Introduction: Mason Jar Coffee Dispenser
Full Disclosure: This is my first Instructable and its a big one!
This is a ground coffee dispenser, casted in bronze, I made for my wife for a birthday present, she loved it. It saves lots of time in the mornings, because at the twist of a knob you can have your coffee grounds ready to be brewed.
This project briefly covers 3D fdm printing, Metal casting, machining. I plan to go into more detail on each of these subjects in later instructables.
The overview of the process is as follows:
- 3D print the patterns to be casted
- "Tree" the patterns
- Invest (cover in plaster) the patterns to make a mold
- Burn out the patterns from the mold
- Cast metal into the mold
- Remove investment cut casting from tree
- Enjoy the beauty and convenience of your new dispenser!
Lots of the tools I use are professional tools but I encourage you to find inexpensive work arounds; that's how I got my start! Along the way I will try and tell you know how you can skimp on costs or take short cuts. lots of the items/tools I use are can be purchased from Riogrande.com (not sponsored by them, but I do work for them-so kinda sponsored by them but not directly for this post)
- 3D printing filament, I used "Moldlay" however "Polycast" is my new favorite filament for this kind of application. Natural (non) colored PLA will also work in a pinch.
- Bronze casting grain (preferred) or scrap bronze
- Knob for cabinet drawers - I got this one from world market
- 8-32 x 3/8 Screw and washer
- Wax rods of various sizes and/or "neusprue"
- sticky wax
- "neusprue" base or rigid & flat piece of plastic
- Investment plaster - Ransom & Randolph Ultravest works best
- Distilled water (ideally) Tap water works too
- 4" perforated flask
- 2ea #6 flathead wood screws
- Almost forgot - MASON JAR!
- FDM 3D Printer - Mine is a Mankati fullscale
- Flush Cutters
- Soldering iron
- Mug Warmer & metal measuring cup
- Vacuum investing table - not necessary but will yield best results
- Cake mixer or drill with mixing paddle
- Stop watch
- Kiln or oven & metal tray
- Casting Machine or foundry
- Pressure washer
- Buffing machine
- screw driver
Step 1: Print the The Files
Download the following .STL files and print in the following quantiles:
Coffee dispenser body - 1ea
Dove tail - 1ea
Measuring rotor- 1ea
Layer height doesn't really matter but the the higher the resolution the less sanding/finishing you will have to do before and after casting. I use at least 2 outer shells and 15% infill
For the Moldlay filament, it can be smoothed with acetone and a rough rag, it does take lots of rubbing. I prefer the Polycast material because it can be smoothed by isopropyl vapor/dunk. PLA will need to be smoothed with sandpaper.
When prepping the models for casting exactly how the surface of the print is is exactly how the surface of the casting will come out. If you want the layer lines no sanding is necessary, if you want perfectly smooth its easier to do on the print than the metal casting.
Another important step is to make sure that the ENTIRE outer surface is sealed from the hollow cavities inside. When investing/plastering if there is a hole the plaster will be drawn into the inside the print and ruin the casting. It is common to get holes where the top layers meet the outer shell - theses must be plugged I use wax and a soldering iron to do this with PLA and Moldlay. The Polycast will usually seal up when you vapor smooth the surface.
Step 2: "Tree" the 3D Prints
Treeing the 3d prints is necessary because this forms the path for the molten metal to flow in into the parts during casting. The tree is made of wax rods and there is typically a thick one with a cone shape at the top, called the main sprue, and smaller ones connecting 3d print to the main sprue called "gates". The cone shape, at the top, is to be able to pour metal into easily.
I use a product called a "neusprue" for the main sprue because it easily threads to a neusprue base. If you just have a wax rod you can just melt the end to a flat surface using the sticky wax and a soldering iron.
Now that the main sprue is attached to the base you can dip the ends of the smaller wax rods to form the gates onto the 3d part. I dip them briefly and stick them the part and hold them there until the sticky wax hardens. Now dip the other end of the gate into the sticky wax and stick it to the mainsprue and hold until the wax hardens again. I like to "seal" the sticky wax to the parts and the mainsprue, I do this by using the tip of the soldering iron and run it around the area where the sticky wax meets the part. This helps make sure the parts do not fall apart.
Repeat this process for the rest of the parts. I have done these parts in several different trees that will be cast separately.
Step 3: Invest (cover in Plaster) Your Tree(s)
The investment is a special plaster that encases the tree and will form the mold that the metal is cast into. The plaster will need some outside support I use a perforated flask (which is a steel cylinder with holes in the sides) but a flask can be made from anything even a cardboard tube.
First wrap the flask in saranwrap to keep the investment from leaking out when you pour it into the flask.
Then slip the the flask over the top of the tree and into the sprue base. Make sure there is at least 3/8" of space surrounding the tree to the flask on the sides; any less and you risk blowing out the metal out the side of the flask.
