Different torque ratings on impact drivers?

[Bucko]

I am wondering if anyone knows why the torque rating between the DC820, DC823 and DC825 are different? They seem to be the same driver with different fastener heads on them. I can understand that perhaps a 1/4" hex would not be able to handle the same amount of torque as a 1/2" square but I wonder what is going on inside that make less torque? Is it just limiting the amount of power the battery delivers to the motor? Will a battery last longer in a DC825 than in a DC820?

[kjones]

They are different because of the amount of surface area that contacts the sides of the socket.  As funny as it sounds, the more direct contact there is, the more efficiently the energy is transferred from tool to socket.

[Bucko]

Thanks for responding. So if I understand you correctly, the motor/transmission are not putting out any more torque but because of the efficiency of the interface, the fastener receives more torque? Sort of like how a manual transmission car can put more torque to the wheels than an automatic with the same engine.

[kanxrus]

There is no transmission in the Impact wrenches/drivers. You can adjust the in-lbs by making the anvil heavier/lighter. If you saw a difference in RPM's, you know their was a gear down. However, all the drivers in question have the same RPM's at 2400.

[kjones]

It is based on the size of the collet (in the case of the impact driver) or the male socket end.  The greater direct surface contact between the male end on the tool, contacting the socket itself, increases the torque.  I asked this same question to our product guys a couple of months back, and they had to explain it to me.  This is illustrated when you look at the impact driver (1/4in hex universal collet), which runs at the same RPM and IPM as the 3/8in and 1/2in, yet the 3/8in has more torque than the driver, and the 1/2in has more than the other two.  

Hope that this makes sense.  Essentially, each of the tools is exactly the same, until you get to the nose piece.  The increase in torque comes from less energy being dissipated through more direct contact between tool and accessory.

[kanxrus]

Well that certainly makes sense, I would think you could also increase the torque by increasing the weight of the anvil, possibly even changing out the spring. However, increasing/decreasing surface contact makes sense as well.

[Bucko]

You guys ROCK! Thanks for the info.