I’m trying to figure out a few things and I am having trouble with the math and finding all the answers in one place so I’m hoping folks here can help me out. Explain the math like I’m in 5th grade. 1.8 degree nema 23 stepper motor 1/8 microstepping 1204 ballscrew how do I calculate the steps/mm I am getting 400 is that correct? (steps per revolution x microsteps)/mm per rev If yes how far does the nut travel with one rotation? 1mm? And once I know steps/mm how do I get to inches per minute for a given rpm? Finally knowing that torque drops and rpm increases what is a good target torque range for milling hardwood. More specifically for a bit of context pocketing contours and 3d carving engraving with 1/4 and smaller bits. Thanks I know the answers are likely around but I’ve had a ton of trouble piecing the above together and I’m sure it will be helpful having it all in one place.
400 is correct as a starting point, subject to calibration for which you can use the wizard in OpenBuildsCONTROL. for a 1204 I believe the distance per revolution is 4mm. 200 steps per rev * 8 microsteps = steps per rev steps per mm = steps per rev / mm per rev = 1600 / 4 = 400 somewhere I wrote a post about calculating steps/mm for a completely unknown system, it is possible (-:
you dont need to know that at all. once the controller is calibrated to go the correct distance , ie it goes 1 inch when told to go 1 inch, the Gcode you send to it tells it how fast to go and the controller figures it out from there. what YOU need to do is figure out the feedrate from the RPM, depth per tooth, and tooth count. RPM is a function of SFM, or surface feet per minute carbide cutters are happy around 1500sfm is most woods (don't bother with HSS in wood) depth per tooth can vary from 0.002 (hardwood) to > 0.010" in softwoods. treat pine like a hardwood, the knots and hard grain are like a hardwood. typical tooth counts are 1 (for 1/8" or smaller) and 2 for > 1.8" pass depth of .25 to .5 tool diameter this page should get you going CNC Feeds And Speeds. A Starting Point. on putting that all together remember that these numbers are all guidelines and the final result will depends on how well you built your CNC, overall stiffness, quality of bits and so on. You want to be making chips not dust, so keep the feedrate up and reduce the depth of cut to keep the machine happy.
Thank you. I understand feeds and speeds. The reason I am asking my original question is to figure out how fast I needs to spin the ball screw in order to achieve a proper feed rate. Typically I run a 1/4 two flute down it but around 200-250ipm at 18,000rpm with .125-.25doc to get feed rate like they I would have to rotate the screw at like 1,333rpm which I am assuming is too fast but I don’t really know. which is why I want to know how much torque I should have in the stepper motor at a given rpm so I can select a motor, driver and power source. also I understand I should probably(maybe?) switch to 1610 ballscrew for faster speeds
I've got 1204 ball screws with 2Nm Nema23 steppers running on 36V on my small (metal cutting) CNC, and its top speed is about 3000mm/min, or ~120 inches/min, so I think you would be wise to go for a coarser pitch.
It seems like there's some mix up over what's the focus? I've never once considered how fast my lead screw/ball screws are turning, or what RPM they're at. I just input my chosen feedrate and let the software and hardware cam/blackbox steppers do the rest. Great to know feedrates, and depth of cut, I just don't know how me knowing my rpm's of my screws would help me. Maybe I'm missing something?
I don't think you are missing anything. The information isn't relevant unless one is trying to design a machine from scratch.
