DFM: Water Color Pallet Box
The aim of this project was to create a personalized box out of two 3" x 3" aluminum blocks using 2.5 axis CNC milling. I worked with a partner on this box where he created the bottom of the box and I created the lid. The goal of our box was to have it act as a small water color pallet and brush holder.
An exploded view of the whole box. The box uses a diamond locating pin in place of a more traditional dowl style pin for one of the two pins in order to reduce the required tolerancing between the two parts.
Renderings of the box in two likely positions. On the left, a "working" position where the box is currently being used as a watercolor palette and water tray, and on the right, the box is being put back together.
A technical drawing of my box lid
The skills I was working on developing in this project were CAM(Computer Aided Manufacturing), and CNC Milling. I used Autodesk Fusion CAM for this project and gained quite a lot of experience in the best order of operations and tool choice for optimizing machining time. I had done a fair amount of manual milling before this project so there was less to get used to when it came to using the Tormach 770M but it was still helpful to be running my own part to get a better understanding of what my CAM program looked like in real life.
A simulation of my CAM setup
A couple of the challenges I encountered in this project were making sure the two halves of the box fit together, getting deep enough pockets to hold the paint brushes and markers, and keeping the machining time under 30 minutes.
For making sure the two halves of the box fit together I used a H7/g6 clearance fit on the locating holes of the lid of the box as it provided very minimal slop with tolerances that were realistic on the CNC mill used. To get around any centering issues between the pins in the bottom of the box and the holes in the lid of the box a diamond pin was used in place for a more tradition dowl pin for one of the two pins.
The issue with making sure the pen and paint brush pockets were deep enough to securely hold pens and paint brushes was a result of the fact that we only had endmills with very short flute length. To get around this I chose two pocket sizes. A smaller pocket size that could be easily drilled out with a standard drill bit circumventing the short flute length problem. And a much larger pocket that would be unreasonable to drill but that could be milled out using a relatively large 3/8" endmill that had much longer flutes than the standard 1/4" and undersized 1/8" endmills.
Finally keeping machining time under 30 minutes doesn't sound like much of a challenge for such a small part but given the low power machines and conservative cutting speeds were were using for this project it did take some consideration to get the machining time under 30 minutes. The major design decision I made to keep machining time down was to keep all interior radius and fillets larger than 3/8 of and inch. This meant that all the pockets on the part could be made with a 3/8 inch endmill which was significantly faster than using smaller endmills. I also made it so that all roughing operations outside of the pockets could be performed by a shear hog of any size making the roughing and finishing passes much faster than is the required an end mill.
The final box in use with both my lid and my partners base
Over all I was quite happy with how my box came out. The biggest issue I ran into was that the 3/4" shear hog I used to rough the sides of my box was wider at the base that at the top of the cutting profile so it left horizontal lines across my part with each cutting pass it made. While these lines were not part of my design I don't feel they detract so much from the design that the box needs to be re manufactured. The box fulfils its purpose quite nicely(see picture below) and outside of the strange finish left by the shear hog has a really nice finish all over. I found this process to be really enjoyable and will be using a lot of what I learned here in my processing fish project.