Looking for insight into converting PM25mv to CNC

So as mentioned above, I am leaning towards the closed loop steppers and drivers from SteperOnline. I would like to buy 'American' both for quality and support but I'm just not going to spend that much (shame on me)...

So the Smoothstepper will be compatible with these drives best I can tell (drivers are CL57T and CL86T) and I will go through the C25 BOB.

I did re-size the motors since it was a different supplier than I originally spec'd out and they all tend to carry different sizes so I will end up with:
nema23 3Nm (425oz.in) for x and y
nema 34 4.6Nm (651oz.in) for z axis - actually for like $5 more, I think I will get the 5.8Nm (821oz.in).
@pontiac428 Most of the hardware conversion kits are nema23 for x,y and nema34 for z so that is the driving factor for mixing them up. I'm sure I could do otherwise but this keeps it simple and I've just seen so many ppl using larger motors on the z relative to the other axes.

@shooter123456 With everything else I have going on (and then throw in a milling machine and CNC conversion), I don't have time to learn Linux. I'm sure I could and I would love doing it but at this point, I'm just going to have to save that for another day.

So that's the build (to be):
ArizonaVideo conversion kit (he has been quite quick and helpful with my inquiries so far!).
StepperOnline closed loop steppers and drivers @ 651 oz.in x,y and 821 oz.in z.
SmoothStepper, C25 BOB and Mach4 (change of vendor... CNC4pc has some good package pricing).
Fusion 360 for CAD and CAM.
Power supplies changed a little bit... will go with a 36v for x,y and a 48v for z. I will not be pushing this machine and it seems the lower voltages will reduce currents and temperatures so, longer life out of components (I'm thinking).

I'm going to get a USB to Ethernet converter and run this as I have read several postings where this has not been a problem. This will cost $14 so not a big loss if I have to go to plan 'B'. Plan 'B' kinda scares me because it consists of plan B1) resurrect an old computer with winXP S.P.3 on it and use it with Ethernet port or B2) buy a new computer. If I buy a new computer (hey, more toys!) I will get a touch screen laptop with an Ethernet port. Amazing that the P.C. I bought just earlier this year doesn't have an Ethernet port. I didn't think a thing about it at the time (didn't have a reason to) but that is a great touch screen laptop with 17" screen that I would have loved to use for this setup.

Well, off to ordering... O.K., will let this post sit for a day just to hear someone else's opinion which will throw me down another rabbit hole! Don't get me wrong, I love all the feedback and input; but it once took me two days to spec out which RIVETS I wanted to use for a project, so I need to move on this at some point. More tariffs are a-coming on those imports...


Thanks all!
 
Sounds like you are on your way:encourage:

If you can afford the good stuff there's no reason not to go that way. Closed loop should make a more predictable machine. I just got my machine up and running this past week so now it's time to start improving. I'm sure there isn't any end in sight with this stuff.

Cheers,

John
 
@Nrpdyer There are a few intricacies to motion control with stepper motors that seem to be glossed over by many online. These are just some things to think about. Sounds like you are on the right track

First, there is a trend that higher torque motors have slower top speeds. This is because as the torque increases so too must the motor's inductance. This causes increased back EMF (the voltage created by the rotating motor shaft, like a generator) which opposes the motor driver. Inductance is a resistance to an instantaneous change in current and eventually the driver is unable to fully develop current at the windings before the next step pulse arrives and the motor stalls. The higher the inductance, the sooner this happens.

Second is a correlation between power supply voltage and speed. Stepper motor drives are constant current devices and act by "chopping" the DC voltage using PWM to maintain the ideal winding current. The input voltage to the stepper drive defines how easily the drive can develop winding current. Higher input voltages allow the drive to push the motor harder between each step and combats the issues presented in point #1. Simply put, higher input voltage equals higher stall speed. And this doesn't come at a large heating expense. As I mentioned earlier the drive will chop the DC voltage to very low values once current is developed so the heating effects are minimal compared to the current setting on the drive. Higher input voltage will not increase torque at zero speed.

Third is the correlation between current and speed. A lot of people think that increasing the current output of their stepper drives will get the moving faster, however the usable torque drops off quickly with speed. The benefits of increasing current output are negligible compared to increasing the input voltage. This increased current adds a tremendous amount of heating to the motor. So unless you need more low end torque, keep the current low. Also consider enabling idle current reduction if your drive has it. This reduces the current output when the motor is not moving and reduces heat. Also remember, motors are made to get hot, this is normal and within reason (~200*F) will not damage the motor.

Fourth is the correlation between micro-stepping and machine resolution. Many people assume that if they set their micro-stepping at x256, then the motor will suddenly have 256 times more resolution. Unfortunately each time you increment the micro-stepping parameter at the drive, the motor produces 1/2 of the torque at the previous micro-step (approximately). For example if I were to set x4 micro-stepping on my drive my motor would produce full torque at the beginning, then 1/4 torque at the first micro-step, then 1/2, then 1/4, then full torque again (as the motor hits the next full step). This pattern continues through each full step of the motor. if I were to enable x8 it would look like 1.0, 0.13, 0.25, 0.13, 0.5, 0.13, 0.25, 0.13, 1.0. At 1/8 (or less) of the motor rated torque, the shaft may not move at all and your extra resolution is lost. The motor will still generate full torque at each full step. Micro-stepping will almost always make motion smoother so that is beneficial enough to justify turning it on, but don't expect the motor to make each micro-step faithfully.

Fifth is the trade-off between speed and acceleration. I look at many home-built CNC machines on the web and notice that 90% of people are very concerned about speed. While good rapid speeds are a great feature, many overlook the importance of acceleration. Especially with modern tool paths, your machine will be making thousands of small movements during each program. In these short moves it is sometimes unusual for the machine to reach the full cutting speed. Instead the cut is dominated by acceleration and deceleration. This necessitates high accelerations to make your cutting time productive (even if your rapids aren't screaming along at 1000ipm). To get these higher accelerations you need motors with high torque.

For my G0704 I used 425oz-in motors and reliably got 100ipm rapids. I do have a gas spring counter balance but kept my gibs quite tight. Maybe I would have been better off with higher torque motors? I don't know.
 
Still learning my machine as I spec out all the items needed to build the electrical cabinet for my CNC conversion and another question has arisen. I am now considering spindle speed control from Mach4 and the SmoothStepper using the C6 card from CNC4pc. This card has apparently caused a lot of issues for people and burned up some electronic equipment due to the grounding. I guess being an electrician, that if I studied this card enough, I could figure it out but what are people doing wrong to burn up their cards? The literature says to use a separate power supply for this component as the grounds cannot be tied together... which parts of this card are they tying together via ground to do the damage? I can see not grounding a floating voltage such as the analog ckt. might be but surely they aren't grounding that ckt? And even at that, using a separate power supply? As long as you don't put power to a place power shouldn't be and don't ground something that shouldn't be grounded, I don't quite understand the comment about separating the grounding. Anyone done this with a PM25?
 
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