Thread: operation cnc

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  1. #81
    Quote Originally Posted by Jonathan View Post
    Jazz will now vote for option 1.
    Won't go there regards stalling/racking has it's all been said.!! But there is more to this than just Stalling motors racking gantry's.?

    The Main reason why I like it is Synchronization.?
    My machine never loses position and the two ball-screws are synchronized exactly the same today has they were when first installed.
    I don't have to worry that on long Jobs the machine will lose sync has the slaved steppers drop the odd step here or there running out of sync with each other slowly racking the gantry.

    Don't have to worry that after 10-12 hours cutting I'm going to find that holes aren't where there supposed to be.!! Or the part isn't actually square after cutting profile out because the gantry slowly racked fraction of degree.!

    The only way to ensure slaved steppers stay in sync is to either have very accurate Home switches or Home to hard stop and do it often. Certainly after every Job to be safe.
    Even then if motors are tuned anywhere near close to the edge, esp regards Acceleration, they can easily lose steps without realising on jobs just a few hours long.
    On Jobs that run non stop for 10-12 plus hours like litho-pains this could and has been for some slaved stepper users disastrous often resulting in not just in in-accurate work but stalls thru accumulative error over hours.!

    Both work and won't argue that fact but I know which works best.!!

  2. #82
    Quote Originally Posted by JAZZCNC View Post
    has the slaved steppers drop the odd step here or there
    [...]
    On Jobs that run non stop for 10-12 plus hours like litho-pains this could and has been for some slaved stepper users disastrous often resulting in not just in in-accurate work but stalls thru accumulative error over hours.!
    I have never seen any evidence of stepper motors on any of my machines loosing 'the odd step'. If it did they would be practically useless - it's either stall and loose lots of step or run perfectly.

    If a motor does stall (which it wont if set properly) then it will only start moving when the step frequency has dropped to a low frequency, so it is possible to loose maybe a few steps (or tens of microsteps) if the motion is very small movements which constantly accelerate each motor, but that's still likely to damage the part whether it's one motor or two. Again, if the motors are tuned properly then, just like on Jazz's machine, you wont loose position so it doesn't matter if it's one motor or two. The only difference worth discussing is the input power considered with the whole system - if the basic calculations show that the motor and driver you can afford to use if just using one will perform better than the same calculation with two motors then go for it. If not it's illogical to use one.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  3. #83
    from a neutral point of view with no experience just thinking about it logically. i'd want to reduce anything that could complicate things.. and to me that means running 1 motor even if that means on this axis you have to buy a big ass one to cope with it.

    if your BoB/drivers are running 2 steppers on the same axis then you have 3 circuits there straight away that have room for error... the data comes along in 0's and 1's and all it takes is for a little interference on one driver circuit and one stepper didnt move as quick as the other.. bam your work is knackered and the machine is out of line....

    now a single stepper has the same interference but this time the whole gantry didnt move.. only problem you have this time is take the wrecked piece of material shove where you like put a new piece down and start again as the machine is still straight


    i'm not saying it wouldnt work.. and i have no doubt that yours works flawlessly jonathan, but my mind tells me to simplify to reduce the chance of error

  4. The Following User Says Thank You to wilfy For This Useful Post:


  5. #84
    Quote Originally Posted by wilfy View Post
    from a neutral point of view with no experience just thinking about it logically.
    [...]
    i'm not saying it wouldn't work.. and i have no doubt that yours works flawlessly jonathan, but my mind tells me to simplify to reduce the chance of error
    That's the point though - by agreeing with that you're agreeing that your logical thinking earlier in the post is based on a false premise, therefore you may not be arriving at the correct conclusion even if the points you are valid. In other words, if my system did have a 'little interference' which caused one stepper to slightly loose position we wouldn't describe it as working flawlessly.

    Either way, if you buy the right electrical parts either system can work flawlessly, so in the end it's just a case of working out which is the most economical.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  6. #85
    Quote Originally Posted by Jonathan View Post
    I have never seen any evidence of stepper motors on any of my machines loosing 'the odd step'. If it did they would be practically useless - it's either stall and loose lots of step or run perfectly.
    Jonathan I've had to correct stuff you made because the fucking things weren't square or correct so don't give me that bollocks.!!

    Also if your going to quote me then make sure you quote the whole fucking picture not just what you want to make fit.!!

    Quote Originally Posted by JAZZCNC View Post
    Even then if motors are tuned anywhere near close to the edge, esp regards Acceleration, they can easily lose steps without realising on jobs just a few hours long.
    On Jobs that run non stop for 10-12 plus hours like litho-pains this could and has been for some slaved stepper users disastrous often resulting in not just in in-accurate work but stalls thru accumulative error over hours.!

    Both work and won't argue that fact but I know which works best.!!

