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DIY printhead

Posted by johnrpm 
Re: DIY printhead
September 16, 2010 08:38AM
Some thoughts on producing a plate with a small hole.

There are many ways to produce a small hole in a plate other than drilling which is very tricky.

1) A hypodermic needle mounted in a larger hole with epoxy or solder. When dry flash the excess needle top and bottom off flat to the plate with a dremel. You could reuse the flashed off pieces of needle to make more nozzles.

(If i remember rightly hypodermics are made by electroplating over a wire....another possible method which could be adapted)...edit (I think they are now made by rolling a larger tube down through dies.)

2) Produce a square hole. two plates bolted together separated by 2 pieces of 0.25mm steel shim. The two pieces of shim are spaced apart around a 0.25mm wire during assembly. The wire is then removed and you would be left with a 0.25mm square hole.

3) Get some Carburettor jets and use them. There are all sizes available quite cheap. ( around £2). Google "Weber jets".

4) Clamp a hard wire of the correct diameter between two blocks of softer material. The blocks will be formed into two semi circular shells. with the wire removed you have your hole.

Edited 1 time(s). Last edit at 09/16/2010 04:39PM by martinprice2004.
VDX
Re: DIY printhead
September 16, 2010 09:39AM
... i have some ten old plotter-ink-needles - it's a steel-tube with maybe 0.3mm inner diameter tapered at the tip to maybe 0.1mm inner diameter ... this could be embedded and cut in the right length, so will give a perfect tapered hole.

Or cut and use the tip as jet with atached capillary without embedding in a plate.

If someone is interested, i can mail some of them ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: DIY printhead
September 17, 2010 10:30PM
Johnrpm, thanks, it is perfectly clear now.

Martinprice2004, lots of interesting ideas. One of the complications is that all of the literature suggests that we need something a bit more complicated than a simple straight walled hole - a conic or pyrimidal opening apparently works much better. I have not been able to find any dimensional drawing of carburetor jets, so I'll probably just have to buy one and take a look.

Viktor, please toss one in with whatever else you end up mailing me and I'll give it a try.
VDX
Re: DIY printhead
September 18, 2010 01:48PM
Hi Jim,

i'll mail you some of the 0.3->0.1mm-tips and some straight throuh or tapered holes with 0.19mm ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: DIY printhead
September 20, 2010 07:13PM
not sure if its right on topic, but i remember someone requesting info on epson print heads design, and recently stumbled around this link, so i thought to post it here maybe it would be of some interest at least

[techref.massmind.org]

Inside article there is a reference, to quote:
"You can find detailed information on Epson head format in US patent 6758544 B2", [patft.uspto.gov] which i think it is the one attached.

Sorry if this is out of place or was posted before or already known, etc.
Maybe it can give at least some inspiration if nothing else.

Edited 2 time(s). Last edit at 09/21/2010 06:08AM by NoobMan.
Attachments:
open | download - epson patent US006758544 part 1.zip (333.1 KB)
open | download - epson patent US006758544 part 2.zip (537.5 KB)
Re: DIY printhead
September 21, 2010 03:40AM
Thank you noobman, all information is welcome, please add anything else you find.


Random Precision
Re: DIY printhead
September 22, 2010 02:22AM
Progress report.

Johnrpm has kindly sent me the acrylic inkjet device he made so that I can attempt to figure out how to make it work in drop on demand mode. It is constructed with a brass nozzle that screws into an acrylic body (with an o-ring) so it will be easy to try out different nozzles while keeping everything else a constant. Since it takes too many words to explain which inkjet device is being used, I'm going to start naming them.

1) The device Johnrpm sent will henceforth be known as Dalek.
2) The first inkjet device that I constructed will be known as Kal.
3) The more recent acrylic one will be known as Za.

Johnrpm, if you don't care for Dr. Who then I apologize for the naming convention.

