a few years ago I stopped using impact drivers for the most part because they're just too darn
loud but I've come to realize they've got one big advantage over driving screws with a drill
and that's that they are much less likely to cam out camo is when the bit jumps over the screw this
happens especially if the bit is not perfectly aligned with a screw but with an impact driver
it almost never happened even with poor lighting so why don't impact drivers came out as much I
used to think it was that one day hammer torque wise they also have her for it a little bit and
I mentioned that in a YouTube video and lots of people corrected me in the comments so I thought
I'd do some experiments so I got a chunk of wood on this bit to keep it from turning in a figure if
it hammers forward as it ratchets it should leave some marks in the steel bar well this was slightly
unexpected it does leave a mark and for comparison this is the same bit leaving a mark when it's just
spun in a drill so the mark from the impact driver is actually much more substantial so
now I'm at a loss does the impact driver hammer the bit forward or does it not do that if the
impact driver does hammer forward a little bit it should be able to drive in and nail a bit further
so it appears not to be able to drive this nail in at all
and it's really not that hard to drive this new
it's pretty hard to test this because as this impact driver ratchets it's pretty hard to keep
the screwdriver bit on top of the nail so I added this block here to help you line it up and then of
course also the bit eventually rips loose in the hole okay that wasn't actually the point of this
video but it appears at least that the DeWalt hammers forward enough to drive in this small
nail these two not so much so while hammering forward certainly helps to prevent camo'd the
point that I wanted to make was that hammering four it isn't actually necessary to prevent cam
out so what causes cam out mostly I get it if I'm driving with a drill and the bit is
not perfectly aligned with a screw which happens sometimes if there just isn't enough room with
it and to demonstrate that I've made a model of a Robertson or a square drive screw and
the screw driver bit and notice that these are actually slightly tapered these square drive or
Robertson screws are always tapered a little bit so here's my screw and here's the bit and if I am
a little bit off-center as I'm driving it seen from the screws point of view it's as though I
keep going around and around like this and if I do that under steady apply torque what happens
even if I keep pushing down on it is it keeps climbing out and here's an even simpler model
of just a flat stick in a slightly tapered slot so as I apply a torque to this and rock it back
and forth it has a tendency to work its way out because it's always easier to slide where the
slot gets wider and every time it slides this way then it slides on the back slides on the
front slides on the back and it works its way up of course I don't want that bit to work its way
out as I'm screwing so I'm always ramming this down as hard as I can but it still happens and
that's because the torque is applied over such a small area that the forces pushing against the
side of the hole here are so much bigger than me pushing down on it so the bit still works
its way out so how does the impact driver prevent that even if it's not hammering the bit into the
screw as it goes well it's quite simple actually because it's just a matter of intimate and torque
so imagine this thing works its way up a bit and then I go on the torque it just drops back in and
the impact driver with it's hammering action has a lot of torque followed by no torque followed
by a lot of torque so as this thing works its way out it's constantly letting it drop back in
and this is also why I don't see as much cam out if you're using a regular screwdriver like this
because as you reposition your hand you're always letting off on the torque and that allows it to
set itself back into the screw and I've had more frustrating cam outs with these Robertson screws
or square Drive screws that I've had with Phillips screws even though these screws are in many ways
superior they the screw just really sticks on there and I think the reason for that is the
effective width of this bit is actually quite narrow compared to say this Phillips here and
that means that the forces the sideways forces on the inside of the screw head here are much greater
which means there's more force effectively helping to pushed a bit out then there is with a wider bit
on here so there I am criticizing Robertson screws even though I'm Canadian and endorsing
Dewalt even though I don't like them all that much I wish they'd at least paid me money to do this