Buying a PM932

I don't push my machine (pm932m) at all!! I'll admit that I'm a panzy but I hope to preserve this mill for a long time..I have my personal limits set to .100 doc for 6061, 7050 or 7076 alumnium...I know the machine will easily take more but I'm in no hurry..I don't have any roughing end mills but have been meaning to get one..Maybe I would be willing to take more depth of cut with a rmr endmill, I don't know..

That being said: I have very limited experience with steel on my 932 to this point..I have milled a little 4150A and went very easy with it (.020 max doc with high quality 4fl m42 end mills)..I think that was some pretty tough stuff..I had to learn how to handle it because it was different from alumnium..

From that very limited experience I can not imagine hogging 1" doc with steel on my mill...Like I say, I'm consertive and have no experience with a rmr end mill yet...But still, there ain't no way....

Mild steel may handle totally different than the 4150 alloy I don't know?? I have some 1018 laying around that I need to play with it and see how it is...

My opinion is that the square collum mill is not rigid enough to go super crazy... I noticed a lot more vibration than I'm use too while milling the steel compared to alumnium.. Once I got my spindle speeds and feed rates dialed in things seemed to smooth out a lot but I still took it easy.. In the end I was able to get nice surface finishes and hold good tolerances..

It may be that I don't have enough experience and I shouldn't be posting this.. But if I were buying a mill for hogging steel it would be a pm935 or similar knee type mill.. The square collum is not rigid enough in my opinion...

Just my .02...
 
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navav2002 said:
I don't push my machine (pm932m) at all!! I'll admit that I'm a panzy but I hope to preserve this mill for a long time..I have my personal limits set to .100 doc for 6061, 7050 or 7076 alumnium...I know the machine will easily take more but I'm in no hurry..I don't have any roughing end mills but have been meaning to get one..Maybe I would be willing to take more depth of cut with a rmr endmill, I don't know..

That being said: I have very limited experience with steel on my 932 to this point..I have milled a little 4150A and went very easy with it (.020 max doc with high quality 4fl m42 end mills)..I think that was some pretty tough stuff..I had to learn how to handle it because it was different from alumnium..

From that very limited experience I can not imagine hogging 1" doc with steel on my mill...Like I say, I'm consertive and have no experience with a rmr end mill yet...But still, there ain't no way....

Mild steel may may handle totally different than the 4150 alloy I don't know?? I have some 1018 laying around that I need to play with it and see how it is...

My opinion is that the square collum mill is not rigid enough to go super crazy... I noticed a lot more vibration than I'm use too milling the steel.. Once I got my spindle speeds and feed rates dialed in things seemed to smooth out a lot but I still took it easy.. In the end I was able to get nice surface finishes and hold good tolerances..

It may be that I don't have enough experience and I shouldn't be posting this.. But if I were buying a mill for hogging steel it would be a pm935 or similar knee type mill.. The square collum is not rigid enough...

Just my .02...
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Your experience is more than those who have never been around these machines. So, thank you for that input. Yeah, I have no intention of abusing a machine. However, I'm just curious what a reasonable depth of cut would be with these two models(pm932 or pm940). For anyone reading this post I will say again that the answer to the question of DoC has many variables to consider and no single definitive answer can be expected. But, a general answer could perhaps be extracted.:cool:(That last sentence of mine sounded like such a nerd.):cool:
 
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Another problem I had milling the 4150 was keeping the head trammed.. I upgraded the nuts and used some nice tooling washers on the adjustment bolts which helped, I still had to take it easy...
 
My Charter Oak 9x40, and the PM940 push the boundary of the definition of a 'bench mill'. These things are massive. And quite rigid for their size.

My 9x40 could do anything my 935 can. The major difference is the knee and articulating head on the 935 makes some operations easier is all.

I will admit that I miss that extra 5" of table length I had on the 9x40 though. :(
 
Having converted my PM-932 to CNC 4 years ago I will add my 2 cents.

I will start with I have no regrets converting a bench top mill to CNC as it has been a rewarding and educational experience. If you enjoy the process of learning and building then go for it. If you just want to run parts on a CNC then finding a purpose built machine (new or used) in working condition would be a better option. Had the PM-940 been available at the time I purchased my mill I would have spent the extra money for the increased Y travel and rigidity.

I got the cast iron base and have been able to make it work for my coolant enclosure but a purpose built stand would provide better use of the space below and allow for better customization.

CNC conversion of the PM-932

Decide early if you want to have manual capability along with CNC or just CNC. If you want to retain manual use then flood coolant is not really an option with the need for a more comprehensive enclosure. Mine is CNC only with flood, mist and air cooling. I believe the benefit of flood coolant outweighs the drawbacks but it is more work to setup and maintain. I can do most manual operation with the game pad pendant but I did miss the ease of use of a manual mill for certain things and have added a heavy duty drill press with an X,Y table to my machinery for manual use.

