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  1. #37
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    Re: Any pics of cnc control cabinets?

    Hey Guys,
    I realize this thread has been on vacation for a month, but I have a couple of related questions.
    I've been running desktop CNC's for 5 years or so and have always tried to keep my wiring neat and isolated, but I'm getting ready to upgrade my machine from a Gecko G540 and open loop steppers to LeadShine controllers and closed loop steppers, so I need to design and build a new control cabinet. I'd like to use DIN rails and components.
    My question(s) are:
    Where is a good reference for general (or more specific) design standards? I appreciate Al_the_Man's link to the NFPA79 document and will search that out. Without going back to school and getting an electronic engineer's degree, are there others?
    Where can I find direction on which components to use for specific functions? I know that's kind of vague, but for instance, it looks to me like a Contactor and a Relay both perform the same general function - turning an electrical component on or off - but when do you use one over the other? Or do I have that functionality wrong?
    I also have questions about when and where to use circuit breakers - only on 120V supply circuits or others in addition?
    Thanks in advance for any guidance,
    Gary

  2. #38

    Re: Any pics of cnc control cabinets?

    Gary, you ask hard questions. This arcane knowledge is normally only passed down from the master to the apprentice, over a period of years. I don't know of any books on the subject other than NFPA, NEMA and UL codes.

    In general you want supplementary protection (fuses or breakers) on both sides of a power supply or transformer.

    Motor loads and drives should be individually protected on the power input side. Normally follow the device manufacturers guidelines for proper protection sizing and type, wire size will be determined by the protection device rating.

    A contactor and a relay are functionally the same. But a contactor is normally directly switching the load (motor or other higher energy device), and a relay is switching the control side of things.

    I hope this makes sense. There is a lot more, but it's pretty hard to try to condense 50 years of experience into a post.
    Jim Dawson
    Sandy, Oregon, USA

  3. #39
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    Re: Any pics of cnc control cabinets?

    Jim,
    Thanks for the quick reply.
    Your advice helps me make a better start.
    Gary

  4. #40
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    Re: Any pics of cnc control cabinets?

    What Jim said: it is a matter of experience and judgement, not of 'rules' (apart from things like the UL guidelines, which are mainly for safety rather than 'good practice').

    Contactors are usually 'bigger' than relays - in voltage and current.

    I have over-current cutouts on each motor driver. You should NOT turn them off that way under normal circumstances, but they do handle cases where the axis has run into a hard limit and the motor current tries to go skywards.

    Neat and tidy, with adequate protection, is always good. GOOD documentation is a pain to create, but utterly vital later on.

    Cheers
    Roger

  5. #41
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    Re: Any pics of cnc control cabinets?

    Roger,
    Thank you!
    Gary

  6. #42
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    Re: Any pics of cnc control cabinets?

    Web browser image searches for "industrial control cabinet" or "Control Panel" have yielded some very good examples of what to do (and not to do). I wish there was a beginner's guide to industrial control panels, but I haven't found one yet.

    I don't do this for a living but I've built a few panels over the past couple of years. Here's what I've learned from some trial and errors; please take it with a grain of salt.

    1. It helps to draw everything out first before you get an enclosure.
    2. It really helps to lay it out in 3D CAD - most vendors have 3D models available for download and you can 'sandbox' the enclosure and components.
    3. If you can, put heat-generating components towards the top. Drives, VFD's, power supplies. Pay attention to the spacing for drives and other heat-generating components published by the manufacturer.
    4. Think about internal airflow and how to exhaust the heat everything will generate.
    5. Make a list of components and organize them by type and voltage.
    6. Try to minimize the different number of voltages. By this I mean try to use drives that are all 240, or all 120, or all DC. Same thing for relays, contactors, sensors - it's a pain if everything is different and you need 5, 12, and 24Vdc in the same cabinet.
    7. Drawing a wiring diagram or schematic first really helps before you start buying things. But don't agonize if you wind up needing another relay or whatever.
    8. DIN rail terminal blocks are your friend. Just make sure to get more than you need, and that the types, amperage rating, and accessories are all the same. Each block manufacturer has their own proprietary jumpers, end plates, fuse holders, etc. Good deals can be found on Ebay, although you might need to buy from multiple sellers to get enough of the same brand/series.
    9. You can never have enough room in the enclosure. If everything fits on paper, go one size bigger (at least)
    10. Make sure you have room for the wireways and enough room between components so you don't need tweezers to make connections. And make sure you have room, terminal blocks, and power for future expansion or re-wiring.
    11. Try to separate power components from signal components. Shoot for an AC side and a DC side. Or put the sensitive (to noise) components in a separate enclosure.
    12. Think about the power flow when you lay things out. Power comes in and goes to a disconnect or fused disconnect. Then to a distribution block. Then to individual circuit protection. Then to contactors (for drives) or directly to a DC power supply. AC from contactors goes to the drives or to line reactors and then to the drives. DC goes to a distribution block and then to DC fuses (or breakers). And then on to components, relays, etc. This is all the 'power' side of things. The 'signal' side of things is what triggers the contactors, relays, motion controller, etc. Usually all DC, and relatively low amperage.
    13. I prefer that all buttons, displays, lights, etc. that the user interfaces with be 24Vdc. 120VAC is permitted by some codes, but I am not comfortable with that on a flood-coolant machine. This adds some complexity by needing a larger DC power supply and extra wiring, but I think it's safer.
    14. Having a dedicated electrical CAD program can make things so much nicer. TinyCAD is free and I use it for everything. Steep learning curve but it rocks compared to paying for something.
    15. Keep analog signals (FRO/SRO), encoder cables, and step/direction cables shielded and well away from 'noisy' stuff, like drives, VFD's, relays.
    16. Star ground - learn it, love it.
    17. Labeling - I started off using a label maker; that was terrible. Then I used a labelmaker and clear shrink tubing for the wires - better, but still fussy and time-consuming. Last job I did I treated myself to a Bluetooth labelmaker that prints directly on shrink tube - OMG. Magic. Same labeler can use regular tape for labeling terminal blocks, components, etc.
    18. Speaking of tools - buy or borrow decent crimpers, strippers, and so forth. You dont' need super-expensive stuff, but having the right tools makes it so much less painful. I like my iWiss stuff so far. Not perfect, but cheap and light-years ahead of the really cheap Harbor Fright grade things.
    19. Get a wire ferrule crimper and a pack of ferrules. So much tidier and you are less likely to have a stray strand touch something it shouldn't.
    20. Think about maintenance and troubleshooting - will what you are about to do be easy to figure out? Does the basic layout make sense? The next guy in the panel will probably be you, and you won't remember everything in a month or year. If you have to change somethign from the diagram - UPDATE THE DIAGRAM.
    21. Wires shouldnt cross over components inside the enclosure. Make each connection long enough to gracefully lay in the wireways.
    22. Spend a little more money on components and buy from places like Automation Direct instead of trying to save a few bucks by sourcing the absolute cheapest things. Having all the relays (or whatever) be from the same vendor/manufacturer makes planning, wiring, and installation easier.
    23. Buttons, knobs, lights, switches. Use the 'industrial' modular stuff that have separate contacts and actuators instead of el-cheapo items like you see at the auto parts store. The modular switches take up more room, but they are easier to wire and generally feel/look nicer to use. You can also stack contacts to have a multi-function switch if you need it. Don't forget that like terminal blocks, modular switch contacts are not usually interchangable between brands.
    24. Before you buy anything, take your list and start making "power budgets." By this I mean:
    - how many amps do you have total
    - how many amps does each thing draw - including inrush current
    - do you have enough 'overhead' on both the AC and DC sides? Or do you need a bigger control/DC power supply or a bigger breaker in your house/shop panel?
    - Can the relays or whatever handle the amps you're sending through them? Remember that power switching devices (buttons, switches, relays, contactors, etc.) may not have the same rating for AC and DC power. A "10A" relay might only be able to handle 5A or 2A when switching DC.
    25. Buy good quality wire. It actually makes a difference, and if you buy way more than you need you'll be less likely to fudge a connection from one thing to another to try and save that piece that just isn't quite long enough.

