Motor sizing
Originally Posted by
mhackney
CR, do you think the 270s have enough umph to turn the stock screws on the X and Y? That was really my only concern thinking about the 387s for the X and Y.
It turns out that Keling takes $10 off the Gecko 540 with a purchase of other items, so there really is no significant savings on the "package".
Perhaps I should pick up 2 of the 270s and the KL-350-48 power supply. That should get me started I think.
cheers,
Michael
In this case more is not better, especially when it comes to stepper torque ratings I just went from nema 34's down to nema 23's which are smaller and have less "holding torque". But what the "holding torque doesn't tell you is what is the torque at speed. I was able to increase my ipm by 40%. This is because with a 50v power supply, the motors are a better match. The nema 34's that I had really needed to be run at 80+v to really go anywhere.
With a 16tpi screw, you will find that motor rpm's are what you need to get a decent rapid speed. I define a decent rapid speed as one in which you can't finish lunch before the machine gets from one side to the other. All kidding aside, if it takes 1 minute for a machine to go from one end to the other, and we are only talking ~12" here,it doesn't take long for you to start pulling you hair out. On my taig, the 425 oz motors are so mismatched with the 30v power supply and driver that it isn't funny. I actually am using the 425's on my router, and will be putting the 270's or something simialar in their place.
When you talk about oomph, how much oomph do you apply by hand???? Not much in most cases. If you refer to having to put oomph in buy hand, you would probably feel that something is wrong.
I have heard many people say that speed is not important because they are not in a hurry. But what they forget is that there is a minimum speed that you need to go in order to cut and not just rub. I also find that when doing a g83 chip breaking drill cycle, that the extra rapid speed can make a huge difference on a deep hole or lots of small holes. My router used to have a rapid speed not any faster than the feed rate at which I was drilling my holes. When doing a sheet of fiberglass parts with a total of 100+ holes, it makes a huge difference in cycle time. These are not production runs, but just a 36"x 36" sheet of parts that I do once or twice a year. In the past moth I have gone from 40v to 50v power supply, then changed to the 425 motors from the taig and then used a g251 to replace the blown g201(my fault) and in each case have seen the speeds go up. I can now reliably rapid the z axis at 200 ipm on a 5 tpi ballscrew. It will actually rapid faster, but during my testing, it would stall out somtimes and I need to be reliable, not the fastest machine out there.
I guess the purpose of my going on for so long is to emphasize that you need a motor that is matched to the load the you are moving, the screw and power supply that you are using, and not go with the bigger is better mentality that has permiated diy cnc for so long.
Best of luck,
Mike
P.s. CR knows what he is talking about. Like me, when his is not 100% right, someone will step in and offer their opinion. ( notice I didn't say wrong )
Warning: DIY CNC may cause extreme hair loss due to you pulling your hair out.