DIY High Speed Spindle update (LONG)

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
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wrote:

More than that. CAT 40 won't handle 32,000 rpm. Neither will ER.
No tapered-shank toolholder is reliable at those speeds. A key word here is "reliable." If you really nurse it, you could get away with it. Whether you need ceramic bearings depends on bearing diameter. Again, it's a question of how well you can nurse the whole affair.
For around 15 years or so there has been extensive coverage of spindles turning in this range of speeds. I kW is a small motor (why CAT 40 with 1 kW?); it does present fewer problems than a 5- or 10hp motor, which is where the action is these days in high-speed spindles. As long ago as 2000, Fischer was making 100-hp spindles that would turn 50,000 rpm, and 50-hp spindles that would turn 100,000.
There's plenty of discussion around about it. I'd start with toolholding systems and work backwards.
--
Ed Huntress

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<SNIP>

The CAT 40 tool holder is stationary. The spindle fits inside it. I'm pretty sure an ER11 or ER8 toolholder will work. According to the bearing calculator I don't need ceramic bearings. I can see my post wasn't clear. I will be making a spindle cartridge that fits into a CAT 40 tool holder which will in turn fit into nthe machine spindle. I hope my calculations are correct. I will be doing them over before starting the build. Fortunately the motor doesn't need to spin at full speed so I can test the spindle at lower speeds and work my way to destruction . Maybe I should order 6 bearings instead of just three. I will post my results. Eric
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On Sat, 06 Sep 2014 09:28:16 -0700, snipped-for-privacy@whidbey.com wrote:

It may not be your post that's the problem. I read it pretty quickly.
It sounds like you know the issues, so I'll bow out. I was involved with Roku-Roku when they moved up from 15,000 rpm to 30,000 for smaller, toolmaking mills, and I reported on spindle developments for aerospace for over a decade. So my perspective is a little different and may not be helpful.
In any case, when it comes to toolholders, it's not just concentricity that counts. The forces involved in gripping the tool -- where they grip, and where they don't -- actually are the bigger issue.
As for bearings, as you apparently know, it's centrifugal force (physics nerds -- don't give me a hard time about that) that is the determinant, not just speed alone. So diameter is important.
Good luck!
--
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On Sat, 06 Sep 2014 12:44:47 -0400, Ed Huntress

Ed, I'm worried about concentricity not just because of vibration but also the possible use of multiflute cutters. And at the small diameters I would be using chip load is very small and even a tiny amount of runout can be more than the chip load per tooth. Whatever the reason though I will be striving for the best concentricity I can manage. Eric
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On Sat, 06 Sep 2014 14:42:41 -0700, snipped-for-privacy@whidbey.com wrote:

Well, sure, that's always a good idea, and necessary at high speeds. Just keep in mind that the thing that limits rpm of tool holders is most often the way they grip. Tapered holders, for example, have less grip at the opening end, and tend to bell-mouth (elastically, not in permanent deformation) when you spin them too fast. The HSK type is vastly better at high speeds, and there are others.
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