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  1. #1
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    Default Help with belt loads

    Please excuse my rudeness. Just so happy to find a group that might be able to help that I got all excited and forgot to introduce myself.
    I'm from Oz and I have an interest in watches.
    One of the lesser understood areas of watchmaking is the printing of dials.
    This is typically done by producing an image into which ink is deposited.
    This ink is then picked up by a silicone pad and the pad is moved over to the dial and pressed down upon which the ink is transferred to the dial.
    I have made a fully manual prototype machine and I am looking to automate the process.
    I haven't actually tried the manual system but expect to do that within a fortnight.

    Some images on dials are overprinted many times to build up the texture of the numbers so I'm looking for a fairly high accuracy for repeatability.

    The difficulty with this whole project is that I am working with so many grey areas where knowledge is gleaned in small slivers and I'm trying to put together the pieces of the jigsaw.

    Actually, the cnc portion is fairly well documented overall but I don't yet have the experience to understand and implement all of the concepts.

    Original post
    I'm surely going to miss providing some of the required information so just ask and I'll provide (if I can).

    The project is to build a pad printing machine.
    This is a boring little machine that has an X axis that goes back and forwards about 110mm and a Y axis that goes up and down the same distance.
    They effectively alternate in operation.
    (As an aside, most commercial machines use pneumatics and I want to use electrics to remove the requirement for a compressor.)
    A manual machine is built using Vslot components and I'm looking to see how much work would be involved to convert this to CNC.
    As I have the prototype I have measured some forces with a digital scale.

    I have picked a travel speed of 500ips (212mm/s) but I don't know how achievable that is. Speed is of the essence otherwise the ink will dry out before it gets deposited on the workpiece.

    So X axis 110mm travel
    Approximations with g=10m/s/s
    Load 35N =3,5kg ~ 7lb
    Speed 500IPM 212mm/s

    Y Axis 110mm Travel
    Load 120N = 12kg = ~25lb. This is needed to press the pad onto the stencil.
    Speed 500IPM 212mm/s

    I have sized some steppers but that is a secondary consideration until I understand what drive system will work.
    I was thinking of using 6mm GT2 belts but when checking the specs I see
    GT2 6mm has a of working tension = 3kg and breaking tension = 56kg
    I could probably use that for X drive but I think commonality would be good so I would try and use the same drive system for X and Y..

    For Y Axis the load (which only occurs at the end of the stroke) appears to be far too high for the 6mm belt.
    I was trying to use 2 x NEMA23 with a holding torque 120Ncm (probably something like a 57HD4016-01-A which is just a motor spec I found on fleabay). At this point I have no idea if the model numbers tell anything about the stepper.

    I was going to use one of the same motors for the X axis as well as I'm thinking that similarity would be helpful.

    My lack of knowledge means that I don't understand how to overcome these items.
    1. Belt load on Y axis is much higher than nominal (even with two belts).
    If I can get it to fit I would expect I'd need a belt width of about 25mm for GT3. (I have downloaded a Powergrip GT3 Derive design manual but I can't see the working tension).
    Or should I consider an Acme thread leadscrew?

    If the GT3 is suitable it would appear that I need a 20mm dia pulley so the torque is sufficient.

    2. I am not sure how simple it is to put the two steppers in parallel. The motors have 2 phases @ 5.2V and 2 amps each. Do I just buy a whopping power supply and plug them in parallel to one drive socket?

    TIA.

    BTW if someone wants to know more about the complete project please let me know and I'll be happy to answer what I can.


    Regards
    Alan



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    Last edited by 1afc; 04-19-2017 at 08:53 PM.


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    Default Re: Help with belt loads

    Is a compressor really that big of a problem? Using air cylinders solves so many problems. End stops for precise positioning are just screws, diameter of air cylinder (and regulators) easily set the applied force, some cylinders have build in cushions at end of stoke...

    Replicating that sort of positioning electronically is easy enough but a bunch more work. Applying force electronically is a chunk harder. Using electronics makes sense if you want intermediate positions. I would avoid steppers and belts if you only need to move between end stops.



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    Default Re: Help with belt loads

    Or you can buy a fiber laser and hatch the designs or numbers of the dial, spray paint it with a urethane paint and wipe the top surface with thinner then let it dry, you can finish it within seconds sir. I tried it but on wood and plastic since we dont have a fiber laser yet for metals but by and by we`ll get there, we have a huge demand now on metal projects. shaping metals no problem but working on the designs on it with the fastest speed that`s a problem, a CNC router cannot beat the fiber laser`s speed on engraving or hatching metals.



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    Default Re: Help with belt loads

    Hi vegipete
    I agree that pneumatics are far simpler but the reasons for electronics/cnc is that it should be a lot quieter and the CNC allows a lot more "tricks" to be incorporated eg wait times while ink dries etc.
    ...and cnc looks like an interesting challenge.


    Quote Originally Posted by vegipete View Post
    Is a compressor really that big of a problem? Using air cylinders solves so many problems. End stops for precise positioning are just screws, diameter of air cylinder (and regulators) easily set the applied force, some cylinders have build in cushions at end of stoke...

    Replicating that sort of positioning electronically is easy enough but a bunch more work. Applying force electronically is a chunk harder. Using electronics makes sense if you want intermediate positions. I would avoid steppers and belts if you only need to move between end stops.




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    Default Re: Help with belt loads

    Hi Khouj
    I think a couple of things mitigate your suggestions
    1. That adds another process which adds time
    2. I'm looking to put lume paint on the dial and also a number of different colors so that may make it quite messy
    3. I may also want to use the machine for standard pad printing
    4. from what I have seen with current accuracy of laser etching, it is not yet up to the quality of good pad printing.
    5. Pad printing also allows multiple passes so one can build texture in to the dial depending on the number of passes.


    Quote Originally Posted by KH0UJ View Post
    Or you can buy a fiber laser and hatch the designs or numbers of the dial, spray paint it with a urethane paint and wipe the top surface with thinner then let it dry, you can finish it within seconds sir. I tried it but on wood and plastic since we dont have a fiber laser yet for metals but by and by we`ll get there, we have a huge demand now on metal projects. shaping metals no problem but working on the designs on it with the fastest speed that`s a problem, a CNC router cannot beat the fiber laser`s speed on engraving or hatching metals.




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