New Guy, New Mill (pm940)

mrbasher

Registered
Registered
Joined
Jul 28, 2016
Messages
26
Hello all!

I've looked at these forums many times but never had much to post so I never signed up. I finally signed up yesterday when I got sick of not being able to look at attachment images full size. haha

Anyhow, my new PM940 mill arrived just the other day and after quite the ordeal getting it up the driveway and into the garage, myself, I have been working to get all of the gunk off of it. The X and Y are now clean and ready to go. However, I want to get at the Z axis clean while the mill is still sitting on the pallet. I figured it might be easier that way... Maybe not. I can't seem to get the dang head pulled off it's mount. I have the head all the way down, supported by the spindle and the back of the head using some aluminum blocks on the table. I loosened the two bolts up... top... (and with that thought...)

I just went out in the garage to check and yep, there's another nut and bolt on the bottom. Jeez. I was just about to ask you guys why the head was so hard to take off and if you had any tips. Taking all the nuts off would be a start!

Anyhow, I'll post some photos of the mill soon along with some more thoughts later on, once I get the thing up on it's stand, etc.

I also ordered the mill with the 3 phase motor and VFD. I'm not interested in changing gears, but the main reason is I plan to CNC the mill in short order. Should be a fun time. :)

Some quick thoughts:

Those of you that don't have one of these, this thing is huge. None of the photos I have seen of it really show the scale all that well. I have a photo of a beer can setting on the table, it's tiny on there. (Edit: attached the pic) I've seen people say you could mill an X2 on it easily. They aren't kidding. I have an X2 sitting near it. I have seen quite a few photos of your standard RF45 clone and this has definitely been scaled up. It doesn't just have larger travels, it IS larger.

A little about me, if you're interested:

I have an MicroMark X2 mill and a Grizzly 7x12 lathe. I also have a Chinese 6080 router which has probably routed about 10 miles of slots in plastic parts. (I'll probably post about that one another time) I've never liked the X2 and tried my best to get by with it but it has become more of a pain than it's worth. I even put some of those iGaging Absolute DRO's on it. (way too slow update speed, drove me nuts) I recently started doing some machining side jobs and the lathe and mill were making the process take FAR too long. I'd quote what was about 4 hours work and it'd take me well over 8. :( I ALMOST pulled the trigger on a kitted out PCNC 1100, but that would have put me close to or over $17,000. Too much, and I'd still just have a tiny lathe. After some research I settled on the PM940 and a PM1340GT. After CNC'ing the mill, I'll have an awesome lathe, AND a decent CNC machine... and still be well below that $17K mark.

I'm not sure if it's allowed for me to post a link to my site, since I sell stuff... However, I make lots of things for simulation racing as well. I'm hoping these two will help prototype some cool new sim racing gadgets for people. If you're interested in that, try googling my username, something is bound to turn up. :)

Stay tuned!

Edit: Pardon the mess in the photo. I'd just finished dragging the thing up my driveway and only cleaned off part of the table on it. Had to take a beer break. :D

IMG_20160723_170146.jpg
 
Last edited:
Welcome aboard. And nice machine! There is a wealth of info on this site about CNC conversions that are applicable to your mill. If you have questions or need information just start a thread and you will get more info than you bargained for. I mean that in a good way.

Tom S.
 
Thanks guys! I believe I've read quite a few posts by the two of you, and Dan, while researching which machines I was interested in. Thank you for the info. You're right, I was just thinking today, it's cool to be part of the club. :)

Here's another pic I took today of one of the Y axis ways. Notice that little spot? Look close, it's like a spatter from a drop of something. I noticed it when I was cleaning up... Today I realized what it's from. It's the sweat from someone making my mill! I found that interesting. Well, it's a good guess at least. I'm basing it on some sweat that dripped off me yesterday while cleaning the machine in the heat outside. I forgot to wipe it off and it left a mark very similar. It wasn't there long enough to be permanent though. Those other specs are just dirt I need to wipe off.