Mix the investment at 100g investment to 38g water ratio and mix enough to cover the entire tree at least by an inch over the top. You can get a investment calculator from Ransom & Randolph website based on the diameter and height of the investment needed.
There are also very specific timing guidelines for mixing an pouring the investment into the flask. The guidelines should be followed very closely to the manufactures requirements.
The process generally goes as follows:
pour investment in to water and gently mix
power mix until 3.5 minutes
vacuum mixture until 5 minutes - Also shake the flask to make sure there are no air bubbles.
pour into flask and vacuum again until 7min and 35 sec max .
quickly place invested flask a sturdy table or the floor and do not move for the next 2 hours while the investment sets up.
Step 4: Burn Out Flask
This is probably the easiest and most passive step.
remove sprue base and saranwrap from flask
place flask upside down ( main sprue hole facing down) in the kiln to make sure the wax melts out of the mold.
The investment needs to follow a specific burnout schedule depending on the manufacturer
it is typically as follows:
- 300F hold for 3 hrs - to dry investment and melt wax out
- ramp up to 1350f at a rate of 240deg/hr hold for 4hrs (or 1 hr for every inch of diameter) - to fully remove any residue of 3d print and harden investment
- ramp down at 240deg/hr until 1000f hold for at least an hour before casting
Step 5: CASTING!
This is the most fun and anxiety inducing step of all! (most dangerous as well) Time to see if all your hard work paid off.
The casting machine I have melts the metal and then automatically dumps the metal into the flask when the proper temperature is achieved. It pulls a vacuum on the outside of the flask to ensure all of the air is out of the mold ( the investment is porous and breathes) and also applies a pressure to the top of the flask to ensure every little detail fills in.
This step can however also be done by melting the metal with a torch or furnace and hand pouring into the flask.
The casting temp for the ancient bronze is 1965f . I dump the casting grain into the crucible of the machine - remove the flask from the kiln and place it into the casting machine... When the temp is right the metal is nice and molten... the machine casts !!! About a minute later the flask can be removed from the machine! hopefully we see a nice little "button" of red hot metal at the top of the flask. If there is no metal where the main sprue is its probably an under fill or blowout - both are bad news. If there is metal spilling out the top its either too much metal was dumped or the mold did not fill up properly.
Now we set the flask aside for about 15 min to cool.
Step 6: Devest and Clip From Tree
And now the moment we've all been waiting for... dunk the still hot flask into a bucket of water; the heat of the flask and water generates steam that shatters the investment from the casting. Hold the flask under until it stops bubbling now you can reach in the water and fetch your casting - careful its probably still pretty warm- aaaand we have a horrible looking black casting! Don't worry this is just fire scale and will be removed either with and acid solution called "pickle" or sand/polish off in later steps. Now take the flush cutters and cut the castings from the tree. Congratulations you now have your castings for the dispenser
Step 7: Grinding/polishing
Now you need to grind or sand the areas where the castings were cut from the tree and make them look uniform with the rest of the surface. The easiest thing for the job is a cratex wheel on a bench grinder/polishing lathe but a dremel sanding drum or flap disk also works good.
To even out the rest of the surface I love using the "sunburst" abrasive wheels they have lots of give for smooth surfaces but have a high rate of removal. You can leave with a brushed finish or work up to finer and finer grits until you are ready to give the surface a mirror polish.
Step 8: Machining
The rotor will need to be machined to closely fit the body and the retaining washers.
First measure the distance of the body casting where the rotor sides into. Machine both sides of the rotor casting to have about 0.01-0.02" over the measured distance. There will also need a 0.05" shoulder for the washers to align to. Finally tap an 8-32 hole on both ends.
Its possible the body where the rotor slides into will need to be cleaned up as well. for this I use a 3/4" dowel that is split lengthwise to accept a sheet of sand paper. I slide into the hole and twist until the rough areas are smooth. Slide the rotor into the casting and rotate to make sure it spins smoothly, if it doesn't repeat the sanding until it does.
Depending on the knob you choose it may need to have the threaded stud cut down a little as well. I only left 3/8" sticking out and cut with a pair of electrical strippers that have a fastener cutter built in.
Step 9: Assembly
Take the 8-32 screw and the casted washer and screw it onto one side of the the rotor.
Now slide the rotor into the body casting add the second casted washer and now thread the knob onto the opposite end of the rotor. Go ahead give it a spin and get all giddy!
We will need to install the dovetail to a rigid surface, make sure to find a piece of wood or stud to hold this onto the wall firmly. Take two #6 flat head screws and screw the dove tail onto the wall with the narrow side up.
Step 10: Fill With Coffee and Enjoy
Now we can fill the mason jar with your favorite coffee, screw the dispenser body onto the jar, flip over and set the matching dove tail of the dispenser body onto the dove Tail wall mount!
Put your French press or coffee maker basket under the dispenser spin the knob a few times and get caffeine fix!
whooo that was a long one! hope you enjoyed and im sure I left out some finer details/pics feel fee to comment and I will try and answer questions,