The Chinese ball screws, nuts and bearing blocks are perfectly adequate. The bearing blocks will need some TLC to get them at their optimum. Use the double ball nuts. I used two single ball nuts on each screw and while it provides better adjustability, it is a pain to work on and requires periodic adjustment. I recommend 20mm on the X & Y and 25mm on the Z.

An oil system for the ways and ball screws is a must. I have separate one-shot oil pumps for the X,Y axis and the Z axis. I originally had a single pump but found that the lines to the Z axis would drain back. The extra pumping was wasting oil of the X,Y axis. Adding check valves could have solved this but that would have required a complete redesign of my distribution manifold. At my next tear down for service I plan of replacing the two pumps with an automatic pump system and new manifold.

Steppers or servos. I personally don't think servos are worth the additional cost for this level of mill. Myself and others who have converted similar machines are running larger steppers with no issues of lost steps. Larger steppers are slower but on this size mill 100 inches per minute is plenty fast. I rarely exceed 50 IPM on most work.

Don't skimp on the electronics. Stay away from cheap no-name breakout boards that have little or no support and lower cost motion controllers like the UC100 are not worth the headaches. For steppers I blew several power supplies and drives before settling on dives with built-in power supplies. Theses have been trouble free. Start out with a controller package than can do spindle & coolant control. Your electronics may be driven by what motion control software you use. I run Mach3 for simplicity. While it has its quirks I find it straight forward to use. If your a computer guy who can deal with Linux then LinuxCNC is a good option. We use it at the high school on the router and it works great. I don't use it since I prefer to stay away from anything that requires command line input for tasks that should be done with a mouse click. Personal problem.

At some point the gear head of the PM932 will become too slow for anything but steel and the noise will drive you nuts. A high speed spindle conversion will probably be seriously considered so it is a good idea to plan ahead for it.

Some kind of power draw-bar system will become a must. Having an idea of how you intend to use the machine will help determine what system will work for your needs. I do a lot of complex parts with multiple tool changes. I went with the Tormach TTS system and a pneumatic draw bar. I love this system other than I undersized the air cylinder based on some bad information and I can have issues with tool pullout when hogging with cutters 1/2" and larger. That is also on my list to upgrade.

My largest grip about the mill is the dovetail column. Because I am driving the head and not the quill to get the maximum amount of Z axis travel the Z axis gibs need to have some drag but still be able to move. This introduces some nod and flex to the head. The nod is compensated by shimming the base of the column. The flex is usually not noticeable expect for heavy drill ops and quick Z moves on 3D parts.

To your question regarding cutting steel. I use serrated roughers for heavy material removal but I prefer fast light passes over slower heaver passes as it it easier on the machine.
 
WOW, thanks for all that hindsight jbolt!!

I built a 3d printer from LOTS of reading back in 2010. That was right before the big commercialization of them. Crazy to think I spent about $900 for that thing and the work envelope is nowhere near what can be had for about half that price for printers today. It was a ton of fun, challenging, and a great learning experience. I envision a CNC conversion will be similar in the ways of reading, researching, collecting parts, learning more electronics, more reading, more purchasing, etc.

I will get to that stage one day and your feedback is most appreciated.
 
What jbolt said. He covered it well in his explanation of converting to CNC.
 
I'm curious how much you spent ($ not the time) on building your enclosures, VFD setup, coolant rigging, ballscrew conversion?
 
stioc said:
I'm curious how much you spent ($ not the time) on building your enclosures, VFD setup, coolant rigging, ballscrew conversion?
Click to expand...

Costs as my mill sits today.

PM-932 w/cast iron base/ delivered $2400

Basic CNC conversion including balls crews, couplers, pulleys, belts, steppers, drivers, power supplies, breakout board, motion controller, computer w/screen & keyboard, control box and switches, limit switches, aluminum stock, wire & cable / connectors, misc hardware. $2800

One-shot oil system. $200

High speed spindle conversion (motor, vfd, electrical cable & wiring, spindle bearings etc.) $700

Pneumatic draw bar system (air cylinder, switch, hose & fittings, regulator, filter, hardware etc.) $700 (not including air compressor)

Flood coolant system (pump, nozzles, plumbing, solenoid switch, tank, hardware, etc.) $350

1/2 height enclosure (custom aluminum sheet metal pan, aluminum panels for the walls, 8020 for the frame, Plexiglas door panels, hardware, etc.) $600

Total $7750
 
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