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Thread: DIY CNC Help?

  1. #1
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    Default DIY CNC Help?

    I have a lot of questions about a CNC machine I am going to build and I'd love to ask at least some of them here as many users of this forum seem very knowledgable and I really like the fact that it is an Australian forum, however, will anyone mind that my focus isn't solely wood? I'm also interested in metals, plastics, glass and foam which complicates things.

    Please forgive me in advance, I am known to complicate things.

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  3. #2
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    Post the questions and people will give their 2 cents.

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    So here goes with some of my questions:

    1. I am keen to start basically tomorrow (this obviously unrealistic though as I don't have the materials yet), but unsure which I should do first. Build the table/gantry, buy the steppers, spindle and other electronics and build a kitchen bench version of the controller, or start with something else entirely?

    2. Are there any alternative designs to a gantry style CNC machine that I should look at? I haven't seen anything else in my internet travels.

    3. If you were building/buying a CNC table, which size would you want and why? 1.2m x 2.4m, 1.8m x 2.4m, 1.5m x 3m or even bigger? I'm currently thinking that I should build a 1.2x2.4m machine as that seems to be the typical sheet material size and space is somewhat limited, but I know you can get bigger material and would hate to be limited later on.

    3b. Who would typically use a CNC machine bigger than 1.2x2.4m?

    4. Is it going to be possible to create a CNC router that can carve wood, mill stainless steel and cut/engrave glass and mirrors? I don't mind if it is slow in performing the last two actions (small passes at a time), as it means that I won't need a laser cutter while space is a concern - hopefully one day I'll have a much bigger space to work with.

    5. I am thinking of using rack and pinion for my X and Y axis, and ball screw for my Z. Thoughts/recommendations?

    6. What is the maximum gantry height anyone might recommend? I'm considering a 50cm gantry height for certain 3D pieces I would like to make using an A axis.

    That's enough for now as I'm sure I'll have many later. Any help is appreciated!

  5. #4
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    1. I normally suggest building the machine itself before buying the electronics as they can eat up a good chunk/all of your starting funds, but you may want the motors for sizing.

    2. Not if you want to build something as large as a 1.2x2.4M table.

    3. It depends on your requirements. 1.2x2.4 is a standard sheet size so its a good sized machine.

    4. wood yes, stainless no, not too sure about glass do they use a scribing bit? if its a cutting bit I'd think you'd need coolant to prevent glass dust from being inhaled.

    5. R&P for X and Y and ballscrew for Z would also be my suggestion.

    6. Not sure myself but I'm building a machine to mill aluminium and I think 150mm is too high which is what I've got before I build up the table.



    Anyone else feel free to post and disagree with me or add additional points/options/opinions.

  6. #5
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    Hi d0vr,

    There is no one size fits all cnc router. What is going to dictate the size and capabilities of the machine is what you want to use it for and budget. if you want to do 3d carving then you are going to need a large Z height etc. If you are only going to be cutting sheets then you don't need as much height.

    CNC machining is great but you first need to really think about what you want to do with it and go from there. There is a huge difference between carving wood and hard metals. I think you will struggle with stainless and I haven't seen anyone gut glass yet, that's not to say it cant be done.

  7. #6
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    Thanks for the replies so far.

    Regarding glass/mirrors, it has been done by this man, I'm just not sure how easy it is going to be to replicate.: [ame="http://www.youtube.com/watch?v=HyI111Tn0Cs"]CNC milling glass plates and mirrors - YouTube[/ame]

    I'm perfectly fine with requiring a cooling system to cut metals and glass if required, I'll just need to do a lot of research into the best way to implement one. Are there any reasons that a vacuum hold down wouldn't work with a cooling system that anyone knows off?

    Quote Originally Posted by Ch4iS View Post
    1-6

    Anyone else feel free to post and disagree with me or add additional points/options/opinions.
    These responses are directed at anyone who wants to help.
    1. Yeh, I was honestly thinking of starting on the controller first.. but am certainly looking for more opinions on that!
    2. I thought as much. I did see a robotic arm being used a few times, but I think that is out of my obtainable limits (for now haha).
    3. Just to clarify, are there any other bigger sheet sizes that are used that you know of? I think I've seen something like a 1.5x3 sheet of something being used somewhere.. not quite sure where or what though. Not to be too vague or anything though
    4. So engraving and cutting stainless steel is never going to happen without a laser cutter in your opinion? Or I can't really combine both a mill and a router into the same design? I'd really love to know why either way if anyone knows. I want to make control panels and cases and would rather SS than aluminum sometimes.
    5. Glad to know I'm on the right page there.
    6. Why is 150mm too high?


