I built a c-beam aluminum gantry type CNC machine and it works great on softer woods, acrylic, etc., but I want to mill metal and I'm trying to figure out if an aluminum extrusion machine can be made rigid enough without breaking the bank. Or do I have to scrap it and use steel. Read on if you're interested.
Step 1: Why Upgrade a Perfectly Good CNC Machine?
Okay, so the c-beam is fairly rigid but in order to mill metal, it has to be more solid or there will be chatter unless you go very slowly and the slower you go, the more time your bits have to heat up. Based on what I was seeing, the c-beam wasn't strong enough so I decided to use v-track and steel bearings to upgrade the z-axis. And while I was at it, I decided to put some stainless channel in there to increase rigidity further still.
Step 2: What Parts Do You Need to Upgrade to V-track or V-rail?
You can buy many different types of v-track: aluminum, steel, hardened steel, polished steel, etc. Same goes for v-wheel bearings: delrin, steel, etc. I decided to buy C53 hardened steel v-rail from Mcmaster Carr. I only needed 2' of it since my z-axis is only 12". I bought the 7/8" track since I wanted to use the t-slots to attach the track to the c-beam. The wheels I got on ebay for about $8 a set which includes a 1/4-20 bolt, washers and a bushing. I decided that 3 wheels per side was enough and I needed 3 concentric bushings and 3 eccentric (for adjustment). I also added a 2mm walled 40mm x 20mm stainless steel channel into the c-beam for added stiffness. Watch the video for the process.
Step 3: How Do You Do It?
Measure your z-axis c-beam and cut the v-rail with an abrasive wheel.The "v" part is hardened, but not the rest so drilling holes for your screws was fairly easy. The difficult part was cutting the 40mm x 40mm x 2mm stainless square tube in half in order to make the channel. Ooftah! I used a ferrous cutting blade on my table saw and almost had a heart attack! Watch the video! Were I to cut a square tube in half again, I would most definitely use angle grinder with a thin abrasive cutting disc.
I did get it to work in the end and I feel that it made the z axis more rigid for sure. However, there is still significant torsion flex in the x-axis. Stay tuned.
Step 4: Re-assembly and Testing
Watch the video to see how effective this upgrade was. Now on to the X axis stiffening. Thoughts and suggestions are welcome. I just want to mill some metal!
See the video on the X-axis upgrade here: Video of X-axis c-beam upgraded with stainless channel, tested...