Archive for the ‘Engineering’ Category

3D Printing

Monday, August 2nd, 2021

Way back when I was an itty bitty boy, I remember reading about rapid prototyping, and seeing pictures of objects created from an SLA printer. The object I remember most was a rook with an internal spiral staircase. Was was amazing about it is that it is an object that would be impossible to injection mold, or carve using a CNC machine. It had amazing detail for such a diminutive object.

When I went to college, we had a pair of powder bed printers that we could use in our manufacturing laboratory. Powder bed printing is extremely versatile because the objects being printed do not require any support structures. This allows for flexibility in design that could be difficult to achieve otherwise.

Since graduating, there has been an at-home 3D printing boom. I recall when the MakerBot went mainstream. It was very interesting, but I was very put off by the quality of the prints. The filament left a very jagged surface, there wasn’t a ton of detail, and the few prints I had seen in person had de-lamination issues in some of the layers. I’ve been very skeptical of filament printers since.

I finally gave in after seeing some prints a friend at work made using his printer. The prints still have the trademark layer lines of a filament printer, but the detail has improved so much. I got a Creality Ender 3 ($260 at time of writing) which seems so incredibly cheap. I am extremely impressed with what this machine can do.

Setup

The printer comes unassembled. It took about 30 minutes to put it together. It really required very little skill, as long as you know how to turn an Allen wrench.

Once it is assembled, the next thing to do is level the bed. This is accomplished with 4 knobs underneath the print bed. Again, it’s a pretty basic process.

Lastly, feeding the filament is a simple task. After that, it’s ready to print.

The first print I did was preloaded on the thumb drive. It was a little dog figurine. It printed perfectly!

Software

The printer came with it’s own branded software. Unfortunately, it is Windows only, but off the bat I was impressed by the ease of use. I’ve never seen or used slicing software before, but I was delighted by how intuitive and easy it is to use. It has basic presets as well as expert settings. For most things, the basic presets are great. I’ve used them for multiple projects without any real issue.

Replacement spool holder for a tape dispenser; Modeled in Fusion 360, Set up in slicer, printed in white PLA

I did eventually find out about Utilimaker’s Cura and downloaded it so I could slice on the Mac, and also so I could test tree supports. Cura had a built in printer profile for the Ender 3, which was great. My first few prints using it for slicing have also been a success.

Printing

Now, it’s not all great. I’ve had my share of failed prints. Many times this is do to positioning something sub-optimally, or trying to print something that’s just too small and delicate. In most cases I’ve been able to work around it by rotating or splitting the object up. Another issue I’ve had is with smaller items sticking to the print bed. Adding a raft certainly remedies these issues, however it uses a lot of extra material.

I did buy an upgraded glass print bed. The plastic mat that came with the printer already had visible signs of wear after just a month or two. The glass bed has been performing pretty well, The adhesion is good, and it seems to be resistant to wearing. I still have problems with larger prints pulling up around the base edges though.

Conclusion

I’ve always steered away from FDM printers because of their inherent drawbacks, such as requiring supports and the inherent layered texture of the printed piece. Despite all those misgivings, I am quite pleased with this product, and equally with it’s affordable price. One thing to be weary of though, I’ve found that with this hammer in my tool chest, most of my problems have started to look like nails.

Chocolate Candy Cups

Thursday, September 7th, 2017

As a young person, I was quite enamored with Reese’s peanut butter cups. Those were one of my favorite candies to eat during the holidays. It’s now been over 5 years since I have tasted them. This isn’t due to amazing will power and good dieting, it’s due to the fact that those candies are lethal to my son. Yet, I still long for those treats.

I decided to make my own that would be safe for my family. I figured I’d be able to find a candy mold for just such a project, but was unable to find any. I was able to make an approximation of a Reese’s peanut butter cup by using cup cake holders, but I still felt that having the correct type of mold would yield better results.

I devised a plan for how I would do it, and then modeled the geometry in Autocad Inventor. The idea is to model the geometry I want (a positive) and use a CNC machine to carve this geometry. From the positive CNC generated shape, I will create a negative mold using a food-grade silicone rubber. Then, finally, I can make the chocolate treats using the silicone mold.

