As you should only start coming closer with your flame very slowly, you should see vapor forming before you would be about to burn anything.
So try to get closer and build up the heat, then when you see vapor you should wait for a little time in this state until it does not get thicker inside that glass.
Sounds a little bit complicated, but the thing is just try it out a few times and you are good to go.
If you *Burn* the spice you will know it as it smells pretty bad then ....
Also perfectly vaporized spice should NOT produce thick clouds. So if the Machine gets completely white like a water bong for weed, then you overdid it.
If you want to be even more safe then just build the *Green Buddha*, it is the GVG-Homemade-Device by the Nexus.
With this it is impossible to burn the spice, if will definetly evaporate before it gets too hot.
With this the vapor is the smoothest it could get for a device with less than 50 $.
For the longterm I highly recommend to build it, as the machine is nice but mostly nice for its cheap and easy producing. If you want to have a longterm item which helps you getting the most pleasant effects you should upgrade to the Green Buddha.
But as for the Machine: Try it out a few times and you will get used to it. Start slowly coming closer with the flame (using a butane torch is ALWAYS recommended because of heat control) and you will see that you will get it.
If it does not vaporize even when you come really close, then maybe decrease the thickness of the copper mesh a bit.