Impact Driver Torque Question

[buckeye95]

All,

I currently own a Milwaukee 14.4 V 3/8 " impact driver rated for 1050 in-lbs of torque. While doing a little research into swapping out the head for the 1/4" hex drive head found on another one of their 14.4 impact drivers, I noticed something interesting while reviewing the Milwaukee parts diagrams.

Milwaukee makes three 14.4 impact drivers:

- 1/4" hex drive rated for 740 in-lbs.
- 3/8" square drive rated for 1050 in-lbs.
- 1/2" square drive rated for 1400 in-lbs.

Reviewing the parts diagrams for each of these, I noted that all share the same motor and same impacting mechanism (spring and "hammer" assembly). I thought it was strange that three impact drivers with the same battery, motor, and impact mechanism would have torque ratings varying from 740 to 1400 in-lbs, so I called Milwaukee CS and asked them.

They stated that the different torque ratings come about due to the different anvil sizes on the heads (the 1/2" anvil is slightly larger than the 3/8" anvil, etc.) This did not make much sense to me, but they said they "confirmed it with engineering". Now, granted the 1/2" anvil is slightly larger than the 3/8" on the parts diagram, but I find it hard to believe this part difference alone yields an additional 350 in-lbs. of torque between the 3/8" and 1/2" anvils, with all of the other parts of the impacting "drivetrain" being the same. I wonder the some thing about the purported 300 in-lb difference between the 1/4" hex and 3/8" square drives as well.

Does this seem to make sense ? The engineer in me doesn't quite believe this, but maybe it's just because I don't know enough about how impact drivers work. If anyone has any insight, I would appreciate any imput.

Regards,

Pete

[onedash]

never even used an impact driver but here is my WAG.
if im holding a hammer in between two boards and it can only travel X inches up and down i would get more power with a bigger hammer assuming the space doesnt change and its always me swinging it.

what do you think?

[LCHIEN]

I'm sure it was designed this way to limit it. Just because something can put out 1400 in-lbs doesn't mean you want to put out 1400 in-lbs.
I'm sure they limited it because common sense says that using smaller 1/4" drives peiple will be using smaller sockets and fasteners, and they don't want to be twisting them off all the time. So they set the torque limit to match the typical range of the fasteners for that size drive.
As a side benefit you probably get longer battery operation with the smaller sizes, as well.

And yes, its probably easy to change the torque by small changes in the geometry of the anvil.

[Jim Frye]

plausible...

Given the number of blows per minute (my 18 volt Ryobi P230 is rated at 3,000 bpm), it should not take much difference in the mass of the hammer mechanisim to change the torque ratings.

[DUD]

When I was with Snap-On Tools many years ago. I learned to repair air and some electric tools. Many of the insides of air tools were the same until you got to the anvil which has the fitting on the end for the socket. I never did ask any questions, I just fixed them. Bill

[Andrew Benedetto]

I have 2 Makita(older Japan manuf)12v,2 Ryobi 18v,Ridgid 12v angle, and a Milwaulkee beast,1/2" drive, 18v(kicks butt on truck lug nuts that a DeWalt corded would not budge @ 160'lbs.
I was going to buy a 14.4 Milwaulkee since I have many of their cordless tools but the motor does not have replaceable brushes,have to replace the entire motor,made in Taiwain(better than China but ,my red tools are either USA or Germany)from a service ctr. info., and is over priced. In the smaller sizes, the Makita is the leader,IMHO.

The Ryobi is a deal but basically disposable if it fails, the Makita, super esp. on the control/weight/balance,unlike DeWalt's version. The 18v 1/2" Mil. is a beast in weight and build and power. That is for heavy work.
If you look at the 14.4v, go Makita,Ryobi for best bang for the buck. All can drive WW fastners to the breaking point on any of them. I never use a drill driver for any fastening now.

[just4funsies]

The action of an impact driver is more about mass and momentum than about tool horsepower. A mosquito at 30 mph won't make as big a dent in a wall as a Buick moving at the same speed. All that is necessary for EITHER is a motor big enough to get the hammer IN MOTION (it may take more time or distance to do this with a larger hammer than a small one, but the payback is in the extra force stored in the hammer with the larger mass).

See? I just KNEW that the college physics I took 35 years ago would pay back BIGTIME if I just waited long enough!