The glass bed on the Makerspace’s Taz 3 printer recently did what glass does- it broke. Time for a repair and upgrade!
I started by cutting the under carriage down and modifying it for a three point leveling system instead of the stock four point undercarriage/bed plate bending scheme.
Modified undercarriage mounted on the printer
The original heater was separated from the shards of glass and glued to the 12″ x 12″ x 1/4″ cast aluminum tooling plate using high temperature silicone. 3x #10 countersunk screws and springs support the plate on heat resistant teflon blocks. The whole assembly stands about 1 cm taller than the original bed plate so I printed a small extension for the Z=0 set screw so it would trip the switch from the higher position. I tested the heating time and found that the bed gets up to 110C in about 16 minutes- a little slow, but we probably won’t be printing much ABS with this open frame machine anyway. Next- run PID autotune for the bed heater and adjust acceleration (greater moving mass means lower acceleration and print speeds).
New bed plate and undercarriage mounted on the printer
Some of you might ask why I would replace the glass bed with a piece of cast aluminum tooling plate. Thermal performance is one good reason. Here’s an IR photo of the original glass bed:
IR image of the Taz 3 printer with original glass bed.
Notice the hot and cool spots- 30C temperature variation across the bed.
Here’s what the new aluminum bed plate looks like:
Temperature variation is just a few degrees over the entire surface (the bright almost horizontal lines are not hot spots- they are reflections of the X axis guide rails).
I have run the PID tuning on the new bed and modified the firmware with the new constants. It heats from 25C to 100C in about 9 minutes.
I officially declare the Taz printer ready for action.
This week I attempted the first test of the chocolate printer cooling system. The cooling system is intended to solidify the chocolate just after it leaves the extruder nozzle so that by the time the next layer is started it will have a solid layer to sit on. The cooling system consists of a centrifugal blower with a brushless DC motor blowing room air into a styrofoam cooler containing a block of dry ice. The air passes over the dry ice and gets chilled as the dry ice sublimates directly into very cold CO2 gas. The chilled air and CO2 mixture exit the box through a port with a hose that will ultimately blow the cold air on the chocolate. At least, that’s how it is supposed to work. It blows air at -12C as measured via a thermocouple, but unfortunately, the air exit port ices up in about 2 minutes and blocks the air flow.
There are many possible solutions. I can add a heater to the exit port to prevent formation of ice, or dry the air going into the box using a dessicant cannister or maybe just use water ice instead of dry ice if the higher temperature will still cool the chocolate adequately. Maybe using an old miniature freezer with an air hose coiled inside would do the job. It would be really interesting if I could use the waste heat from a freezer to keep the chocolate liquified and flowing. Back to the drawing board!
Chocolate printer progress continues. This week was devoted to the print cooling system. The chocolate will come out the extruder nozzle in a semi-molten state. It needs to solidify by the time the next layer of chocolate gets deposited on it, and I’d prefer it doesn’t drip or sag, so it needs to be chilled right after extrusion. The current plan is to blow chilled air over the chocolate just after it leaves the extruder. The chilled air will come from a foam insulated box containing a block of dry ice. There will be a blower pushing air into the box and a hose delivering the chilled air/CO2 to the print.
A couple weeks ago I got a blower from American Science and Surplus and this week I got it running by using a model airplane ESC and servo tester to drive its brushless DC motor. It appears to be capable of blowing much more air than I’ll need. There are many unknowns yet to test. How much chilled air/CO2 will it take to solidify the chocolate after it leaves the extruder? How long will a block of dry ice last when used this way? Will ice build-up inside the chiller box adversely affect its performance?
I designed and printed three parts for this system- a mount to attach the blower to a foam box up to 1.5″ thick, a hose coupler to allow delivery of the chilled air/CO2 to the print, and a hole saw to cut holes to fit the other two parts. The printed parts fit as if they were designed for the job!
My last post showed how I made a plunger for a 3.5 liter syringe. Today’s post is the results of the first ever test of that syringe assembly including the plunger. The goal of the test was to determine if the syringe pusher would be able to push very thick, viscous paste (sort of like melted chocolate) out of the 1/4″ syringe nozzle. It was also a test of the ability of the previously made silicone plunger to maintain a seal even against whatever pressure develops inside the syringe as it is pushing.
I mixed about 1 liter of extra thick pancake batter to a consistency that I thought would be much thicker than molten chocolate (pancake batter is much cheaper than chocolate) and shoveled it into the syringe, then bolted on the pusher and hooked it up to a power supply:
Looking back, I probably should have loaded the syringe from the other end.
Syringe loaded with super thick pancake batter.
Here’s the actual test. It gets especially interesting about 1 minute in:
The syringe continued drooling after power was removed due to air that was trapped inside the syringe. As the plunger pushed, the air was compressed. When the motor stopped the compressed air continued to push out the batter. I will have to be careful to eliminate air bubbles in the material when it comes time to use this in a printer.
It only took a couple minutes to clean out the syringe after the test was done.
The pusher did its job much better than expected, and the plunger held up just fine, too. I feel confident that this device will be able to extrude chocolate. Now the real work begins…
My latest project is a 3D printer that will produce chocolate objects. Like many other chocolate printers, it will include a syringe to dispense the chocolate. Unlike those other printers, the syringe in my printer will have 3.5 liter capacity to enable printing large objects.
The syringe is made from PVC pipe using mostly standard fittings. One piece that wasn’t standard was the plunger that fits inside the syringe tube and pushes on the chocolate contained therein. I had to design and fabricate the plunger. PVC pipe isn’t perfectly smooth or perfectly round inside, so I needed something compliant enough to ride out the pipe’s bumps and constrictions while maintaining a seal. The seal needed to be tough, yet safe for use with food because it will be in contact with the chocolate inside the syringe. I found some food-grade silicone casting material and ordered it.
While waiting for the silicone to arrive, I designed a 3D printable core for the plunger and a mold and jig. The core fits on the end of a linear actuator that will provide the push. The jig centered the core a few mm above the bottom of the mold. The mold was tapered and the widest part -the bottom- was a few mm larger diameter than the pipe, and several mm larger diameter than the core. The silicone envelops the core and is locked in place by holes that connect top and bottom side of the core. The plunger squeeze-fits into the pipe to maintain the seal against the uneven inner surface of the pipe.
Mold, jig, and core for syringe plunger
Mold, jig, and core for syringe showing core inserted into jig.
Mold, jig, and core assembled for silicone over-molding.
I measured and mixed the silicone, coated the core with it and then set the core and jig in/on the mold and let it cure for 24 hours. Then I removed the jig and broke the now silicone covered core out of the mold. Result: a perfect, tight fit inside the syringe tube.
Core in mold with silicone.
Finished plunger removed from the mold. The mold had to be broken off by design.
Plunger mounted on linear actuator.
The assembled syringe.
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