Tweakie good morning! I was thinking about two things. 1) how i will be able to achieve shades in the engraving mode if I will  change the laser output with analog way manually.I suppose I will set the potentiometer to a certain value and I will not be able to change it through the engraving.During cutting I will not have this problem because the laser output is the same and doesn't change.
2)If by connecting my pin 9 ,that gives a pwm pulse eguivelant to 0-5v, on the TTL(L) ,I will damage my PSU?
Thanks.

** Until now the laser output in the engraving mode was connected someway with the feedrate!

ntlaser,

Within Mach disable PWM spindle control.
When I refer to your pin#9 I am referring to the pin#9 from the computer's LPT parallel port.
Configure your pin#9 to the Digital Trigger and set active low.
Ensure that pin#9 is not configured or enabled to any other function within Mach.
Connect pin#9 to the PSU’s “TTL(L)” terminal (see earlier diagram).
Set the potentiometer mid travel for testing and adjust as necessary but make sure you don't set it too high and exceed the tubes maximum current specification. If you don’t already have a milliamp meter (0 to 30mA) connected in series with the earthy end of your laser tube then you should obtain and fit one.
Make whatever safety interlock, water flow etc. connections to the “WP” terminal of the PSU.

Shades are achieved within the Engraving plugin by varying the Pulse Repetition Frequency (not PWM) on the digital trigger output. A PRF of 100% would be equivalent to maximum power and a PRF of 0% would be equivalent to minimum power. In practice the Engraving plugin never gets anywhere near to a 100% PRF (see my pdf document for values related to feedrate http://www.machsupport.com/forum/index.php?action=dlattach;topic=12444.0;attach=26734 ) but manual control of the maximum tube current can, to a large extent, compensate for this.
The manual control of tube current can be adjusted at any time during operation to achieve the appropriate laser power for the job in hand. A multiturn potentiometer with calibrated dial is good because the adjustment is quite fine and the dial enables the correct settings to be recorded so that they can easily be used again at a future date for a similar job.
The Engraving plugin, as mentioned earlier, controls the laser’s output power by adjusting the PRF and this, in turn, is directionally proportional to federate and pixel value (high federate = high laser output power : low federate = low laser output power : no feed at all = laser off). It’s really just as simple as that.

I hope I have explained all your questions.

Tweakie.

I have already a miliamperometer!!I will try it!!!!! To see what will happen!!Fingers crossed:) ..Thanks

I finally got around to making another "Che" coaster and more or less got the cut-out dimensions right this time. The problem is that, for the same power settings and feedrates, different types or wood veneers laser cut with different kerf widths. Still, I am quite pleased with the result - just need to make a couple more, with different images for the set 

Tweakie.

Hi Tweakie,
  Hopefully, the set would include one of him with a bullet hole in his head .... and / or maybe hanging from a tree. 

He is very pretty, but I'd think you could find a better subject given the atrocities he's responsible for. 

Beautiful work none the less.
Thanks
 

Thanks Russ, you are of course quite right, but he did finally meet a fitting end. 

Tweakie.

Last week I urgently needed a couple of gaskets so, just for fun really, I used the same technique used a couple of years back to make the crankcase gasket for my OS61. Provided the casting or part requiring the gasket is small enough to lay on the platen of a flatbed scanner it is fairly easy to get an image then, after a bit of cleaning up, an outline DXF can be produced and converted to GCode.
My laser will not cut all types of gasket material and there are limits to the maximum thickness for the stuff it will cut but these fellas are 0.8mm thick and came out pretty well. I only needed one of each but made an extra while I was at it. 
Gaskets made this way would be ideal for Steve, building his excellent V8, where neat and precise cutting is important but it takes time, mainly in the preparation and cleaning up of the artwork.
This took me just over the hour to make some parts which I probably could have cut with scissors in 10 minutes but it has made a very tidy job of something, with a bit of luck, I may never ever see again. 

Tweakie.

Only sissies take the easy way out with scissors anyhow. Good job Tweakie. (as usual)

Thanks Sam, I never really thought of it like that 

Tweakie.