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3D Print Finishing
I was looking at trying my hand at doing some detailed finishing of a 3D print. Since most 3D printers lay material down in small layers (.3 mm) the print has a layered and striped look. With ABS prints you can soften the layering the effect with acetone. The acetone will dissolve the plastic a little bit before evaporating, thus smooth over the layers. Too much acetone will leave the part a bit droopy looking. But with PLA that process is not as easy. And larger prints come out looking better with PLA (more uniform, less shrinking, less warping). Also a friend of mine was looking to try to apply a mirror/chrome finish to a 3D print and I knew exactly the model I wanted to try some finishing techniques on.
Enter the Trimaxion Drone Ship from the 1986 ‘Flight of the Navigator’
Here is the trailer for those who don’t know.
In the movie the ship was mainly CGI. But that shouldn’t stop me.
I found a model of it here.
http://www.thingiverse.com/thing:357472
I would describe the shape as a silvery stretched out acorn squash. I liked the shape because it was simple, symmetric, smooth for the final product, and clearly defined lines. I knew there was going to be a lot of sanding and I didn’t want to worry about sanding small holes or something.
The print came out in two parts. And even through I printed it out in PLA there is still a little warping. So the first step was to sand down the two meeting faces to make them flat as possible and then glue them together. After I glued them together I applied some automotive body filler (Bondo) to fill in the crack. After the bondo set I sanded with 100-200 grit sandpaper. The first pass is below.
After that I did some wet sanding with 400-500 grit sand paper.
Next step was to apply some primer.
After that the process is wet sand-prime, wet sand-prime…
In the pictures below you can start to see the lines disappear. But still more wet sanding and priming.
And below I’m starting to get to what I want.
And finally I did one last wet sand with 1000 grit sand paper. I painted it with a three coat system from spaz stix. You start off with a back coat, in this case black, then apply the chrome paint, and finally a clear top coat.
Here is final product.
Lessons or what I would have done differently.
- Start with a slightly larger model. This wasn’t too bad, but a little bigger would have sanding the lines a little easier.
- More coats of bondo or other filler. I only used one coat of the two part bondo. They also have a one part that is meant for smaller details. I would have used the two part mix for the gap between the two sections. Sand that, then applied the one part over the entire thing. I think I spent too much time trying to fill in with primer.
- Use more filler primer. There is a type of primer that leaves thicker coats of primer. Again, save time on paint-wet sand cycles.
- More gentle with the final paint coat. I was using spray cans and that can be a little difficult to regulate the amount of paint that gets applied. Spaz Stix has jars you can get that you can use an air brush to apply the paint.
- Take more time between coats of paint. When I was finishing with the top coat a small pool of paint formed on an edge. That pool dissolved everything down to the primer. Also I marred the surface a little when I was moving the model to paint the underside.
Overall it was a simple project. I got to learn some of the basics and will inform me on my next project.
Crockpot Sous-Vide
As I was upgrading my 3D printer, I wanted to use an alternative heated platform. This new heated platform is a rubber silicone heating pad. You can take this pad, plug it straight into the wall outlet and it will eventually heat up to over 400 degrees Fahrenheit. The issue is you want to limit the temperature to the heated platform to around 200 degrees Fahrenheit. The way you limit the platform temperature is put the pad on a relay, attach a temperature sensor to the bottom of the pad, then program a micro-controller that reads the temperature sensor and toggles the relay off and on to maintain the proper temperature.
To prototype this design out I decided to create a device that is similar. I took my crock-pot and converted it a sous-vide cooker.
So what is a sous-vide cooker? Well if you ask Wikipedia she says:
Sous-vide (/suːˈviːd/; French for “under vacuum”)[1] is a method of cooking in which food is sealed in airtight plastic bags then placed in a water bath or in a temperature-controlled steam environment for longer than normal cooking times—96 hours or more, in some cases—at an accurately regulated temperature much lower than normally used for cooking, typically around 55 to 60 °C (131 to 140 °F) for meat and higher for vegetables. The intent is to cook the item evenly, ensuring that the inside is properly cooked without overcooking the outside, and retain moisture.
So generally the crock-pot maintains the water bath. The long black cable in the first picture is the temperature sensor. The wood box is a variant of my box generator script. I configured the box to hold the crock-pot up front and electronics in the back so it is an all-in-one device that I can easily move it about.
I cut an opening in the front so I can still access the off-low-high switch.
The original code came from Adafuit, but I added my own controls with the three way switch and two knobs.
