High Speed Spindle for SIEG X2 Mill - getting technical

[whelen]

High speed spindles are complicated and pricy, as I've learned. KDN Tool & Automation Engineering will provide a belt drive for my MicroMark MicroLux #82710. KDN Tool & Automation (www.kdntool.com) is in the process of converting my mill to full CNC. The SIEG X2 can get up to 2,500 rpm with the stock gear drive. KDN Tool & Automation has an option, to belt drive the spindle, getting it up to 4,000 rpm. Going higher is not recommended.

I am not recommending that anyone do what follows!!! I'm only brainstorming.
You could purchase a Proxxon Micro Mill MF 70, from Tool-Switch for $300 + shipping and taxes. The Proxxon motor and spindle assembly, turns from 5,000 to 20,000 rpm. Proxxon is a quality made machine. The application for the MF 70 is "Small precision mill for lab, optician, jewelry, electronic, and model projects". I want to engrave. The maximum power is 100watts. So lets see if the Proxxon motor and spindle assembly can be adapted for engraving. Back of the envelope scoping calculations. I worked as an advanced development engineer up to 20 years ago. I switched to planning, marketing, and sales management - it paid a lot better. So I'm rusty on my Manufacturing Engineering (did that before becoming a Mechanical Engineer) -please feel free to correct me in my calculations.

Torque (N-m)=depth of cut (mm) X width of cut (mm) X feed rate (mm per tooth) X number of teeth X machineability factor (0.145 for aluminum, 0.435 for steel)
depth of cut (mm) 1 mm 0.039 in
width of cut (mm) 1 mm
feed rate (mm per tooth) 0.18 mm/tooth high speed steel cutter, on brass
number of teeth 2 a pointed engraving cutter
machineability factor 0.29 half way between aluminum and steel

Torque (N-m) 0.104 N-m (ref: one N-m = 0.74 foot-pound)

Next determine the torque of the Proxxon MF 70 spindle, assuming a constant power of 100 watts. (Who knows what the torque speed curve is)

Torque (N-m) = [Power (kw) X 9,550] /rpm
Power (kw) 0.1 0.1 0.1 0.1
rpm 20,000 15,000 10,000 5,000

Torque (N-m) 0.048 0.064 0.096 0.191

It looks like maybe somewhere between 5,000 and 10,000 rpm it might work, but not knowing the torque speed curve for the Proxxon MF 70 motor, it's only a guess. Well it was only an idea.

Lets look at price points for "high speed spindles"
Sherline (from DiscountCampus.com)
#33050 High Torque DC Motor & S/C Assembly $210 discount to $194.25
#33060 DC Motor & Headstock Assembly W-S/C $312 discount to $288.60
#33070 10,000 RPM Headstock, Motor and $402 discount to $371.85
Speed Controll Unit

Taig
#200-55CR Spindle Motor (1/4 hp, 3,400 rpm $110
Continous Duty

High end engraving machine spindles (I don't know if the price includes motor)
Spindle unit High-torque spindle unit 3,000 - 12,000 rpm
High-speed spindle unit 5,000 - 20,000 rpm
High-torque milling spindle $800
High-precision milling spindle $1,800
High-speed engraving spindle $1,700

Specialized 50,000 rpm "engraving" spindle and motor $5,000

Now, the article "High Speed Spindle Design and Construction" Engineering Research Center for Net Shape Manufacturing - The Ohio State University - by William Popoli, President, IBAG North America - on the web site MMS Online (http://www.mmsonline.com/articles/hsm9802.html) shows that amongst the many critical factors, the bearings play an important role. The article developes the knowledge required to select proper bearings.

Now I've got a spindle that came with the machine. What if Little Machine Shop were to develop replacement spindle bearings, good for 30,000 rpm, continuous duty, permanently lubricated, no forced water or air cooling. That were pressed into a SIEG X2 spindle casting (will need ceramic balls and specific design criteria for selection of the proper bearing, and don't want to brinell the raceways or crush the ceramic balls when pressing them into the casting and on to the spindle). So a shop needs to do this (tooling).

Now we can turn the $549.79 (including shipping) MicroMark MicroLux milling machine #82573 into a 30,000 rpm mill for the price of a few bearings. If you want to try this yourself Boca Bearing sells bearings one at a time (www.bocabearings.com). They may even work with you to develop a selection for your parameters.

But where's the motor? Good question. In all my searching there is very little out there about high speed spindle motors. In this day and age there must be all kinds of candidates out there. I'm not an Electrical Engineer, so is there anyone out there that can help? Assuming the formulas for spindle torque are correct, what is needed is a motor (not an air motor - too noisy) that can be controlled, continuous duty cycle (some "engraving" jobs could take 24 hours non stop), self cooling, and can run at 30,000 rpm and deliver quiet, reliable, smooth Torque.

