Mechs(Mechanical Mods) are great looking devices, and it can be easy to just get one when you’re thinking of upgrading, and not realise that there are some important considerations that need to be thought over.
Saftey features.
VV/VW devices have built in safety features. This is the big plus point about them when you have only been vaping a short time, as you don’t need to think about what could happen, because its already been taken care of with the electronics that control them.
Mech mods have no built in safety whatsoever. The only safety feature on a mech is you.
Why is this an issue?
Well it’s because of the batteries that you will be using in them.
Although IMR batteries are relatively safe under normal conditions, there are certain conditions that can arise that will make them unstable. If not treated in the correct way they can even, vent gases under extreme stress. But should stop when those stresses are no longer present. Other types of battery are no longer recommended for use in mods ICR batteries have a protection circuit built in because they are more unstable under stress and these are the type that may have a thermal runaway reaction if the protection circuit was to fail.(Not likely when using IMR Batteries).
Why does this happen?
There are a number of reasons this can happen
1. Edited out : Reason not accurate information. The other 2 reasons are accurate and relevant.
2. Shorting out. If a battery shorts out it will start to discharge its power at a rate that it won’t be able to sustain. If this continues for any length of time then it will go into a state called 'Thermal runaway'. When this happens the battery heats under the extra stress up to a point where it will ignite the chemicals contained within it. At this point all you can do is stand well back. The result will be either the battery burns out, or explodes due to the pressure of the burning chemicals contained within the battery.
Usually if your coil was shorting out and you press the fire button, the section of wire that was creating the short would instantly heat up and melt, and once this had happened, the circuit would be broken and all would be ok. But if that piece of melted wire was to fuse itself between the positive and negative contacts, the battery would continue to discharge all the time the fire button was held down. This would cause the battery discharge and heat up very quickly until it became unstable, and we are back to what could happen, as mentioned above.
In a VV/VW device the battery will not fire if a short is detected.
3. Not knowing the resistance of your coil can be hazardous due to the higher current (amps), required when using low resistances in your coil. If you exceed the safe limits of your battery, again the battery will be discharging to fast and the longer you do this the more it will overheat and it will start to become unstable again.
In a VV/VW device you will not be allowed to fire a coil if the resistance is to low, or the current to high, for the device.
All this is not meant to put you off, it is just to make you aware that some precautions need to be taken when using a mech.
Knowledge of your batteries limits is a must.
Here is a useful video that discusses Mod use and safety.
Below are some links to some guides and accessories that will help you get on the road to owning that mech
There are some accessories that can improve safety when using a Mech. ' Kicker's ' can be added that will detect a 'hard short' in the mod, shutting the mod down. vape safe fuse, and a 'hot spring' is designed to collapse if the battery starts to overheat dangerously. Hot Spring
A guide to Batteries can be found here. battery guide Also a little look into Ohms law wouldn’t hurt, That and a full explanation of volts, watts, and resistance can be found as part of my VV/VW guide. VV/VW for beginners
If you don’t know Ohms law there is a link so you can easily work out how many amps your pushing. Steam Engine Calculator
Also a resistance meter, or some way of measuring the resistance will be needed resistance meter, and a pocket 510 voltage checker of which some do both is a good idea to measure and keep track of your batteries voltage. 510 voltage checker
Safe vaping everyone. 
Part 2: Making a coil to suit.
Now we have covered the safety side of things we can look at how to set up a mech so we get a vape that we are happy with.
As a mech has no regulation of voltage, we have to rely on the resistance of the coil to regulate the power, and allow for a drop in power as the voltage of the battery drops.
As an example if we liked to vape clearo at 12W on a vv/vw mod, then we need to have a coil at the right resistance to get the same from a mech.
Using Ohms law or steamengine we can work out what resistace coil we need to make.
If we use a 1.4 Ohm coil we will use 12.6W on a fresh 4.2V battery, which is pretty close to what was being used on the vv/vw mod.
If we look at how the voltage dropping will effect the power being used we can see that by the time the battery gets to 3.5V our power has dropped to 8.75W
This 'window' between 4.2 and 3.5 is what we have to play with before needing to change the battery over. We could change over earlier if we wanted but it would mean doing more battery swapping throughout the day.
If we bring that resistance down a bit we could get a better vape when the batteries voltage started to drop.
By making a 1.25 Ohm coil we would use 14W at 4.2V and this would drop to just under 10W at 3.5V and our 12W would be at 3.9V.
As long as you weren't getting a burnt taste or dry hit at 14W then setting up your clearo or RBA like this would give a better vape during the window between 4.2V and 3.5V.
Many who use kayfuns , taifuns , foggers ect, vape at higher power and will tailor the coil to deliver that power.
Making coils from .9 Ohm down to .5 Ohm or lower is not uncommon.
This is where using a mech has its advantages as the only thing that limits what you can do is the safe Amp limit of the battery you use.
