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Solder paste and flux dispenser

DIY for hobby use

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WIP!

Next level DIY dispenser.

  • Github - Firmware & assembly manual (upcoming).
  • EasyEDA - Schematics / PCB / BOM (everything can be ordered in couple of clicks).

  • Attaching threaded shaft

    Vitaly08/10/2019 at 12:33 0 comments

    To push paste out of syringe, we need threaded shaft. There are 2 ways:

    • Use coupler and threaded rod
    • Use gearbox with built-in long threaded shaft

    Coupler with threaded rod

    You can take this coupler 2.3mm to 3mm. Use 2.5 mm drill bit to enlarge hole, then tap M3 thread and insert 60mm M3 rod or screw with loctite.

    Disadvantage is loosing 20mm of movement length (or increase length of device). Let's leave this for Plan B.

    Gearbox with built-in long shaft

    There are no ready mini stepper solutions with M3 shafts, but we can assemble it from two donors:

    In may sound strange, but those parts are compatible!

    See photo. Donors are on left side, result on right side. Total cost with delivery will be about 10$. Not ideal price, but acceptable, requires zero efforts and is the most compact.

    If you decide to combine other components - check gearbox sizes, those should be equal (the most popular can have 10x12mm or 12x14mm plates).

    If components go out of stock - we still have Plan B with coupler. Both solutions do not require complicated tools and can be reproduced by anyone.


  • Motor & gearbox

    Vitaly08/10/2019 at 06:33 0 comments

    Many hand made dispensers use 28BYJ-48 motors. Those are very cheap, but not enough small and not convenient to mount. We need something better:

    • More compact.
    • Precise enougth.

    Let's estimate desired gearbox ratio.

    All small 10-15mm steppers usually have 18° step (20 steps per turn). Gearbox can be:

    • Plastic. Usually up to 1:50
    • Metal. Up to 1:295 (sometime up to 1:600)

    Other data:

    • Pusher uses M3 shaft with 0.5mm pitch.
    • Inner dia of 10cc medical syringe is about 15mm (a bit more for pneumatic syringe, but not principal now
    • Volume of paste for 0603 resistor pad is ¹/₁₂ - ¹/₁₆ mm³.
    • Let's say we need to dispense one 0603 portion with precision about 10%.

    Desired portion size per single motor step is 0.006 mm³.

    Let's calculate, what stepper with plastic gearbox 1:50 can give us:

    (3.14 * 15² / 4) * 0.5 / 50 / 20 => 0.09

     0.09 mm³ is very bad. It's 1.5x more than portion size and 15x more than desired precision. What can we do?

    • Use metal gearboxes with better ratio
    • Decrease syringe dia (use 3cc or even 1cc)

    1cc syringe has dia about 5mm. Portion per step will decrease in 9x. Better, but not perfect. Let's use metal gearbox 1:295.

    Estimate for 3cc syringe (9mm inner dia):

    (3.14 * 9² / 4) * 0.5 / 295 / 20 => 0.005

    Estimate for 1cc syringe (5mm inner dia):

    (3.14 * 5² / 4) * 0.5 / 295 / 20 => 0.001

    In total:

    • 3cc syringe & 1:295 gearbox - 0.005 mm³ per step, very good for 0603 components. With some reserve for smaller pads.
    • 1cc syringe & 1:295 gearbox - 0.001 mm³ per step, should be enough for all.

    Of cause, we could use dynamic model (quick step forward and back) and cheat with paste viscosity. But that's much more complicated and result will depend on paste temperature. Also, it's not good idea to use micro stepping, because it's not precise with cheap motors and consumes more power.

    Conclusion

    • Mini steppers with metal gearboxes are preferable over plastic ones.
    • 3cc & 1cc syringes are most optimal for soldering paste.
    • 10cc syringes still may be interesting for fluxes and glues.

    That's all with boring maths, next time I'll try to post some pictures :)

  • Buttons

    Vitaly08/07/2019 at 03:55 0 comments

    For dispenser it's important to have soft control button. Because if you need to apply big force, needle may shift out of small pad. There 2 main parameters:

    • Operational force
    • Button form

    Human skin is "soft". To be convenient, button should have big height or big square. To be sure, buttons with low operational force, available at LCSC, were tested:

    The most promising are:

    • Panasonic EVQQ2B03W (in left bottom corner, white button)
    • ALPS Electric SKHCBKA010 (left side, blue pusher)

    EVQQ2B03W looks preferable - more compact.

  • Review of existing projects

    Vitaly07/21/2019 at 23:59 0 comments

    Since it's not interesting to reinvent wheel, it worth to inspect existing projects, and decide what can be done better. Here I will comment the most interesting ones.


    28BYJ-48 based dispensers

    All projects above are opensource. But while those are very cheap and easy to do, BYJ motors are not convenient for compact design. If you have TS-80 or TS-100, you should understand what i mean.

    Pen-like

    Though that project is not opensource, it's very nice. Author is professional engineer and shares interesting technical details.

    Notes:

    • It uses machined parts for pusher. May be nice for manufacturing, but not convenient for hobby DIY.

    Intents

    Let's try to formalize, what would be interesting to do (and why that combination of features will be new or unique).

    1. We need "popular project" - easy to do, no machining, cheap enough.
    2. It should be small, pen-like. Instead of syringes replace, it would be more convenient to have multiple dispensers.
    3. It would be interesting to support fixed portions dispense, instead of constant flow. But that requires additional considerations about interface usability.

    Seems ok. Now we need to do some estimates about precision.

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MikeM wrote 08/10/2019 at 14:21 point

OK Vitaly - correct this alliexpres link is a plastic gear motor which I DO NOT use.

  Are you sure? yes | no

Vitaly wrote 08/10/2019 at 15:03 point

Sorry again, that mistake was not intended. Your dispenser is certainly the most interesting and beautiful of currently available. Goal of my logs is to share technical experience, not to say anything bad about other's work.

  Are you sure? yes | no

MikeM wrote 08/10/2019 at 13:46 point

Hi - my dispenser (5V DC USB Dispenser)  has all gears metal- your statement that I use plastic gears in my dispenser is incorrect - please do not make Statements which are based on your assumptions. 

Thanks

Mike

  Are you sure? yes | no

Vitaly wrote 08/10/2019 at 13:58 point

Mike, sorry for that. I was confused with motor look, and recognized it as different model https://www.aliexpress.com/item/32969821590.html. Removed that paragraph. Thank you for pointing out my mistake.

  Are you sure? yes | no

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