The electronics that take the impulses from the computer and make the motors turn.
By Sam_CNC
AJ Quick,
Thank you for providing this website and the information regarding CNC. I am working on my first CNC/Mill project. I have 2 questions, Would you please help me with them:

1- My Y axis is heavy, so I will have 2X 3A NEMA 23 step motors on it. I also need to add a step motor to a rotary table. In this case, I will end up with 4 axis and 5 motors, each motor is 3 amp. My thought is to use your unipolar 4 axis controller and branch from the LPT signal for the Y axis and add a fifth sla7078mpr. In theory this will duplicate the action of both stepper on the Y axis? Do you think this will work? I have limited knowledge in electronics hardware, however I did build PCBs in the past. I also build a PIC based project to drive small step motor through ULN2003. Based on your answer. I can re write the schematic and the PCB if it is OK with you!

2- I am planning to install 6 limit switches. 2 for the Y, 2 for the X and 2 for the Z. How to wire them? I read about this and I have a lot of conflict information.

FYI; I did not mess with the software yet. I will wait until I have my project completed.

User avatar
By AJ Quick
Hi Sam, sorry for the slow reply.

To answer your questions, yes it will be possible to branch off the signal from the LPT port to control what is known as your Slave axis motor. You could also setup Mach3 to just clone the axis as A or B for that Y axis and then you wouldn't have to worry about breaking out that signal manually. It would be done with the settings in the Mach3 config.

With limit switches you have two options:

NC (normally closed) switches and then wire them in series. If the switch is triggered anywhere on the series chain will be broken and trip the input.


NO (normally open) switches wired in parallel. Likewise if any of the switches are broken, it will trip the input.

Hopefully that helps.
By Sam_CNC
Thanks for the replay, Two more question:
1- Is all the switches need to go to a single input? or to 3 inputs (one for X, one for Y and one for Z)?
2 What the home switch? is it the same as the above?
User avatar
By AJ Quick
1. For limit switches, you should have each axis go to its own input. That way the software knows which axis is hitting the limit, and it will work better with the software.

2. Home switches are essentially the same as limit switches. For those I believe you would want to wire the switches to one single input. (Unless you can configure the software to use the limit switches for homing).

The difference between limits and homing are this:

Limits are used in cases of emergency or accident. If the axis goes out of control, it will hit the limit switch shutting off the system (hopefully) and preventing mechanical damage.

Home switches are used to calibrate the machine during the powering on process. You run a home and the machine will run slowly toward the home switch. When it hits the home switch it will stop, backup and then set your zero value. It will do that for all 3 axes and give you a set machine coordinate zero position each time.

I can't recommend which one you should setup to use. I used to think limit switches were very important, but once I had a homing setup I found that I could add in virtual software limits in Mach3 that would prevent the machine from crashing through software. I don't have to worry about the limits as long as the machine has been homed to zero during start up.

Hope that helps.

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