High Speed Spindle for SIEG X2 Mill - getting technical

[tokyocrow]

Whelen,

I took a much closer look at the Proxxon motor(s) today when I was in the tool shop. I don't think they'd do so well after all - the cont rated duty cycle for the best Proxxon motors including the one Flashcut is using is 30 mins max. That was for 100v, 110v, 220v, and both 50/60hz.

--TC

[whelen]

Tokyocrow
I looked into the CNCMasters idea you suggested. It looks like a router solution. Also I've continued researching "high speed spindles". They can be deadly. At speeds even as low as 2,000 rpm a broken bit or loosening collet can cause a lot of damage. Of course safety glasses are mandatory. I prefer a face shield. But what about the rest of the body. At high spindle speeds the flying bit becomes a projectile and can kill. By the way I'm not coming down on your idea. It's just the reading I've done has alerted me to the safety issue of high speed spindles. I've always wondered why engraving machines are enclosed in a "bullet proof" box. Well now I know. I'll be encasing my "engraving" mill within a "bullet proof" box. The articles I've read say that conventional engineered tool holding forces are NOT sufficient to hold "bits" at high spindle speeds. Using a technology engineered to cut wood for cutting metal is a very serious risk. Tokyocrow, thanks for your ideas.

Whelen

[whelen]

Halfnutz, I've looked into the air motor approach to high speed spindles. It looks like a great idea. To generate the CFM (cubic feet per minute) air flow for the required torque, a good size air compressor is required. And the noise level of the air motor is very high. Economical solution but noisy.

Whelen

[whelen]

Tokyocrow and Jon, you are right, an "engraving" tool is removing very little material, so high speeds can be used and still be within the chip load requirements of the tool. Yes carbide burs can be used for a roughing tool path which leaves material for a finishing "cut" with the engraving tool. The Designs Computed, Virtual Sculptor VS3D/VScad3 software allows you to design (CAD) in raster space and converts to vector space. It generates the tool path (CAM), and can rough cut and finish cut by allowing the precise specification of the cutting tool geometry(s).

As far as watts of power to do high speed engraving/sculpting/burnishing - the company to emulate is Roland. A leading Japaneese digital CNC engraving machine manufacturer. They have a machine for every price point. I'm trying to emulate the MDX-500. It comes with a high-torque spindle unit, 3,000 to 12,000 rpm or a high-speed spindle unit, 5,000 to 20,000 rpm. The spindle motor is dc brushless, 400 watts when with the high-torque spindle. So this gives an idea of the power required for a high speed engraving spindle. Tokyocrow, you were right in concluding that the Proxxon micro mill was under powered. My calculations also seemed to indicate that.

Also to repeat, these high speed spindle engravers are housed in a protective transparent box. A broken bit or loosened collet can cause a disaster.

Our conversations are interesting as they are similar to what we did in the concept phase, when I worked as an advanced development engineer 20 years ago.

By the way KDN Tool & Automation Engineering ( www.kdntool.com ) is studying a concept to get my stock SIEG X2 2,500 rpm bench mill to 9,600 rpm for engraving. They are interested in solutions as well as CNC conversions, and will work with you to get you to your application objectives.

Whelen

[Halfnutz]

Whelan, Its definately a once in a while deal, not something for heavy use. I geusse the best use for it is pc board drilling, I've got a set of drill bits so tiny it's unbelievable, Ive tried using them with a 1/8" R8 collet at 2500 RPM and its too slow, they stick and break.
But yeah, for less than 20 bucks its a nice little tool to have in the shop, I use the little grinder for all kinds of stuff. Its easier to hold than a dremel, and at those speeds it makes a difference.

[tokyocrow]

Whelen,

High Speed Spindle Safety is not really a concern for me as my wife makes sure I'm bound in leather, goggled, and plugged when I play - A full face shield would be a bit cumbersome though and detract from the pleasure as I couldn't see so well for closeup RCH work!! On the serious side though you're darn right about safety issues and I've seen less mention of it within CNCzone (why isn't there a safety forum?) and any other site as well, also lots of evidence (photos and videos) its a passive subject (as commonly the case everywhere) though it shouldn't be. BTW whatever CNC machine I wind up building/buying will be inside a 2cm thick composited granite enclosure with brushed alum frame and plexan portals and loads of exceptionally bright LED lighting. I have to admit though its actually less about safety and more about noise abatement and style (kind of cool design ain't it?) - we live in a Tokyo apartment where the expectations and tolerance of noise is quite low in comparison to the U.S. thus the heavy stone.

Engraving .... high speeds ... what a confliction eh? Arrrgghh! I've gone around full circle on high speed spindles. The machine I've pretty much decided to buy has a 220v 0-7500rpm VFD driven spindle (2HP). For some of the work I do however I'll have to go a lot faster. My current handheld runs at 35,000 and does a pretty good job. The problem for my work is that CNC at our ¥/$ level doesn't have any means to measure torque nor provide smart feedback to control how fast the tool takes a bite thus I think I'll need 40,000~50,000 with a light bite, slow feed rate, and plenty of experientiamentanation <as W would put it>. I know very little about feedrates, chiploads, cooling etc etc. and that somewhat frightens the analytical controlled process engineering side of my brain, however I keep on the right side of my brain the knowledge that shops all over Bangkok finish and engrave work for folks like Cartier and Harry Winston with about the same level of knowledge as I have using an accurately driven CNC mounted 50,000rpm tool that curiously has the same part number as a dental drill when sold in Japan.

