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Discussion in 'Tutorials' started by Symlink, Apr 14, 2017.

  1. Symlink

    Symlink New
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    Hi guys,

    I am pretty new to the whole world of CNC. Could someone walk me through the basics and tutorial on how to build one. I do not have unlimited funds and I don't mind tinkering.

    I am looking for an average size CNC. I want it to be as sturdy as possible and as precise as possible.

    I will be doing mostly aluminum/plastic parts.

    1- What would be the best frame to do what I want? Are kits worth buying?

    2- Best motors ?

    3- Controller board. Is an arduino fine?

    4- What should I avoid ?

    5- I live in Canada where do you guys buy the parts or do you get them made for you?
     
  2. Jonathon Duerig

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    (1) The reason you want a kit is because you have a community of people who have experience with the same problems you are likely to encounter and a supplier who makes sure that everything works together and can send a replacement if a part is defective. The first CNC router I assembled was from a kit and I'm glad that I went this route. It gave me the experience and insight to design my own later on, and also helped me understand the things I really needed/wanted most in a CNC router. There are some packs here (like the C-Beam Machine) which are both sold as a bunch of parts that will work together and have a lot of people who built them. There are a few other builds here that lots of people have built even though there isn't a kit available through the official store (like OX).

    (2) Typically you want stepper motors and at least NEMA 23 motors. NEMA 17 motors are a bit underpowered for CNC routing even though they work well for 3d printers.

    (3) Most of the CNC machines I have made just use an Arduino with GRBL. It is cheap even if it has limitations. And if you later upgrade, you will have a baseline understanding of what you really care about when upgrading.

    (4) I'd avoid generic kits on ebay/aliexpress. If you buy a kit, you want the community and the support of a consistent supplier. OTOH, if you want to buy a bunch of parts for tinkering and experimenting, there are some great deals there. Some things quality matters more than others. If you order an aluminum rail that is bent, then it is useless. But if you order a pack of 100 T-Nuts and a few aren't threaded properly, then it might still be a good deal.

    (5) I think there is an OpenBuilds distributor for Canada. It would be worthwhile to look. Otherwise, I think you can still get it shipped from the OBPS. I've used most of the parts from the OBPS on one project or another and they are good quality with good follow-up if they make a mistake.

    -D
     
    Rick 2.0 likes this.
  3. Symlink

    Symlink New
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    Thanks alot for your reply :)

    Is there a guide or tutorial if let's say I was to purchase the C-Beam CNC.

    I understand there are assembly instructions... but as for the electronic part.

    Are there any good tutorials to get going with Arduino?
     
  4. Jonathon Duerig

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    Aside from the C-Beam Machine build page and thread, I'd look at the GRBL wiki:

    Home · gnea/grbl Wiki · GitHub

    And depending on whether you want a gShield or an xPro, I'd look at their respective wikis. gShield is cheaper and connects to a standard Arduino as a shield. xPro has an embedded arduino and has everything on a single board. I use both and they both work well.

    You might also want to look at the Shapeoko wiki (though some of it might be out of date with the latest releases of Grbl). My first kit was a Shapeoko so i learned a about how to use GRBL from there at first:

    Electronics - ShapeOko
    Grbl Configuration - ShapeOko

    -D
     
  5. Symlink

    Symlink New
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    So if I am purchasing this kit :C-Beam Machine Mechanical Bundle

    From what I am understanding I am gonna need an arduino + gShield

    A power supply, wires and tools.

    And of course reading :)
     
  6. Jonathon Duerig

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    If you get that bundle, you will also need:

    Spindle/router + power supply
    End Mills
    Homing/limit switches
    Controller (arduino + gshield) + power supply
    Wiring
    Dust collection
    Workholding
    Z-touch plate

    This is the list of indispensable stuff I found I could not do without when using a CNC.

    In terms of tooling, this is the number one tool I'd recommend:

    Balldriver Screw Driver Set

    Being able to screw in the cap screws with a driver instead of the L or T hex wrenches is a huge improvement.

    -D
     
  7. Symlink

    Symlink New
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    You are the man.. thank you very much for spending the time to help me out here.

    I am unsure of the purpose of the Z-touch plate.

    Correct me if I am wrong.

