At 02:21 PM 8/21/2013, veegee wrote: >Note: hammer drills are different from rotary hammers. Hammer drills >have a generally weaker metal-on-metal hammering mechanism. Rotary >hammers are generally much more powerful, easier to use, and have a >gas-cylinder-piston hammering mechanism. They can be run in hammer mode, >drill mode, and both - which is probably critical for drilling a hole >that size. Around here, we call the cheapo hammer drills "percussion drills" to=20 differentiate them from rotary hammer drills. Its pretty easy to see=20 which type the drill is from the name plate on the drill - percussion=20 drills are rated in how many BPM (blows per minute) they have=20 (usually high hundreds to low thousands). They give off a=20 high-pitched grinding sound while operating. The rotary hammer drills have a much lower operating frequency and=20 are *much* more powerful. I have both types - my first hammer drill was a percussion drill made=20 by Walter / Metabo and I still have it today. My most recent battery=20 drills (Dewalt & Milwakee) are also percussion drills. My rotary hammer drills are big and heavy. The oldest (AEG something=20 or other) is about 35 years old and weighs at least 20 pounds, the=20 newer Chinese clone is about 10 pounds. I tend to use the newer,=20 lighter drill these days - most of the holes I'm drilling are fairly=20 small. But I'll grab the big unit whenever I have to punch a hole=20 for electrical conduit through 12 or more inches of concrete. Its kinda cool - the big rotary hammer drill uses a pneumatic slide=20 hammer / piston and it takes a few seconds of operation for the=20 hammer piston to synchronize with the driving piston. I describe it=20 as the drill riding on an "air cushion". The drill essentially pumps=20 up and actually lifts itself / pushes away from the drill bit. The=20 most effective drilling operation occurs when the drill is riding on=20 the air cushion. The drilling effectiveness decreases dramatically=20 if you push too hard and force the drill to the bottom of the air cushion. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .