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1300x2500mm OX - guidance needed

Discussion in 'CNC Mills/Routers' started by timmywo, Jun 27, 2016.

  1. timmywo

    timmywo New
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    Hello all,

    I am planning on building a large 1300x2500mm OX - the main job for this router will be cutting 1200mm x 2400 x 18mm plywood for a wiki house build.

    I have read over many posts and builds collecting information and details of the challenges with such a large machine. Below are the challenges I am aware of and where I am looking for more guidance from the community as this will be my first CNC build...
    • Stepper motors - plan to use NEMA23 on all axis. I believe High Torque versions are needed, but unsure how much Torque I should aim for?
    • Y axis length - I hope to source 2500mm V slot rail from aliexpress
    • X axis strength - I read a lot about moving to C-Beam? Is this really needed?
    • Was planning on using GT3 5mm belt, but have seen many large builds use ACME threaded rods, what benefits do I get from this?
    • Controller - I plan to use the Raspberry Pi CNC Board with Drv8825 Stepper Motor Drivers. Has anyone used this controller?
    Also I am very interested in any other comments anyone may have with areas of the build I need to pay special attention to or should consider adapting beyond the standard OX design.

    Many thanks all!
    Tim
     
  2. Florian Bauereisen

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    Hi,
    steppers do not need to get stronger just because machine size increases, so just get reasonable strong ones.
    a bigger machine flexes more than a smaller so problems increase by square ... you need all the strength you can.
    Use at least belt to belt setups as your belt-stetch increases with lengh too... if you can (dep. on design) i would use a wider belt and belt on belt design.
    Long acme/ ballscrews will start to whip with length so there its where it gets expensive.
    A good quality ballscrew at that size will set you back a couple of thousand... either use low quality or stay with belt(s) as mentioned above..
    Don`t know anything about the Raspberry sorry.

    hope that helps a little
     
  3. timmywo

    timmywo New
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    Thank you Florian, this is very helpful! Would you mind if I ask two questions...
    • Can you clarify what a "belt to belt setup" is?
    • What would you say a reasonable strong stepper is?
     
  4. timmywo

    timmywo New
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    Thank you JustinTime and Florian!
     
  5. tparsons

    tparsons New
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    Hi Timmy, I am hoping to do a very similar build so will be keen to hear how yours goes.
    Regarding the Y axis- Have you managed to source a Vslot rail longer than 1500?
     
  6. timmywo

    timmywo New
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    Hey, yep I managed to get all parts delivered and vSlots at the required lengths - this is the supplier I used, I sent them an email with details of what I needed and they completed the order perfectly: XINLONG FACTORY SHOP - Small Orders Online Store, Hot Selling and more on Aliexpress.com | Alibaba Group

    Right now my workshop (an old barn) has two foundations that need to be rebuilt and a floor before I can start the build, looks like I may have to wait until next year as weather is not great now :(

    Here is my full build spreadsheet that you may find helpful: OX Parts
     
  7. timmywo

    timmywo New
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    Hey all, I'm back at work and starting to build the machine - now I am starting to hit issues and fixes, but looks like I may have royally f****ed up on the electronics - frustratingly...

    Few notes...
    • Not all the M5 screws I purchased were low profile, I have been lucky and swapped a few around where needed. Save yourself the stress and be sure to get all low profile
    • Way underestimated the number of Tee Nuts (50), with the table support I need more in the region of 200
    • Like a tool I cut the V-Slot 20x40mm X Axis Back Brace by mistake, new one is on order
    • The "5 Hole 90 Degree Joining Plate" for each corner did not appear to be up to the job, so I made my own out of a few metal plates
    • Trying to find a tapping drill bit was impossible, so all V-Slots ends where manually tapped if needed
    Now, for the electronics, this is what I have purchased...
    The issue was discovered when reading up on how to configure the Current Limit on the DRV8825, they are limited to 2.2 A - my NEMA23 are 3A. I have read that it is fine to provide a lower current to the motors, but also read that it may mean they will not run at all. So, the best thing to do is a test, but, I have not ordered a PSU for the motors.... this order was made last year so I can only guess that I was planning on using the Spindle 48V PSU, but, the RPI CNC Board is limited to 12-30VDC. Buy a 24V PSU..? But, is that now a waste of time and money as my NEMA23 require 3A?

