An interesting comment by e57 prompted me to start this thread. "A hammer drill, by design, will self-destruct".
I've been using hammer drills for about 20 years now, usually for 1/4" holes in concrete to mount electrical boxes or supports. Then I got on some commercial jobs and started drilling holes in cement block for 1/2" or 3/4" emt. I also started trashing hammer drills.
Thanks to the posts of the more experienced tradesman here at ECN I came to the realization that hammer drills are good for drilling 1/4" holes. It may be a 1/2" drill, but if you want it in your truck instead of in the garbage can you'll use the 1/2" chuck for 1/2" high-speed steel bits, not for masonry bits...especially 1" masonry bits.
For holes over 1/4" you need a rotary hammer. I just happened to have one on the truck. I used it for 3 years as a light-weight chiseling machine, but then it seeped into my brain...ROTARY hammer..."Hey, I'll try a masonry bit in this thing". I couldn't believe the difference.
Now I even use it for 1/4" holes. I opened up one of my broken hammer drills...an $89 Makita...and there isn't much there for the hammer action.
I just got a new Bosch bulldog about three weeks ago for about $220 and it is one of the best investments I have made in a while. I purchased a slew of bits and chisels with it and I am extremely please with it, it made me feel silly for loading a 1" concrete bit into my cordless. Last week I drilled a 3/4" x 2' hole in some solid blocks then changed out to a chisel to open up the block above the ceiling, it couldn't have gone better.
I use a DeWalt SDS hammer. Give you a hint ... never loan it to a rookie to use as a chisel. About the third time he chiseled in and tried to pry the chipped brick out with the chisel bit he tore the head bearings out. They sure are expensive to fix.
I guess it is time I elaborated on "A hammer drill, by design, will self-destruct". This is especially true for light-wieght designs. And even well made hammer-drills will not last for-ever, especially if not properly used. Many people just abuse them, or use them far past thier abilities, or design. Using cheap, or dull bits, is a common no-no. And even though they make a 3/4" masonary bit (intended for soft brick) that will fit in a 1/4" chuck, I see people using them on hardend concrete and burning through rebar, or should I say attempting to.
To me a cordless hammer drill is just invitation to buy more tools. Lightwieght plastic casing, or worse plastic gears with a metal piston bouncing back and forth. These drills are only barely designed for an occassional 1/4" hole. Using one all day for larger holes is tool suicide.
A Bosch Bulldog with the proper hardend and sharp bit will run all day for for 1/4 - 3/8" holes. But use a cheapo bit, or a good but over-used one, the effeciancy goes way down. You then have a drill working harder, and over-heating, especially on hardened concrete with aggregate. Stick 3/4" - 1" bit in it and you're over working it.
Now go to the Rotor hammer and put a dull 3/4" bit in it and you'll have to rest the drill before the thermals kick in and it shuts off anyway. A good bit allowing the drill to do the work and you're done before you know it. Put a ground rod driver on it in aggregate soil, and you're done. Try driving it through serpantine bedrock like I occasionally must do, and you'll be spending another $600 soon, not to mention wasting a whole day, where a slide hammer or demo hammer would have done the jobe much faster. They also make huge bits that will fit these beasts. I have seen people use 2" bits and try to go throgh 2' of concrete, nearly breaking their arms when they hit the rebar, yet power through it, and take all day doing it. Me, I call a proffessional to do that job, and often will have core drilling NIC. This guy shows up mounts his diamond wet core drill, he's done in a half an hour. I pay him $250, to do what I foolishly would have attempted all day at low - mid jouneyman wage ($25 - $30 x 8) for a guy to risk getting hit in the face with a drill, go on Comp' and have a burned out tool, and a worn out bit. If the hole is crooked, the core saw guy will "staighten it" for free. ( I figure it's a bargain!) My guys on a rotor hammer are not cheap!
Anyway, that is my speal on hammer-drills. And, yes, I have thought about going into the core saw buisiness! Add that to GPR (Ground Penitrating Radar), and you have a money maker!
Mark Heller "Well - I oughta....." -Jackie Gleason
OK it has been one whole day since my speal on cordless hammer drills. And guess what? I bought one! Now, you're gonna say that's screwy!!!!!!!!!!!!1
Well, I tell you why I did. A guy comes into work today with brand new Dewalt impact driver today, and says "Yeah, I got a great deal....... $229.00 for an inpact driver and a HAMMER DRILL, 2 batteries and a big bag for them both." $229.00 you say? That's the price of the impact driver alone. Yep! They're on sale at Home Destructo! Really?
So yeah, after work today, I went and got an impact driver, and a spare (hammer) drill, you know, for around the house. Will I use it as a hammer drill, probhably not.
Mark Heller "Well - I oughta....." -Jackie Gleason
Dave, you're right. I've learned that a 'hammer drill' ought to be limited to small holes; for the larger ones I use carbide core bits (hole saws). Fine Homebuilding ran a good piece detailing the differences between a 'hammer drill' and 'roto hammer.' The Harbor Freight roto-hammer has served me well- and, now that I have a 'real' truck, I can carry it with me all the time.
As I accumulate more, specialised tools, I do find that the basic ones last longer,as they are 'pushed' or 'made to work' less.