Spindle Speed Control for Hobby CNC

[canyon289]

I recently bought a Zen Tools CNC machine (3 axis desktop 7x7in cutting area) to wet my feet in CNC machining and although it is a great kit I would love to add computer spindle control.

Currently I can only run the spindle at one speed, on or off at 30 volts. I was considering getting a variable power supply but this would require me to put stops in and then manually fiddle knobs when I want to change the speed.

I would like somehow implement a way for Mach3 to automatically control the spindle speed.

My spindle runs between 24 and 48 volts and should draw less than an amp. Here's a wiki page for more details if necessary.

Spindle DC Motor Kit - Zen_Toolworks_Wiki

How do the professional machines regulate speed and is there some way I could implement this easily and cheaply with my cnc?

[kretov]

You can use a simple opto-isolated PWM switch. I have created one for the DC spindle of my CNC lathe running at 24V DC, drawing approximately 3 or 4 amps. See the scheme attached.
The device is a digital switch on IRF520 transistor. The LPT input is isolated from the power circuit by TLP 521-1 optocouple. The device acts in reversed way - the voltage is applied to motor when "Mach 3 signal" is low, so set "Active low" option in "Ports and pins" settings. For my motor, the best PWM frequency setting in Mach3 "Spindle setup" section appeared to be 100. You can try different settings and see at which the motor runs smoother.
D2 does not necessary have to be 15ETH06 - it can be any diode that will handle input voltage and current.
I had to clean up the schematics to make a screenshot and I'm almost sure that it is all right However, if you are going to make the device, please, test it carefully before connecting to a motor. The test is simple - apply voltage to pins 1 and 2 (using a fuse, just in case) and check pins 3 and 4 with multimeter - there should be a voltage on them. Then apply 5 volts to J1 and make sure that voltage between pins 3 and 4 has disappeared. You can also test it with some scrap DC motor.
Hope it will help Let me know if you have any questions.

[canyon289]

Would I be able to buy one off of you directly? At the moment I live in an apartment that I am not allowed to solder in, otherwise I would try this out myself. Thanks for the schematics and the help!