[bobhare]

Hi
I've just built a 3-axis machine and the max speed i can get out of the axes is woefully inadequate for machining aluminium.
The gear I'm using is a kit bought from Longs and works well. It is made up of:-

1. BOB DB25-1205
2. Stepper motors 23HS9430
3. Drives DM542A
4. 36V power supply

I have used, Slowing 69.16.243.61&c=1&t=42677.5054872685, to estimate the maximum motor speed and the result is as shown below.
Imax(Amps) 1
Inductanc(milliHenries 6.8
Voltage (Volts) 36
Steps/Revolution 200
Maximum Power(Watts) 36
B-polar serial
Minium Time/Step(ms) .756
Maximum Speed(RPM) 397.2

I have checked traverse speeds and they are equivalent to 350 rpm; a pretty good correlation. I'm using using metric gear and the lead screw has a 1.25 mm pitch which translates into a traverse speed of about 420 mm/min but I backed it off to 360 mm/min or 14 ins/min.

I'm new to machining but i understand from using, Milling Speed and Feed Calculator, with a .5ins cutter, a SFM of 1200, a feed per tooth of .007 ins I would need a feed rate of 130ins/min.

Possible solutions:-

1. I intended to change the lead screws to give me 4 mm/rev which would increase the traverse speed to 45 ins/min and could use 4 start lead screws that would double this to 90 ins/min.
2. I could increase the input voltage to say 50V which would give a further 35% but i don't know whether the motors would take this. I now have 121.5 ins/min; getting close.
3. The motor speed is a function of impedence and ironically inversely proportional to current. If I increase current they run more slowly. I didn't know this at the time so I bought bigger motors than I probably need. I could buy smaller motors with a lower impedance but i can't go lower than 1 amp with my driver. For example the 23HS8430 with an impedence of 3.5mH which doubles the traverse speed.

The questions are;-

1. Is my assessment correct?
2. Can i run the motors at a higher voltage and if so what is it? The driver spec indicates it can operate at up to 50V
3. Are there any simpler ways of increasing the speed?

Thanks
Bob

[awerby]

Yes, more voltage would help, but 50v is still short of the 83.4v those motors really want. The simplest thing would probably be to replace the motors with some that have less inductance. Whether your home-made machine will be able to machine aluminum effectively will depend on the rigidity of your machine as a whole more than the speed of your steppers, though.

[CitizenOfDreams]

What I would do is replace the woefully slow 1.25mm screws with something faster. If you use T8 4-start screws with a lead of 8mm, that alone should give you 6 times the speed (2000+ mm/min) and reasonable resolution (0.04mm per full step).

As the previous poster mentioned, your machine will not necessarily be able to mill aluminum anywhere near that speed, but having fast rapids will help you stay sane. My small desktop machine has 1.25mm screws too, and the rapids at 800mm/min (NEMA 17 motors) are just painful to watch.

[bobhare]

Andrew
Thanks for taking the time to read my lengthy post and as i wrote it i was drawn, sadly, to the same conclusion.
I think the machine is rigid enough but haven'measured it's stiffness and if i did i wouldn't know what to do with the number. Only a trial will tell.

[bobhare]

It looks like new lead screws and motors; but that's life.

[bobhare]

Just ordered a 23HS8404 with an impedance of 1.8mh and some 4 start 8mm lead screws.
I'll report back when re-assembled.
Thanks

[CitizenOfDreams]

Just ordered a 23HS8404 with an impedance of 1.8mh and some 4 start 8mm lead screws.

I should do the same with my machine, considering that T8 screws are dirt cheap. One of those days...