Jim Miller wrote:
>OK, this is probably off topic, but seems it has been carried right up
>to this question. Sorry if not. Just tell me where to go. I've been
>told before so I know the way.
>I can't imagine a "normal" hammer drill (I have a Milwaukee) working
>very well at all for installing ground rods. Not nearly enough
>"hammering" (pretty miserable, actually) and can't turn off the rotation.
>WHAT is the difference with the SDS drills besides the type of "Chuck"
>Does it have a mode where it only hammers?
>Does it do a better job of hammering?
>What is the big deal with SDS anyway?
Right... sorry this has turned out so long, but I didn't have the time
to make it shorter :-)
Every home handyman probably has a compact electric drill with a keyed
chuck, and an optional "hammer" action which makes it much better for
drilling brick or concrete. The hammer action is produced by a rotating
ridged plate... but if you think about it, this mechanism is wasting a
lot of impact energy by moving the whole chuck, which has much more mass
than the drill bit. Also, the ridged plate produces more of a vibration
than a true hammer-blow.
Way up-market are the large industrial electric breaker/drills that have
a powerful hammer action and also can rotate. The hammer action in these
tools is quite different. It is actually electro-pneumatic: the electric
motor drives an air cylinder, which propels a striker like a captive
bullet. The striker delivers a very sharp hammer-blow directly onto the
end of the drill bit - and that's what makes these drills so effective
at hammering and breaking.
To avoid wasting impact energy in the chuck, the drill bit must be free
to slide, so the impact goes right on through to the sharp end of the
drill. That is why all these big hammers use some kind of splined or hex
chuck with a snap lock. Unless it's rotating, the chuck doesn't move at
There was an obvious gap in the market between these two classes of
tools. Into that gap came the Bosch SDS system. This puts the best
features of the big electro-pneumatic breaker/drills into a compact
one-hand power tool.
The system you see in compact drills is "SDS Plus" (often called just
"SDS"; SDS Max is its big brother, used in the heavier breaker/drills).
SDS+ has a splined chuck that takes bits with about a 3/8in shank, and
inside is the genuine pneumatic "captive bullet" striker system.
The difference from the old-style "hammer" drill is unbelievable! You
really do have to try it to know, because you just don't expect that
kind of drilling power from a tool you can pick up in one hand.
Spiral drill bits are available in a wide range of sizes and lengths,
out to 1.0 metres which are very good for making pilot holes for ground
rods. The surprising thing is that the SDS+ system delivers a very
effective hammer action down to the tip, even from such a long distance.
SDS+ started out with Bosch in Germany, who creamed off the market for a
few years and then started to license the technology to other
manufacturers. In Europe there is now a very wide choice of models,
broadly classified by weight. Drills in the "2kg" (5-pound) class are
one-handed, in-line, pistol-grip and look like a slightly stretched
normal electric drill. The "4kg" (10-pound) class are two-handed, with
the motor at right-angles to the drill bit.
Both weight classes have exactly the same SDS+ mechanism. The dead
weight of the drill has very little effect on the hammer action so most
people prefer the lighter drill. SDS+ is the one you'd want to own for
yourself and use regularly. For the times when you need a more powerful
hammer action, then by all means rent a big industrial breaker/drill...
but don't underestimate what SDS+ can do until you've tried it. (We live
on rock here, but I haven't needed a biggie yet.)
SDS+ seems to have been available in the USA for a long time, but well
hidden in the general fog of confusion about "hammers". The key feature
to look for is the 3/8in snap-lock chuck - if it doesn't have that, it
isn't any kind of SDS.
You are now beginning to see some real competition in the USA from Far
Eastern own-brand imports driving the prices down... but there are some
real dogs out there, which have the SDS+ mechanism but may be lacking
important features like hammer stop, rotation stop, good speed control
and a safety clutch. Watch out for dumping of models that haven't sold
well in Europe.
For the rest of the story about choosing an SDS+ drill, see:
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
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