Over the last couple days, we have been testing the performance of the black HDPE frames. We’ve gotten a lot of interest in a plastic-based frame over MDF. However, we have found several issues with making the frames out of HDPE that leads us to believe that it is not a good option for our customers and we will not move forward with manufacturing them. If you want to learn why and our impressions of using this material to make the frames, please continue to read.
One of the biggest disadvantages of using HDPE is the fact that it is not as stiff as MDF. This makes the machine less rigid. Initially, we believed that this would be negligible, especially based on our previous experience using the material. However, when we assembled a prototype, we found that the reduced rigidity in the HDPE introduced decreased performance and reduced quality in milled test parts.
One of our tests was to make aluminum bitcoin tokens. On the bottom is the test piece milled on the HDPE frame machine. The one on the top is made on a machine with an MDF frame. You can immediately see that there is a clear difference in the finish between them. Both were made using the same gcode, with 1000mm/min feedrate at 0.35mm stepdown using an 1/8″ bit.
Both samples (above)
Sample milled on HDPE frame machine (below)
Sample milled on MDF frame machine (below)
We noticed far more chatter and experienced a more difficult time milling with the HDPE machine. This is also reflected in the milled part quality.
When we received the parts for the frame from our manufacturer, we noticed substantial warp in the material. We decided to go forward with testing since we believed that some of the warp would be taken up when the machine was assembled. The warp would be pulled straight by the brackets and rails. For the most part, this did occur, but the fit with the acrylic shield was still subpar. There was a sizable gap with the groove for the shield.
In the future, we would need to look into a more dimensionally stable material or have the material stress relieved to prevent warping. This introduces more cost and perhaps would make this upgrade uneconomical.
Although HDPE looks nice and has great water resistance, due to its lack of stiffness compared to MDF, as well as warping issues, it is not a suitable material to make frames out of. Further research and development will be needed to create a frame that avoids those issues and offers performance comparable or better than MDF. As of right now, we will not be moving forward with manufacturing HDPE frames. Please stay tuned for more updates on frame development, and if you have any suggestions for other materials we can try, make sure to get in touch!