PM940 conversion

halfstep

Halfstep
I am attempting my first cnc conversion. There isn't a lot of info out there that pertains to converting the PM940 so it makes it a little more challenging. I've got the electronics enclosure done for now until I do some upgrades later. Since this is my first conversion, it is hard to know exactly how to customize the enclosure until I have had a chance to use it and see what I want to add or change. So for this reason, I did a basic enclosure and will make changes as I go. Here are a few pics. Any advice or recommendations are welcome. Since there aren't any ball screw kits available for the pm940, I will just make my own. I have given a lot of thought to how I will build it and have been doing some research on how others have built ball screw mounts for similar mills. Maybe I can get this thing closer to making chips someday soon.
 

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halfstep

Halfstep
One more. I have trouble getting these to go thru so that is why I post one at a time.
 

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machinedude

machinedude
box looks empty with no drives :) a plus side is you save money on a smaller enclosure I guess. since your strictly DC that makes things a bit easier and cheaper as well. I had to look at clearpath to see what it consists of. pictures looked off until I seen what you got going on there :)
 

halfstep

Halfstep
Yeah, it's a big box, 24x20. I got a good deal on it off ebay. It was old stock but unused. It's a heavy nema 12-13 box. I bought a back plate for it. I drilled out the 4 holes bigger in the back plate so they would go over the standoffs. This let the back plate go down to the bottom of the box giving me more depth for the clearpath power supply. It is a bigger box than what I needed but at the time, I didn't know if I was going to buy Clearpath servos or DMM. I have a couple of Sanyo denki sanace 60mm fans for the box and a small Sanyo denki sanace 30mm fan on the power supply. I bought a longer WIFI antenna lead and a longer antenna. I have 2 SDSK 3421S-RLN for X and Y. I have 1 SDSK 3432S-RLN for the Z. I bought an extra Clearpath 10ft. 8c control cable and cut it into 3 equal pieces for the wiring of the box from the aviation connectors to the Masso. I bought the USB panel connector, the DB25 panel connector and the VGA panel connector from L-com. They are shielded sub panel connectors. I shortened the Clearpath power supply cable and crimped on new pins for the Molex connector. I used the cut off portion of the power supply cable and crimped on new Molex connector pins and made 3 short power cables for wiring inside the box for the X, Y and Z . They are 2c wires and go from the power hub to the aviation connectors. Everything is mounted on din rails which makes it nice and easy.
 

machinedude

machinedude
hopefully those motors are able to move your loads around? one of the things about the clearpath motors I noticed was the lower speed and the torque speed curve associated with them. I felt the DMM did a lot better in those areas. since your machine is a bit bigger than most bench top machines you have some weight to move around. your machine stock out of the box most likely is sett up on dovetails with gibs so you have lost efficiency in that area. adding ball screws will help but linear rails on bearing blocks is pretty standard on most machines. X and Y are more forgiving if your slightly under powered but the Z axis will be your biggest challenge.

I don't know much about the clearpath stuff. I went with DMM on my current build. i'm running on single phase 240v AC so my set up is a lot different since I have a lot of extra stuff in my controller for noise and what not. that adds a lot of extra cost to the controller build no doubt. one key thing is my max rated speed is 5,000 rpm vs clearpath's 1,100 to 1,200 rpm so right off the bat your rapid rates are going to be lower from your limited speed and your holding torque looks like it will drop pretty good after 600 or 700 rpm's on your motors. so your pitch on your lead screws could be an important choice? I've always stuck to around a .200 or 5mm lead and had good results from my experiences. you would probably end up with a max feed rate of around 150 imp on a 5mm lead screw. it's a trade off between resolution and speed and what your needs are. I never really looked into any mechanical advantages of the pitch on your lead screw so that might be something to look at closer?

hopefully it all works out for your build. I'm curious to see where you end up when it's all done regardless.
 

halfstep

Halfstep
I plan on using 2005 ball screws on the X and Y and 2505 on the Z. From any research I have done, the servos I have should be fine for the pm940. With it having dovetails and gibs, the rapids will be somewhat limited anyways. At least not as fast as one set up with linear rails. The DMM servos are nice and I might regret not getting them but I think the Clearpath are good servos as well and I don't think I will be disappointed. The Z axis is the biggest issue with getting a motor big enough. I know the Precision Matthews offered the 940 in a CNC model a few year ago and they used steppers. They used nema 34 640 oz. on the X and Y and nema 34 1200 oz. on the Z. I'm using the 3421S-RLN which are 1094 oz. for the X and Y. And the 3432S-RLN which is 1396 oz. for the Z. I know there is a little more to it than just the oz. rating but I should be more than fine. I will probably use the China ball screws from linearmotionbearings with double nuts. From my understanding, (which isn't much), running rolled ball screws with the pre-loaded double nuts at higher speeds can generate a fair amount of heat and one shouldn't get too overly aggressive with their rapids. Since this is my first conversion, I can't speak from experience, just doing a lot of research and going off of what I have read. Once I get my ball screw mounts finished and things up and running, I will upgrade to a VFD and 3ph 3hp motor and would like to go with a belt drive. The motor it has now is a D90 face with a short 19mm shaft that fits down into the gear hub. Most D90 face motors have a 24mm shaft. So I can't really upgrade the motor alone unless I make a motor shaft reducer and space up the motor. If I do the belt drive at the same time I go to a 3ph motor, then I have more options on motor selection. Any recommendations for a 3ph 3hp motor? The motor it has now is a 2hp 220v.
 

machinedude

machinedude
the 2 hp motor you have is not a bad start the only down side to what I seen on that machine is it's gear driven and has a limited number of speed choices. the range of speed you have s not bad for steel but you are lacking on the RPM's for aluminum for example. my plan is to use a 750 watt DMM servo for my spindle. it's only 1HP but it has the RPM's I was looking for on a 1:1 ratio. they are rated at 5,000 rpm's but will actually do around 6,000 on 240v.

DMM has larger servo's that have like 2.5 HP but they max out at 3,000 RPM's so if you go to a 1:2 ratio you get the speed of the smaller 750 watt motors but you basically half the torque and end up with only a 1.5 HP drive motor as a result.

I personally like the servo as a drive motor since you have everything needed in one package. If masso ever does rigid tapping your bases are covered already. plus spindle orientation for a ATC is already there as well. just seems logical to go the servo route on a spindle in my opinion.

the only gain on 3 phase would be the reduced amp draw. but if you are like me you don't have that option unless you upgrade your power supply. more money more time more initial headaches :)
 
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