    [quote=marty989;1532744]There is no one size fits all cnc router. What is going to dictate the size and capabilities of the machine is what you want to use it for and budget. if you want to do 3d carving then you are going to need a large Z height etc. If you are only going to be cutting sheets then you don't need as much height.[QUOTE]

    Budget is what I require to get the job done I suppose. And I do plan on doing 3d carving in wood, foam and aluminum - I already have jobs that I want to run on this machine.

    CNC machining is great but you first need to really think about what you want to do with it and go from there. There is a huge difference between carving wood and hard metals. I think you will struggle with stainless and I haven't seen anyone gut glass yet, that's not to say it cant be done.
    I know what I want to do with it, unfortunately it's quite varied and will very likely be used for both uses 50/50. Half of the time it will be being used for sheet work, and the rest for milling metals and carving in 3D. I'm hoping to make molds to use for lost foam casting, and for making rubber/plastic castings. I also need to cut some shapes that I don't want to do by hand out of mdf or plywood. I would like to build furniture with it. And I'd love to make some control panels with it as well. I could also see myself making 3D signs of course.

    I've seen everything I want to mill/cut happen in video, but I'm struggling to find a clear answer about whether I can do both in the one table with the right spindle, design and other required equipment. I am hoping to produce a commercial quality machine, not just a hobby machine (not that there is anything wrong with hobby machines! It's just not right for what I am wanting it for).

  8. #7
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    I don't know anyone who has built a laser that can cut metal. Most of the self builds so far have been CO2 lasers which will at best etch metal.

    Coolant systems and vacuum tables are difficult because you don;t want your coolant sucked through your vacuum . With vacuum tables a lot of the time mdf is used as the spoil board which isn't coolant friendly.

    The higher you go in z axis the more difficult it is to keep the machine rigid. The complexity of keeping the machine rigid also increases with size of the machine.

    Can you weld? For large machines ie mechmate style all require welding. If you can't then extrusion based machines will limit your size.

    The requirements for your machine are quite varied and I think it would be quite expensive to build.

    You have to build the electronics with the machine size in mind as well. Your stepper motors and drivers are all going to be dictated by the size of the machine.

  9. #8
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    Quote Originally Posted by marty989 View Post
    I don't know anyone who has built a laser that can cut metal. Most of the self builds so far have been CO2 lasers which will at best etch metal.
    So that rules out any form of lasers then for engraving. Any ideas on how I can transfer the milling of ferrous materials that I've seen done on small CNC mills to larger tables? Without wanting to sound too uninformed, it is just a better spindle of some form being used? If it's not going to happen, then it's not going to happen and I will have to build/buy a separate machine for milling steel and stainless steel, but it just seems a little redundant having several machines of the same size with similar motors in it.

    Coolant systems and vacuum tables are difficult because you don;t want your coolant sucked through your vacuum . With vacuum tables a lot of the time mdf is used as the spoil board which isn't coolant friendly.
    They were my exact two concerns. Is there anyway to separate the cooling fluid from air as it goes into the plumbing under the table or to successfully suck the fluid away from bit afterwards before it even gets to the plenum? And is there any other material that could be used as a spoil board when working with metal perhaps? Alternatively, I just might not be able to use the vacuum hold down when milling metal..

    The higher you go in z axis the more difficult it is to keep the machine rigid. The complexity of keeping the machine rigid also increases with size of the machine.

    Can you weld? For large machines ie mechmate style all require welding. If you can't then extrusion based machines will limit your size.
    It will be a steel machine like the MM, except bigger/bulkier. It's not being designed for easy transport, but instead for being a beast of a machine. Hopefully it will be very flexible in what work it can do, and extremely accurate. Welding will likely be under the watchful eye of a family friend who does metal work for a living. I've also already been thinking of some gantry designs to help keep it rigid - I can show them when I get to putting them on a computer model.

    The requirements for your machine are quite varied and I think it would be quite expensive to build.
    I know it'll be expensive, I have a small loan that works like a credit card which I will be using to help fund this machine, and I can pay for things over a bit of time. I'm more concerned with what's possible feature wise at the moment.