Enough babbling ... my handheld's manufacturer recently introduced a new handpiece which I've been drooling over, now I've convinced myself that its the candidate for hanging on the CNC machine I eventually will get ... albeit its low torque compared to an air driven beast but a lot quieter. There's a lot of theory to shoot it down here in the forum but I'll make it work somehow the same as the guys in Bangkok do!! Take a look ... http://www.saeshin.com/new%20products.htm .. peek at the Forte 100. Not a lot of info on the English side but I'll pick one up when I'm in Seoul later this month. They also make a fine line of natural diamond burrs and toolends I swear by now.

--TC

[whelen]

Tokyocrow, here are some speeds and feeds referances.

#1 http://www.gatewaycoalition.org/file..._Machining.ppt

#2 http://www.niagaracutter.com/techinf...ook/speedfeed/

Here is information on High Speed Machining

#3 Basic Math For Ball Nose Tools
#3 http://www.mmsonline.com/articles/1103rt3.html

#4 Lending a Hand to the Handbook
#4 http://www.mmsonline.com/articles/080309.html

#5 Industrial Engraving
#5 http://www.mmsonline.com/articles/1102bp2.html

#6 Four Tool Holder Quality Factors
#6 http://www.mmsonline.com/articles/119804.html

#7 What is High Speed Machining
#7 What is high speed machining

#8 Even slow spindle speeds can throw a dangerous projectile
#8 Safety at High Spindle Speeds
#8 http://www.mmsonline.com/articles/hsmdm/cut6a.html

Hope this helps.

Whelen

[whelen]

To the people that have responded to my post. As I've mentioned, I finally realized that "high speed spindles" are a subset of "high speed machining". And that "feeds and speeds" have changed dramatically due to the advances made in "high speed machining" technology. I'd like to share some of the information I have found during my web searches on the topics: high speed machining, feeds and speeds, end mills, machining plastics, and chatter. I there is a company associated with the referanced web site, I have no affiliation with it - I just found the information interesting.

Starting with machining plastics - from what I have found it seems that the most productive way to machine plastics in a CNC milling machine, is with router speeds, and router tool bits. That goes for soft as well as hard plastics. The information in the following site was facinating to me, as I will be using plastic materials for my applications. The information is on three related web sites: http://www.onsrud.com , http://www.plasticsmachining.com , and http://www.plasticrouting.com - they are all related to Onsrud Cutter, or seem to be. The site with the most information (they are all packed with information) is http://www.plasticrouting.com/van.asp .

The next site contains speeds and feeds specifically for end mills, by diameter from 1/16" through 3", for premium cobalt high speed steel, and regular high speed steel, by material to be machined.

"Chatter Myths: Pieces of the puzzle in maximized machining", the end of the article gives an example #4, of 1/4" ball mill and its natural frequencies as related to rpm, and chatter. http://www.moldmakingtechnology.com/...es/090402.html

Proper Colleting and Collet Maintenance in CNC Routing of Plastic.
http://www.plasticrouting.com/pdf/Pr...aintenance.pdf

GATEWAY - Traditional Machining - Department of Mechanical Engineering, The Ohio State University - by Dr Gary Kinzel
http://www.gatewaycoalition.org/file..._Machining.ppt

Milling Tips - High Speed Machining
http://www.manufacturingcenter.com/t...99/1199ctk.asp

The Ins and Outs of High Speed Machining
http://www.millstar.com/techarticles/article_008.htm

Niagra Cutter - New Concepts in Milling Handbook
http://www.niagaracutter.com/techinf...ook/speedfeed/

Hope you find these interesting.

Whelen

[whelen]

I forgot to post the url for:

"The next site contains speeds and feeds specifically for end mills, by diameter from 1/16" through 3", for premium cobalt high speed steel, and regular high speed steel, by material to be machined."

End Mill Training - Speeds and Feeds
http://www.endmill.com/pages/training/spdfeed.htm

Also here are the articles that caught my attention - routing tool bits for CNC milling of hard and soft plastics.

http://www.plasticsmachining.com/mag...01-11/Van.html

http://www.onsrud.com/pdf/The%20Router%20Way.pdf

Whelen

[whelen]

When I wrote up the subject of this thread I made a mistake. The mistake is in the calculation of the scoping torque required to engrave brass. The error is in my selection of the feed per tooth. I used 0.18 mm per tooth. I should have used 0.01 mm per tooth!!!!!

I found this out in a conversation with the gentleman that wrote the article which had the torque equation. I found the initial value of 0.18 mm per tooth in another referance. I only read one page and should have read the other 65 pages.

Backing up - I was calculating the torque required to engrave brass with a pointed engraving bit. The bit has a 60 degree included angle, and the depth of cut is 1 mm. Assume a rpm of 20,000. So re calculating:
1 mm depth of cut
1.16 mm width of cut ( up 1 mm from the point )
0.01 mm per tooth feed per tooth
2 teeth number of teeth
0.29 machinability factor for brass

0.0077 N-m Torque
0.77 cN-m Torque

462 mm per min Feed rate
18.2 inches per minute

Big difference in the resulting torque required. I guess the PROXXON might work. But may not hold up to a continous duty cycle, as Tokyocrow pointed out. But for the money, Tokyocrow has found better alternatives.
I got the new feed per tooth of 0.01 mm from the assumption of 1 percent of the tool diameter (1.16 mm) per tooth.

Whelen

[JFettig]

Whelen, just a quick idea, I have engraved around 10ipm with a 3000rpm spindle. at 18.2ipm and 20,000rpm your going to be burning up bits.

Jon

[whelen]

JFettig
Thank you for taking the time to help me get back down to earth. The cost to "reliably" get to 20,000 rpm, and the consumables cost for the bits I will be burning up don't add up.

Again thanks for your help. Also I enjoy reading your posts, helping others with their problems.

Whelen