Greetings All, I posted some questions a while back about making a high speed spindle for doing engraving work. I envisioned using a BLDC motor made for an RC vehicle or plane. I found a couple motors that look good and the drive electronics for them. The basic spindle design is done. I have had a hard time choosing bearings. I have been using the Timken (or was it the SKF? I dunno, I'm tired) bearing calculator app for this. There are many variables and since this is something I don't normally do it has been a slow process. Trying to figure out the loads the cutter will be seeing and transferring to the bearings has been tough. There will be three bearings, two back to back angular contact bearings in the front and a single bearing in the back, either a deep groove or an angular contact. So the spindle shafts have been ordered, I'm using ER collet holders. One shaft arrived and the taper runs out .0002. I hope this is good enough. It may not be. I might end up assembling the spindle and grinding a new taper with the spindle running in its bearings. The motor will be liquid cooled with coolant from the mill coolant system. I have designed the labyrinth seal for the front of the spindle. I will be using filtered positive air pressure in the spindle to blow out any contaminants that may want to be sucked into the spindle through the labyrinth seal as it cools and during operation. I ordered two motors, a 1000 watt and a 450 watt motor. I was dubious that one of these little motors would really work despite what they are rated at. But I found during a web search a site where a guy has posted his siccess making high speed spindles using the same basic type of motor that I will be using. This is good, somebody has done this before me so the idea isn't totally whack. He uses outrunner motors, where the O.D. of the motor spins. His spindles have the motor hanging out in the air for cooling purposes. Anyway, his spindles are doing real work and doing it well. I will be using an inrunner motor so I can put the whole spindle assembly into a modified CAT 40 tool holder. I am concerned about balancing the spindle because the initial target speed is 32000 RPM. I have found some info from a cursory look on the web about piezo vibration detectors and software used with them to analyze and determine how much out of balance and where the balancing needs to be done. I am mostly concerned about the motor rotor being out of balance as all the components machined by me will be as consistent and concentric as I can make them. Since this is something I'm good at I'm optimistic about getting parts balanced well enough right off of the machine. I am going to try using high quality stock ER collets but if that doesn't pan out I'll just make solid collets and shrink them onto the engraving cutters. There is the issue of the engraving cutters being one flute cutters as this may cause too much out of balance. If this is the case then the solid ER collet can be ground on to fix that problem. Ultimately my goal is to have the spindle act like just another tool in the tool carousel. I will need to make some type of automatic connector that will connect air, coolant, and power to the spindle as well as keep the CAT 40 tool holder from turning slightly from the reaction of the spindle running, sort of like the part that keeps tapping heads stationary, but more positive, with no slop. Even though the goal is to have this cool connector block that does everything described just above the first iteration will just have some sort of stabilizer and I will have to connect power, air, and coolant manually as well as turning on the spindle manually. The mill already has the relays and available M codes to turn on the spindle from the program. If the initial spindle works out well I am going to try for 40,000 RPM. I have not yet found a stock motor that spins that fast while at the same time fits the other requirements for torque, size, and reliability. I am amazed by the sophistication of the electronics that control these motors and the motors themselves and they are made for toys. Anyway, that's it. I guess I ran on a little. But maybe someone will read this and find something I overlooked and have some good advice and maybe someone will read this and decide to build their own spindle. If someone does it will no doubt be better than mine and I can learn something from them. Especially if, like me, they don't know when to stop typing. Cheers, Eric
- posted
9 years ago