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  1. #21
    Quote Originally Posted by Desertboy View Post
    Not sure the specs but you cannot use 12v inductive sensors on a ramps board directly you need to wire some resistors to drop the voltage as it will fry the arduino so I would err on the side of caution.
    I can believe that - most of the motion control boards have the same limitation. The basic electronics is 5V and won't handle more than that on any digital input. With the Arduino, the digital input pins go direct to the Atmega chip and that is rated at 5V on all inputs. However, the power supply via the Vin pin should be happy with 12V as this goes to a voltage regulator to give 5V for the rest of the board. In fact, if you are not supplying 5V via the USB connector, the recommendation is to run the Arduino on at least 7V as the regulator needs a bit of headroom to work correctly.

  2. #22
    Quote Originally Posted by m_c View Post
    One is for where the work piece is, and one for the size of tool ;-)

    I'm sure the work piece offset doesn't need explained.

    Whether tool offsets are any use, depends on if/how the controller implements them. For mills/routers, the two offsets are tool length compensation, and tool diameter/radius compensation.
    Tool length is only really much use if you have some way to switch tools and reliably repeat the previous tool length I.e. something with a tool changer.

    Diameter/radius compensation is more important, as it allows g-code to be used that doesn't rely on a certain size tool being used. In a nutshell, with diameter compensation, you can produce G-code that simply traces the outline of what you want to cut, the controller then applies a suitable offset based on the set tool diameter, and cuts on the inside or outside of the g-code line. If you want to use a different diameter tool, you just change the set tool diameter and the controller adjusts to suit the new offset.
    Without the compensation, you need to produce G-code that already follows the offset cutting path based on the diameter of the tool you plan to be using. If you want to swap tool diameter, you would need to re-generate the G-code to have the correct offset for the new tool.

    It can be argued what method is better. Using cutter compensation makes the g-code more versatile, but is reliant on the correct tool offsets and modes being set in the controller. Without compensation, eliminates the issue of having to set tool offsets and simplifies using the machine.
    With any decent CAM, there's minimal difference in producing the G-code for either. Regenerating for a different tool diameter is usually a case of just setting the new diameter, and clicking a button, so not using compensation is hardly a major problem given how often you're likely to need to alter tool diameter.
    The hardest part, is making sure the post processor is producing the correct codes and format for your controller.
    Thanks mate, that's been very clarifying. I do most of my CAD in fusion 369 which has an inbuilt CAM tool patching and code generator, I'm not sur elle if you're familiar, but that's what I plan to use!

  3. #23
    Quote Originally Posted by Neale View Post
    BTW, on the subject of Arduino power - I'm pretty sure that the Uno spec says that it is happy with 7-12V as it has onboard regulation to give 5V for the Atmega chip, etc. I think my Sanguinololu 3D printer controller (that dates me...) uses 12V. I'm in the process of developing an Arduino-based controller for a different kind of machine at the moment, which is why I was looking this up on the Arduino site a couple of nights ago. It may be that the shield does not pass its power to the Arduino purely because its acceptable input voltage range exceeds what is acceptable by the Arduino.
    Yeah, the most likely reason is the variable input. While the RAMPS is designed specifically for 12V without modding, this board takes 12-36V so it's not a simple matter stepping down the voltage for the Arduino. Saying that... I've previously bought a whole load of really cheap £0.99 tiny little boards that take 5636V and transforms it into 5V then through a USB socket. These boards are about the size of a postage stamp and do the job. So actually building one into the board wouldn't cost much...
    I think therfore that it's just not been upgraded as both that and SD and screen support should be decently simple for someone with the know-how.

    I really love the open source market in some ways, I'm just not able to contribute to that in any meaningful way... yet. I try to think outside the box and take different approaches with my machines for the sake of expanding the database and share that information where I can though :)

  4. #24
    Quote Originally Posted by AcrimoniousMirth View Post
    Well said! I'd like to add that it's even cheaper than £25 now! CNC shield and Arduino UNO coming to about £10-15 total now including the cheap pololus.
    I knew I'd be using NEMA23s (part of the limitation of me recycling old bits) so I reused some old DRV8825 drivers which as you say are capable of 24-36V and higher currents, so are suitable for the NEMA23s. Those back in the day would've cost me about £7 so you're right, cheap as dirt for hobbyists :)
    I'm going to buy 4 AM882H and a 60v power supply when I finish my build but at moment finishing the Z axis and mounts seem to be more important.

    But now you can buy 5*DRV8825 for £7 from china delivered which is crazy.
    Last edited by Desertboy; 28-06-2017 at 10:54 AM.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  5. #25
    On the software side had you looked at Estlcam It is primarily a hobbyist CAM package with 2D and 3D machining including carving lots of functionality and apparently it can control the CNC directly through grbl. We've been using it for a year now in an educational setting.Its not perfect but it's amazing value for money £43.00 and it's much better than the shapeoko stuff like easel. It definitely doesn't have all the fusion 360 stuff but its free to try and would offer a simpler workflow.

  6. #26
    These look cool
    http://wiki.protoneer.co.nz/Raspberry_Pi_CNC

    Pair with a touchscreen lcd and you have an all in one solution for a desktop mill.

    Not worth it for me though as I have a spare dell laptop which has a flip touchscreen to work as a pseudo tablet which should be ideal to build into the machine and gives me a much bigger screen to work on and a very neat solution and if I do need the proper keyboard and I flip it back round.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

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