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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
     
  15. timmywo

    timmywo New
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    Hello all,

    Update on progress and pleased to say I am cutting! But, there is still much to learn \ action.

    Few points for anyone following...
    • 3 * DQ542MA Drivers fixed my X and Y axis not moving
    • I have a 10x20mm cable chain that is really not up to the job, will be upgrading too at least 15x40mm I think
    • Frustratingly, after setting up the machine my usable work area is only 1115x2234mm. I was aiming for OSB sheets of 1200x2400mm, also to make matters worse OSB sheet size in Poland is 1250x2500mm!!
    • There is flex in the machine, C-Beams would have been much better and I am tempted to fix my flex and small work area size by moving to C-Beam (how to hide this cost from my partner....)
    • Limit switches are a must, use them, very helpful when homing and setting up your work area
    Here are some photos and videos of me cutting: https://photos.app.goo.gl/Wonvn9q8R2S9tUlc2

    I know that I will be learning a lot about CNC and my machine as I continue to use and adjust it, there are a few things I would love to get a head start on and ask the more experienced members here...
    • Feed Rate
      • I have been readings and researching this last night and ended up nowhere and going with SketchUcam default of 2540mm. To my surprise, this worked and my machine chomped its way through 18mm OSB at 4mm depth with no issues. But, I quickly dropped this down to 500mm after a few cuts noticing the machine was struggling. The info I can find to calculate this asks for...
        • Surface Speed - cannot find this for OSB
        • Chipload - no frigging idea, I have these 6mm Single Flute End Mills, I cannot find any info on manually calculating chipload
      • I know that I should have chips of wood when cutting and not dust, my photos in the above link has a photo of the "waste", is this dust or chips!?
      • Any suggestions on Feed rate for OSB to get me started?
    • Offsets
      • The wiki house designs I am cutting have joints that should crush together, you need to set a 0.25mm offset for cuts to allow some tolerance in fitting the parts together. Is there is any way in bCNC, SketchUcam or GRBL to set such offsets or would I need to adjust the original SketchUp model?
    • Spindle Control
      • I have been able to control the Spindle from bCNC by using a Low Pass Filter, but I only get half of my spindles speed, I have it configured as follows...
      • Code:
        PMW (Pi CNC Hat) > 10k resistor > 4.7 uF capacitor (POS) > VR (Spindle Controler)
                                          4.7 uF capacitor (NEG) > GND (Spindle Controler)
      • Any suggestions on what the issue maybe?
     

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