Dalek experiments
I was not able to get the Dalek to work in drop on demand mode. I was able to see a very small change in the shape of a tiny drop of water resting over the top of the nozzle in response to pulses of the piezo. I was able to see the same effect on Kal before changing to a tapered nozzle, so I high hopes that a new nozzle can be made to work.

I'm hoping to start testing new nozzles this next weekend. Gathering all the necessary pieces always takes longer than expected.

Za experiments
The piezo used on Za died, or rather, faded away. It still makes sounds in responses to pulses, but the volume is very low. The cause is not known, but the major suspect is either damage due to the mounting or due to water.

This did give me a good opportunity to replace the piezo with one with a resonant frequency of 6 kHz, as opposed to the 3 kHz device that died. As expected the new piezo works. However, the voltage required to make it work is significantly greater than the voltage required with the 3 kHz piezo, and even then it does not work nearly as well. It is possible that this effect is due to unintentional differences in the way in which it is glued to the acrylic, but I think it is probable that it is due to the thicker metal plate on the 6 kHz device. Another parameter to test...

It turns out that making the inkjet work reliably when the nozzle is pointed straight down is more difficult than when the nozzle is pointed off to the side or somewhat upward. It will work, but only in between the large drops of water that drizzle out of the nozzle. If the water level in the external storage is just right, it does work, but there is little room for error. While the problem of drizzle does occur when the nozzle is pointed in some direction other than straight down, it seems much more manageable. Time to start thinking about different nozzle materials or coatings, I think.

Air getting in through the nozzle is a constant problem, especially since I end up turning the nozzle to point in different directions a lot. I think that changing the shape of the chamber such that there are no flat surfaces for the air to rest on (when the nozzle is pointed up) would help a lot, as it would make it much easier to remove the air from the chamber.
Re: DIY printhead
September 22, 2010 03:25AM
I did not know you could get Doctor who in the USA, I have not watched many since john pertwee, prefer lord of the rings, sad aren't we.

Could you remind me, what nozzle diameter are you using, it may be that air is being sucked back on each "stroke"
so when it is facing upwards it draws fluid from the wet face but air when it is facing down ???????.
I did measure the discs diameter and thickness of the different types I have, if that info is any use.


Random Precision
Re: DIY printhead
September 22, 2010 11:16AM
The nozzle diameter is about .343 mm (#80 drill bit).

I believe you are correct about air getting sucked back in.

I would like to know the thickness of the piezo on the device you sent, if you know.

There is no question that Lord of the Rings (the book) is much better than Dr Who. It is almost sacrilege to even compare them to each other ;-)

Edited 1 time(s). Last edit at 09/22/2010 11:19AM by madscifi.
Re: DIY printhead
September 22, 2010 06:06PM
Here are the sizes I have to hand of the piezo bimorphs

20 dia, .17mm thick, 6 Kh
25 dia, .1mm thick , 1.8Kh
25 dia, .3mm thick , 4.2Kh
41 dia, .1mm thick , 2.8Kh
50 dia, .2mm thick , 2.8Kh

Edited 2 time(s). Last edit at 09/24/2010 05:59AM by johnrpm.


Random Precision
Re: DIY printhead
September 24, 2010 11:18PM
The specs on the ones I'm using (20mm diameter) are:

6.3 kHz, .2 mm plate thickness, brass
3.6 kHz, .1 mm plate thickness, brass

I've also discovered that there are ones with .05mm thick plates available:

20mm piezo, .05mm thick

I'll order a couple to add to the test pool.

The other question I have concerns the max voltage rating of the devices. I cannot, even in the spec sheet, find the max voltage for the devices that I have.

The device with the .05mm thick plate lists 30 volts, peak to peak, as a max rating. All of the devices by that manufacture appear to list 30 volts. The .05mm thick device also has a much greater capacitance, 90nf as opposed to 10nf for the ones I already have. More bits of information that I have not assembled into anything meaningful yet.

