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  1. #1
    Quote Originally Posted by Bush Flyer View Post
    I have just done a member search on ebay but aliexpress have not been trading in the last 12 month
    But I will take your advice and order 3.1Nm stepper and four separate drivers.
    By aliexpress I didn't mean the eBay seller, I was referring to the website:
    Cheap CNC! Wantai 4 PCS Stepper Motor Driver DQ860MA 80V 7.8A 256micro CNC Router Mill Cut Engraving Grind Foam Embroidery-in Motor Driver from Industry & Business on Aliexpress.com

    Quote Originally Posted by Ross77 View Post
    Jonathan also mentioned aiming for a higher design speed to give headroom on the constant cutting speed but this head room is not wasted as you can have fast rapids when moving between cuts (subject to mass/inertia limitations of course) cut at 5m/min move at 10m/min
    True, but it's worth noting that a high rapid speed (up to a point) doesn't make much difference to the overall job time compared to a lower speed - 5m/min vs 10m/min is a good example. Often you'll find even doubling the rapid speed will only reduce the overall time by a few percent. This is because in general the machine is moving much slower and in many directions with a finite acceleration. The acceleration often limits how fast the machine will go, since every time it moves to a different position, or changes direction, at least one axis has to accelerate (or decelerate) and the speed is often limited by this. One good example is detailed engraving - the individual moves are very short, so each axis is almost constantly accelerating (and decelerating) whilst cutting, and in addition the rapid moves will generally be short so the machine may not get up to the full rapid speed, hence the speed is likely to be limited by the available acceleration.
    Similarly, if the G-code is well written then the proportion of rapid moves will be quite small (clearly there are exceptions). Suppose the rapid moves comprise 10% of the total time taken for the job. Here, doubling the rapid speed will only take 5% off the overall job time.

    Clearly there are exceptions - if the rapid speed is limiting how fast you can cut, then having more speed (so long as the acceleration is sufficient to use it) will decrease the machining time noticeably. An example of this is surfacing an MDF bed, where cutting at 10m/min would be perfectly reasonable (I do it)...but then how often do you need to surface the bed?

    Often it's a compromise between maximising speed and acelleration, since increasing either requires more power and the motors only deliver a finite amount of power. With pulleys you can adjust the ratio to optimise for better speed or acceleration, but in the end you still need motors with enough power - hence my suggestion to get the 3.1Nm motors as their power output is plenty and they're better priced than virtually all other realistic options.
    Last edited by Jonathan; 31-05-2013 at 08:33 PM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  2. #2
    Jonathan thanks for the update in finding that site, I have now placed a order for drivers and have also bought the 3.1Nm stepper motors that you advised, That was a good saving in cost. Thanks.
    Last edited by Bush Flyer; 03-06-2013 at 10:17 AM.

  3. #3
    Been a while since I did any work to my CNC router as I was in Hospital again for a few days and the wife has band me from the garage. But I did get some wiring done, but have a lot more to do, I'm waiting on a E stop switch and more wire.
    So just some photo's where I stand at this time. I hope to get going again in the next couple of weeks.

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    Last edited by Bush Flyer; 13-07-2013 at 01:31 PM.

  4. #4
    I am managing to get back to the garage for a hour here and there still real sore. I have finished the control box for my cnc but I still have some wiring to Finnish on the limit switches.
    I also got some more of the cnc assembled, the next job is to build a table that will house the computer the controller and the cnc router all in one. Then fit a new wall plug in the garage and a bracket to the wall for the monitor.
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  5. #5
    Love the model aircraft. Router looks good too. G.
    Last edited by GEOFFREY; 12-08-2013 at 07:21 PM.

  6. #6
    Looks like you are nearly ready to start cutting. Just got a couple of concerns with the power supply. Firstly I can't see in the photos how you are going to cut the power with the e-stop. Also you may have problems with noise bundling all of your signal and power cables together. Anyway, looking really good.

    Regards, Ian.

  7. #7
    Quote Originally Posted by irgonomics View Post
    Also you may have problems with noise bundling all of your signal and power cables together.
    Ian's correct here.! . . The worst thing you can do is use un-sheilded cable and tie signal and power cables together like you have here.!!

    Things may appear to work ok just jogging around etc but the potential for problems increases big time while cutting with noise getting on the signal wires causing all sorts of strange things to happen.? . . . .Everything from sudden limit or E-stops trips to sending phantom signals to motors causing them to either go in wrong direction or increase steps etc.
    Honestly Complete nightmare tracking down where it's coming from so anything to minimise the better and you've done everything to maximise with those cable ties and unsheilded cable on signal wires.!

    Other than that looks Good and happy cutting.!
    Last edited by JAZZCNC; 13-08-2013 at 09:09 PM.

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