New project need assistance

[NorthWheels]

Hi everyone,

I am new to the CNC world. I am building a screw driver application that is required for a part of wheel assembly we are doing. I am not sure where I can find this help.

I have a steeping motor mounted with a handle and a custom made chuck. This chuck need to turn a certain amount at a desired speed stop and then repeat. This will be controlled by pedal activation. The program I loaded is Drufelcnc. The communication works but it requires G Code to fuction. I have done some reading on Gcode but not sure how to mange this in the software or write it for this purpose

The process ( Chuck interface must start and stop at an exact location ) and reapeat with the pedal activation.

Stepping motor: Nema 17 1.2A 17CA02A-120
Driver: DM556
Motion controler: Breakoutboard Mach 3
Pedal: Foot pedal
Software: Drufelcnc

 

[kellys_eye]

You can't (shouldn't) do it with just the stepper motor as there is always the possibility of missed steps or something else interrupting the movement. You should use some form of switches to detect the start and end stop positions - slotted opto's maybe - and count the total revolutions.

Better yet fit a slotted disk to the motor output shaft and detect on a per/whatever angle you need for accuracy.

 

[Bluejets]

You can't (shouldn't) do it with just the stepper motor

Most cnc if not all, operate quite well without having the need for limit switches on each and every movement, just relying on the instructed number of steps from a "home" position.
If the stepper motor and it relative controls are designed and setup well with sufficient power and drivers to suit there should be no need for extra limits.

The position feedback would be fine although a lot extra work in the programming.

 

[danadak]

The limit switches used on almost ALL modern CNCs are to limit gantry
and tool change heads and tables from colliding into their mechanical end
travel limits and causing catastrophic damage.

So code does keep track of positions of CNC tools, etc, under ideal conditions,
but CNCs are far from in ideal environments. Large electrical fields and noise due
to motors (largely), welders, etc.. And material and tool breakage also impacts
sensors and machine operation. So never defeat or remove limit switches unless
you want to destroy high cost manufacturing machines.

Their presence is driven by careful and complete design decisions and personal
safety considerations.


Regards, Dana.

 

[kellys_eye]

The best CNC's don't use stepper motors but use SERVO motors that are fitted with feedback (slotted opto) mechanisms to ensure no step-loss during movement.

A 'single' missed step in a stepper controlled process will create an error that is carried throughout that process and will amplify if further steps are lost/missed.

Only repeatedly returning to a reference (start) position can such errors be eliminated in a stepper controlled CNC.

In the OP's example they specified:

must start and stop at an exact location

The key word being 'exact'. This is only truly possible by detecting that EXACT location which is (not impossible) impractical by total reliance on a stepper that doesn't have some form of feedback.

 

[bidrohini]

Determine the specific movements your screwdriver application requires. You'll need to know the coordinates (position) where the chuck should start and stop, the speed of rotation, and any pauses or delays. You can load the G-code into Drufelcnc for execution. Make sure that the communication between Drufelcnc and your CNC hardware is set up correctly.

You can see this offline G-code sender too. This may help you in CNC-related projects.

 

[Harald Kapp]

An alternative would be closed loop stepper motors.