Just brain storming, why can't a dc servo motor be used?

Whelen

[JRouche]

Originally Posted by whelen and can run at 30,000 rpm and deliver quiet, reliable, smooth Torque.Whelen

Nice article.

I would use an overly powerful, slower electric motor running through belts and cogs or pulleys to get the speed. Quieter, cooler and easier on the wallet. JRouche

[tokyocrow]

who thinks the proxxon motor would work. If you look closely down the page here http://www.flashcutcnc.com/html/mach_acc.html#8000 you'll notice what appears to me at least to be a Proxxon motor repackaged as a high speed spindle. It doesn't have the same packaging as the micromill you've mentioned if you look at the Toolswitch site -however- the same motor is used in the handheld at Toolswitch - see http://www.toolswitch.com/prx-us-38481.php and as well the Proxxon micro mill sold here in Japan has the same yellow green motor housing with slightly different ratings (we're 100v/50hz here).

I'd be interested in hearing the Flashcut price for that spindle hehehe...

-tokyocrow

[whelen]

Tokyocrow, youre right. Here is the pricing. Thanks for the great information.
Whelen

http://www.flashcutcnc.com/html/ord_price.html
Accessories for the 8000 Series Mills

NF-PM-148-211, NF-PM-148-275, NF-PM-148-952, NF-PM-148-260
Spindles / Dispensers
NF-PM-148-211 Spindle 100 W; 5,000-20,000 RPM; 1/8" Collet; Mechanical Height Compensation
NF-PM-148-275 Spindle 150 W; 5,000-60,000 RPM; 1/8" Collet; Automatic Height Compensation
NF-PM-148-952 Dispenser for liquids, grease, oil, paste, silicon, glue, sealant, paint, etc.
NF-PM-420-003-0500 Spindle 500 W; 11.000 - 25.000 RPM
NF-PM-239-110 Collet set .039" to 1/4" (14 pieces)
NF-PM-239-120 Collet set 3 to 8 mm (7 pieces)
NF-PM-148 991 4000 Spindle 500 W; 300 - 24000 rpm; 1/4- or 1/8 inch Collet; Tool changing system with length measuring sensor.

Part Number Description Price Spindles / Dispensers
NF-PM-148-211 Spindle 100 W; 5,000-20,000 RPM; 1/8" Collet; Mechanical Height Compensation $345
NF-PM-420-003-0500 Spindle 500 W; 11,000 - 25,000 RPM; ¼" and 1/8" Collets $495
NF-TI-6990 600 Watt 8000-24,000 RPM; ¼", 1/8" and 6mm (.236”) collets $545
NF-TI-2311 600 Watt 80-2500 RPM; 3/8", ¼", 1/8" collets, accepts other ER16 Collets $1,295
NF-PM-148-275 Spindle 150 W; 5,000-60,000 RPM; 1/8" Collet; Automatic Height Compensation (Floating Head for Engraving) $2,995
NF-PM-148 991 4000 Spindle 500 W; 300 - 24000 rpm; 1/4- or 1/8 inch Collet; Tool changing system with length measuring sensor. $4,995
NF-PM-239-110 Collet set .039" to ¼" (14 pieces) $295
NF-PM-239-120 Collet set 3 to 8 mm (7 pieces) $265

------------------------------------------------------------------------------

http://www.toolswitch.com/prx-us-38481.php
Proxxon Hand Held Rotary Tool IB/E (Looks like the Flashcut NF-PM-148-211 for $345)
Price: $ 105.00
This high-revving motor has full-wave electronic speed control capable of producing continuously variable speeds between 5,000 and 20,000 rpm and is usable for extended periods at a time. The ground steel spindle runs in a ball bearing assembly, minimizing play. Six high concentricity collets sized 1/32 in., 1/16 in., 5/64 in., 3/32 in., 7/64 in., and 1/8 in. (1.0, 1.5, 2.0, 2.4, 3.0 and 3.2 mm) along with a collet nut are included.
MICROMOT steel collets are hardened and thus have a high, consistent flexibility. They also maintain prolonged accuracy, even after regular use. The triple-slit collet is substantially more difficult to manufacture than the four-slit type, but offers a better load-bearing surface. This is especially important for cutters with small shank diameters. These collets should not be compared with unhardened, four-slit collets of brass and aluminum.
Features
· Ball bearing spindle of ground steel, with lock button for rapid cutter changing.
· Streamlined die-cast aluminum head for exact bearing seats and optimal stability.
· Quiet, powerful 100 W motor with full-wave electronics for continuously variable speeds between 5,000 and 20,000 rpm.
· Complete with six triple-slit steel collets covering 1/32 in. to 1/8 in. (1.0 - 3.2 mm).
· Packed in durable plastic case, complete with the 34 bits & cutters as shown above.
Package
· Rotary Tool IB/E
· Six triple-slit steel collets covering 1/32 in. to 1/8 in. (1.0 - 3.2 mm).
· Durable plastic case
· 34 bits and cutters
Technical Data
· Speed: Variable (5,000 - 20,000 rpm)
· Volts: 110-120V AC, 60 Hz
· Max Power: 100 W
· Length: 9 in.
· Weight: 1.1 lbs