  7. #86
    Guys, I welcome all your comments, but really didnt mean to cause an argument. Lets just put the subject to bed.

    Im in one of these junctions in the road now. Whatever I decide I dont want to alienate myself from advice from either of you.

    I must say however, I think wilfy's comment summerises my present thought chain. and as I have genuinely lost, Yes Lost. one of my 3 steppers it was a case of buying two more for the X axis anyway. So simplifying the bits you cant bite (ie the electronics) and only having to buy one (bigger) stepper & a longer belt & some pulleys seems to me a favourable way forward.

    Don't have to worry that after 10-12 hours cutting I'm going to find that holes aren't where there supposed to be.!! Or the part isn't actually square after cutting profile out because the gantry slowly racked fraction of degree.!
    This machine has cost me an arm and a leg. Im worrying about lots of aspects of it all the time, so Simplifying this area I guess is one less thing to worry about.

    On a seperate note; Im also worrying about how accurately I have mounted the gantry to the slide plates. I mean with my Set Square its bang on; when i slide it along the rails; the rails dont move out or in (however I havent yet bolted them down I think im looking to see if it gets tighter at one end) but if the gantry is not square like Jazz has mentioned above the work wont be square... I guess Il find out in time... Its this kind of think that is doing loops in my head everytime im down the workshop. I find myself standing there drinking coffee and smoking staring at it just thinking about (and questioning) the accuracy of my work.

  8. I have not assembled a thing yet and this scares the hell out of me too, with buildings (what I'm used to on a day to day) the tolerances are like 5-10mm no 0.00 something! My thinking for what it's worth is that If you build enough adjustment into the design then you can shim things to perfection later...

  9. #88
    Guys i really think you are worrying about very little. I've used twin steppers and it was fine. I have belts running my machine with a single stepper on the X axis. It works great for the home machining i do......But! i have two ballscrews sat there ready to change to once i get round to it. If i can make a belt fit to control the screws from one motor then i will, if can't then i will just use two motors. Stick to your budgets up most and don't let bling go to your head. At the end of the day you are machinists now whether you like it or not, your nature will want you to change things later. There is no right or wrong way just preferences? I like both!
    If the nagging gets really bad......Get a bigger shed:naughty:

  10. #89
    I'm glad to see that I'm not the only one worrying about how accurately the machine has been put together. I've just (mostly) finished one side of my frame so I've done a quick test fit. The bed rail and the guide rail are 0.1o out of parallel. Doesn't sound like much but that equates to just over 3mm over the total length according to my calculation :-(.

    It's looking great though KC, keep the good work.

  11. #90
    Quote Originally Posted by JAZZCNC View Post
    Jonathan I've had to correct stuff you made because the **** things weren't square or correct so don't give me that ****

    Yes you have once because the machine started off not square and I didn't realise. When it finished cutting I'm sure it was just as far out as when it started! If the machine had gradually lost 'squareness' then the cutter would have broken and the finish would have been terrible since they were so far out. Since then I have corrected the problem.
    Also, I should add that the customer you're referring to didn't even tell me there was something wrong with the parts before asking you to fix it. If anyone has a problem with something I make, then I will do my best to fix it, but I can only do that if they tell me there is a problem. He also lied about where he'd sent the parts, but that didn't take much working out.


    Quote Originally Posted by JAZZCNC View Post
    Even then if motors are tuned anywhere near close to the edge, esp regards Acceleration, they can easily lose steps without realising on jobs just a few hours long.

    Easily solved - don't tune them anywhere near close to the edge. If you need to do that then you should have bought better motors or drivers.


    There is an easy way to check how square the machine is once it is assembled and working:


    1. Set the machine to drill 3 holes of the same diameter at the corners of a right angled triangle in some scrap, with one side parallel to X.
    2. Push drills or bar the same diameter into the holes.
    3. Measure using digital calliper the side lengths of the triangle by measuring the centre distance of the drills.
    4. There are now various ways to find how off-square the machine is. You can draw the triangle (which will be scalene if the machine is not square) in a CAD program and measure the angle that should be 90 to find how far off it is. There are of course several ways to calculate this angle, or you could just use Pythagoras' theorem to see if the hypotenuse is longer or shorter than expected, then at least you know which way to compensate.
    5. Correct for the error, then repeat until error is acceptable.
    6. If two motors set the home switches appropriately if you have them, or you can put marks on thepulleys you can accurately align.


    I got mine within +-0.01 using this method, but that was with a 600mm calliper. Still with a 150mm digital calliper you can get it very close. Also when measuring the hole spacing parallel to X or Y you should find they're within a few tens of micrometers:

    Click image for larger version. 

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    There will be a slight error due to the lead error on C7 ballscrews, but as the images above show, at least in my case, this is very small - about 0.01mm in 600mm.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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