    1- Spindle/router is pretty self explanatory
    2- End mills.. cutting :p
    3 -Homing / limit : while I do understand the limit switches purpose (so the axis have a maximum traveling distance or space) I am not sure about the homing ? or are they the same
    4- Controller I got that power supply as well
    5- wiring of course
    6- Dust collection is mandatory or just a bonus?
    7- Workholding would be like the mounting plate ? isn't that in the kit?
    8- Z-touch... I googled but can't seem to grasp the concept.
     
  8. Jonathon Duerig

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    (3) Homing switches can also double as limit switches and vice versa. The idea of homing is that whenever you turn on your machine, you home it which sets the machine zero point for all axes. This makes everything repeatable. If you don't have homing, you can never get back precisely to where you were.

    Homing switches make everything easier:

    - If a job stops (or you stop it) halfway through, no problem. Just fix the problem, don't move your work piece, then home again and start. Now it will go through the precise same cutting motions and finish the job (even if the first half is just cutting air).

    - You can easily make permanent pegs or stops for your wasteboard. Then simply align your workpiece to those stops, clamp it down, and run your program without a need to move the spindle to the correct spot first.

    - Basically any time you might need to figure out where exactly a position in your computer is on the board, homing will make that consistent.

    So you can have a machine that works without homing switches. But they are so cheap that I would never consider making a machine without them again. If you can't guess, my first machine didn't have homing switches. :)

    (6) I found dust collection to be mandatory for all but a few test cuts. If you are cutting wood, sawdust will go everywhere and settle on everything (including in your lungs) without dust collection. When cutting plastic, swarf will collect in the cut paths and make it more likely to melt on future passes without dust collection. I've not tried cutting metal with a CNC machine yet. Build your machine first without dust collection. But I think you will find it a priority once you start actually cutting. There are lots of DIY ways to do this. For a while, I used an upside down plastic bowl with holes cut out of the top, for example. The only part you can't DIY is the vacuum.

    (7) You will need to get your MDF spoilboard locally since it doesn't come with the kit. And then you have to figure out how to solidly attach your workpiece to the spoilboard while cutting. There are a lot of different techniques, but you need to get this right or you will end up with broken bits and/or pieces flying off the spoilboard and hurting you or causing damage. For light cutting of soft materials, tape might work. For wood, people sometimes use plastic nails. There are low-profile clamps (then you must make sure your path doesn't intersect the clamps). And then you have to make sure that if you are cutting something out entirely that it stays in place during cutting with tabs or an onionskin or an additional clamping.

    (8) When cutting, you will need to accurately find the z-position relative to the spoilboard. There are a few different ways to do it. One involves jogging the bit very close to the spoilboard and stopping when it just touches. Either by sight or using a piece of paper and stopping when the paper catches. This is very laborious and is another reason to have homing switches (so you only do it once when you change the bit rather than for each job).

    But the other involves using electricity to figure it out. You have a 'touch plate' which is made of copper or somesuch and connect that to a pin on the GRBL. Then you have another wire that you clip onto the end mill (which also conducts electricity) and wire that to ground. There is then a G-code command which will lower the bit until it detects that contact between these two items is made. At that point, assuming you have a well-known thickness on your touch plate, you know exactly how far the bit is from the spoil board and you can set that as one of your zero points. This is still a bit annoying, but not nearly as error-prone and fiddly as the paper method above.

    Lots of people make DIY touch plates by buying a little copper plate and soldering on a wire. Or you can spend money on a pre-made one. The one I use is somewhat spendy, but the plate is on a spring so that if there is a problem and the bit doesn't stop at the touch plate, I can hit the E-stop button and my bit won't have been damaged by the pressure (since the spring just yields).

    You can start cutting without a Z-touch plate. But you will likely want to buy or make one soon because it makes everything much easier.

    BTW, this does remind me of two other things to think about. First, getting a physical E-stop button is handy so if you notice something wrong, it is never hidden in another window or something because it is a physical button.

    Second, if you get Arduino + gShield, you should also get a screw shield. Something like this (I don't know this company in particular, so I am not recommending you get it from them and you can also find this kind of thing elsewhere):

    Screw Shield for Arduino-DFRobot

    It comes in two parts and sits between the gshield and the Arduino. What this will let you do is easily connect wires to various arduino pins that aren't used by the gshield itself like homing pins, etc. If you don't have a screw shield and want to use homing pins, you will have to solder on headers yourself onto the gShield (or at least this was the case with my gShield).

