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My First Design & Questions

Discussion in 'CNC Mills/Routers' started by GinoTheCop, Feb 4, 2016.

  1. GinoTheCop

    GinoTheCop Master
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    Hello world!;

    I came across this great forum while I was trying to mod a G5 Powermac computer case and found out that hand cut parts are not sleek and accurate enough.

    So I have been spending a lot of time reading, inspecting parts and designs and try to create a BOM for my CN build.

    I came up with a design that is a mix of c-beam and OX and of course other fellow builders already been there.

    I have 3 main concerns for my design (please note that I am a total newbie with openbuilds parts and cnc world)

    Please take a look the overall design first; (According to my calculations it will have a 815mm by 720mm cutting area)
    [​IMG]

    QUESTION #1;
    Will the below gantry setup work? Please note;
    a- I used 2 Anti-Backlash nut blocks (is this applicable?)
    b- I used another 20*80 horizontally laid at the bottom and the wheels are sandwiched in between (is this applicable?)

    [​IMG]

    QUESTION #2:

    Will below setup be sturdy enough in regards to the stock plates used? Or do I really need stronger setup here? (Please disregard the nut-spacer orientation between the wheels-I didnt have time to correct that yet-)

    [​IMG]

    QUESTION #3:

    Will this motor mount (only 2 points of mounting) be sturdy enough for Nema23s? I have seen this is widely used but still wanted to make sure. (A riser block to the end of C-Beam End Mount would do the trick to have a four point mount) Can I use other stock connections here?

    [​IMG]

    Thank you so much in advance for those who read this and direct me to the correct setup.

    I need to order the long pieces (v-slots, c-beam slots, lead threads) soon as I am running out of time as it is critical for me to have a friend bring them to me.

    Final note: I am using sketch-up and thea render plugin with it to create these quick renders.
     
  2. Chillimonster

    Chillimonster Journeyman
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    Not sure on any of the answers, but thought i'd comment to say the design looks superb!
     
  3. Rick 2.0

    Rick 2.0 OpenBuilds Team
    Staff Member Moderator Builder

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    Beautiful work. You might consider a career as an industrial designer.

    1a) The potential problems with using two anti-backlash nuts are probably greater than any benefits. The main problem is the amount of friction they put into the system. Two nuts means double the friction and that is something that the motor has to overcome. Second, if you don't get them both tuned properly together they will actually lock up your screw.

    1b) Two problems here. Sandwiching the wheels won't work. Think in terms of the wheel's rotation. The opposite side of a wheel moves in the opposite direction. So while one side of the wheel is nicely rolling along in the groove, the other is dragging against the opposing rail. Second, the mini-V wheels are a different thickness than the solid V-wheels and getting them both to align on the center line of the rail is a bit difficult. You need to add extra shims behind the mini-Vs and there are no stock shims of the proper thickness. You will need to make your own and get them all to the same and proper thickness. The solution to both these problems however is fairly simple, use mini-V wheels in all 4 rows. This eliminates both the rubbing and alignment issues. You should note, in order to use 4 rows of wheels like this, you will need to put eccentric spacers on at least three of them.

    2) Depending on what you are cutting, you may find this arrangement a little weak. But on the upside, once you have the machine up and running if you do find them a little weak you can always cut something better to replace them.

    3) I really can't offer an opinion on this as I haven't built anything with this system but remember, the motor is only turning the screw, there is no push/pull here. Also when you say NEMA 23s remember there is a vast range of strengths to these motors, anywhere from 150 oz-in to well over 425 oz-in, so just questioning based on frame size is not a real question. As far as if they will work in general, I don't recall seeing any complaints from others using this system and with as many systems out there someone should have had a problem if there is going to be one.
     
    GinoTheCop likes this.
  4. GinoTheCop

    GinoTheCop Master
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    @Rick 2.0

    Thank you so much for very useful information. You covered almost all question marks in my mind.

    For Q1a: I am dropping the idea of using 2 anti-backlash nuts, I was thinking exactly the same problems you described.

    For Q1b: I am dropping the idea of using sandwiched bottom wheel. I will use 4 rows of mini V wheels.

    For Q2: I will go with the stock plates to start with and after the machine is up and running I can always design and build my own custom plates.

    For Q3: Again start with the stock C-Beam End plates and see if a solution is needed and if so build my own custom solution for that.
     
  5. Florian Bauereisen

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    HI,
    nice effort - really.

    Just a few more thoughts about Q3:

    The motor spacers are an often overlooked weak point.
    Eventhough in general the steppers "only" have to turn the spindle, in reality they fight against the momentum of your spindle vs. movement of gantry. If the force of the bit within the material is big enough the stepper will actually twist the screws instead of accellerating the spindle.
    This causes setups like yours to lag in accuracy.
    Solid coupling or a (big) square metal tube "layed sideways" and drilled to suit are much more adviseable. Quite easy to do too.

    greets

    flo
     
  6. GinoTheCop

    GinoTheCop Master
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    @Florian Bauereisen ;

    Thanks for your comments. I really do not like the way the motors are attached with 2 screws only. Having both of those screws on the same side of mounting is another weakness imho. Although I am not an engineer, I can sense the momentum should be divided equally for a stronger structure.

    A square tube would make the installation of the coupler a bit difficult, so maybe adding an extension block to the stock c-beam end plate using the 2 screw holes (which are already there) and attaching remaining 2 legs of the motor to that extension block would be slightly better.

    Can you explain more about what a solid coupling, you have in your mind? Do you mean a custom single c-beam end plate long enough to house all 4 screws to the motor?

    Thanks once again
     
  7. Florian Bauereisen

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    hi
    solid in a sense of no "single" standoffs for the stepper. 4 standoffs (or poles if you like) will be better than 2 or 3 but still they might corkscrew.

    About the square tube:
    access would be easy - two sides to get in (providet tube big enough)

    so cut a square aluminum, lay flat on the side, drill upper and lower side with 5 holes (like a dice) - 4outers for the stepper the one in the middle for your coupler.
    Attache with either long screws through everything or 8 short ones to make changeing steppers easy.. access screws and couplers through the open sides ..
    might find a pic somewhere...
    this is just a way of attaching a stepper in general.. attaching to your machine is another thing...

    greets

    flo
     
  8. GinoTheCop

    GinoTheCop Master
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    @Florian Bauereisen

    Thanks for the explanation, I now know what you mean and it sure is going to be a strong fit!

    Tonight I worked on the model a bit more and corrected above issues except Q3.

    Here are the results:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
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  9. GinoTheCop

    GinoTheCop Master
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    I tried to double-check my measurements and improve my design.. Took me the whole day with all details, double checking etc.

    I think I am there now.. My BOM is ready and I (think) am ready to place my order...

    This is where I am at right now:

    [​IMG]
     
    GrayUK likes this.
  10. JustinTime

    JustinTime Master
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    Man...those rendering are just unreal! What program did you use?
     
  11. GinoTheCop

    GinoTheCop Master
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    @JustinTime

    Hi, Thanks for that comment,

    Am using Thea Render and its plugin for Sketch-up.

    Glad you liked them
     
  12. JustinTime

    JustinTime Master
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    400 Euro for Thea Render??? Wow!!! A little bit out of my price range. :D :D
     
  13. GinoTheCop

    GinoTheCop Master
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    @JustinTime haha no i paid something like 40 EUR as far as i can remember (that should be 2-3 years ago).. I am still a Ph.D Student so I can benefit from student prices :rolleyes:
     

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