because they are available in the OpenBuilds library on my CAD software ...

    I cannot run those maths as I don't know of any formula ... I don't know wether they can be easily understood or a full mechanical engineer training is needed :/
     
  13. Joe Santarsiero

    Joe Santarsiero OB addict
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    Downloads - Huntley, Illinois- HIWIN Corporation

    Linear Guideways PDF Starting on pg.6 of the pdf.
     
  14. Ptiwee

    Ptiwee New
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    Thank you for your precious help. I haven't quite yet understood all of the formulas, yet the documentation has been precious.
    My biggest concern was regarding the side rails being vertical and not horizontal, but according to the documentation the loads are equivalent.
    I ordered the pieces recently and am waiting for everything to arrive.
    I started 3D printing the plates as I sold my OX CNC before changing the design ... The 15mm thick plastic seems quite robust and should be sufficient in order to cut the plates out of aluminium, as only the drill needs to be precise.

    I'll keep you updates once the parts are ready. Definitely alignment will be a challenge ...
     
  15. Joe Santarsiero

    Joe Santarsiero OB addict
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    Yes. Most profile rails are very sturdy in all loading situations. If you spend some good time working through the math you can come to a decent conclusion as to what will be sufficient and what will be overkill for the loads they will see while in use. Light, rigid, and least expense to get the job done are the goals.
    If you need some help interpreting the math then ask around. Kahn Academy is also a great source to brush up on math skills.

    If you plan your 3d prints correctly to mirror important errors and your printer is reliable then you shouldn't have many alignment issues. If you want, you can mill the new plates, install them and mill them a second time to reduce errors a little from the 3d printed parts. I suggest that when you print initially you try to butterfly them in pairs. For instance, the left screw drive plates are butterfly'd open with the insides facing up and then the right screw drive plates with the right facing up and opposite to the left plates. Same when you remill a new set of plates. ehhh. That's tough to explain here. I'm sure it'll work out for ya regardless.
     
  16. Ptiwee

    Ptiwee New
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    Unfortunately I have more money than time ...The issue is not about the maths but more about the variables. I have no idea about the forces that would be applied.

    I'm quite confident with my Prusa doing a correct job. Let's see if I got you correctly, I should print them as follow :

    Y-Axis Plates.png

    Because I don't really like long prints, I'll go with the second solution. After some tests it seems better to have the inside facing down as the surface is a bit flatter. Also to avoid warping on such big pieces I print them without top/bottom layers, letting the infill pattern being exposed, this pattern being triangles.

    It'll look something like this :

    Capture du 2020-05-29 10-40-19.png

    For sure this will flex, but I hope the 15mm thickness will be enough to hold the machine while cutting the real plates.
     
  17. Joe Santarsiero

    Joe Santarsiero OB addict
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    I think you'll be alright.

    Prusa makes a great printer.

    This might be a good idea. Let us know how it works out. You really only need them to cut new plates anyways.

    You could hold them together to see how well they line up with each other.
     
  18. Corey Corbin

    Corey Corbin Well-Known
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    I 3D printed almost all of the plates for my sphinx cnc except the right and left uprights to the X axis. 3d printing the plates make a great drill guide for the drill press. I taped the printed parts on to the aluminum plate drilled the holes. Then got a 10" nonferrous cutting blade for my table saw and cut plates out.
     
    Joe Santarsiero likes this.
  19. Ptiwee

    Ptiwee New
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    Hi everyone,

    It's been a while but the project is not dead, the parts took quite a long time to arrive from China.
    I eventually assembled the machine last week, and do some tiny modifications (regarding the Z axis for easiest mount). Here's a picture of the machine assembled :
    IMG_20200903_211856_01.jpg

    Some features are still missing before the first cut (I need to retrieve some wood for the waste board). I am quite satisfied with the 3D printed part, yet the side panels are a bit too weak and the z axis wobble a bit if I force by hand. I created a new design to reinforce the part, I will give you the feedback once I receive the parts :
    X-Axis.png
     
    #19 Ptiwee, Sep 15, 2020
    Last edited: Sep 16, 2020

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