Yeah, the accessibility is amazing when you think of it - CNC, laser, 3D Printer, vinyl cutter - so many things people can do; so many things you can learn.
Even when things didn’t go to plan - looking back now - it was good for me. When my Dewalt brushes were getting low it started putting out massive EMF that caused my Arduino to keep restarting. I obviously didn’t know it at the time, so I tried so many different things (learned how to modify/flash firmware, replaced my Arduino then replaced my RAMPS, then my drivers - all of which I learned a great deal about). Eventually the Dewalt just wouldn’t turn on which finally showed me what was really the problem (wasn’t the electronics at all). Now, at the time it wasn’t good, but again, looking back now - there’s no doubt that even when things weren’t working for me - I was learning new things that would come in handy later.
I’ve done so much cutting that my replacement router, the DWP611, also needed brush replacements. Interesting thing though - the DW660 when the brushes got low it put out so much electrical noise that you noticed something was wrong weeks ahead of time, but the DWP611 - no electrical interference, no prewarning problems - it works, you turn it off, go to turn it back on, and it won’t start. Even that though has been a positive because now I know motors have brushes (yeah, I didn’t really know how motors worked before the MPCNC - didn’t know how incredibly easy it was to open them up and replace brushes, I would just replace the motor needlessly).
So now I started second guessing all the things I checked in the very beginning of this machine. So I just checked out full step vs 32nd steppin on the z axis (looking for more free power). Since these all articles quote micromo’s paper (now behind a registration wall) they say at 32nd stepping we should have 9.8% max holding torque, so you’d think if I put the z axis into full step mode I could notice a difference…nope. Full step does sound kinda nasty, but I didn’t notice any different in power while in motion or just holding position. Again I got super scientifical about it and used my finely calibrated fingers. But for me if it isn’t obvious it isn’t worth the update confusion.
Full step doesn’t make much sense with the stepper drivers we use because the DRV8825 limits the current in full step mode to just 70% of what you have set. Half stepping at a minimum makes sense when you consider that.
I tried it at each setting, 1/32, 1/16, 1/8, 1/4, 1/2, and full. You could hear how nasty full stepping is, would vibrate/oscillate badly if used. Either way series to my surprise is a huge difference, step rate is minimal to zero difference as far as I can tell. MicroMo posted that paper that everyone quotes but there are others showing that Microstepping down to 1/64 show no difference. One was an actual test on the steppers and showed zero difference in torque when using microstepping. Makes me think Maybe the micromo Paper was about a specific type of stepper or something but When I went to read it again, it is behind a registration wall now.
Now set up mine in series, did not change microsteps, still 1/32, lowered voltage to .7v (even my steppers are rated to 2A), could not run my mpcnc too fast cause i switched to Estlcam / Arduino uno and it can not handle 195mm/s, but who cares, i got plenty of time. But i am thinking of going down to 1/16 for Z axis to lower the overall stepload for the small Uno… Dunno if this is really required, will test if it makes any difference.
At idle it is just about 300oz-in, but at just 5 revolutions a second (at 8mm a revolution that would be 40mm/s) at 12V instead of 300oz-in it is just 100oz-in, but at 24V it is still 250oz-in. If you need more torque or want to go faster wouldn’t it make a lot more sense to modify your electronics to accept 24V rather than bumping up current?
I would think series wiring would just amplify the whole torque over speed at 12V drop because of the additional resistance of the extra wiring to the other stepper.
Just to make sure no one takes this thread the wrong way, I’m going to keep this here. I have never, ever, not once, had a power issue on the x and y axis, even when running steppers half the size that we use now.
Yes 24V is beneficial, but not by very much. Most of my cuts are run at 15-20mm/s. I like that speed so if I need to I vary the depth of cut more than the speed of travel. There are lots of ways to squeeze out a little more, but series has been by far the most dramatic, it surprised the hell out of me.
I tried series because of this tread and yes, with my magical fingers I feel the difference of torque.