    You have to build the electronics with the machine size in mind as well. Your stepper motors and drivers are all going to be dictated by the size of the machine.
    My current plan of attack is as follows:
    1. Work out what features I want in my dream machine [Done]
    2. Research which features are actually possible, and in which combination [Current step]
    3. Decide which features I need immediately, and which can be added later
    4. Finalize desired size and power requirements and purchase steppers and spindle and other electronics
    5. Build 'kitchen bench' control (perhaps start working on pendant and control panel designs)
    6. Draft and 3D model of final table design
    7. Build table
    8. Mount electronics, test, refine, finish controls, test, refine, add any finishing touches (like paint).
    9. Add additional features later over time if required.
    10. Master the machine and produce lovely pieces of functional (and some not so functional) art

    Does this look like the right approach?

    By the way, please don't take any of my comments as disregarding advice or anything as these are the exact type of comments I am after! I'm getting more and more excited and can't wait till I can start buying some materials.

  10. #9
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    I had a post between the current #5 and #6 but it's gone for some reason. No idea why..

  11. #10
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    Just to clarify with lasers cutting metal I meant for self builds. There are commercial machines that can cut metal.

    I believe the main challenge in cutting ferrous metal is rigidity.

    People also use plasma cutters for cutting ferrous metal on mechmate type designs. It doesn't leave as nice a finish as milling, waterjet etc. It also can't be used for any 3D type cuts.

    Looking forward to the build

  12. #11
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    Quote Originally Posted by marty989 View Post
    The higher you go in z axis the more difficult it is to keep the machine rigid. The complexity of keeping the machine rigid also increases with size of the machine.
    The longer the arm from the bearing the greater the movement caused by any play in the bearing. Increasing the distance between bearings by a large amount would reduce this affect.
    There are lots of machines that have the rails mounted up high which overcomes a lot of that but are a pain to load from the end. The framework to lift the rails could be uber strong which would make it an order stiffer. I was thinking of a machine with the raised rail on one side of the gantry but one side with the lower arrangement so it would be easier to load.

    Mike

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    That's okay Marty, no need to clarify as I knew what you meant regarding lasers cutting metal. By any kind, I meant any kind that I can make. My options are either very expensive laser cutting/engraving system that I can't afford or a milling system that at least have a good fighting chance of making!

    I also want some 3D as well, so it rules out the other options (plasma, waterjet etc). And glad you're looking forward to it, I shall keep everyone updated as it happens.

    @Mike, by rails mounted high, I assume you are referring to the MechMate style design that has the two side rails above the table height? If so, I have an idea that will hopefully give me the best of both worlds.

    If anybody in Perth who has enough knowledge about CNC designs and some time who likes coffee, wants to meet and chat about my plans, I would be all ears. Same goes if any could please show me a working CNC in person rather than just the YouTube videos I've been watching?

    And thank you for all your help so far. If possible, I would appreciate some pointers with picking the right servo motor and drive combination? So far I have heard good things about Oriental Motors, but they seem expensive. I've also been looking at Teknic motors and drives (teknic.com) which are used by CAMasters Cobra (Untitled Document) which seem very reasonably priced and suited to the possibility of selling a router to anyone who might want one in the future. Not that I plan on doing that, but I don't want to plan to not do that

    Any thoughts on those options, and also can anyone please offer some resources on how to calculate what size/torque/power I require?

  14. #13
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    Hi d0vr

    Standard sheets are actually 1220 x 2440 and you'll want to be able to cut to the edge so you will want some overtravel equal to the diameter of the bit your using. Add to that the rails need to be long enough to accomodate the width of you gantry head.

    On my machine I was limited by the ball screws I had which were 2500mm which allowed 2460mm max travel once you take off the ball nut length.

    I too designed for a large Z axis but dealt with the over reach and rigidity by making the table able to lower for large work but remain close to the gantry for panel work.

    Making a machine this size capable of milling ferrous metals is a huge challenge IMHO. Stiffness and machine mass would need to be substancial to avoid tool chatter, I'd think this would mean cast granite style construction.

    If you put a receiver tank between the bed and your vacuum pump any coolant should collect there rather than be sucked thru your pump. If your vacuum bed is working properly and you gasket inside your cuts then it should not have leaks anyway. Then again a coolant tray could be fixed onto your bed for this type of work so the MDF board becomes a non issue.