IMG_20160728_152512.jpg
 
On another note. I did some research today on ball screws, servos and drives. I spoke with someone at DMM and he was extremely nice, very interested in what I was doing. I think I found some C5 ball screws that should do the trick, I hope... I almost just ordered them but decided to wait and do some research. They are 25mm diameter, which is the same as the lead screws. Actually, I'm pretty certain the lead screws are 1", so they are barely smaller than what is on it. Should be fine for x, y and z all around. So far it's only looking like I will need to whack away at the saddle a little to make the ball nut fit. That's basically a given it seems. Once I have figured out what I'm doing I will post up my plan of attack. :)
 
On another note. I did some research today on ball screws, servos and drives. I spoke with someone at DMM and he was extremely nice, very interested in what I was doing. I think I found some C5 ball screws that should do the trick, I hope... I almost just ordered them but decided to wait and do some research. They are 25mm diameter, which is the same as the lead screws. Actually, I'm pretty certain the lead screws are 1", so they are barely smaller than what is on it. Should be fine for x, y and z all around. So far it's only looking like I will need to whack away at the saddle a little to make the ball nut fit. That's basically a given it seems. Once I have figured out what I'm doing I will post up my plan of attack. :)

You may want to take a look at Linear Motion Bearing ball screws and nuts on eBay. They have very good prices and delivery is very reasonable despite shipping from China. For example, I recently purchased double ball nuts for X, Y and Z. Price was $96 delivered and they showed up about 2 weeks after I ordered them. Chai is the sales contact and is knowledgeable and responsive.

Tom S.
 
On another note. I did some research today on ball screws, servos and drives. I spoke with someone at DMM and he was extremely nice, very interested in what I was doing. I think I found some C5 ball screws that should do the trick, I hope... I almost just ordered them but decided to wait and do some research. They are 25mm diameter, which is the same as the lead screws. Actually, I'm pretty certain the lead screws are 1", so they are barely smaller than what is on it. Should be fine for x, y and z all around. So far it's only looking like I will need to whack away at the saddle a little to make the ball nut fit. That's basically a given it seems. Once I have figured out what I'm doing I will post up my plan of attack. :)

Congrats on the PM-940. I'm looking forward to following your CNC conversion. I would have gone the same route had the 940 been available when I bought the 932. The extra travel will serve you well. I like that they got rid of the stupid troughs on the base that collect crap (and coolant in my case).

I would recommend you disassemble the table and cross slide and measure everything before settling on the ball screws. The size of the ball nut (and ball nut mount) may determine how large a screw you can use. When I did the conversion on my PM932 using the Chinese ball screws the largest I could fit under the table was 20mm. The 20mm screws have been more than adequate. I use 20mm on the X & Y and 25mm on the Z.

The DMM stuff looks really nice. I thought about it but went with an over sized servo system to keep within my budget.

What is the max spindle speed on the variable speed model? Last year I did the high speed spindle conversion replacing the taper roller bearings with AC bearings and a 2-step belt drive pulley to increase the RPM. I run 6k max but with the right motor could go 7-8k.
 
You may want to take a look at Linear Motion Bearing ball screws and nuts on eBay. They have very good prices and delivery is very reasonable despite shipping from China. For example, I recently purchased double ball nuts for X, Y and Z. Price was $96 delivered and they showed up about 2 weeks after I ordered them. Chai is the sales contact and is knowledgeable and responsive.

Tom S.

Tom,

Thank you for confirming that. I was just looking at them this morning. I'd seen them mentioned about 6 years ago by some people and wasn't sure if they were still good. Do you have them on a machine currently? If so, how are they working for you?

I keep going back and forth on ground vs. rolled. I think I've decided to go rolled C7. .002" error in 12" seems quite minimal and that is the MAXIMUM. It's quite possible, and from what I've read likely, I'd end up with much better than that. In the end, I'll be running Linux CNC anyhow and can map the ball screws. Most of the parts I'll be doing won't be sized greater than that 12" envelope anyhow. I'm sure I will be putting an array of parts across the table, but that is not the same thing. :)

Congrats on the PM-940. I'm looking forward to following your CNC conversion. I would have gone the same route had the 940 been available when I bought the 932. The extra travel will serve you well. I like that they got rid of the stupid troughs on the base that collect crap (and coolant in my case).

I would recommend you disassemble the table and cross slide and measure everything before settling on the ball screws. The size of the ball nut (and ball nut mount) may determine how large a screw you can use. When I did the conversion on my PM932 using the Chinese ball screws the largest I could fit under the table was 20mm. The 20mm screws have been more than adequate. I use 20mm on the X & Y and 25mm on the Z.

The DMM stuff looks really nice. I thought about it but went with an over sized servo system to keep within my budget.