    So, as you can see I have gotten myself into a bit of a pickle. Before I make a purchase in anger, I would like to get feedback on the following questions...
    • Am I correct in thinking that I should give up with the DRV8825 and order 3 * DQ542MA?
    • As the DQ542MA are External Drivers (RPI CNC Board can support this), do I need a PSU for each one or can I run all 3 from one PSU?
    • Any suggestions on a reliable EU source for these parts? I have made an V-Slot order with OpenBuilds Poland but they are ignoring my messages for an order update and looks like ill have to ask PayPal for a refund
    Thanks in advance for any advice, it appears I have fallen into the common noob electronics mess. Also, apologies to @JustinTime who clearly said "276 oz/i and about 2A" - I clearly missed the 2A part of that :(

    A few pics of my progress to date...
    IMG_20170610_171338.jpg IMG_20170625_163831.jpg IMG_20170625_163825.jpg IMG_20170625_163818.jpg
     
  8. timmywo

    timmywo New
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    Hey, thanks JustinTime, that sounds positive, ill purchase a 24V 17A 400W Power supply from vslot-europe.

    I plan to only be cutting OSB and plywood for now.

    The RPI CNC Board can take up to 30V, so this PSU should be fine. I will at some point get the proper drivers, how would I calculate the PSU size I would need to power all drivers and the controller? Is there a calculator somewhere or formula I could follow? (Have looked around but could not find anything common across threads).

    Thanks again for your help, almost there!!!
     
  9. timmywo

    timmywo New
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    Great, order made - will post another update soon, I hope!
     
  10. eleethesontai

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    Where did u find 276oz nema 23 @ 2a? All the ones I have seen 170 or higher are 2.8a to 3a. The openbuilds 170 is 2.8a


     
  11. timmywo

    timmywo New
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    Quick update...

    I have now setup the 24V 17A 400W Power Supply with the RPI CNC Board and DRV8825 Stepper Motor Drivers.

    Z Axis using the NEMA17 (Current / Phase:1.5A) is working fine, X and Y Axis with NEMA23 (Current / Phase:3A) are not working. I get a sudden very small movement when trying the Y or X and after that, the motors just make a clicking sound with no movement when I try to move them.

    I am assuming this is due to the DRV8825 struggling to power them, I have the DRV8825 VREF Current Limit set to 1.1V (limit 2.2A), also tried 1.5V (limit 3A) with no joy.

    I have 3 * DQ542MA Drivers on order that I hope will resolve this. Shame, as I was hoping to have all electronics nicely hidden in a box on the Y Axis.

    Will post my progress later this week once I have the parts, any other suggestions please let me know!
     
  12. Chris Garcia-Cox

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    V-rails can be joined together with rails, this will save you money in shipping from China. If your base is strong you should have no trouble. I´m also working on a similar build, but I´m also testing steel (not t-slotted) as an alternative. If you have experience with soldering, you should look into steel.
     
  13. Chris Garcia-Cox

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    I´m using these from Amazon: https://www.amazon.com/gp/product/B01G55LNPO/ref=ox_sc_act_title_3?smid=A2OCOGC9B25845&psc=1

    they can take a beating.
     
  14. timmywo

    timmywo New
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    Hey Chris, would love to see some pics of your build and how you have connected the v-rails. Looks like after adding spindle I may have a working area that is short by 10cm, whats frustrating.

    Also, that motor controller looks very good value, I have my 3 * DQ542MA delivered and just at the final stages of getting the spindle wired, hope to be cutting next week!

    Will provide an updated post soon
     

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