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  1. #11
    Hi Clive thanks for your responce. In terms of design I have dfx files for a mechmate but am reluctant to go down that path I want to build something simlar using welded steel box section

    I only really want to cut mdf and ply sheets if the machine is capable I may make a few bits for my rc car out of alloy but thats not important as I dont need to if I cant

    As for tolerance id like repeatability withing 0.5mm and accuracy of the same over a meter span. Its not overly imporant over the distance of the table

    do you think im beong unrealistic?

  2. #12
    Hi. if you follow the advice from some of our more experienced members, you will find it difficult to build anything that ever could be as inaccurate as your current requirements!!! In practice I feel sure that when you have a machine that performs really well, you will end up doing taking on work that would benefit from greater precision. PLEASE, listen to what Irving, the "3 J's and others tell you and you will end up with a machine that performs well and will save you some of your hard earned cash. Good luck with your project. G.

  3. #13
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 8 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    I'll answer the why are those controllers crap?
    They use a very common, but failure prone stepper driver chip, especially if you try pushing them anywhere near thier limits. Which given the size of machine you're planning on building, you would have to do to get even moderate performance.
    Individual leadshine drives (be that older M452s? or the newer digital drives) will allow for far more powerful motors, and far better performance. These cheap combined controllers/drives seem like a bargain, but when one of the axis goes pop, which they are renowned for, unless you're good with a soldering iron, the whole lot is junk. And you'll soon regret the purchase when watching your machine crawl doing rapids, as the drives just aren't capable of reliably moving it any quicker.

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  5. #14
    Quote Originally Posted by dangerousdave View Post
    People keep saying them boards are crap but have offered no alternative? I know there cheap crap thats why im here to get opinions and learn more about what others are using.
    I bet you can't find a finished build log on this forum which doesn't show/tell which drivers they used.

    Your question is like asking someone 'what engine should I buy for a 2.5m long van?' Nobody is going to tell you to get a specific engine because we don't know anywhere near enough about the van. Granted, a lot of people use the same drivers and similar motors, so we could mention one of those - but aside from being an argumentum ad populum, that would be irresponsible since you'll very likely end up with a poorly matched system. Don't think that just wanting to cut MDF and plywood makes things easier, as it's actually optimal to use the highest feedrates for cutting those materials.

    Pick a few of the build logs from this forum at random and read them:
    Gantry/Router Build Logs
    Also read some for smaller machines so you can see the important differences you must consider for your relatively large machine.

    Edited to add:
    What are you prepared to pay for the whole system? As a rough guess I'd say minimum 2k to make something good enough, but good enough is the enemy of the best...
    Last edited by Jonathan; 10-01-2014 at 03:44 PM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  6. #15
    Hi

    am a newby so can only offer an opinion, i am building a large machine like you, but a bit more ridged for stone. Like you, i first though get the motors, but, as i was told, WRONG WAY ROUND.

    I would suggest



    1. Design/Build your frame then gantry ( or pick one of the designs on here, most of them are good enough for what you want to do )

    Think about rail sizes, and gantry weight in the design stage

    2. Then ask on here about motors/servoes and cards. I was given some very good advice in relation to driver boards on my thread onb here. have a look atg them.

    As a general ball park, i think your est of motors/driver and card should be between 500 and 700, depending on what you want to end up with.

    The next part being quite important if you want to keep cost down and build easyer.

    Do you actualy need a machine that big, As maybe a 4 foot by 4 foot, is cheeper, but a lot easyer to build. When you go bigger, you start running into engineering problems, all are get roundable, but none easy or cheep.

    re the Chinees cards you link to

    Ther eis an upgraded version of the driver chips, ( V3 ) that seems to get round the problem.

    If you do get one of these NEVER GET ONE WITH THE STEPPER DRIVER ON BOARD, always seporate drivers. secondly. If you read up on here, you will realise that a lot of the power packs, sold with these kits, are to low power for heavy use of the motors,

    So, for a cheaper 4ft by 4ft, thats not going to be cutting solid material all day, maybe, ther are worth a punt, but, the support on these chiness cards is none exsitant, i know that from experience. and the all in one cards ( with settper drivers on boards ) are a nightmare to use/setup and maintain.