Position one with the switch means device is on and the grey heat knob sets the water bath temperature. Position two lets me set a count down clock in minuets with the black knob. Position three will start the clock to the count down. When it hits zero, the device will turn on to the temperature set by the grey knob.
The purpose of the countdown lets me take out a frozen bag of food, place it in the water bath to defrost before I go into work in the morning. Lets say I set the count down to four or six hours. The sous-vide turns on and it is ready when I get home. Or if I am late or something I won’t be able to over cook the food too far because it will only go to the preset temperature.
Here is a picture of the guts in the back:
Here is the arduino with the seeed studio relay shield.
Here is the standard 120V double wall outlet. The left side is triggered by the relay shield. So that is where the crock-pot is plugged into. The right side is always on. In this case a 5V transform to run the arduino.
The device works great. I can still retro use it as a crock-pot by just leaving the black temperature sensor out. The other thing I got out of this project is working with a PID controller. A PID controller is required to better maintain the heated bed of the 3D printer.
Thing-o-matic Printer
Way back in 2011 I joined the 3D printing craze and got a Makerbot Thing-o-matic kit. I put it together over the course of a few weeks.
Here is a picture of my Makerbot Thing-o-matic #6001
Appearently they started at number 3000. So at least 3000 were sold. Notice the spool holder I printed and the brown little trinkets surrounding the machine. It was a wonderful little machine.
Here is a sample of some of the things I made on my Thing-o-matic.
A weird twisted not:
Heart Gear:
Two litter water bottle rocket adapter to easily launch it with an air compressor:
Hemostat:
Planetary Gear Model:
I still have the husk of the machine. But once MakerBot moved on to selling the Replicator I knew it would be harder to get replacement parts. So eventually I got print size envy and cannibalized the moving parts and electronics and created a larger machine.
Wood Gears
I have always wanted to work with gears. A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque, in most cases with teeth on the one gear being of identical shape, and often also with that shape on the other gear. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source.
When I first got my 3D printer I made a 3D printed grandfather clock.
The clock worked ok. I printed the parts on a machine that was a little small for the design. The machine would work for a short time but I was able to see how the parts work. But I still wanted to design and build a machine of my own.
Several people on Thingiverse, a website dedicated to the sharing of user-created digital design files, have various models and scripts that create gears and gear based machines. I feel as I explore more mechanical design ideas, I will need to explore basic simple machines like gears to fill in gaps between motors and the work I am trying to drive.
On Thingiverse the user Leemon Baird shared his script to generate Public Domain Involute Parameterized Gears. This script simplifies lots of the details. For example, according to wikipedia, details like the angular velocity ratio between two gears of a gearset must remain constant throughout the mesh. That sounds difficult and would overwhelm someone new to making gears. Leemon made a function that takes 9 parameters but you only need to enter 4. These variables are: the circumference of the pitch circle divided by the number of teeth (millimeters per tooth), total number of teeth around the entire perimeter, thickness of gear in mm, and diameter of the hole in the center in mm. With this basic script to went to task laser cutting gears out of thin plywood panel. I had to goal but to see how many I could put on a board and see hard/easy to drive the gears.
As you can see from the picture above I made a lot of gears. They were a little rough to drive all of them at the same time. I was having alignment problems as well. As I was moving the gears some wouldn’t engage. I placed an acrylic guide over the main drive gear, the one with the handle, to try to resolve the alignment issue. And the gears where attached by 3mm bolts. So the entire surface of the gear was rubbing against the attached panel.
After the laser cut gear experiment I had a few lessons for my next attempt. First, I need the cut the gears out of thicker material. The laser cutter is nice because I just load in the parametric design into the computer and cut, but the laser can only go through thin material. Second, I need to keep the gear floating above whatever it is attached to so I don’t get that surface drag. And third, I need the gear to use bearings and bushing to reduce friction on the fastening bolt.
CNC Panel Router
So to cut out gears out of thicker material I need to learn a new tool. And that tool is the stinger CNC router.
A CNC router is basically what it sounds like. The machine has a router mounted on an arm that moves in the X,Y and Z axis and the arm is controlled by a computer. You can load a computer design file into the computer, the computer will determine the tool head path based on the design file and the type of bit on the router. This machine can use the same files I generated for the laser cutter, but can cut through up to 3 inches of wood. There is a little more setup involved that the laser cutter. The laser beam is a simple point and doesn’t change, it simply follows the line. The CNC router is a bit that can be one-eighth to three-quarters of an inch thick. So when you define the tool path you need to specify whether you follow the inside or the outside of the line.
