Rotary Hammer Sizes

[Cheng Liu]

I am wondering why SDS rotary hammers are rated for different sizes i.e. 1/2", 3/4", 7/8", 1".... Aren't all SDS bit shanks the same diameter?

[DR99]

That's the hole size they are recommended to drill most of the time.

[jeffmcmillan]

Because the impact energy is distributed over the diameter of the bit tip there's a sort of cutoff after which the hammer action effectiveness drops off rapidly and the hit pattern becomes ineffective.  Rather than try to communicate all those properties and leave it up to buyers to figure out they just give a max hole size rating.

[A_Milwaukee_Engineer]

That's the hole size they are recommended to drill most of the time.

 

As Jeff said, it's the maximum hole diameter you should use the tool for.  Can the tool drill the hole?  Yes.  Is it the speed you'd be satisfied with for frequent use?  Probably not.  For the usual size, divide the max rating by 2 and add 1/8" or 1/4".  Usually gets you pretty close.  

 

If you were drilling 1" holes all day, you wouldn't want to be using SDS.  SDS-Max would be more appropriate (with 1-1/2"+ max rating).

 

SDS or SDS+ or SDS-Plus are all the same thing with a common shank size.  SDS-Max is a different, larger shank size.