What is the max spindle speed on the variable speed model? Last year I did the high speed spindle conversion replacing the taper roller bearings with AC bearings and a 2-step belt drive pulley to increase the RPM. I run 6k max but with the right motor could go 7-8k.

jbolt,

Yep. Not looking forward to it much, but I'll be taking the saddle and table back off to get dimensions on everything. I should have done it when I was cleaning but impatience got the best of me and I wanted to try things out. It's not hard, just takes time. Plus the table has to be well over 100 pounds on it's own. I'm gonna put it on a scale when I take it off because I'm curious.

The plan is to draw things up in solidworks then I can get all the dimensions, etc. worked out easily.

I'm not sure what the max spindle speed is yet, I'd guess it's limited by the motor itself. The motor runs 1880 rpm @ 60hz. I don't know what it can handle without grenading... The VFD can obviously run it past 60 hz, but again, I'm not sure what the motor can do. I tried looking up the model but it just comes up with old aliexpress listings that don't give much info. I'm sure Matt would give me whatever info he has on it... I should ask. I was reading a thread in here yesterday where someone was talking about running their 940 (CNC version I think) at something over 5K. I'll see if I can find it. I believe the VFD and motor I have are from the CNC version.

I'm going to have to check out your belt conversion as I'd like to do the same at some point.

With regard to measurements... There is ALMOST 2 inches of space between the table and saddle. While that seems like a lot, the ball screws I was looking at would require a bunch of screwing around in order to make them fit. So while they are ground C5 and about 1/3rd the cost they would normally be, the nut is just too big for my liking. I may still go that route, but I doubt it. The rolled ones I am looking at won't require nearly the same amount of "surgery."
 
I did the same thing and modeled everything is Solidworks. I disassembled the mill, measured and modeled each part with the necessary dimensions and reassembled the mill to manually machine all the parts.

The taper roller bearings are limited to about 3k, after that you need the AC bearings. I run my 1755 PRM motor up to 105Hz max. With the 2:1 pulley ratio it gives me 6k.

I will be curious to see how the motor is coupled to the spindle on your machine. On my setup the belt drive eliminates the quill travel but I have no need to operate the machine manually by handles. I can manually machine just fine using a game pad at a pendant when I need to.

I also have rolled ball screws from Chai. You really cant beat the price for economy ball screws and you can get the ends machined to your specifications. Ground ball screws would be awesome but it is tough to justify the cost for a hobby machine. Your situation may be different. If you go the Chinese route I can send you an example of an order form to get the end machining to you specification.

I think Tom S originally went with a single ball nut and later changed to a double ball nut. I have not heard how this has worked out for him. I went with two single ball nuts on each screw and set the preload with Bellville washers. I prefer the adustibility over the double nuts but it can take some trial and error to get it dialed in.
 
My spindle is gear driven from the motor currently. They basically just took the standard motor off and bolted this one up. I need to do the rest myself once the VFD shows up. I'm not overly concerned about connecting it. I've programmed the ridiculous hyuang-whatever-it-is VFD I have on the 6080 router I have, the Hitachi should be a comparative breeze. At least the manual is understandable. (and readily available!)

I just checked out your CNC build thread jbolt. Looks awesome! Out of curiosity, what are the dimensions of your column? I keep looking around for the sake of comparison and I can't find anything.

I'm still not sure what I'm going to do for the motor sizing for each axis. At this point I'm looking at their DYN4 drivers and 750w servos for X and Y, and the 1.3KW for Z. I'd like to go direct drive if I can, but I haven't decided. I can always go direct drive first and if it doesn't pan out, use some reduction with pulleys. I did some calculations using this: http://www.daycounter.com/Calculators/Lead-Screw-Force-Torque-Calculator.phtml For the Z, I intentionally over-did it on the numbers. I put in 400 lbs for the head and friction at .25. It spit out 7Nm to lift the head. The 1Kw servo from DMM would probably do it, but... I also want the gibs fairly tight on the Z. I can always counterbalance it as well. Thoughts? I know you have a monster stepper for your Z and it's direct drive.

I'm not overly concerned about X and Y. The 750w servos seem to have enough guts to get the table moving around nicely. If not, I can use some reduction and still have pretty ridiculous rapids.
Unless my calculations are wrong:
Rated speed is 3000 rpm, ball screws will be 5mm lead. So... 3000 x 5 = 15000 mm/min. or about 590 ipm. Even if I did a 2:1 reduction, that's well over 200 ipm. We shall see!

As for what I'm using it for... Ideally, I'd like to stay under .005" tolerances in that 12" "cube" if I can. That seems doable enough... Hell, that 6080 router I have, which really is a bunch of cheap stuff in my opinion, and not rigid at all, can do that.

I am of course open to suggestions!
 
Back
Top