[whelen]

JRouche, thanks for the idea. Turns out that is what KDN Tool & Automation Engineering Co. is doing for me right now, as a part of their CNC retrofit to my SIEG X2 MicroMark MicroLux Milling Machine #82573. They know the capabilities of the X2 milling machine motor, and spindle bearings, and are implementing for me a belt drive conversion (nothing new, Little Machine Shop has such a conversion kit). But it seems that a spindle speed higher than 4,000 RPM is possible with other modifications to motor and spindle configuration. Which they are implementing.

Again thanks for the indormation.

Whelen

[Halfnutz]

Wow, the specs on that Proxxon are impressive! Just all those colletts are worth having! And the price is great too.

(The oppinions above are the authors and do not represent those of CNCZone or its management.)

[tokyocrow]

Whelen,

An option not mentioned yet ... just to throw it in the pot. Take a look at this beauty - it'll remind you of your last trip to the dentist!!

http://www.cncmasters.com/accessorie...g%20attachment

There's a lot of drawbacks to air driven in general but 40,000 revs via an induction motor regardless of gears, belts or direct drive would have its own unique set of issues to deal with too.

--TC

[JFettig]

I havent been able to read this entire post, but heres something that needs considering,
What max feed rates can you run? can you still take a decent chipload or will you just be burning?

At 30k your gonna need to be cutting at over 100ipm.(I didnt do the math, just a good estimate)

Jon

[Halfnutz]

I have a 55,000 RPM air driven pencil grinder (from Harbor freight for 16.00 on sale) that fits into a 5/8" R8 collet with a tubular drawbar to feed the air supply. The TIR on mine is not good, but there are other more expensive models available. I saw the set-up somewhere and decided to try it out, and I'm in the process of making the hollow drawbar (god, I forgot all about that project). Its a neet way of getting an 1/8" bit to go 50,000 RPM on a mill, but I dont know how well the set up will work yet. Heres a copy of the link I got the idea from.

http://www.homemetalshopclub.org/new...eb04.html#mill

(The above oppinions are the authors and do not represent those of CNCZone or its management.)

[tokyocrow]

Jon,

Hmmmmmmm. I had to stop and think about this for a bit. I routinely use a 30000 rev handheld for sculpting aluminum (JIS H 4100). At first thought you think "hey if can do it manually at 30000 than why can't a machine do it slowly at 40000?" ---but-- when I visualized the motion I make with the tool its probably very high rate strokes indeed although I doubt it would approach 100ipm. I think based on his previous posts Whelen is wanting an precision engraving/relief sculpting rig. Much the same as I am trying to figure out. I would assume he will be using tiny ball mill ends with 1/8th collet and not taking more than a few 1000ths at a time with thousands of passes thus chipload and feedrate would not be such a problem although maybe not in theory optimal for CNC in a machinist's context. As I'm new to CNC I think I'm missing something here though so anything you might have to add would be highly appreciated - I'm looking for a tool similar to Whelen's though with more workspace.

--TC

[JFettig]

its not the speed you move it, its the speed it needs to be moved. if its rigid, you should be taking around .0005-.0008" per flute,
Any carbide has a suggested chip load, if you dont get that chip load, it will die prematurely, good luck running hss that fast


Jon

[tokyocrow]

Jon,

Thanks for the info. I've obviously have a lot to learn hehehe. Is there some type of chart to read and calculate these ?

BTW right now I'm using CVD diamond tipped tools on 2mm (approx 1/8th inch) shanks - mostly ball shaped with no real flutes (more like a burr). I quit using anything but diamond because as you indicated they burn up too quickly. When and -if- I do get a mill I'll probably continue to use diamond though not CVD exclusively. Every bit I've bought in diamond I still have and use - even on green porcelain and sometimes on an occasional screwup I use them on bisque porcelain which is about like a grindstone to any tool. As a note for some reason in the U.S. diamond tools cost about 2x the price here in Japan.

--TC