    -D
     
  9. Symlink

    Symlink New
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    Thank you for this.. This will probably save me alot of time and money.
     
  10. Giarc

    Giarc Master
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    Jonathan did a great job answering your questions, so I will just add a couple thoughts to it.

    The z-touch plate is a good idea, but I have found (for me) that the best way to set z zero is to lower the cutter close to the spoilboard. I then loosen the collet and let the cutter "drop" down to the spoilboard. Then I tighten the collet. I set the Z-zero to this position. All my gcode files have the spoilboard as z-zero. Then, if my 19.05 mm piece of wood is only 19.04 mm thick, I do not cut into my spoilboard 0.01 mm. Since I started doing it this way, I have not cut into my spoilboard (that I can see) and my parts are cut out cleanly. To me this form of zeroing the Z is quicker than using my z-touch plate and typing in commands.

    I do not use MDF as a spoilboard. I use particleboard (not to be confused with oriented strand board -OSB) which is also dimensionally stable. It is also significantly cheaper than MDF, and if you end up doing what I do and screwing parts you are cutting to your spoilboard so you do not need to cut tabs, the screws will hold much better.

    I also like the Arduino, but after trying it with the cnc shield and DRV8825 drivers, I decided to switch to using the DQ542MA drivers OpenBuilds sells. The DRV8825s are barely (if that) up to the task of driving my NEMA 23 motors (176 oz Z axis and 260 oz X and Y) and the motors would heat heat up, especially the Z motor. The drivers would sometimes start to overheat and the motors would miss steps. The DQ542MA drivers run so much smoother and my motors run cooler. Kyo has a great video in the resources section showing how to wire them up to an Arduino. He also explains it on his Sphynx build. Basically, if you buy a $12 arduino board and 4 of the DQ542MA drivers, you are spending as much as you will if you buy an all in one board, but it will be able to handle larger motors. Then, if you spill a beer onto one of the drivers while it is powered causing it to burn out, you just need to replace that one and not the entire board. Don't ask me how I know.
     
  11. Jonathon Duerig

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    Giarc, I've been considering following your lead, buying four DRV8825 drivers and running them directly from an Arduino via GRBL. Before now, I've stuck with the all-in-one driver boards. I watched Kyo's video and was intrigued. So I have a few questions of my own about your setup:

    (1) What are you doing to power them? Do you use 4 different power supplies with 4 different AC adapters for them? Or do you wire them all to one power supply?
    (2) What voltage are you using?
    (3) What is the wattage of your power supply (or power supplies)?
    (4) When switching, did you notice any change in the speed or acceleration that was possible with the motors?

    -D
     
  12. Giarc

    Giarc Master
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    First, I got rid of the DRV8825s and went to the DQ542MA drivers. I assume that is what you meant, but I just wanted to clarify.

    1) I use one power supply.
    2) It is a 36 Volt switching power supply and it is 11 amps.
    3) 400 Watts
    4) Honestly, I didn't really pay attention to the speed and acceleration. I only used the DRV8825s for a few engraving projects then made the switch. With the engraving of photos, there wasn't a lot of acceleration and speed happening. ;) After the switch, I noticed my motors were running cooler, they seemed to run smoother, and I didn't have to worry about a thermal shutdown. With the DRV8825s I had to have a fan blowing on them or they would overheat and shut down. Even with the fan blowing on them, I had a couple incidents where, when they were making long cuts at speed (3000-4000 mm/minute) or jogging long distances, one or the other Y driver would miss steps causing the Y gantry plates to bind. I just never felt like I could trust them for heavier duty cutting. My gantry may be heavier than a lot of people's which may also have affected the smaller DRV8825 drivers. With the DQ542MA drivers, I will easily cut through the 5.2 mm Home Depot plywood in one pass at 3000 mm/minute at 10000 rpms with my Makita router.

    What I have mentioned is strictly based on my experience. Other folks have had good luck with the all in one boards and CNC shields utilizing the DRV8825 chips. For all I know I may have received sub-par drivers and, do to my limited experience with them, assumed they were all of that capability.
     

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