Variable Speed trigger for DeWalt DW292 electric Impact wrench

Hi to Everyone, I am from India & my problem with  Dewalt DW292 electric Impact Wrench 220V 7.5 Amp 710Watts which is having FIX Speed trigger but i want to vary the speed , i tried it through electric fan regulator but it failed to vary the speed 
Please suggest me some idea , THANK in ADVANCE

I claim the usual trick for varying the speed of a universal motor, is a circuit with a TRIAC, that only gets turned on for a fraction of each half-cycle of the AC waveform.

Moreover, I claim that TRIAC circuit is the same circuit used in TRIAC based lamp dimmers, and it is possible to use a use a lamp dimmer to sort of "throttle" mains power to universal motor.

I have actually tried this, using a lamp dimmer to control the speed of the motor in a "shop-vac" style vacuum cleaner, and also an electric kitchen mixer. By the way, these experiments I have done, were done with 120 VAC mains power, and a lamp dimmer and loads rated for the same.

I am naively assuming that lamp dimmers made for 220 VAC, and rated for power greater than 710 watts, or however much power the load uses, can be found in India.

The only thing that has me worried a little bit, is you say already tried something similar; i.e.

"i tried it through electric fan regulator but it failed to vary the speed"

However, I do not have a good mental picture of this "electric fan regulator", of what that is.

Perhaps it is not the same thing as this TRIAC based lamp dimmer I am thinking of.

If it is the same thing, well, obviously it would be dumb for me to recommend you try something you already tried.

By the way, similar chatter on this topic can be found by asking your favorite search engine to tell you more about, "how variable speed drill works triac universal motor",