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  1. #1
    Ok well this Thread is in response to this post and request from a new builder in another thread.

    Quote Originally Posted by joe.ninety View Post
    Dean,

    I've seen this said a lot but I think what a lot of your seasoned CNC guys forget is that beginners, myself included, have no idea how many IO's they are likely to need? Or really what they're even needed for? I'm kinda guessing homing/limit switches and the like but can't think of much else.
    If you get the chance (and I know you said in another thread you were very busy at the moment) could you just do a post about IO's and what the main needs for them are. I think it would help a great deal of people, the OP included.

    Cheers
    I'll try my best and it will take a few post's to do it justice so bare with me.
    -use common sense, if you lack it, there is no software to help that.

  2. #2
    So let's start with How many I/O.? ( or Inputs & Outputs for those who are brand, brand new and thinking let's start with WTF does I/O mean...Lol)
    With the term I/O I'm talking about General Inputs and Outputs which we can use for machine control and not MOTOR OUTPUTS which are slightly different but can be used for I/O in some controllers but I won't go into that here.!

    I'm also working based on a Router but a Mill isn't much different.

    Ok well, the simple answer is you don't actually need any in most cases.? The machine can be set up so it will quite happily to work without talking or receiving messages from the outside world.
    However, that wouldn't be very safe so as a minimum you need at least 1 INPUT so an E-stop signal can be sent to the INPUT when you hit the "Oh Shite" Button.!

    Next, you might want LIMIT switches.?
    These can be wired in several ways depending on switch type etc ie: series or parallel and how the builder wants them to work on the machine. Each way will use a different number of INPUTS. This can range from 1 INPUT for the whole machine or between 1-2 per axis.
    For instance, if you use simple micro switches and are limited on I/O you would use 2 SW per axis (+/-Limits) and wire ALL SW in a series connection which would only require 1 INPUT. If any 1 switch trips then ALL axis will show a LIMIT as tripped.

    At the other end of the extreme, you could have an SW for each end of travel, so each SW would require an INPUT so for typical 3 Axis machine that would be 6 inputs.! However, this would show which Axis tripped and which end of travel.

    In practice you would most likely use 2 SW per axis wired in series and use 1 IN. Totaling 3 INPUTS for 3 axis machine. This setup would show which Axis Tripped but not which end of travel.
    OR you can have just 1 SW which travels with the axis and looks for a target at each end of travel. This still requires 1 INPUT but with only 1 SW, it still only shows which axis tripped and not which end of travel.

    Then you might want HOME switches.?
    This would require 1 INPUT per axis and if it's a 3 axis machine that uses slaved motor effectively making it 4 Axis then you would need 4 SW each using an INPUT if you want to square up the gantry.

    Now if I/O is limited then it is possible in some cases to combine HOME and LIMITS so they use the same SW. This does mean however that when homing the LIMITS will be turned OFF so it's a little less safe. Usually, with a stepper system, this isn't a problem because you HOME slowly and the motors will stall if something goes wrong. However for instance with a Servo driven machine then if they decide to take off then all hell could break loose and you are not protected by the LIMITS so you would fit separate home SW.

    So lets do a quick count up.
    2 I/O = E-stop and series wired limits.
    4 I/O = E-stop, with limits per axis or combined homes and limits
    5 I/O = E-stop and Slaved motors with shared home/Limits.
    7 I/O = E-stop, per axis Limits, per axis Homes.
    8 I/O = E-stop, per axis Limits, per axis Homes with slaved motor gantry using squaring.
    10 I/O = E-stop, per axis Limits, per end trip, per axis homing.
    11 I/O = E-stop, per axis Limits, per end trip, per axis homing with slaved motor gantry using squaring.

    A typical above basic but safe machine will use 4 or 5 INPUTS depending on 3 or 4 axis.

    The next post will be about OTHER INPUTS, I'll get to OUTPUTS later.

    EDIT: I forgot to point out that it is possible to use limits and homes with just 1 INPUT but it's not recommended because it means using NO (normally open) switches and that's not safe for the limits because if a wire breaks you won't know about until the machine crashes when they don't work.!!
    Last edited by JAZZCNC; 2 Weeks Ago at 09:25 PM.
    -use common sense, if you lack it, there is no software to help that.

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  4. #3
    Ok so Other INPUTS.

    These can be anything from the door bell ringing to kettles boiled.!! . . However common ones are Probes, Drive faults, Spindle faults, low coolant levels, etc.

    Then going to slightly higher level machines you have ATC ~(automatic tool changer) these require INPUTS to signal to the controller that things like the pneumatic drawbar is open or closed, the carousel is in or out or at a certain location. Counting the tool positions etc. A typical ATC can require 10+ INPUTS and nearly as many OUTPUTS.

    INPUTS also allows you to use external buttons or switches to control features found on the screen so you can make control panels etc. Things like Cycle start, feed hold, Spindle on/off, coolant, etc can all be controlled from buttons feeding signals back into the INPUTS.

    Using INPUTS and OUTPUTS you literally can control anything from turning the kettle on to being told when it's boiled and it's for this reason and the fact you don't actually know what you might add or need in the future that you can never actually have too much I/O.

    So the best advice is if you think you'll upgrade in the future then buy a controller with the most I/O your budget will run too or at least buy a controller that can add I/O at a later date using cards etc.
    Some times you are better paying a little more at the beginning for extra I/O or a better quality card that lets you add it because it will save you money down the road when you need more I/O.
    -use common sense, if you lack it, there is no software to help that.