Edited 1 time(s). Last edit at 09/25/2010 12:14AM by madscifi.
Re: DIY printhead
September 25, 2010 06:39PM
Just to say I ceased to idea (for now) to use this head for PCB. I found that using a 1000€ 40W CO2 laser may give the results I am looking for.

I am still interested on this work and I am following this forum message. And as you may know, Makerbot and RepRap, both have now software and heads for pen plotting! Later, if this piezo print head works, it may exchange the pen plotting technology, since it should be easier and give better printing quality.


---
New cutting edge RepRap electronics, ARM 32 bits @ 100MHz runs RepRap @ 725mm/s:

[www.3dprinting-r2c2.com]
Re: DIY printhead
September 26, 2010 01:10AM
Test nozzles, or the more I try the less I know.

I made up 5 brass screw-in nozzle holders for Dalak that can have thin plate nozzles glued on them. Since I don't have a lathe they were milled starting from brass hex bolts. Since I have never milled brass before, I made something of a mess of the first couple, but in the end all of the holders were usable.

The picture below shows 4 of the nozzle holders.




From the left:
1) Has a straight wall hole drilled (#80 drill bit) through a 0.27 mm sheet of polystyrene.
2) Has a tapered hole (#80 drill, manually tapered with 60 degree etching bit) through .016 inch aluminum. Sadly, the taper is on the outside, not the inside.
3) Has a tapered hole (#80 drill, 60 degree etching bit) through a 1.58 mm thick sheet of delrin. This is in the process of being glued, which is why there is a little bit of scotch tape shown holding the delrin in place.
4) Nothing yet attached, shows the backside of the nozzle holder.

The final nozzle holder (5) has a straight hole (#80 drill) through .016 inch aluminum. This was on the print head at the time the picture was taken.

The setup at the moment is to connect a syringe filled with water to the print head so that the water pressure can be easily manipulated. This configuration is not really useful in a real device because the pressure continues to change with each drop of water ejected from the nozzle, so it eventually stops working long before any significant quantity of water is ejected. However, it is easy to work with and allows the pressure to be adjusted so that the device works when pointed down. So it is useful for some initial experiments.

Nozzles 1, 2 and 5 have all been shown to be capable of producing single drops. The voltage required is inconsitent at this point, partly due to the setup, but as little as 33 volts was required. An interesting observation: sometimes it is possible to have drops produced in a range such as 33 to 66 volts, with both lower and higher voltages resulting in no drops. I did not expect to see this at the high end.

Nozzles 1, 2 and 5 have all been shown to work when the nozzle is pointed straight down. However, you can sit and watch a tiny stream of bubbles flowing up to the top of the device as drops are generated. That is the reason for nozzle 3, a thicker sheet of plastic with a tapered hole. Hopefully, air can be kept out of the device while still allowing easy ejection of drops.

I tried the original nozzle again with the current setup and I was still unable to produce any drops. The original nozzle is most likely too long, or too small, or some combination of the two.

The tiny air bubbles are difficult to deal with as they stick to the first surface they encounter and they are very difficult to remove until they get large enough to respond to tapping the device sharply against the table.

All of the nozzles produce chaotic drops - the drops are rarely consistent in their path or apparent size (based on brightness of the drops in a back light). Often it appears that there are multiple drops following different paths.

Being able to swap nozzles back and forth is a big improvement for testing. However, until I can produce a consistent looking stream of drops there is little point in attempting to determine which nozzle design works best. At the moment, none of them produce a usable stream of drops.

I also just noticed that the piezo is now sparking along with the pulses whenever the voltage is above about 60 volts. This means I'm slowly destroying the device. I don't know if it has been doing the from the start (where I was using the device upside down and so I would not have noticed), or if it started later. I used some kapton tape to protect the back from water, and that appears to have worked, so i don't think the cause is due to water getting on the device.

I can imagine possible solutions to all of the issues except for a reasonable method of purging the device of air.