    Just my opinion and remember am a newby ( quite good at math and engineering though )

  7. #16
    Quote Originally Posted by dangerousdave View Post
    I really dont think this is a huge project.
    Mistake No1 Assumption is the Mother of all Fuck UP's

    Quote Originally Posted by dangerousdave View Post
    Im by trade a qualified engineer albiet a cnc turner thats never worked with wood but cant be that hard :p..
    Means Nothing I've helped every type of person with CNC from Engineers to Doctors and I can tell you the ones who build the fastest and have the least hassle are usually the ones who wear the Suits.!!. . . . .Because they Admit they know nothing and Listen then Act.!!. . . . . Those that waste money or fail do it the other way around.!!

    Quote Originally Posted by dangerousdave View Post
    but thats why im asking about the electronics side of this. The router bed is for me the easier bit. People keep saying them boards are crap but have offered no alternative? I know there cheap crap thats why im here to get opinions and learn more about what others are using. Im sure not everyone is using expensive gekodrives? Surely someone uses some alternative? As far as a time scale goes maybe 6 months would be a realistic one.
    Sorry Dave but you didn't ask advice on what to use you asked about that specific board and got a reply, it's not our fault if it's not what you wanted to hear.

    Regards what to use then Jonathan Van engine example is correct but it's worse than that. . . . . What your actually saying is your planning to use R&P with possibly 4Nm motors for cutting wood.!! Fair enough you'd think.??

    But back to the Van, What your actually saying is you'd like to know what MAKE of electronics to run 4ltr engine on to get 8000MPH but without telling us the MAKE of the vehicle, WEIGHT of the vehicle or what FUEL your planning on using what size WHEELS and how many GEARS it will have.???

    MAKE = Materials to be constructed from.
    WEIGHT = Mass to move IE gantry etc
    FUEL = Voltage running motors at.
    WHEELS = Pinion Size
    GEARS = Ratios

    Now you can't give us this information because you don't know it your self because you haven't designed or planned the machine. So therefore we can't possibly tell you what to buy.

    I could offer suggestions now but that would be wrong at this stage and exactly why I offered the advise I did when I did.
    If you choose not to follow any of our advise then more fool you and I'll wish you good luck. . . . But I and many others on here don't suffer Fools lightly, We will suffer Insults and even the Odd Idiot no problem but Fools will get very little response back and absolutely NONE from ME. . . . . . DONT BE A FOOL . . . and take the advise in good faith.!!

  8. #17
    Hi Dave

    MAKE = Materials to be constructed from.
    WEIGHT = Mass to move IE gantry etc
    FUEL = Voltage running motors at.
    WHEELS = Pinion Size
    GEARS = Ratios
    Just to give you a heads up

    WEIGHT = Mass to move IE gantry ==== Frame steal 80mm by 4mm or 100mm by 4mm or 5mm. == Gantry, either steal or ally. Its quite easy to calculate the weights, it will be the gantry weight thats important, not the frame

    FUEL = Voltage ==== The gantry weight will tell you what motors and drivers are required ( most of the time nema 23/4 sometimes geared. ). ==== also, your power pack ratings are important,

    WHEELS = Pinion Size ( or ballscrews, ) Again, your gantry weight/style will help you decide this, 16mm or 20mm if ballscrews i suggest ( i dont know enouigh about R&P ), same with rails

    GEARS = Ratios ===== This is about the speed and accuracy that you want from the motors, its a curve, higher speed, less accuracy.

    Most supplyers of metals give the the weight per meter, and you might even fine something suitable for the frame ( with adjustments ) at the scrap yard if your trying to save a few .

    My opinion if your going the cheep route.

