? on Impact Drivers

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  #1  
Old 01-06-05, 09:30 AM
ejmeier
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? on Impact Drivers

First of all, what are they?

No seriously, they look to be just a specialized drill that uses a quick-connect coupling. (I am thinking of the ones with the 1/4" coupler on the end.) They seem to put out a ton of torque for their size.

Sorry for the stupid questions, but I just can't figure theses things out.... They have a given "bpm" rating - so how do they really differ from hammer drills? Is it true that they can "melt" screws into wood? Couldn't a hammer drill do the same? (I know they are for drilling into concrete, but they also have "blows" too....)

Also, I was trying out some square drive screws (I love 'em!) and I forgot to tighten up the bit in the drill (just a regular 18v cordless) and the square recess fit the bit so well, that I actually pulled out the bit from the drill when I was finished driving the screw - which leads me to one other thing I was thinking - with a quick coupling on an impact driver, wouldn't the square-drive bits be always falling out??? I can't imagine building a deck (one of my intented purposes...) using a quick disconnect bit. Am I missing something here?

Thanks
 
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  #2  
Old 01-06-05, 02:58 PM
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Lots of power in a small package

I drive 3" deck screws every month with one. They are also used to assemble or disassemble metal-skinned buildings with sheetmetal screws.

The bit does NOT fall out of the chuck since it has a groove around its circumference at the base. The collar of the driver is pulled back to insert the bit. When released, a mechanism inside grabs the groove. You must pull the collar back again to release the bit.

This device is similar to a cordless impact wrench. When the screw is first started into material such as wood, penetration resistance is low, so the driver spins it in like a cordless drill with no clutch and no noise. (RPM mode)
As more of the screw threads engage, the impact hammers inside the unit kick in to transfer torque at each hammer blow. (BPM mode) The rate of driving is slower, but there is almost no transfer of torque back to your wrist (unlike what would happen with a heavy-duty corded drill).
The screw will continue to drive, limited usually by the length of the bit.
Either the screw head will countersink or break off if the trigger is not released. 1000 in. pounds is substantial in such a small package.

Because power transferred in impact mode is in short rotational blows, it is not necessary to use as much force to keep the bit sufficiently seated in the head of the screw. Stripping out the recess in the screw head is almost completely eliminated.

Several manufacturers make these units in everything up to a 24V cordless.
Most of the home centers will have at least 1 or 2 display models in case a contractor needs one, though they are quite expensive compared to ordinary cordless drill drivers.
I am told that they don't drill very well, but I cannot confirm nor deny this statement.
 
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Old 01-06-05, 03:18 PM
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Old 01-06-05, 03:56 PM
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A hammer drill isn't quite the same thing. The impacts that make a hammer drill do its thing are perpendicular to the rotation of the tool. That is what forces the bit through concrete.

The impacts of an impact driver are in the same plane as the rotation of the tool. Each impact helps the screw along without a whole bunch of excess torque. Torque is what twists your wrist with a regular heavy duty standard drill.

Yes, an impact driver will "melt" screws into wood or sheet metal. The operator will have much less fatigue as a benefit. My 12v Makita impact will out screw my 18v Milwukee drill any time.

Bits will not fall out of the quick release chuck. Some models have a pull to release collar, some are push to release. I would suggest a pull to release model. Once you try the quick release system, you will like it. Saves lots of time.

Impact drivers do not drill very well, especially when the drill size is over 1/4 inch in diameter. You must buy quality drill bits with the quick connect built in. Cheap ones have the 1/4 inch hex part swedged into place- it is not a single machined piece.

Makita makes a special chuck attachment designed for impact drivers. If your bit has any burrs on it at all, the tool will lock the chuck to the bit. If you use a Unibit with the machined flats, and the chuck jaws do not engage the flat sections, the chuck will not let go of the bit. The Makita impact driver generates enough force to break the Loctite holding the hex adapter into the chuck- I had to fix mine with JB Weld. My chuck lasted only two years until the hex adapter sheared off at the bottom of the chuck. It was destroyed while removing the Unibit I was using. The guys at the local tool emporium recommended a regular keyed chuck as a replacement, and said not to use a keyless model.

I no longer use the impact driver to drill holes over 1/8 inch.

Choose a model with a metal nose if you want it to last. The magnesium nose on my Makita did not last, and it was replaced with an aluminum one under warrantee. It developed excessive shaft play. Plastic nosed models are light duty only.

I use mine every day, and there is nothing better out there to drive screws. If I had to buy one again, I would look at the 9.6v models for what I use it for. Less weight than the 12v.
 
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Old 01-06-05, 04:49 PM
ejmeier
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Thanks guys, your responses helped a ton. The info on the coupling is good to know - I think I may be getting one of these someday.

Though, I still cannot figure out why these would not be good for drilling holes??? I guess the screw threads do the advancing and the impact wrench just uses the threads to drive it in - so maybe if there were no threads (ie - a holesaw) then the driver might behave a little goofy... not sure. Couldn't you just use a 1/2" nutdriver and then just slip a giant holesaw in the end of it? I can't understand why something like that wouldn't work???
 
  #6  
Old 01-06-05, 05:39 PM
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I think the drilling problem is related to how the anvil works in the driver. The drilling resistance makes the driver hammer more and rotate less. If the bit keeps spinning, it will drill ok, but as soon as the bit slows down, the hammering starts. When the drill bits stop spinning, they bind up and the hammering aggravates the problem.

I tried mine with a holesaw... not good. A good way to take some life out of the tool.

I also thought the impact driver would be ok for drilling a variety of holes.... it is not. Works for 1/8 inch rivet or spotting holes, that is about it.

I now have a separate 12v Makita drill for hole making... got it cheap without a battery, uses the impact driver batteries.

The impact action and rotational speed works nicely for small holes in concrete with a carbide tipped bit. I only do this for a couple of holes at a time, and not frequently.

The only drawback to the impact drivers is their noise, but I will never willingly go back to a regular drill for setting screws.
 
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Old 01-07-05, 09:24 AM
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Right tools for the job

Screw driving or nut driving - impact driver (Makita 14.4V 2.6 AH NiMH)
Concrete, brick and stone - Bosch rotary hammer (7/8") or better
Drilling holes in wood or steel - Milwaukee 1/2" drill or Hole Hawg or equivalent

A hammer drill is a good compromise across all 3 tasks:
It's a little too fast for driving screws or nuts
It's somewhat slow drillling in masonry
It's about right for holes in wood, but is a bit light for larger holes in steel.
 
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