Mach does not thread in Demo mode, you however have a licence so that is not the issue.
On to your controller,does it just connect to the parallel port or do you use a plugin?
Hood

My controller connects directly to the parallelport.
The C3 board is directly connected to pin 15 on my PC.

Per

Ok then in that case you should not see  spindle readings as  you do not have the spindle relays enabled.
If you are seeing spindle readings then I am not sure why, because as far as I know you need spindle relays enabled, even if you are not using them to control the spindle.

Hood

Hmm, I enabled spindle readings but there was no differnce I am afraid .

Can I do something wrong with the G76 code? I am using the wizard in Mach.
When the code enters the G76 line the Z-axis moves about 1 mm in , then it stops...

The jumpers on the C3 board, could they make a differnce?

Per

Do you see the Index LED on diagnostics page if you rotate the spindle round manually to the sensor?
Are you commanding a spindle speed and also a spindle command (M3 or M4) from your code.
As far as the jumpers are concerned, afraid I have no idea, I have never used anything other than a standard opto or an encoder index pulse, and have never used any of the CNC4PC cards.

Hood

Yes the Index LED is turned on and turns off when the spindle reaches the hole on the mounted disc on the spindle.
I start the code with M3 S440.

But another thing is wierd. I turned off my spindle when the G76 code was running and when S true value was about 230 the G76 cycle started... Can the speed be to high?

Change the active state of the index in Ports and Pins and see if that helps. The index LED should be out until it is activated.
Hood

When using the Wizard one should click the "Calc number of passes" button and that will confirm  and show that your velocity and accel
 are adequate for the spindle rpm you input.
RICH

Hi!

I changed the active state for the index LED and it worked, finally ...

I tried to make a 1mm thread but it did not turned out perfect. When I measured the thread it seems like it is 0.9 mm.

This is the code from the wizard.
G0 G40 G18 G80 G50 G90
G00 G53 X0 Z0
T202M6
G00 X37
G00 Z2
G00 X36
M03 S440
M08
G76 X35 Z-12 Q1 P1 J0.006 L45 H0.4 I29 C1 B0.0001 T0
M9
M5
M30

When I press the "Calc number of passes button" it tells me that:
Axis will move 440 UPM and will Accel in 0.5378Units". I am not sure what that means? Does this seems right at all?

Per

Are you using a recent version of Mach?

Regarding the info, it is telling you  that your axis will move at 440 Units per Min (so mm or Inch depending on your native units) and that it will accelerate to that velocity in 0.5378mm or inch.
Hood