Puzzled over the claimed torque of impact drivers.
I have battery & mains Makita impact drivers, both claiming torque of 130 + Nm. Both certainly punch in screws & coach bolts with ease, much better than a drill driver.
Two examples lately where they failed to cut the mustard. Inserting 140mm x
6 mm multi monti's into brick (correct size pilot, clearance & depth of hole) where the impact driver simply stopped leaving an inch of the fixing protruding.
Another where a customer had used some 300mm timber connectors on railway sleepers & his drill driver left several inches protruding. Tried the impact driver which still wouldn't drive them completely flush.
In both cases I used a chuck adaptor in a mains SDS & drove the fixings right in. No torque figures for the mains SDS, a 600w green Bosch with a clutch, but I'm certain it wouldn't be 130 + Nm.
What's going on here? Is there 'torque' & 'torque'? Is it something to do with Clarkson?
To me an impact briver is a thing about the size of a half pint milk bottle with a bit on the front that you bash with a hammer to loosen the screw/bolt attached.
I'd guess not. Assuming it's running at 150 rpm, to deliver 130 Nm of torque would need 2.74 horsepower And there are 746 watts per horsepower - but only with a 100% efficient motor. Your drill is likely a true 3/4 HP.
"Finally there are some (relatively rare) situations where in spite of their significantly higher torque, they will be unable to move a fixing that a conventional drill driver will move. This only happens when the fixing you are trying to turn is quite elastic and able to absorb the full moment of the rotational impact, without the end already driven into the wood turning. Moving this type of stuck fixing requires continuous torque to "wind up" the fixing and absorb the backlash."
That's 'cos you are an Old Fart. I have one of those too and am, too, an OF. The world has moved on, and impact driver means a nasty noisy thing that tries to make up for lack of clout by rattling a lot (I don't have one of those).
Impact drivers don't have "torque" as a useful figure, because they're dynamic rather than a static torque.
A torque wrench (i.e. simple lever and weight) applies a constant static torque, a petrol engine might vary its torque a little as it rotates between strokes (esp. 2-strokes). An impact driver though delivers all of its torque in a single blow (or series of separate blows) and the actual torque at a moment in time varies through a curve that increases sharply with impact then tapers off. It's the difference between pushing a hammer head against a nail, or swinging it. The total energy might be the same, but delivering it over a short time interval gives a far higher peak figure for force (or torque). You still care mostly about the impulse delivered (i.e. the integral) rather than the peak force, but the "gimmick" of an impact driver is that this short pulse allows high instant forces to help unstick things.
Really though, to measure the "grunt" of an impact driver you have to measure the integral of this torque over time (i.e. the area under the curve). Even then there's likely to need to be some scaling for perfect realism, as higher torque is "better" in a non-linear fashion for unsticking rusted bolts (maybe consider the integral of the square of the torque?). The integral though is likely to be closely proportional to motor power and battery power consumption, although obviously reduced by the efficiency rating.
If you're in marketing though, the ability to lie through numbers comes in. Rather than taking a sensible "grunt" rating, the temptation is to find any number that's best on your brand regardless of its true value. Peak instantaneous torque is an obvious candidate. Now if this is _too_ high, it's likely to be "real" and "measureable" but it also wastes too much power and integral grunt in short-term bending of the socket and drive etc., rather than anything you can use.
Agreed, however there is more to it than just total "grunt" - it also matters how its delivered. Using your own example, hitting a nail with a hammer will be far more effective than simply doing the same amount of mechanical work pushing it against the nail.
Indeed, and you can see this in the circumstance that Dave mentioned above - an elastic fastening that can simply absorb the rotational impact and then spring back, without actually turning.
Remove the screw and dip in grease. Then use grease on them all after. With an Impact Driver just let the hammer work. The screw may not be turning but the hammer is still smacking the screw. I have had it where the screw then starts to to turn after I kept the driver on for a minute or so.
SDS's on low speed are great and will drive almost anything in.
I was using "grunt" to indicate an exactly proportional measure of benefit. How you map measurable torque and time onto this invented "grunt" is quite another question 8-)
(According to Russell Crowe though, "grunt" is measured in feet)
one thing the FAQ does not point out (unless I missed it) is that an impact driver can deliver a higher torque to the bolt (or whatever) than could normally be sustained by the operatives wrist. this is becuase of the inertia of the tool; the operative feels the (lower) average torque rather than the peak torque.
Many SDS drills have their gearing set such that their top speed is in the 900 - 1200 rpm range. That tends to be somewhat lower than ordinary single speed drills, and closer to the low gear on a two speed gearbox drill.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.