spindle power vs speed vs torque in a small mill

[ihavenofish]

so, im working on a spindle project. the goal is to achieve the best performance possible and advanced features, while still keeping its size and pricing in the upper end of the hobby market.

in tweaking performance with available motors in this price point, you come up against a bit of a dilema.

where do you draw the line sacrificing low end torque for usable high end speed?

ive been talking to some custom motor builders and ive outlined 3 of my possible options in the attached chart. ive also outlined the fanuc robodrill high speed spindle as something of a dream target, and my colombo rv55 air cooled router spindle as a practical inexpensive high speed option.

as you can see, if i try to match the fanucs low end torque, i limit myself to 8000rpm or so. if i try to best its top end performance at 24000rpm, i have fairly weak low speed performance. the sweeter spot is in the middle at 12000rpm.

in all instances, im at least 75% more powerful than the colombo at any speed. note that all of these examples have some higher intermittent torque available.

so, if you were looking for a versatile spindle for your small sized mill (hobby or industrial), which of the 3 custom motors would you pick and why?

[ihavenofish]

heres a video of the robodrill cutting stainless to get an idea of the power in use (mostly at lower rpm).

[nomedia="http://www.youtube.com/watch?v=4NNlIAmk4xk"]YouTube - Methods Machine Tools High Speed High Feedrate Robodrill Demonstration[/nomedia]

[HimyKabibble]

What kind of machine, and what kind of work do you plan to do? A 3HP motor on an X2 would be useless, due to the lack of rigidity. OTOH, if you do most of your work with 1/2" endmills, a 24KRPM spindle is rather useless. I'd opt for the 12K custom, as it gives reasonable top-end speed for small tools, and (looks like) reasonable torque at low speed, for larger tools. Not clear if the low-end torque would be sufficient, however, from that graph. It's pretty hard to exceed 1HP on the spindle with anything smaller than a knee mill, or a very large, stiff benchtop (like an RF45). On my knee mill, I do most of my work with 1/2" and smaller tooling, and almost always operate in the 5-8KRPM range, even with 1/2" tools. More RPM would really help with smaller tools. But, it's easy to add an accesory spindle for that, to get all the way up to the 24KRPM range.

Regards,
Ray L.

[ihavenofish]

i said upper end of the hobby market. x2's need not apply, haha. wer talking mills that are closer to 1000lbs and up, like tormachs and novakons and such. particularly with linear rails slowly creeping into the segment. these will also apply to industrial machines well out of the hobby price range.

my little kx1 had .95NM up to 5000rpm. its right on the borderline of being too much for the machine to handle.

in contrast my big novakon nm200 (1500lbs) has 2hp at 3500rpm (4NM), and its well within the machines rigidity envelope. this is an induction motor, so i dont really know what the torque curve looks like.

my new mid size novakon (700lbs) has 1.5hp to 6000rpm (1.8NM). ive not pushed it yet, so im nto quite sure if its too big or too small or just right yet.

last but not least my router has the colombo spindle, and its a good match. the thing runs almost exclusively at top speed in wood though.

anyhoo, thanks for the feedback. the questions you asked are for YOU to answer. thats the point here. i can put in any of those 3 motors for any given customer. im just trying to determine which ones people think are most ideal and why.

your reasoning is fairly sound for the middle one, however i do disagree in the general sense about the 1/2" tools for high speed. at least in aluminium. thats only 3100sfm, and well within spec of many specialised end mills and insert cutters. 1/2" depth, 1/8" width, 24000rpm at 246ipm is 3.5hp, or 1NM. right on target for continuous work.

wind down for some 4140HT cutting at 5350rpm, drop the radial cut to 10%, and a more modest 60ipm feed, and you are still comfortably in continuous duty for this spindle at 1.5NM.

face milling will take us into less impressive territory, but you should still be able to take .010" cuts in 4140ht steel at 30ipm at 1500rpm with a 2" cutter at 1.5" width.

so the 24000rpm model isnt useless at low speeds, but definitely not a hogging spindle. needs a very light calculated approach. its high speed performance will more than make up for it if you do any volume of aluminium.

to contrast, the 8krpm model will swing that face mill at 50ipm and .02" depth.


i used the kennametal calculators for this cutting data - a calculator that has generally done me well on my machines though tools and materials in real live will be variable.

[hoss2006]

your big novakon nm200? Did you buy the one your neighbor owns that you've been borrowing?
Hoss

[ihavenofish]

your big novakon nm200? Did you buy the one your neighbor owns that you've been borrowing?
Hoss

its a long stupid story, but the shop is now mine.

[hoss2006]

its a long stupid story, but the shop is now mine.

Congrats.
Hoss

[ihavenofish]

Congrats.
Hoss