    This is getting long, sorry. And I don't have 50 years of experience. Photos below of what what I thought was OK, as well as some examples of how not to do it (sometimes in the same photos).

    -Ralph

    First real attempt at CNC wiring. My mill - pretty bad, but at least it works reliably and I kept the high-power stuff in a separate enclosure from the signal components.




    Getting better on #2 (pic rotated). DIY plasma for friend. Zero noise-related issues after a year of almost daily cutting.





    Think I'm getting the hang of this, but still not a pro. (#3) Industrial automation machine w/Clearpath servos. Note how I separated the AC and DC top and bottom, plus extra terminal blocks & PLC I/O for future expansion. This was an actual paying job.



    Operator station for the same machine. Field wiring not fully tidied up in this photo.

  7. #43
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    Re: Any pics of cnc control cabinets?

    A lot of good advice there.
    More room, more room!
    Document! Label!

    Cheers
    Roger

  8. #44
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    Re: Any pics of cnc control cabinets?

    Ralph,
    Wow, your post is full of information and obviously took you a long time to write.
    Thanks very much!
    Gary

  9. #45
    Community Moderator Al_The_Man's Avatar
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    Re: Any pics of cnc control cabinets?

    Also contactors generally have a HP rating on them as well as the usual amperage value etc.
    I agree it is a good idea to draw up a decent schematic of the installation, especially for future trouble shooting. Ladder format is my preferred method.
    One thing you might see out there is many examples of ladder diagrams that include contactors and overloads (O/L's) that show the O/L drawn on the R.H. side of the contactor coil.
    This was done many moons ago for convenience sake when wiring motor starter P.B. stations.
    It is now considered a no-no as borne out by NFPA79 examples etc.which show all control contacts on the L.H. side of the coil.
    I also use TR64 for control wiring as it has smaller insulation thickness than TEW/MTW etc.and doesn't fill raceways up so much.
    Use suppression devices across the contactor coils, Resistor/capacitor (R/C) for AC types, and diode rectifier for the DC version.
    Al.
    Attached Files Attached Files
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  10. #46
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    Re: Any pics of cnc control cabinets?

    I guess I started writing and just thought of all the really stupid stuff I did that caused me irritation while stumbling through the "zero experience to working control panel" learning curve.

    Well, maybe not stupid, but certainly ignorant.

  11. #47
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    Re: Any pics of cnc control cabinets?

    Well, it's been a while, but here is my new control box that I've been working on for a couple of months. It's a 16x20x10 Hoffman box I scored on Craigslist for $50

    120V Power comes in the left top to a 25 Amp circuit breaker. From there individual leads go through fuses before powering the individual power supplies, except for the 36V psu and the VFD. Those leads go through a contactor first which gets tripped by a relay on the Acorn board once the Acorn boots up successfully. The VFD is front ended by an EMI filter.

    This is a 2 axis machine running Leadshine drivers and NEMA23 closed loop motors.

    Thanks to Gary Campbell and Jim Dawson and Ralph (spumco) for design ideas and Marty and Keith at Centroid for troubleshooting help.

    I wanted to show you guys that I didn't just steal your help and not use it.

    Thanks very much
    Attached Thumbnails Attached Thumbnails Centroid Acorn Control Box.jpg  

  12. #48

    Re: Any pics of cnc control cabinets?

    Looking good :cheers:
    Jim Dawson
    Sandy, Oregon, USA

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