    How big of 3d metal milling do you want to do?

    Cheers
    Mark

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    the larger the stepper motor , the less RPM you get , any thing over 1200 oz/in , go for servo's

    a direct drive 5mm pitch ballscrew off a 200 pulse per rev stepper , will give you a resolution of 0.025mm per step ( 1 thou/in ) gear it down more and it will be so slow you will run it over night with no one watching ive been known to do that , 8000 rpm servo's are available if you want to gear it down more , larger ball screws suitable for 2400 span might only come with a 25mm pitch , so its your choice ,size or speed or accuracy or money , none with out the other , and its exponential , 2x the size cost 4x as much , 2x the accuracy costs 4x as much as well ,accuracy at the cost of speed is the cheep way ( yes i have ran 12 hour 3d cuts before) if you want double the " power " (4x) ,double the accuracy (4x) ,double the speed (4x ) it will cost 4x4x4 , 64x as much , the big industrial 1200x2400 are cheep at $120,000 , ( the one at my work 1220x2440 cost $750,000 a beautiful machine )the china made import are a trade off for $3000 if you dont have $2000 for a china 6040 + a grand for mods ,bits , materials , forget about it , this hobby aint cheep , you could bye one off Rrod for 2x as much for a 4x better machine , ( hint )

    i use a 65lt old car LPG tank for a receiver off my vacuum pump , it must have 20kg of carbon fibre resin in the bottom by now ( they say water is bad for vacuum pumps?) 5 years and still going , but still works
    LPG tanks have 3 holes , in , out , and one can be modified for a drain , a bit of extended plumbing , and rooting around to fill it too 14psi , then blow the water out ( mount it on an angle ) out of date car LPG tanks are free , and a vacuum is only -14PSI , not a problem

    there are vacuum pumps that run off compressed air , there loud and next door will complain , i use a 3 cubic foot refrigeration maintenance vacuum pump and put up with the oil fumes


    so some questions
    1 accuracy , will 1/1000 of an inch do ?
    2 power , with a huge amount of power , you can mill steel , but it will have too be the proverbial brick #### house of builds
    3 speed , , a trade off between , power /accuracy / speed / size /dollars
    4, budget , yer i fell for this one and bought a china import for 2 grand , against my " MORE POWER ? MORE SIZE ? MORE SPEED? wishes

    cheers ken
    how come a 10mm peg dont fit in a 10mm hole

  16. #15
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    Quote Originally Posted by mhasting2004 View Post
    Hi d0vr
    G'day Mark, your post is exciting to me as it confirms a few of the design decisions I've made so far and gives me a lot of new information that is very important. I too am planning on utilizing a moveable work platform, as I thought that would allow for more rigidity in the gantry itself, and I doubt I would cut below the half way point, especially if I was using a 4th rotating axis for 3d models. Do you think I will still be able to get a rigid gantry if it is 30cm high?

    If milling steel is possible, any steel work I do on this machine, will likely be 2.5D work, rather than 3D work. I would like the possibility of making control panels and custom enclosures (like custom computer cases). True 3D work will likely be done in foam or wood, which I will use for molds if I require other materials - such us using lost foam casting for aluminum shapes.

    Based on the sheet size you said, I think I will make the work platform 1500x2500mm and make sure the rails/gantry are long enough for the spindle to reach the entire area. I mentioned above that I was planning on using rack and pinion for the X/Y axis, and a ball screw for the Z axis.

    Is there any reason you used a ball screw for your Y axis Mark?
    Also, could you please show me an example of what you mean by cast granite style construction? When I searched Google, I only found machines capable of cutting granite. Is that what you meant, or did you mean machines made out of cast granite?
    If you could also elaborate on what you meant by how big of 3D metal milling I want to do and where exactly a receiver tank would go, that would be great. If I'm not mistaken, I think you mean use the plumbing for the vacuum pump for the coolant to go through, and let gravity remove the coolant into a receiver tank before it hits the pump, but I could easily be wrong and confirmation either way would be great.

    Here are some links to some metal work I would love to be able to replicate, or produce similar items of:

    http://www.haitimetalart.com/i/Tree_...HR-443-500.jpg
    www.haitimetalart.com/i/Fish_Sealife/HR-393-24-500.jpg
    http://www.uniquesteelart.com/images...3-0734an-1.jpg
    http://img268.imageshack.us/img268/8711/img1877zt.jpg

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