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  6. #4
    Nice summary. I think it is fair to say that building a CNC machine involves lots of choice at each part of the process and that many of the options are not better or worse just different. If you enjoy building machines this can be part of the fun but if you are a beginner you don’t even know what the choices are !
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  7. #5
    Now it's OUTPUTS.

    You tend not to use as many OUTPUTS as you do INPUTS which is why you'll often see cards with 5-IN 2-OUT or 12-IN 6-OUT etc.
    OUTPUTS tend to only handle low currents so they mostly are used to turn on other devices like relays or Transistors which only draw low currents but can handle heavier loads through their contacts etc.

    Some common uses for OUTPUTS are Spindle ON/OFF, Coolant ON/OFF, Vacuum ON/OFF.

    But again they can be used for just about anything and going back to the ATC type setup of a more advanced machine they would be used to control pneumatics. So the Drawbar to release the tool would have a solenoid which was controlled with an OUTPUT, the carousel would have a motor that was turned on/off to rotate it to the next tool or motor or pneumatic actuator to move it in or out of position.

    So OUTPUTS turn things on or off, that could be anything from a light bulb to a Kettle and again going back to the control panel with INPUTS sending Signals from button presses an OUTPUT can do the opposite and send Signal OUT that reacts to that INPUT press so for instance when you press CYCLE START it could turn on a lamp on the panel.

    Again only your imagination and the amount of I/O you have can limit what can be done.!

    Hope this helps some of you and just ask if not sure of anything.

    Edit: Suppose I should mention this for clarity.! There are also ANALOG I/O's.

    These are similar to the standard I/O but they accept or output a voltage range usually 0-10v or 0-5v.

    These would be used for things like controlling the speed of a spindle where an A-OUT would send a voltage based on the commanded speed, so, for instance if you had a 24krpm spindle, 0v= 0 rpm 10v=24k so if you command 12,500rpm then approx 5.2v would be sent from the A-OUT to the spindle controller.

    Likewise, the A-IN would accept a voltage between 0-10v. These would be used for things like setting up external feed override or Spindle override dials using a potentiometer or Spindle Load or RPM feedback from spindle controller. THC (torch height control) on a plasma is another use for A-IN

    So basically an ANALOG I/O sends or receives a voltage range to do with as you please.
    Last edited by JAZZCNC; 1 Week Ago at 01:56 PM.
    -use common sense, if you lack it, there is no software to help that.

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  9. #6
    Quote Originally Posted by routercnc View Post
    Nice summary. I think it is fair to say that building a CNC machine involves lots of choice at each part of the process and that many of the options are not better or worse just different. If you enjoy building machines this can be part of the fun but if you are a beginner you don’t even know what the choices are !
    Yes exactly no better or worse in lots of cases but knowing the difference helps and one can suit better than the other in some situations.

    I think I/O or the lack of it is often the one thing that holds many people back from playing and automating things which would make the machine more fun or easier because if you haven't got it in the first place adding it later can be expensive.

    End of the day it's what you want the machine to do, if you just want a workhorse then KISS works. But if you want a few whistle n bells then I/O is key.
    -use common sense, if you lack it, there is no software to help that.

  10. #7
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 11 Hours Ago Has been a member for 2-3 years. Has a total post count of 595. Received thanks 78 times, giving thanks to others 15 times.
    Very helpful Dean, should be a sticky.

    For those of us using the old fashioned parallel port on the PC with a breakout board (BOB) the number of ins and outs is quite restricted, though 4 combined limit/end-stop inputs, an E-Stop input and a spindle start output work well enough for a basic beginner machine using LinuxCNC or MACH3. However that setup is getting long in the tooth now and even a cheapskate like me wouldn't advocate using it for a new machine.

    Kit
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  11. #8
    I am in the process of rebuilding my control box and my intention was to use 4 inputs :- E-Stop, Limits, Homes and Probe. Where practicable, I will be using travelling switches on the X and Y (but not Z). Limits will be NC in series and homes will be inductive NO in parallel. I have to test this arrangement of Homes works, but I have a box of the switches to play with.

  12. #9
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 11 Hours Ago Has been a member for 2-3 years. Has a total post count of 595. Received thanks 78 times, giving thanks to others 15 times.
    Some applied cunning can reduce the total number of outputs needed if you are limited. My cheap Chinese BOB has a total of one! The cooling pump is on the same mains switch as my VFD and runs continuously which allows better post-job cooling in my opinion and so doesn't need a BOB output. The one output is used as the spindle start output but is also used to switch a mains relay which starts the dust extraction.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  13. #10
    Quote Originally Posted by Kitwn View Post
    The cooling pump is on the same mains switch as my VFD and runs continuously which allows better post-job cooling in my opinion and so doesn't need a BOB output. The one output is used as the spindle start output but is also used to switch a mains relay which starts the dust extraction.
    Often VFD's provide an output Relay which you can use to turn on the water pump when spindle starts or have it turn on another relay which starts water pump and Vacuum when spindle starts. Better than having a pump running all the time VFD is on but spindle not spinning.

    You will probably have to change a parameter in the VFD because often the relay is set to activate when a fault happens but can be set to turn on when start command is given.
    -use common sense, if you lack it, there is no software to help that.

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