Stepper on Z question

[SScnc]

My Grizzly G8689 is due Tuesday and thanks to advice I got here on the forum I ordered the 3 axis stepper kit from Keling and it's due Thursday. Thanks for the advice !

I'm planing to make the stepper mounts myself using Hoss's DXF files (thanks Hoss) and the X and Y don't seem to be any problem.

I am however wondering what is the simplest, least expensive method of converting the Z axis ?

Also, has anyone connected a stepper to the fine control of the Z ? I searched and didn't find anything on it.

Or, is there a kit that is "affordable" ? I know about cncfusion and it's expensive (for me anyway) and it appears it connects to the side of the spindle head. Wondering if that creates a binding problem.

Thanks for any advice, I can't wait to get started,

Steve

[Crevice Reamer]

Try these:

Really cheap X2 CNC conversion:

http://www.cnczone.com/forums/showthread.php?t=50277

http://www.cnczone.com/forums/showthread.php?t=51449

CR.

[SScnc]

That's exactly what I had in mind, thank you very much for those links !

Now to order the parts.

Steve

[Crevice Reamer]

BTW: Welcome to the Zone SScnc!

Just make sure you choose your stepper motors wisely.

Choosing the right stepper motor:

For OUR applications, it's best to wire the motor in Bipolar Parallel mode. This, plus the maximum voltage that the driver can handle, determines the power supply voltage.

One of the most common mistakes in DIY CNC is poorly matching the power supply to the stepper motor.

Just because a motor SAYS it is, say 425 oz of torque, doesn't mean that YOU will get that performance. Each stepper has its best performance voltage. The aforesaid 425 oz motor needs 83 volts and 2.8 Amps to deliver that much torque and full power at top rpm. If you run this motor with less volts or less amps, you will get less power. If you run an 83 Volt motor with 24 volts, you may get only a little more than 1/4 of the rated power out of it.

Now maybe you don't CARE about getting the fastest rapid speeds, but you SHOULD care about motor stalling and lost steps. The closer your motor is running to best power voltage, the less likely that the motor will stall and lose steps.

And you can ALWAYS slow a motor down by upping the microstepping--But it may be very hard to speed-up an underpowered motor.

The formula for best power voltage of a given stepper motor is 32 times the square root of the inductance. This particular 425 has 6.8 mH of inductance when wired Bipolar Parallel. The square root of 6.8 = 2.607, and 32 times that = 83 Volts.

Now, this is not the voltage that the motor is rated at. The above motor is only RATED at 4.17 Volts. Won't this burn up the motor? No, because stepper motors do not run on continuous current, but pulses of current. Each pulse from the driver moves the motor one step. A micro stepping motor could need thousands of pulses just to turn one revolution.

Using the best performance voltage charges the motor coils very quickly and therefore imparts much more power per pulse than a lower voltage would.

So, when choosing a motor, you may find that the OZ torque readings are misleading. When you calculate best power voltage--A lower oz motor may perform better than a higher oz motor at a given power supply voltage.

CR.

[SScnc]

Thanks for the welcome CR. This is a fantastic site and you guys have already helped me allot and I appreciate it !

And thanks for your reply,very informative. I've read allot of your posts and am learning allot. (and need to)

As for the stepper selections, Hoss and Jalessi recommended keling and I've already ordered this with the 36 volt PS

Hopefully this will be good enough, on a tight budget at this time.

Please let me know what you think about it, I just got a shipping notice yesterday.

Steve

[Crevice Reamer]

Your drivers limit the maximum voltage to 40 volts. The motors however, have a best voltage of 60 volts. Thirty Six volts is better than 24, but might give only a little more than half of the rated power. This was a better choice than the 425s though, and they should be fine.

None of Keling's steppers will give best performance with 36V. Many are best at 48 volts though, and some are best at 72V.

CR.