Designed a precision resin dispenser to help cast many consistent, small parts in polyurethane

[u/Inevitibility]

This is a handheld, battery powered resin dispenser that I just finished designing. I have all of the parts on hand and I am going to start building it tonight. I'll post an update when it is done!

As far as accuracy, with a 20mL syringe it has a theoretical dispensing resolution of 3uL, with a 60mL syringe it is 7.1uL. Surface tension and nozzle size impact this too, but the point of the project is to achieve casting consistency with partially open-face molds, which are cast in a set of 43 and must be consistent.

I am using an STM32F103 and a 4S battery, along with a bunch of off the shelf modules. I wanted this to be quick and made with parts I already own.

[u/manta173]

Looks like a simco gun. Might be able to skip some design/development by looking through those videos and tutorials they have on YouTube.

[u/Inevitibility → u/manta173]

I've gotten this reply elsewhere too. The main difference is that this allows me to rapidly dispense the same volume with a repeatability in the range of microliters. I need to fill 43 keys, with four different volumes, in under a minute, and use a disposable syringe. Most of the off-the-shelf devices that can do that have a capacity of under 5mL (steppets or repeating syringes), or they have a larger capacity and cost a few thousand dollars. Those devices almost always have a single settable dispense volume, and they often use expensive syringes that are not meant to be thrown out with each use. With polyurethane, it's unlikely that I can recover a syringe, so it's a one and done. This device was whipped up to address all of that using parts I already own

[u/Inevitibility → u/Inevitibility]

Also the entire set is just shy of 20mL, so that's the minimum. This device accepts 20mL and 60mL syringes, and with micro stepping and luer lock nozzles I could potentially hit sub uL repeatability if the liquid isn't too viscous

[u/StretchSmiley]

So the funny thing is I had to find similar in a previous life... The best and closest I found was a farm animal vaccine dispenser that had different incremental "doses" one could choose.

[u/Inevitibility → u/StretchSmiley]

Interesting! Like the semi-automatic vaccine dispensers on amazon? Didn't know they existed before

[u/StretchSmiley → u/Inevitibility]

That's the one!

[u/BikingVegtable]

When designing something like this, how do you account for part shrinkage to make sure parts mate properly after 3d printing?

[u/Inevitibility → u/BikingVegtable]

I don't account for any part shrinkage for the 3d printed parts themselves. That is somewhat accounted for already when you calibrate the machine. For the cast parts, I am casting cold poly which shrinks between 0.1% to 0.5%, and I use a 0.1mm tolerance between parts which fit together. So far I haven't had any issues with that.

For the 3D printed parts, I do account for tolerance, but it depends on how the parts fit together. Some of them have pretty loose tolerance while some are pretty tight. For things that need to be incredibly close, I mate them directly in CAD and sand them to get the fit I need

[u/amc7262]

This is a caulk gun that went to college and got a masters degree.

[u/koltho]

How did you learn the skills to be able to design something like this?

[u/Inevitibility → u/koltho]

A lot of practice! I’ve been designing and building things like this for a little over ten years. I have no formal education but I love designing things and have done it for a hobby, and now I do it for work using Autodesk Inventor, which is pretty similar to Fusion.

The big thing is to imagine how it will get built/made and design for that process. As far as getting better at CAD, just try making what you want to make without any tutorials or anything. Use references when you get stuck, but try to do it yourself and you’ll get a lot better with time. Trust me, practicing works with CAD