3D Printer Cooling Fin Design

Did you know a 3d printer can upgrade itself? Alas, I have manufactured the new heat sink and am now testing it out. Below you can see the new heat sink upgrading itself by printing a fan duct for the filament cooling fan. The filament cooling fan is the large black fan that was temporarily zip tied to the print head. So far, the new design has shown impressive results with its ability to print even the finest of details as seen on the MJS logo etched on the duct.

Plug and Play Construction

Below you can see the construction of the heat sink upgrade. The whole goal of this design was to make it as plug and play as possible. The Ultimaker relies on a clamp style mounting bracket. Part #8 (the aluminum lock collar) was cut from a piece of aluminum post stock and had to be slightly thicker than the clamping space (part #’s 10 and 16) to fully constrain it. Before tearing the original design apart, I used the printer to print out a plastic collar I designed (part #7) which would add additional support to limit the effects of torque from the Bowden tube. However, the most important part was part #13, or the aluminum coupler tube. This piece started as an 8mm OD, 3.2mm ID standoff spacer that I ordered from Mcmaster. As you can see from the drawing below, I had to modify it a bit to get it to work with my design. Starting at the top of it, the diameter had to be 6.5mm to accept the Bowden tube. Then, it would transition to 3.2mm (inside diameter of the Bowden tube), and then transition out to a threaded portion for the heat break (part #9). The threads had to stop at a critical distance to prevent the 8mm aluminum tube from coming in contact with the aluminum heat block (part #3). More on this in a minute…

Screen Shot 2018-01-19 at 1.34.13 PM — Part #13

Fin Mounting

As you can see below, the aluminum tube was critical to this design because it allowed for the mounting of my modified cooling fins. If I had a CNC mill, I would have just designed an all in one block with a coupler and heat sink built in.

More on that one thing…

Ok, more on that one thing I was talking about above. Below, you can see where the heat break connects to the heat block (the block where the red heater cartrige wires are going into). Material is important in this case. I will break down what materials are coming into contact. To start, we have a copper nozzle which screws into an aluminum heat block. Then, a stainless steel heat break is screwed into the heat block butting up against the copper nozzle. The heat break is then coupled to the aluminum tube and heat sink. As mentioned above, it is critical that the aluminum tube and heat sink assembly does not come into contact with the heat block. This is because aluminum has a relatively low thermal resistance as compared to the stainless steel. If the aluminum comes into contact with the aluminum, all of the heat is channeled quickly to the heat sink and transferred to the environment by convection. What happens? well, the temperature readings on the 3D printer display drop dramatically, and the printer cannot sustain necessary printing temperatures. Also, thats why I’ve been calling it a “heat break”. It literally slows down the heat transfer so the fin is not parasitic to the goal of 3D printing, which is to heat up plastic. This was also explained briefly in my Ultimaker 3D Printer Cooling Fin Design Study.

Project Conclusion

This was a really fun project. I applied some heat transfer course knowledge to solve a problem to improve one of my hobbies. Before I end this project though, I should point out some obvious things that I could have changed or could improve. First, where the heat sink clamps to the coupler tube. The way I modified the heat sink was by cutting it down to its calculated size and fin number, and by drilling a hole in the center. To get effective clamping force, I toleranced the hole slightly smaller than the coupler tube, but due to inaccuracies in my cutting method (two halves clamped together in a vice and cordless drill), there were some gaps in the mate to the coupler tube. This leads to unknown clamping force related inefficiencies. In addition, after drilling the hole, the mating surfaces ideally should have been polished to reduce contact thermal resistance. Second, when modifying the coupler tube, I should have used a drill press. I found that this was especially important for the tapped portion. When fed into the print head, the filament would get caught on a jagged portion where it transitioned from 3.2mm to the heat break. This was especially annoying when loading, because it would require me to twist the filament around until it slid past the uneven portion. Lastly, I noticed that as the print head moved, the Bowden tube created a moment on the printer head. This would cause slight movements at the print nozzle. On large prints, I noticed that the base layer lines had slight gaps due to this small movement in the nozzle. Perhaps I could have secured the top of the aluminum coupler by designing a washer that would fill the space between the tube and the plywood, (part #16).

Below is the final design of the upgrade. I ended up not using the fan duct I designed and just made one out of gutter sheet metal material.

Some things I printed…

The coolest part of this project is that it allowed me to create some of my other most recent projects. Below are some of those things. You can see that the level of detail is there, but like I was saying above, the base layers were not as good as they could have been.