The sound level, when the device is full of water, is much, much, greater when a spark occurs - presumably I'm hearing the spark, not the piezo. I suspect at this point that the previous piezo that "died" did so due to the sparking problem I'm seeing here.

Edited 1 time(s). Last edit at 09/26/2010 02:04AM by madscifi.
VDX
Re: DIY printhead
September 26, 2010 03:33PM
Hi Jim,

... i've culled two tapered tubes, two smallest dispenser-needles and two 0.18mm drillbits, made some small holes in 1mm-POM and put it all in an envelope - i'll try to dispatch it tomorrow ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: DIY printhead
September 27, 2010 01:47AM
Broken piezos and sparks

Here is a close up of the piezo on Dalak that is now sparking at higher voltages.




I was concerned that the sparking was destroying the device, but that concern was misplaced. The device is already broken. The black arrows are pointing to a crack just that goes just to the left of the solder connection of the red wire. This crack completely isolates the top conductor of the piezo into two different regions (verified with an ohm meter). The tiny region that is connected to the red wire, and the much larger region that should be, but is no longer connected to the red wire. The sparks occur along the crack.

The reason that the device sounds so much louder when sparks appear is not that the sparks themselves are making any significant noise. Rather, the spark occur when the voltage is high enough to bridge the crack, effectively turning back on the rest of the piezo for the one pulse, resulting in a much louder noise.

The bad news is that this means that I cracked the piezo by accident some where along the way.

The good news is that I'm seeing drop on demand behavior with 30 to 40 volts even though only a tiny portion of the piezo is fully functioning.



Viktor, thank you. I look forward to trying them out.

Edited 1 time(s). Last edit at 09/27/2010 01:50AM by madscifi.
Re: DIY printhead
September 27, 2010 03:13AM
I know its difficult to see, but is the crack through the ceramic as well as the conductive paint layer?, I would love to know how these discs are polled, to visualize how they bend, it may be that they do not bend in a uniform manner but along lines???.

Could you solder the wire on in a different place?, I hope it was not cracked when I sent it, if so sorry.


Random Precision
Re: DIY printhead
September 27, 2010 11:24PM
I'm pretty certain that the ceramic is cracked. It is difficult to tell with certainty.

I'll probably try just bridging the crack along one edge with a bit of solder. I don't know how long that will hold up, but it sounds worth trying. If that fails then I'll move the wire.

I'm about 99% certain that I broke it. I was using a spring hand clamp to clamp the needle value body to a support, and I "missed" a couple of times and clamped the body of the device to the support by accident (with the piezo against the support) and I suspect that is what broke it. And if you sent a it already broken it makes no difference. I seem to recall that I was the one "begging" to get a copy of one of your devices.

I've got a new support structure put together, so that particular mode of destruction should not happen again. No doubt I'll find some new way to break things shortly.
Re: DIY printhead
September 28, 2010 09:47AM
I have read this thread with interest.

One of my long held dreams with RepRap is to get rid of the heated extruder but still deposit plastic. I would do this using the nylon rope trick (or rather the chemistry behind it) or to give it its proper name condensation copolymerisation. Essentially if you take the two liquids that make nylon and layer them one on top of each other (they do not mix easily and are of different specific gravity) you can draw the nylon out from the interface. And all this at room temperature.

So I thought this could be printed, and build 3d structures. All we need is a two nozzle version of the kind of drop dispenser you have been designing and if we get the drops to touch each other then we will deposit nylon (or any of the other condensation copolymers). And the smaller the droplets the better (greater surface area per unit volume). I am not quite sure how quickly the nylon forms, so we might even be able to push the two liquids into a 'y' forked nozzle, and deposit the setting nylon in one spot.

The two liquids are a diamine and a dicarboxylic acid. For the most common nylon (6-6 nylon) the two are 1,6-diaminohexane and hexane-1,6-dicarboxylic acid. I seem to recall from chemistry lessons that these two are not especially unpleasant or difficult to handle (but my last chemistry lesson was so long ago that we were allowed to handle mercury).

