I had today to myself in the ye olde shoppe, so I decided to work on some CNC projects. One of the projects that has been stalled for quite a while is the creation of a tool plate for my X3 mill. For this project I purchased a 3/4” thick piece of aluminum. The idea behind the thickness was that I could anchor the edges with short screws so that no part of the fasteners holding the plate to the table would poke out above the top of the plate. Interesting idea, but probably not work the effort. First, it’s really really annoying to try cutting that size chunk of material.
While trimming the material, I broke one bandsaw blade and two 1/8” endmills. First I tried the bandsaw, but I got too eager and broke the blade. It seemed like a good plan to try my mill instead. That worked fine until the endmill made it to a depth of about 1/3”, at which time the cutter was unable to evacuate chips. After two broken cutters, and a failed attempt with a jigsaw, I put a new blade on the bandsaw and took my time cutting through the material. Worked fine.
By the way, VRML extra cool bonus points. Download and install this viewer, then click this link to view the file in 3D. Be sure to push the tilde (~) key to switch to rotation mode. The VRML file is large, so it may take a moment to download.
In Home Digital Machinist I saw an article where the author discussed using a drill bit to remove material. His rationale was that drill bits are much better equipped for removing material. The drawing above shows the toolplate. It is 6”x12”X.75” with a .75” drill pattern throughout and .75”x.25” edges at each end. In the illustration above, the red columns represent drilling to remove material with a 1/2” bit.
Drilling to remove material worked really well. Unfortunately I got overconfident and choose my cutting parameters poorly. I used a 1/2” endmill to pocket the ends and then took a 1/8” deep cut. This ended up causing a lot of trouble. The spindle tried stalling, and the machine chattered quite a bit. I finally broke down and created a new NC program to use a 1/4” endmill. By that time, the steppers were pretty warm. Eventually I heard the telltale sound of missed steps. I’m not sure exactly what the reason was. The irony is that I had already attached the fittings for feedback encoders on the X and Y axes. Had I chosen to finish that project first, the toolplate would have gone a bit smoother. Once I suspected that I was missing steps, I shut everything down and called it quits for the day.
Lessons learned…drilling is good. Large cuts in aluminum, not good, even with extra material removed. Next time I’ll go with a faster program using a smaller cutter and shallow cuts.