Sherline spindle to 30k RPM -- am I crazy?

[Scott_bob]

This is what I like about the zone, brain storming! Experimenting! Let's take it apart, and make it go faster! Pretty cool.

I just wanted to suggest a little perspective though.
How much faster can you feed with 3-4x the spindle speed with your existing CNC control?

We also tried higher spindle speeds (30k) but found poor life, and frankly poor results due to the inaccuracy of the machine control not the spindle. Even at 10k RPM we got poor performance. So there was no point in increasing the speed of the cutter if the machine could not take advantage of it.

Mold and surface machining require smooth imperfection free motion 1st. Then "if you have that", increasing your speed by 3-4x will give you feeds that can take advantage of this.

What kind of CNC control do you have?

[ESjaavik]

Use 2 angular (15 degrees) bearings at the bottom and a regular bearing at the top. It can probably be smaller as it carries less load than the bottom bearings. X-mounted preloaded angular bearings can actually run at higher speeds than non-preloaded.
And try to avoid plunge cuts. Enter the cut at around 20 degrees. This because you don't have any thrust bearings. They will not like the speed.

[c-c-cncboy]

It's clear that Esjaavik has done this work before! Spiral lead-in or ramp lead-in will help the tool, the bearings and (why are we here?) the cut finish. Many low-cost CAM packages don't offer much choice on lead-in style. Even if you need to go back and alter the code manually it's essential. Regards, Terrence

[steveg]

back from 3-12hrs
Colin one of the things touched on by ESjaavik is the
need for a bearing seal. the bearing that you have chosen
have no sealing at all!
spindles normally use a labyrinth (non-contact) seal to keep all the nasties out.
Sherline uses dust-shielded bearing, and a thin steel plate to do the same.
This makes the conversion more than a simple drop in.


One quibble with ES however , angular contact bearing ARE
thrust bearings! so the consern about plunge
cutting is maybe overstated.

Scott_Bob raises an interesting question about your control
and machine. One aspect of "high speed" and/or hard machining is to
run the machine at high ipm but with a tiny chip load, in this case
you get the metal removal rate
you are looking for as well as the speed and surface finish
you need.(edit: the point of this comment is of course
that if you could improve your control/machine the
kavo spindle might do the job you want)

About lubrication, many new machines lubricate their
spindle bearing with a mist lubrication system , really just
an elaborate air lubricator. this has the added benefits of
both cooling the bearings and placing the spindle under
positive pressure, keeping everything out.
The down side of mist is that you have to remember to add oil.
I just recently removed and reinstalled, after being
sent away for rebuild, a BT40 12000 rpm spindle that failed
because the air mist feed line broke! (in fairness the
spindle allready had about 24000hrs on it and had been sounding
a bit tired for the last year)
Grease on the other hand is for life and requires no attention.

One last thing Colin, check with a few local bearing houses
I've always felt that those large catalogs were Way overpriced.

[IJ.]

I've looked at a "Richmill" high speed spindle and they are using an air line for positive pressure inside to keep dust out of the bearings my guess is it provides some cooling as well as this has to be a factor at 30000+ rpm (it's good to 50000).

[c-c-cncboy]

Found this in "Manufacturing Talk" today: http://www.manufacturingtalk.com/news/fid/fid111.html
It's a nice reminder that reducing spindle bearing wear by cooling them with water sometimes can be a problem in itself. I still smile each time I walk by one of my chilled air cooled lil beauties. BTW bearing makers distinguish between "seals" and "shields" and I chose metal "shields". Regards, Terrence

[steveg]

usefull design guide http://www.ca.nsk.com/webadmin/resou...oaded/c859.pdf

[IndHobby]

Sorry wrong thread

[VWSatOz]

Originally Posted by IJ. I've looked at a "Richmill" high speed spindle and they are using an air line for positive pressure inside to keep dust out of the bearings my guess is it provides some cooling as well as this has to be a factor at 30000+ rpm (it's good to 50000).

Anyone have info on Richmill high speed 50k spindles
bought on but cant get over 1000rpm and no instructions at all came with it
Airline inside was kinked over shut so may have gotten too hot

[VWSatOz]

The spindle cartridge is an NSK and is brushless with a tiny 40 slot encoder at the end.
I would like to pull the motor out from the end, looks like I need to unscrew a brass threaded nut/collar so will have to make a hollow tool to fit that.
The spindle at front seems to have backlash so must have dog-coupling to the separate motor at the back, and its front spindle bearings feel free and smooth, but the motor seems to bind occasionally and I assume motor has very low torque ability as as only 170watts input at the 240v. hence it stops itself if torque is too high
spindle has one 6mm collet, assume would only have grunt to drive tiny cutter though at max 50k rpm say 1 or 2mm diam ie engraving or tiny slot milling with CNC no rotating at all.
Whole assy mounted on a 50int heavy taper but was able to strip all that off and bravely open it up, Circlip off the front allows an outer sleeve to fall off exposing t 1/2 clamp shells that hold the small spindle cartridge. end cap off and cable unplugs allows cartridge to slide out without having to desolder any wires.
The air hose bend had kinked and blocked off, so NO cooling - shielding air was passing through out the end labyrinth dust seal collar.
May have got too hot and varnish or metal fines causing fielding drag? If I could slip it out an clean it up it might be a goer.
The box detects if air pressure is there &switches air on when power switch is on.
The drive box seems to get very hot after 20m or so, and cut itself out when temp too high but that might be from heatsinks having to absorb 49K off the rpm as I can't set it above barely 1000 or stops and red light comes on.
I have driven it at 2500 rpm with electric drill rubber bushing pressed against the collet chuck, and while sucking through with vacuum cleaner from tail end (BUT risk is this might draw front dust through from labyrinth plate?) can only vac and spin with fingers while sucking through from front, and this freed up the motor to turn very freely, but I reckon must be muck inside that is disturbed by heat or magnetism, as it seems to get lousy again once reassemble. Tried squirt tiny bit of CRC spray in airline to blow through to possibly old-grease-dried gummed bearings, BUT assume should be bone dry, no moisture or lube, motor must have its own separated highspeed bearings?
Any help out there? Can I download a manual on this from Richmill Japan?