Even without the 'y' forked nozzle, depositing one layer and then shortly after the second layer should not be a problem, although if the second layer is too long in arriving the first liquid might flow off the existing surface, which would limit the overhang angle.

David
VDX
Re: DIY printhead
September 28, 2010 10:45AM
... it would be much easier to use a paste-dispenser - here you can dispense all materials that can be cured by hardening on air or with UV or by heat.

Look at the fh-syringes or my paste-dispenser ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: DIY printhead
September 28, 2010 11:00AM
except that you do not need to cure it with anything, just mix it where you want the nylon to grow. Also these liquids are of a similar consistency to water, so would they not simply run out of the dispenser uncontrollably? Two of them could be arranged in a V, coming together at the point of deposition. How slowly can you run liquids out of the dispenser, and how well can you stop the flow?

David
VDX
Re: DIY printhead
September 28, 2010 03:34PM
... the throughput is dependant of the viscosity and inner diameter of the nozzle - you can push water through a short tube with 0.06mm inner diameter, but not much smaller ... hot 'light' wax is more fluid than water!

Most pastes used with dispensers have higher viscosities, so you have to select the nozzles accordingly - but if you don't have air embedded in the cartouche, the fluid won't leak free, it comes out only if you push the piston ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: DIY printhead
September 28, 2010 11:46PM
I suspect the Viktor is correct, it would be much easier to print a UV curable paste using a syringe. However, there are some papers available on the web related to using inkjets to combine precursors and produce an end product in situ.

Fabrication of Two and Three-Dimensional Structures by Using Inkjet Printing

Reactive inkjet printing of polyurethanes

ROTATIONAL 3D PRINTING OF SENSOR DEVICES USING REACTIVE INK CHEMISTRIES (See particularly the section titled "Plaster Inks", on the page labeled 318.)

1,6-diaminohexane is not exactly benign - it is a level 3 heath hazard: "Short exposure could cause serious temporary or moderate residual injury (e.g., chlorine gas)". So you will want to do some research and make certain you have the facilities to safely work with the materials. I have not lookup up the other component.

I image that there might be all sorts of issues related to mixing of the components, and whether or not the nylon produced in the individual drops would link together or remain separated. Spending an afternoon using Google Scholar (or your local university library) might turn up some information concerning the use of nylon precursors with inkjets, or it might not, but either way you'll undoubtedly run across a lot of interesting material.

One of the first questions to answer: what is the viscosity and surface tension of the components? Microdrop Generation lists viscosity in the 1-30 cS range and surface tension in the 20-60 dynes/cm (no, i don't really know what that means either) as necessities for high stability ejection. If the values are too far outside the above ranges then it might be very difficult to inkjet them at all.
VDX
Re: DIY printhead
September 29, 2010 03:45AM
... AFAIK the main problem with the 'online'-synthesis of Nylon is the shrinkage when drying away the embedded not activated precursor-fluids.

When i remember correct my scool-experiments, or Nylon-fiber out of the pot was thick and wet, so we had to heat-drying it for use ... and it wasn' as solid as comercial fibres.

Maybe the comercial fibers are remelted and pressed/pulled through a thin nozzle to receive a solid core?


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: DIY printhead
September 29, 2010 04:23PM
Davidgoodenough,
Thats an interesting concept, I have only seen vidio's of it pulled out of a beaker like string and
have no feeling for the material, could a pinch wheel do the pulling?, does it harden over time or can it stay soft?,
could it be a support material?, could it be post processed to change its properties?.
would you take it up as a project, maybe start a wiki page, I would follow progress, if not, post your stuff here if you prefer.

Edited 1 time(s). Last edit at 09/30/2010 03:08AM by johnrpm.


