Limit/home switches on converted machine

[hobbybob1]

Hello,

I am rather new to CNC'ing.
I just converted a 3 axis engraving machine to CNC, using a chinese 3 axis stepper driver board. Before fitting the board, the machine was using a serial interface and after turning on the machine , the machine homed itself.

Now after the conversion i want to do that in mach 3.
The machine has 3 limit switches on all axis (X, Y and Z).

When i jog the machine to hit the limit it shuts off and i cannot jog it off the limit switch (i have now made a bridge button, which temporarily disconnects the limit switches GND), then hit reset holding the button and i can jog it off.
After that the machine works just fine.

Now my questions:
1. How can i let the machine "find" the switches and then automatically move a bit off to some sort of home position and call that 0,0,0 ?

2. And how can i set the limits the machine may travel measured from the limit switch, since i only have a limit switch on 1 end of all the axis, when i move it all the way to the other side i want it to stop before hitting the end of the axis. Is there some way telling Mach3 that it has to stop after 12 inches ? Even if there is no switch on the other end ?

[ger21]

When i jog the machine to hit the limit it shuts off and i cannot jog it off the limit switch (i have now made a bridge button, which temporarily disconnects the limit switches GND), then hit reset holding the button and i can jog it off.

Check Auto Limit Override on the Settings screen. Then you'll just need to click reset, and you can jog off the switches.

1. How can i let the machine "find" the switches and then automatically move a bit off to some sort of home position and call that 0,0,0 ?

In Ports and Pins, set up the switches as home switches (Just assign the same pins the limits are using). You can use a switch as both a home and limit.
Then just click the "Ref All" button to home the machine.

2. And how can i set the limits the machine may travel measured from the limit switch, since i only have a limit switch on 1 end of all the axis, when i move it all the way to the other side i want it to stop before hitting the end of the axis. Is there some way telling Mach3 that it has to stop after 12 inches ? Even if there is no switch on the other end ?

Config >Homing/Limits, Enter the Softlimit Min and Max, and then turn on Softlimits on the program run screen.

[hobbybob1]

Hi Gerry,

Thanks for your answers.
I had the auto limit override on (i think). When it hits the limit, i can press the fix this for me now, reset and then i can jog of very shortly, sometimes the machine moves a bit and immediately stops again (it would help if it could last for 1 second or so, so i have enough time to jog of the switches...)
When i hit reset and press OK again i can reset again, most of the time that is enough to jog of, but will check the setting.

for question 1, i had them configured as limit++ limit -- and home switches.
But i didn't know i had to press the ref all, will check this tomorrow right away. Suppose the machine runs in the wrong direction when homing (away from the home/limit switches, how can i fix that ?
Cool, i was close but your answers help me tremendously !

For question 2 about the soft limits will check this also and let you know.
Thanks so much for helping me out.

What a knowledge is gathered on this forum.

One more question:
I have caculated that in the motor tuning config i had to fill in 533,33 for the Step per setting.
200 steps per revolution motors
1/8 steps on the driver card, making for 1600 steps per revolution
10x3mm thread, so 1600 steps is 3mm movement
So 533,33 steps per unit (in my case mm).

However i have the idea that for instance when i put in g-code G20 G90 and then drill a hole at current position and then do G1 X4.5 and drill another hole, i measure 11,51cm instead of 4.5x2,54 which is 11,43.
How to adjust to have the machine really at size ?

What did i do wrong ?

[ger21]

Suppose the machine runs in the wrong direction when homing (away from the home/limit switches, how can i fix that ?

In Config > Homing/Limits, there's a column labeled Home Neg. that will reverse the homing direction.

[hobbybob1]

wow, thanks again Gerry for your great directions !
Will try all those settings out tomorrow....

If someone knows the answer to my second question about making the machine be precise i would be very delighted.

[hobbybob1]

Thanks Gerry !
Worked like a charm, when i now press ref all, the machine first zeroes the z-axis, then y- and the the X-axis. Really cool.

When i jog to the end of the tables y i find 278mm x=330mm z=70mm
So i set the soft limits MAX on 275 , 325 and -65.
That works and the machine won't pass that point.
But what to set for minimum ? If i fill in 0, sometimes the machine immediately hit softlimit when i start a g-code and the machines moves an axis ?
I have now -100 , -100 for X and Y and +1 (or -1 now i am lost) for Z.

Is there a way of when starting Mach3 that machine automatically homes to 0,0,0 ? And is there a way to set it after homing to 5,5,5 for instance and then make that zero (to have more margin to stay of the limit switches) ?

Furthermore my motors are now serial driven (5.1V 1A), would switching them Parallel give them more power (at higher speeds? or more power at same speed ?)

And would the TB6560 board be able to drive that ?
At first i was driving the motors with 36V (since that was the max of the board as i understand ?) But someone warned me that driving them at 36V was a bit too high for this TB6560 card (although it says 35V often this breaks the card) So today switched to 24 volt and turned it up to 26V.
Works ok, but that's why i am wondering wheter running parallel would work better ?

Lots of new questions hope someone can fill me in ?
So far this forum has really helped me getting started with the machine, it's amazing to see your own machine doing stuff.

[ger21]

Z+ should be up, and Z- down, so your Z softlimits seem to be backwards.

And is there a way to set it after homing to 5,5,5 for instance and then make that zero (to have more margin to stay of the limit switches) ?

In Config > Homing Limits, set the Home Offsets for X and Y to -5, and the Z to +5. Then edit the homing script, using Operator > Edit button Script, and clicking the button. When the VB Editor opens, change the code to this.

DoButton( 24 )
Code "G53 G0 Z0"
While IsMoving()
Wend
DoButton( 23 )
Code "G53 G0 Y0"
While IsMoving()
Wend
DoButton(22)
Code "G53 G0 X0"
While IsMoving()
Wend

Is there a way of when starting Mach3 that machine automatically homes to 0,0,0 ?

Yes, but it's a little more complicated. You need to create an M Code macro.
With the code open in the VB editor, Save As with the filename Mxxx.m1s (xxx will be your M code, 555 for instance.)

Then, in General Config, in the initialization string, add M555. When you first hit reset after starting Mach3, it'll home automatically. You probably want to uncheck "Use with all resets", so it doesn't home every time you hit reset.

With the Home Offsets set to -5, you'll be able to set softlimits to 0, or even -4.

Parallel is faster, provided you can supply double the current.

[hobbybob1]

Hi Gerry, thanks another time !
Will first connect the steppers parallel and try the other suggestions.
Thanks, cool that it's so customizable !