Modeling

Modeling the shape was pretty easy. I figured out the basic dimensions I wanted and modeled accordingly. The final shape should be about 2 inches in diameter and .5 inches tall. Even though I have no intention of wrapping these in paper, I did some careful math to make sure the ridges were appropriately shaped to allow a circular piece of wrapping to be applied. This was done by making sure the perimeter of the ridged top was equal to the circumference of a circle whose radius is equal to the bottom’s radius plus the length of the side.

The goal is to have a void in the chocolate where anything can be put inside.

CNCing

With the model looking okay, I CNCed the geometry out of some scrap hardwood left over from another project.

After CNCing, I removed the positive geometry, and sanded and filled the wood as best I could.

I then put 4 of the positive carvings in a void made out of particle board. Once glued, the whole thing was coated with black enamel to fill the gaps and hopefully make the silicone not stick.

Casting

I ordered a small supply of silicone casting (Smooth-Sil 945) from Smooth-On. This particular product is food-safe, and is activated using a 50:50 mixture of A and B parts, so it’s really easy to use.

Using some simple geometry, I figured out exactly how much material I would need. I poured the correct amounts into disposable bowls and mixed thoroughly, then poured the material into my mold. 6 hours later, I was able to pull the mold out. It turned out very well!

Chocolate

The next step was to take chocolate, and lightly melt it. I used Guittard chocolate, which is nut-safe. I tried different types, but liked the more milky flavors the best (Milk Chocolate 30% Cacoa). Not being a chocolateer, I have a bit to learn. From what I understand, the key to successfully making chocolate treats is to temper the chocolate by melting it at about 115 degrees, then letting it cool slowly at a temperature of 75 degrees. I could be wrong, but it did seem to work.

I was left with things that look like Reese’s, but have an opening and a void on the bottom!

Soy Butter

The delicious insides is a combination of Wowbutter brand soy butter, butter, brown sugar, and powdered sugar. The butter and soy butter are heated, then sugars are added, and then cooled.

It ends up as a dough that isn’t as sticky as the soy butter began. This allows it to be put into the chocolate shells rather easily.

Finishing it up

Now upside-down, additional chocolate is poured to cover the opening and seal in the delicious center.

Conclusion

The result was very tasty, and completely satisfactory. It’s time intensive. The chocolate takes a LONG time to harden. 4-6 hours at room temperature. This can be sped up by placing the chocolate int he refrigerator or the freezer, but cooling the chocolate too quickly can have negative results.

The Reese’s company (Mars) clearly doesn’t make their cups in this manner. Since the paper liner appears to be the actual mold for the chocolate, I suspect they do it in the opposite fashion. They pour the chocolate into the cup with a removable core that leaves a void when removed. The insides get inserted via extrusion, and then the cup gets topped off with chocolate and packaged once solidified. Empty cups that popup online from time to time seem to confirm this theory.

No matter what, I am happy with the result, and my son can now know of the exquisiteness that is a Reese’s cup.

CNC’d Relief Carving

Friday, August 4th, 2017

I was tasked by a friend to create a relief carving based on a low resolution photo. The subject matter is a baby hand holding onto the daddy’s finger.

I’ve never needed to do any sort of relief carving like this, and I’m not real handy with a chisel, so I decided the best way to do it would be to generate a depth map and feed it into a CAM program that would generate the g-code to carve the relief. A depth map (also known as height map and bump map, depending on the program) is a grayscale image where each pixel represents a height based on it’s brightness; white being highest, and black being lowest.

There were a few ways I could go about making the depth map. I thought that the path of least resistance would be to bring the photo into Photoshop and manually paint a depth map over the image. Here is a gif of some of my iterations.

DepthMap

It took about 18 or so revisions before it got accurate enough that the final result was acceptable. In the CAM program many imperfections are readily noticeable, however the final product often looks better due to the maximum effective resolution of of a ball-nose cutter for a given size on wood.

MeshCamI looked at quite a few programs to decide which would handle the depth map the best, and ended up using MeshCAM. MeshCAM was the most straight forward of the software I tried, and it also is available on the Mac. All I had to do was import the image, specify the wood dimensions, and the maximum cut depth, then adjust the speeds and feeds. The smallest bit I have for the CNC machine is a 1/8th inch ball nose.

Here is the final result. My friend said it was perfect for what he needed.

In retrospect, it might have been easier to import the image into Blender and model the hand and fingers in 3D space. The results might have been better, however the method I chose was an enjoyable challenge and not too time consuming.