    There is no cheap route with motors and drivers, you will just need what you need, and its machine specific

    Spindle - ebay 2.2kw, water cooled with VDF around 250, Aldi ( or other cheep place ) cheap 30 dremile type. You get what you pay for. The cheap one will not last long on even modrate use, but it will cut/mill thin stuff ( slowly ) ( just add a cooling fan ), If you got the mounting plate right on the Z, you could even use a cheep router. You might try with the cheap one, to convince yourself you need to pay for the more expencive one, and 30 is not a big loss,

    Software -- for what you want to do, Mach3/4 would be good ( 120 ), there are cheaper alternatives, some free, but unless you have reasonable programming skills, and a good understanding math, you wont beat mach for the support for newbies. In all honestly, with mach, the 120 is worth it just for the support,

    I hope with what i have put above you have an idea at what parts you can go cheeper on and what parts you can not. If i was you, i would give myself a scrapheap challange, and go looking for something you can use for the frame, your luck might be in. and what you save on that, put into the electronics.

  9. #18
    Quote Originally Posted by george uk View Post
    FUEL = Voltage ==== The gantry weight will tell you what motors and drivers are required ( most of the time nema 23/4 sometimes geared. ). ==== also, your power pack ratings are important,

    [COLOR=#333333]WHEELS = Pinion Size ( or ballscrews, ) Again, your gantry weight/style will help you decide this, 16mm or 20mm if ballscrews i suggest ( i dont know enouigh about R&P ), same with rails
    No disrespect meant George but what your doing is dangerous and quite missleading to new users.? . . . . I'm tempted to say Blind leading the blind but I know you have done lots of reading upto now but still you need to be careful what you post to new users because you can send them in wrong direction quite easily, all done with good intentions I know but still misleading and wrong.

    For instance you Say Mostly Nema23 and sometimes geared.!! . . . . Actually Often for a 8x4 machine using Rack n pinion then Nema 34's are prefered for there higher torque and 99.9% of the time you'll always have a gear ration of at least 2:1

    Also suggesting 16mm ballscrews for a machine this length is totally wrong unless very specific things are done, like using a Rotating ballnut. I won't use 16mm screws much over 1500mm and wouldn't dream of using a 16mm or 20mm rotating screw at nearly 3000mm.

    Not picking on you here and know your only trying to help but much better advise rather than trying be specific, unless you have first hand experience is to suggest Nothing and tell them to go look around and learn. Then ask questions that are more informed and specific to there needs.
    Last edited by JAZZCNC; 10-01-2014 at 07:08 PM.

  10. #19
    hi jazz

    I was suggesting options for 4ft by 4ft table, up to a full size table, and just trying to give him a general idea. . If you read my post, i had suggested that, i also said i did not know enough about R&P.

    If price was not an issue from him, i would say 25mm rails and screws and servoes, but he is clearly looking for cheaper options, and it is that i offered advice on, but he clearly want to have a crack at this on the cheap. and it is doable, i was just trying to help him understand, that he can not go cheap on motors and drivers. I do have some experience with that type card

    ther are many wrong approaches to machine building, but there are also a few right ways. not just one. If it was like that, you would just point him to this thread, and say build that

    http://www.mycncuk.com/forums/gantry...g-machine.html

    Well engineered, well built, and he lists what he would change

    But he is clearly looking for cheap options, and wants to hobby build. and remember were the hobby built cnc machine started, For me, a graph plotter with a drill strapped to it, 1989/90 machine running it was amstrad 1512, and we had to write the actual code that run it, My current main hobby ( robotics/electronics ) and previous hobbies ( UAVs and RC stuff, kart racing ) all work on very fine tolerances, am used to having to get things a lot more refined than is needed for cnc design, granted, on a smaller scale. I do clearly mark any post that i have given advise on thought that i am a newbie,

  11. #20
    Quote Originally Posted by dangerousdave View Post
    nor do I want to spend a grand on electrics I would have liked to got electrics all sorted for 2-300 quid including motors and psu. What would you recomend for me?
    A rethink !

    Quote Originally Posted by dangerousdave
    Im by trade a qualified engineer albiet a cnc turner thats never worked with wood but cant be that hard
    I've found that the softer the material the harder to get good tolerence. You just have to compare hand cutting dovetails in hardwood and softwood to see that hardwood is much easier.
    Last edited by EddyCurrent; 10-01-2014 at 09:13 PM.

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