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:

whatsapp-image-2016-11-30-at-14-49-08

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:

whatsapp-image-2016-11-30-at-14-50-53

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:

whatsapp-image-2016-11-03-at-20-50-54

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:

whatsapp-image-2016-11-03-at-20-50-541
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:

whatsapp-image-2016-11-30-at-14-51-58

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:

whatsapp-image-2016-11-19-at-12-48-25

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

whatsapp-image-2016-11-19-at-13-32-08

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

flats

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

whatsapp-image-2016-11-30-at-12-44-30

whatsapp-image-2016-11-30-at-12-42-55

whatsapp-image-2016-11-30-at-12-43-20

whatsapp-image-2016-11-30-at-12-44-02

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:

whatsapp-image-2016-11-30-at-12-45-25

whatsapp-image-2016-11-30-at-12-45-47

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:

IMG_20160501_170354

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:

IMG_20160501_150428

This is my wallpaper for the time being:

IMG_20160501_150328

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

IMG_20160501_152847

 

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.

Spineless II: Poor man’s ball joints.

Today I’m going to show you how the spinal prop ball joints where made:

Aria

Materials/Tools:

  1. Threaded balls.
  2. Polycaprolactone, a.k.a. friendly plastic.
  3. Access to a lathe, or a friend that has one for a small turning job.
  4. 3 lip chamfer tool (and power drill/lathe)
  5. Clamp.
  6. Scissors.
  7. Pliers.
  8. Ball’s appropriate allen key.
  9. (optional) Plastic dye.

First of all, you must understand what you want to do. You want to encase the ball in some material wich allows it to swivel freely, more or less something with this profile:

Ball joints 014

Ideally, that would have the thickness of the support, but that presents a bit of a problem when the ball is already odd sized:

Ball joints 013

I don’t have a 5.4mm drill bit for the anvils to encase the ball. Also, this kind of arrangement won’t provide any ball centering, so it IS going to be off to one side or another.

The solution? make a flange on the anvils so they fit snuggly in the hole of the support:

Ball joints 015

That, of course, comes with it’s own set of problems, first of all, the odd sized holes:

Ball joints 016

Again, I don’t have a 5.6/5.7 drill bit at hand (I usually only have x.9 bits to use prior reaming an even sized hole). You could always modify the thickness of the support so it gives you a better hole size, but any variation will mess up that fit. Nothing that a bit of ingenuity can’t solve.

For now you can build the anvils, taking care of drillng the holes for the ball slightly smaller than the contact points (I could have used 5.5 mm in this case, but went with 5mm because I didn’t want to take any chances). Also, since you’re at it, drill and tap one of the anvils so you can screw the ball in there, and doesn’t move on further operations.

They should look like this:

Ball joints 018

Now comes the trick. Using a chamfer tool to eat away the corners, slowly fit both anvils until you can’t rotate the support around them (so their spacing when resting against the ball, matches your support thicknes, in my case, 4mm)

Ball joints 017

And they will look more or less like this:

Ball joints 006

Ball joints 007

Also, altough the drawings show a smooth bore, you must provide a means for the ball brace to stay in place, otherwise it will slip out of the support.
I just drilled a hole from the free end of the support and 2mm onto the cylinder’s body itself:

Ball joints 003

And now it’s time to assemble some ball joints!

First, melt some friendly plastic (I dyed mine black for aesthetic purposes only, be warned, it’s a mess, use gloves!) then loosely press fit it in the hole you are going to use:

Ball joints 004

Trim the excess:

Ball joints 005

Now, before everyting cools, submerge both the support with the plastic and the ball holder anvil in very hot water to ensure that the plastic doesn’t cool quickly and flows around everything:

Ball joints 008
(I couldn’t hold both and the camera at the same time ^^U )

Now, do both these steps QUICKLY!

Assemble the support with the hot plastic and the COLD (room temp.) anvil:

Ball joints 009

Then press fit all, use the clamp to ensure everything stays in it’s place:

Ball joints 010
Note how the plastic oozes from the hole, that’s good, it means it probably filled everything as supposed to.

Wait for it to cool a bit, then, grabbing only the support…

Ball joints 011

Pull the cold anvil from it:

Ball joints 012

If you look carefully, you can see the metal from the ball, as there is almost no material left between it and the oozing plastic from the cold anvil:

Ball joints 019

Using the pliers, just rip off the leftover. If you didn’t wait long enough, the soft plastic will deform and mess up the joint. If so, just melt everything up and start again, friendly plastic doesn’t mind it:

Ball joints 020

Assuming all went well, unscrew the ball with the allen key, but DO NOT, I repeat, DO NOT, wiggle the ball yet. Unless you waited a lot, the plastic in contact with the ball is still soft and will grab the ball and deform if you move anything. Leave it to one side to cool down and repeat the process. I was able to do three joints with a very hot glass of water, (didn’t had a thermometer to monitorize water temperature).

Ball joints 021

If you applied enough pressure, that bit of flash should come off easily:

Ball joints 022

Now you only need to break-in the joint. Move the axle to one extreme and then all around the range of the joint. That will loose it enough to move smoothly but still have very little play:

Ball joints 024

And that’s it! now you wave fully functional ball joints for normal temperature conditions. I suppose you could thread the exit hole from the support and thread a nozzle from a 3D printer to inject ABS plastic. But that’s delving into high temperatures and performances I don’t need at the moment.

And now, let’s watch it one more time in this glorious shot:

I bet you didn’t mind the vertical video. XD!

Also, remember I said you needed to provide some sort of anchorage for the ball brace to hang into? Here’s what happens if you don’t:

Ball joints 023

POP!