Stimpak, an overkill mechanical paste dispenser.

In the age of internet, some people think it’s weird not looking up if something exists. I myself I’m in the leage of “buy the tools if possible”, because I don’t like spending time creating the tool I need AND then more time to do what I intended to do in the first place.
However, in this case, it didn’t cross my mind that it could be possible that what I needed already existed (not in a egotistical way, I just didn’t thought much about it). Anyways, I wanted a mechanical paste dispenser.

Easy enough, a screw, a syringe, and something in between to hold everything together, right? Well, normal metric screws do not bear well with pressure, they tend to bind, so I figured that, at least as a test, I could go by with a micro fine pitch screw. As I didn’t had such a screw (or tap, for that matter) at hand, I had to make my own:

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That’s like half a millimetre or less pitch screw in a 8mm diameter shaft. That would need a keyway guide AND machining the end to accept a standard plunger tip:

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Since I had made it at home, I also had to make a tap for the nut/actuator wheel, wich was simply done by putting a cone on a threaded shaft and some relief cuts so a sharp edge with all the threads would engage on the nut material:

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The point here, tough, is that the shaft was 8mm, so in order for the tap to work, I had to make an undersize hole, probably in the order of 7.8mm or so in the nut, but I don’t happen to have a drill in such diameters at hand AND they are usually expensive. However, if I freezed a drill bit to -12ºC, I could achieve somewhat the same effect:

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Super cold alcohol+water mix to freeze the drill bit.

And there we go!

whatsapp-image-2016-11-30-at-14-53-22Shaft threads haven’t been deburred yet on this photo.

So, did it work? Well, more or less it did:

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However, the nut bind easily because of the shape of the screw threads AND the friction against the backplate. As expected,  I stripped the nut threads, as acrylic is not the best material to machine high load/friction parts. But the concept was there and somewhat solid, now it needed a real trapezoidal screw, a technic material for the nut and some bearings.

As before, a tap is needed for this screw:

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With that I could thread a delrin wheel and machine the leftover screw end to accept the plunger:

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Also machined two flats on the screw, as I did not like the keyway idea in the first prototype:

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With all that done, a needle bearing (and some acrylic machining I did not photograph) there it was:

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The bottom plate captures the syringe in place, and the top bearings both grab and guide the axle so the gear can do it’s job. The needle bearing removes stiction between the top plate and the gear.

It is made to be easily removable/serviceable:

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In action:

Note how fast stops the paste extrusion. (nothing exceptional, just that it does XD! )

It will have a ratchett mechanism to actuate the wheel and a small nut on top to make the needle bearing captive, but it sorta works now, wich was the objective.

Dragonfly

Sometimes I wonder if I should change the blog’s name to “The Electromechanical Mercenary”, mostly because I keep doing things like this:

Extras:

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Those were developed in just under one and a half weeks, so they should count only as prototype. I am preparing a fancier version with hollow axles on all gears, better pneumatic mechanical advantage and overall higher quality in design, mostly because I can, but also to show-off at Eurosteamcon 2016

versions

Some more shots of the beautiful model that wore it:

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This is my wallpaper for the time being:

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Lastly, the blue in the wings is high quality automotive reflective tape, so you must avoid taking pictures with flash, or this will happen:

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WTF?!

Can’t remember on whose computer I saw this, but…I feel insulted:

fuck this shit
Silver bracelet and COMPUTER CHIP.

Where? that’s just a PCB! holy mother of all fucks!
I will concede that it is well mounted and properly jeweled (seen the girl’s shop in person, she works well) but still, that’s NOT a chip.