The CNC router also allows other options that a laser cutter doesn’t. First, you can specify the depth that you can cut down. You can cut all the way through or just a shallow cut. Second, there are different drilling profiles. You can drill hole, a pocket where all material is cleared away, cut on the inside or outside of a profile, engrave a shape into a surface, or cut a relief on a surface.
For the gear I needed three things, the ability to a gear profile out of a piece of three-quarters inch plywood, drill a hole through for a bolt and bushing, and a pocket for a regular skate bearing. I was able to take the files from my lasercut gears and use them to generate some vector files for routing. I can select each line in the vector file and create a different cut style. For example I can select the teeth profile and tell the software to route all the way through the plywood from the outside of the line. The inner two circles have a different cut path. The center most circle will cut all the way through from the inside of the circle. And the outer circle will cut a pocket half way through the plywood. Below are some pictures showing the a vector art being loaded into the tool path generation program.
I configured the tool path generation to use two different bits. The Teeth profile and center circles can be cut with a single end-mill bit. This bit will leave straight edges. The lettering will be engraved with a 90 degree V-bit. After generating the tool path and then saved out the commands into two files. I am now able to load the tool path data into the CNC router driver software.
Once to plywood is loaded onto the machine and the bit head is aligned and configured I can let the machine cut out the parts.
Once I can take off the gears I just need to place in the bearing, screw on the bolt, and attach a magnet to the bolt so the gears can attach and slide on a metal surface.
And here is the final product.
Pi Day
I milled a Pi shape out of 4 sheets of plywood.
I then created a pie crust with some savory filling. (sausage, potatoes, onion, chives, egg binder)
Fill the mold with pie crust and filling.
Parametric Box Script Generator
A few years back I was prototyping a data collecting product with an arduino at it’s core. The arduino would have a SD card shield to collect the data on, a motor driving shield, and poll data from various types of sensors. I developed the prototype in my garage and I was looking to transition the prototype to the field. I wanted to transform my prototype from a bundle of wires on a rack to an enclosed device with well defined plugins, ports, etc, so non-technical people could just plug it in. I tried using a simple enclosure from a well known retailer, and it would hold everything with space to spare, but customizing ports was a bit of a pain. My first goal as a member of my local hacker space, Sector 67, was to use the laser cutter and design a parametric box that would be quick to make, and easy to take apart and redesign.
So what does parametric mean? Basically parametric refers to the ability to alter the structure of an object (usually a computer model) by simply changing one or a few parameters, and the model is structured in such a way that sub-elements have built in logic to adjust themselves accordingly. For example, programs from companies like Solidworks, Autodesk, and others have the ability to build parametric designs. The software I used for this box is an open source program called OpenSCAD, OpenSCAD.org.
OpenSCAD models 3D and 2D objects via a scripting language. The software allows you start off with basic primitives (2D: circle, square, polygons ; 3D: cube, cylinder, sphere) then add, subtract, union, etc until you get the object with the geometry you need. The language has features to define variables, for loops, modules and allows you to pass variables that will give the user the ability to redefine the model via these parameters.
My requirements was to build a script where I could supply an interior box dimension with a length, width and depth, and the script would spit out a parts outline document that I could just take to a laser cutter, cut out the parts and assemble with 3mm bolts.
When I was done building the script I had the basics of what I wanted. But I also added a parameter for the material thickness the panels were cut out of and the slots and bolts would adjust themselves accordingly. I also added a parameter for how thick the tabs are, how long and wide the bolts are, and the length of the nut is to secure the bolts. I also added a parameter for the number of tabs on the length, width, and depth dimensions individually. I also designed the code is such a way that I can cut square, circle and polygon holes through individual panels to pass wires and mount buttons and controls on. Finally I coded the ability to toggle the visualization of the design between an assembled box as shown above and the flat design files ready to be cut and assembled.
The box is then assembled with 16mm long 3mm bolts with the nut embedded into the panel and the bolt is inserted from the outside to hold the box together.
And finally the assembled box.
And below is an example of a prototyped Raspberry Pi device utilizing this script for an enclosure. As you can see the base of the box is plywood and the top is acrylic. The plywood is nice for a box because if you don’t quite have your holes in the right area ,or you just forgot to add the holes, or you want to mount it on a wall, you can easily drill out a hole.
I made a variant on the parametric box script where the tabs are nested into the receiving panel. This script became the basis of my 3D printer that I upgraded.