(Moreover, just to thanks Ryan: I have now a 75cm75cm6-8cm MPCNC 525, with a 500W Chinese spindle and classic steel pipes 25mm. With a single flute 1/8, I can mill MDF with 2-3mm DOC, feedrate 15-20mm/s, plunge 3-6mm/s with a final tolerance of 0.2mm maximum. That’s a huge improvment of my first MPCNC (more than just an improvment in fact). To sum up: it works well! I still have to try other materials like plastic or aluminium now. Thanks again).
For me personally doing 3D carvings, the Z axis is where I would really like to boost things if at all possible. Every line of gcode for the 3D carvings is at a different Z height, so I’m limited to the speed of Z for all cutting. The bit’s tip is 0.5mm and 1mm with stepovers of 20% and under so even at 30mm/s Z speed I have some stuff that takes over 16 hours. What do you think has more bang for the buck - going from 12V to 24V or going up to a larger Z motor - to improve Z speed above 30mm/s?
You can improve you z speed by decreasing your step rate, it works great all the way down to quarter or even half stepping. Full steps are kinda rough. No problem, but 30mm/s not gunna happen. Too much inertia on large moves. You just want faster accelerations for small moves.
Go to half stepping and torture test your zaxis to increase the z max speed to maybe 12-16mm/s and accel as high as you can go before loosing steps. I have some torture test scripts on here.
any good schema on serial wiring the steppers, they now are parallel, the vicious way!.. would love to change my parallel build but hesitating to cut the wires!!
or is there some truth in the wiring from the shapeoko forum?
Currently the drivers are getting too hot, nearly to the thermal shutdown… (and sometimes I hit and do not dare long runs now!
I’m doing 30mm/s now, was thinking of either going to 24V or going with a NEMA23 for the Z with the goal of 60mm/s hopefully. I have a lead screw (with antibacklash splitnut) so that’s why I’m able to do 30mm/s now.
Or who knows - I bought an Arduino Due for $13 along with 30lbs of 4043D plastic (Ahh, Filastruder - nothing like $2 a lb plastic to print with) the other day during one of Ebay’s ‘spend $50 get $10 off’ so I’m going to be trying out TinyG G2Core’s firmware which supposedly can do some amazing things with acceleration because it bases everything on constant jerk instead of constant acceleration. Maybe that better acceleration management alone can get me up to at least 40mm/s if I do 30mm/s already without problems.
I went with a 4 start 2mm pitch lead screw though for my Z so it’s only 200 steps per mm at 1/32 stepping.
I looked at Smoothieware/board too, it seemed like it would be a lot easier to switch to, but apparently even with the increased CPU power the actual firmware for Smoothieware is the same constant acceleration as Marlin/Repetier so I wouldn’t see much benefit. TinyG G2Core’s acceleration is apparently much different - but comes at the cost of being harder to switch to - it uses JSON (Chilipeppr) instead of normal gcode senders like Repetier Server or Octoprint and doesn’t have any presupported ‘all in one’ board available that supports 3D printing AND CNC cutting like RAMPS. Seeing it’s acceleration management though is amazing, here are some videos of it in action: https://www.youtube.com/watch?v=tEXy6E8G154 (see how the ball swings left and right but then barely swings when the carriage stops moving) https://www.youtube.com/watch?v=Om0wTqFA-Dw (it runs at 50,000mm/min and isn’t losing steps - granted it can’t print at those speeds obviously) https://vine.co/v/hvYIdvQeZpK (swinging a big hammer around, and coming right up to but not touching a pair of buttons on both sides)
The lead screw has been doing good - the original nut developed some wear and I ended up buying a split nut antibacklash one instead ( http://www.ebay.com/itm/322207703521 ) and as it wears the spring takes up the slack. The top part is kept from spinning by the legs coming down the side, so it can move up and down but not spin.
Even with the worn nut though I wasn’t really seeing any effect on my cutting though - just that I could move the Z assembly up and down a little without turning the screw. I don’t know if it was the weight of the tool/Z assembly holding it down during actual cutting that made it not cause problems with cutting, but I just didn’t like the play being there so I got the antibacklash nut anyway.
