Replies

1. 
   Lateapex911 | Dec 24, 2003 04:00am | #1

   I'll take a shot at a basic definition. A hammer drill, rotates but the bit actually hammers it's way down. The mechanism is, I believe, mechanical.

   A rotary hammer is a more serious version. Go to Boschtools.com for a description of the technology.  The Bosch unit I just picked up has a switch that allows it to change between three modes: Rotation, rotation with hammering, and hammering only. So, it could be uded to just drill, to drill in hard materials, or, with chisel bits, to act as a jack hammer.

   Impact drivers have a mechanism that adds a ton of torque to the rotation in an impact mode. The impact force is rotational, (around the drivers axis) while a hammer drills impact force is logitudinal with the drill bit, (along the drivers axis).

   I think hammer drills are lighter units for lighter work, esp. on a ladder.  Serious concrete drilling is the rotary hammers forte', and the impact driver is great to tighten up the nuts on the anchors you just installed in the holes you used the rotary hammer to drill.   (There's a good case for having all three!)

   I hope you can make some sense of this!

   Jake Gulick

   [email protected]

   CarriageHouse Design

   Black Rock, CT

2. 
   clwebb | Dec 30, 2003 03:19am | #2

   I'll Throw in my two cents. Lateapex911 is right and maybe I can help clarify things.

   Hammerdrills are usually a two speed half inch drill with the addition of a gear in the transmission which when in the hammerdrill mode causes the shaft and chuck two bump up and down as the drill rotates on the gear which causes the impact action on the drill bit itself. Hammer drills are limited in the distance that the bit can move because of the way it is made.

   Rotary hammers come in three basic forms sds plus, sdsmax, and the biggest is spline drive. Rotary hammers work totally differently then hammerdrills to some extent you can improve the efficiency of a hammerdrill by leaning on it harder. Because of the way they are made rotary hammers lose their effectiveness when leaned on. Just use enough pressure to keep the bit on target.

   Rotary hammers have a tube in the drill in line with the end of the bit. A piston driven by air from the motor travels back and forth in the tube striking the end of the bit and driving it forward. when the bit has traveled all the way forward the piston travels back and creates a suction which pulls the bit back, and all of this happens very fast while the drill rotates and on some models the operator has a choice of rotation and hammer, rotation only, or hammer only. The end of a rotary hammer bit looks totally different then a regular masonry drill bit. (So they will not fit a traditional hammer drill,) they have a setup of grooves and keyways that allow the bit to still turn with good torque and have maximum travel back and forth. Actually that is what sds stands for Slot Detent System. Sds plus bits won't work in sds max or spline drive hammers without an adapter. Sds plus or max is pretty affordable for many do it yourselfers, but spline drive hammers which have splines on the end of the bit can run into the triple digits to purchase the bits.

   Impact drivers use a quarter inch hex drive mechanism instead of a three jaw chuck. Unlike most cordless drills impact drivers do not have a clutch to regulate torque. They typically turn at a higher rpm than cordless drills and because of their design have lots more torque thatn a cordless drill of the same voltage.

   Impact drivers have a couple of steel anvils on the actual shaft and a large hammer mechanism regulated by a large spring, the  hammer hits these anvils as you use the tool which in turn increases the torque in the direction of rotation. The tool acts like a regular drill driver until the torque increases to the point That the spring is overidden and the hammer kicks in  unlike hammerdrills or rotary hammers, impact drivers apply their force in line with the rotation of the drill hammerdrills and rotary hammers apply their force perpendicular to the rotation of the tool. Impact drivers are typically lighter torqier, smaller, louder because of the impact mechanism, and more expensive than cordless drills. You can also purchase a three jaw chuck for impact drivers, and you can also purchase an impact driver that accepts sockets instead of bits. Hex shank drill bitds are available also for impact or "rattle guns".

   I hope I haven't confused you and I hope this helps.

   Used to sell tools.

   Chris  

1. 
   SBerruezo | Dec 30, 2003 05:10am | #3

   So if my understanding is correct, the impact drivers will provide force with the rotation of the bit. 

   The Hammerdrill has a gear that makes the entire chuck, with bit included, move up and down?

   Rotary hammers uses a form of pneumatics to force the bit up and down?

   What about the little rotary hammers? I thought I saw them offered by Makita and Bosch...Maybe they were hammer drills, and the owner didn't know better.

1. 
   clwebb | Dec 30, 2003 11:01pm | #4

   That's right,

   Most makers make different sizes of rotary hammers, some are small with a pistol grip, or a dhandle grip. Most of the larger ones have the motor mounted vertically which makes them a little more comfortable to use and gives them a shorter length.

   Another advantage with rotary hammers is that the bits last alot longer.

   Hope this helps.

   Chris

1. 
   kostello | Jan 02, 2004 08:59pm | #5

   "Another advantage with rotary hammers is that the bits last alot longer"

   don't i know it!!

   when i got my SDS drill about 6 years ago i ordered 10 of each drill size upto about 3/8"

   still not half way through them

1. 
   mitch | Jan 02, 2004 10:44pm | #6

   thanks for all that.  i'm more than a little bit of an "implement prostitute" and love learning more about them.  had never heard that rotary hammers' impact drive mechanism was typically pneumatic or what "SDS" stood for (always thought it was just a difference in chuck type and duty rating).  also interesting to know about the relative effect of pushing on regular hammer drills vs. rotary hammers.  keep 'em coming.

   m

2. 
   clwebb | Jan 05, 2004 07:45am | #8

   No problem,

   I have learned a few things over the years. Actually that is one of my favorite "tool topics". There was a good article in FHB a couple of years ago on the difference between rotary hammers and demolition hammers. And one a while back on impact drivers, sorry I don't have the reference numbers. That is one tool I will never be without is a rotary hammer. Sometimes though they can give you some trouble mainly in cocncrete block, like with tapcons. Because rotary hammers are more powerful than hammerdrills, sometimes tapcons won't hold as well, so I usually give myself some options in size when I drill a hole. For example if I am going to mount an electrical box I will usually start with the smaller 5/16 anchor then if it doesn't hold I will go to the 1/4" or if I drill a hole for a 1-1/4" anchor if it doesn't hold as well I go to a longer one.

   Yeah it makes my teeth hurt to see someone with a rotary hammer and they're just a leanin on it. Because you can feel and hear a difference in the tool when you have the right pressure on it.

   Hope this helps, I don't know it all and I am constantly amazed at the wealth of knowledge and experience passed along on this site.

   Chris

2. 
   rasconc | Jan 03, 2004 03:02am | #7

   On the impact drivers the impact helps in rotation only, it does not impact inline with the bit as hammer drills and rotary hammers do.  The last two do sort of like the old stardrills with a hammer.