Random Precision
Re: DIY printhead
September 30, 2010 05:27AM
My idea is to create the nylon in situ where it needed, NOT to create a nylon filament that gets deposited. A droplet of each
chemical would be deposited together, and react to produce the nylon (or whatever condensation copolymer you chose). If we get the drops small enough and the proportions right then there should be little or no unused precursor material - we want it all used up to produce nylon. In fact what we really want is a small directed (and controlled) mist of each chemical that meet at the point where we want the nylon to grow.

I was thinking of trying the misting approach first. And just spraying a thin mist of first one, then the other chemical, and see if nylon forms properly and what gets left over. I was going to try taking one of those aerosol scent dispensers to bits and use that.

Victor mentioned that it is wet. Of course it would be - it is drawn up through the upper fluid. And yes, it might need drying (if I recall the chemistry there is some water left over) but I do not think that is going to be much of a problem - a little hot air should suffice.

David
Re: DIY printhead
September 30, 2010 08:14AM
David,
Now I see what you are doing, apart from the mist test, would it be worth having two syringes with the needles
intersecting?, or one needle inside the other some how.

edit, airbrushes?.

Please keep us informed of your progress.

Edited 1 time(s). Last edit at 09/30/2010 10:50AM by johnrpm.


Random Precision
Re: DIY printhead
September 30, 2010 11:03AM
One thing I do not know and can not find any data on is how quickly the copolymerisation happens. I think (or rather as I remember if from chemistry lessons 40 years ago) it is near instant, so in that case I would not want the nylon to form in the needles, but rather at the deposition surface. If it took a little while one might improve mixing by generating the two droplets, mixing them and then depositing them, but I doubt it.

So I would want the two needles from the dispensers nearly touching so that they dropped at the same point. So a V but with the points not quite touching. If (and again I am working from memory) the ratio of the liquids is 1:1, then the same motor can drive both syringes if I go the syringe route, or if I were to use your bimorph discs then the same electronics would drive both bimorphs.

My biggest difficulty is that I have no machining capabilities. I have a RepRap, but the heated extruder never worked reliably enough to make anything.

So after my mist test to see how well the mixing of droplets works and how well it builds structures (simple ones like bars so that I can spray it by hand) then I try to scrounge some dispensers from somewhere and try it out.

David
Re: DIY printhead
September 30, 2010 05:24PM
would a chemical etch work to produce a small enough nozzle possibly in thin brass or copper shim stock? perhaps the needle and solenoid EDM approach could be used to produce a fine nozzle.
Re: DIY printhead
September 30, 2010 06:08PM
davidgoodenough
Not sure if this would work, could you have a bath of one of the liquids and dispense the other material through a needle, sort of submerged reprap?would the layers bond?, I know you do not want the filament approach, but worth a thought.



sdedalus2000
Years ago we had a Arcout, I think it was called, for removing broken taps, a very crude EDM, but it did the job, so yes I think it could work
for nozzles, at present Madscifi is trying to get to grips with the nozzle geometry, does it need a taper, radius, etc, so if it does need a profile
the EDM approach could well be ideal.


Random Precision
Re: DIY printhead
October 01, 2010 02:09AM
Dalek producing single drops of water, pointing down (the animation is a fairly accurate record of the orientation), 31 volt, 500 us pulses. Nozzle is #1 from an earlier post (straight wall hole drilled with a #80 drill bit through a 0.27 mm sheet of polystyrene).




I used a small bit of solder to bridge the crack on the piezo. The device will work in this configuration as long as I keep the water level in the external reservoir in between a rather small range. Drops can be produced at any rate up to 1 every 30ms. At 25 ms between pulses the production of drops appears random. As long at the voltage is not turned up too high then air does not appear to enter the device via the nozzle. I'll post details of the setup this weekend. I'm very close to a setup that can be used to reliably test different nozzles and print heads, but I have a couple more issues to work out yet.

Edited 1 time(s). Last edit at 10/01/2010 12:11PM by madscifi.
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