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Planning PM-30MV Conversion

Landmark

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I just received a new PM-30MV mill for a CNC conversion. There are a few things I haven't seen talked about very much in the forums.

1) How do you disable the quill? Do you remove the course and fine gears and all the other quill components? How do you lock the quill from moving?

2) Why don't CNC controllers use the DRO installed on mills?

3) Does it matter which side of the X-axis the stepper is installed on? It seems that most people mount it on the left side.

Thanks for any insight into these burning questions.

Mark
 
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JohnnyMill

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1. My Sieg X3 has a quill lock. I just tightened that. Occasionally I still use the quill to manually drill a hole so I would try to keep the quill functioning and find a way to lock it in t he up position.
2. The DRO is not really needed but it is convenient when tuning the CNC and checking actual movement compared to commanded movement. The DRO is also nice when doing manually milling via the pendant. My DRO is right where I can easily see it. In some cases you can use the output of the scales as feedback to the CNC controller for a closed-loop system.
3. Doesn't matter. Which ever side is mechanically convenient. Or, if you buy a conversion kit the kit will make the decision for you.

Hope this helps
John
 

Landmark

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1. My Sieg X3 has a quill lock. I just tightened that. Occasionally I still use the quill to manually drill a hole so I would try to keep the quill functioning and find a way to lock it in t he up position.
2. The DRO is not really needed but it is convenient when tuning the CNC and checking actual movement compared to commanded movement. The DRO is also nice when doing manually milling via the pendant. My DRO is right where I can easily see it. In some cases you can use the output of the scales as feedback to the CNC controller for a closed-loop system.
3. Doesn't matter. Which ever side is mechanically convenient. Or, if you buy a conversion kit the kit will make the decision for you.

Hope this helps
John
Thanks for the information.

My mill is still sitting idle. I haven't even cleaned off the cosmoline grease from shipping. I purchased the Centroid Acorn controller but still haven't figured out what drives / motors to use.
 

Uguessedit

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Depends if you want additional feedback but typically if using servos the encoders are enough although we’re building a CNC here that will integrate both using 1 micron scales. Doing so gets more complicated and I’d recommend slowly integrating if that’s your plan otherwise move the dro to another machine. Out the servos wherever you have the room to swing the most distance and not wrack yourself on when waking past.
 

spumco

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2) Why don't CNC controllers use the DRO installed on mills?
Previous replies are right on the money, and there's another couple reasons - the DRO outputs are too slow or the signals too fast.

Assuming you have a CNC controller capable of closed-loop control, either single or dual if using servos, the quadrature signal from the scale read head may not be fast enough to keep up with the commanded move. I have a cheapo scale on my lathe - works great but I'm pretty sure there's enough lag that using it for closed loop CNC would be impossible.

Or if you have a 1 micron scale the signal frequency may be too high during fast moves for the controller to process. This is where doing some math ahead of time would pay off.

Figure the max desired rapid speed and the signal frequency of the scale output at that speed. Then compare to the controller & breakout board max input speed. Nicer electronics can handle signals in the Mhz, cheaper ones are down in the Khz range. I know I ran in to this problem with a spindle encoder and had to change to a lower PPR encoder so it didn't overwhelm the BOB.

Depends if you want additional feedback but typically if using servos the encoders are enough although we’re building a CNC here that will integrate both using 1 micron scales.
Minor hijack...but LinuxCNC? or some other controller?
 

Landmark

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Previous replies are right on the money, and there's another couple reasons - the DRO outputs are too slow or the signals too fast.

Assuming you have a CNC controller capable of closed-loop control, either single or dual if using servos, the quadrature signal from the scale read head may not be fast enough to keep up with the commanded move. I have a cheapo scale on my lathe - works great but I'm pretty sure there's enough lag that using it for closed loop CNC would be impossible.

Or if you have a 1 micron scale the signal frequency may be too high during fast moves for the controller to process. This is where doing some math ahead of time would pay off.

Figure the max desired rapid speed and the signal frequency of the scale output at that speed. Then compare to the controller & breakout board max input speed. Nicer electronics can handle signals in the Mhz, cheaper ones are down in the Khz range. I know I ran in to this problem with a spindle encoder and had to change to a lower PPR encoder so it didn't overwhelm the BOB.



Minor hijack...but LinuxCNC? or some other controller?
Thanks, that is good information. I never thought about the speed of the scales. I decided to use the Centroid Acorn controller.
 

Bill MFG

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Aug 16, 2019
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Thanks for the information.

My mill is still sitting idle. I haven't even cleaned off the cosmoline grease from shipping. I purchased the Centroid Acorn controller but still haven't figured out what drives / motors to use.
Got clearpath servos. Driver is built in and they are basically plug and play with the acorn.
 
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