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Light duty "precision" impact screw driver?

M

Mcgyver

Ultra Member
Merry Christmas all.

I'm looking for something that I'm not sure exists. I've got a Klein impact screw driver, you know, the type you hit with a hammer. Hitting it imparts downward force as well as torque so you don't strip those ghastly Philips screw lesser beings use in assembly :).

It's a beast, but too much so for some jobs. It takes a bit of a wallop to persuade it to do anything which can damage light assemblies.

So how do you get a very tight Philips screw of such a, light, fragile assembly. (A plastic router case in my case).

What I'd Iike is a "precision" light duty manual impact screwdriver. Something were little taps work so I don't damage the work (in other disassembly work, I've learned 100 little taps can suffice for a damaging big wack) .... or better still power version that imparts not just torque but downward force (like the manual one) so you don't strip screws.

Any ideas?

Thanks
 
All the Wera tools I have are amazing. I LOVE their small torque drivers. I'd vouch for the ones Stuart posted without hesitation. They are worth the coin.

Use a JIC bit. They bite better even on non-JIC heads.

If all else fails, drill out the remaining screw head which removes the torque tension on the screws, then remove the part, and then remove the remaining screw studs with vise grips or glued on nuts.
 
I have a theory about Philips screws, they are the work of the devil . When you encounter them, you end up cursing and with a stuck one ,you start cursing everything, soon you might even end up cursing the All Mighty. You can see where that could end up.
 
I would reach out to Wera and ask them to clarify/confirm the statement that “The pound-thru blade ensures complete power transmission (zero loss).” I can’t see how any hammer-driven driver can convert all (or even most) of the downward force into rotary force.

The application video does include an important step - before switching to the impact setting the driver should be struck a few times to help loosen a stuck screw:



For your specific application I would look at an adjustable torque impact driver like the Bosch PS21-2A:

IMG_8829.jpeg


PS21-2A on Amazon

PS21-2A Kit Page on Bosch Website

I have an older, non-adjustable version, but have added this one to my wishlist since I already have the batteries & charger.

EDITS:
1) Added link to Bosch Website
2) Found a "Renewed" version of the bare tool on Amazon (which qualifies for a 4-year protection plan)
3) I ordered it!
 
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I use an impact driver a lot. I consider them to be one of the greatest portable power tools ever invented. Right up there with the variable speed reversible drill motor, I remember the first Skil ones, what a revolution. I have found the impact driver hardly ever wears out a bit, unlike a drill motor. Of course I'm using Robertson headed .screws . On a drill motor, a slip and the bit should be tossed.

Wera has excellent warranty, unlike Knipex which has none.
 
I think I'll try Wera. I've also found them to be excellent. Spend the kids inheritance, wtf, its Christmas and I need a present lol.

For your specific application I would look at an adjustable torque impact driver like the Bosch PS21-2A:
Click to expand...

don't the power impact drivers just apply torque? The manual hammer ones keep the bit solidly in the screw (downward force of the hammer) during the instant the torque is being applied. That's the magic combination that loosens without stripping.

I've also found a lot of Bosch is the typical made in China quality.
 
Mcgyver said:
don't the power impact drivers just apply torque? The manual hammer ones keep the bit solidly in the screw (downward force of the hammer) during the instant the torque is being applied. That's the magic combination that loosens without stripping.
Click to expand...

Yes, yes, and yes! Couldnt agree more. It isn't that I don't like impact guns. I do. But loosening small screws is not a time when I would use one.

Most important is a good fit.

I have spent a small fortune on Wera and I love every Wera tool I have.
 
Mcgyver said:
I think I'll try Wera. I've also found them to be excellent. Spend the kids inheritance, wtf, its Christmas and I need a present lol.



don't the power impact drivers just apply torque?
Click to expand...
Yes, you apply "thrust" through the pistol grip.

Mcgyver said:
The manual hammer ones keep the bit solidly in the screw (downward force of the hammer) during the instant the torque is being applied. That's the magic combination that loosens without stripping.
Click to expand...
My experience with both my Craftsman 5/16" hex and GoFastInnovations 1/4" Hammer Drivers is that a significant amount of the hammer blow goes inwards, and I would hesitate to use either on a screw attaching a plastic case to a tool.

Mcgyver said:
I've also found a lot of Bosch is the typical made in China quality.
Click to expand...
While I don't use them on a daily basis, I've had my Bosch PS40-2 10.8V Impactor 1/4" Hex Driver (New?, 15+ years), PS31 12V 3/8" Drill (Renewed, 10 years), PS11 12V 3/8" Right-Angle Drill (New, 5 years) & PS50 12V Oscillating Multi-Tool (New, 15 years) with no issues. I look forward to my Renewed PS21 performing similarly.
 
I'm gunna stick my neck out more than I should here. The problem with an impact gun are many fold.

1. You cannot apply as much thrust through the handle as you can with a hammer.

2. Even if you can, the thrust time profile is not synchronized with the torque time profile.

3. The multiple rapid impacts bounce the tool around allowing for uneven screw contact.

4. The large drive forces too easily break the screw or strip the screw recess.

That's my engineering view.

Also, I don't recommend the large driver for small screws even with small bits.

I can also add practical experience. I've never successfully loosened small screws with a small impact gun. I either strip them or break them eventually. I don't use them for that anymore. Small nuts and bolts, Robertson, Allen, and Torx screws yes. Philips no.

The nice thing about a small driver is that all the forces can be closely controlled and monitored starting with very low forces applied as many times as wanted.
 
ChazzC said:
While I don't use them on a daily basis, I've had my Bosch PS40-2 10.8V Impactor 1/4" Hex Driver (New?, 15+ years), PS31 12V 3/8" Drill (Renewed, 10 years), PS11 12V 3/8" Right-Angle Drill (New, 5 years) & PS50 12V Oscillating Multi-Tool (New, 15 years) with no issues. I look forward to my Renewed PS21 performing similarly.
Click to expand...

Agreed they were a good make with a good reputation ...... then KKR bought in them 2017. You know what happens next .... hold price, surf on the brand and cut costs to the core. For these three rollers I spent about $200 + 50 to get them thinking I was getting good German quality. Instead made in China near junk. Flaking chrome, centres are way off from the OD (I needed to turn the bearing mounts down) and a hole for the pin is a mess. I fixed it, but still, that for German prices? Also sent a die grinder back two years ago because of the vibration.

Granted, its just a couple of parts .... but those are low end made in China parts at German prices and that's what firms like KKR are reputed to do. Just giving the rationale behind my negative statement about Metabo.


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_M809816-1200x800.JPG
 
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ChazzC said:
I would reach out to Wera and ask them to clarify/confirm the statement that “The pound-thru blade ensures complete power transmission (zero loss).” I can’t see how any hammer-driven driver can convert all (or even most) of the downward force into rotary force.
Click to expand...

At first, I was puzzled by your question Chazz. I'm not speaking for Wira. But I think that's not what they meant. I believe it refers to the fact that the driver column is solid. So any impact applied via the hammer is purely translated into both vertical and torsion without any losses in plastic or rubber energy absorbing materials as would occur in a regular screwdriver.

Fundamentally, such a mechanism cannot convert the hammer force into 100% torque. But it can be translated into thrust plus torque.

NOTE that 30Nm is 22 ftlbf. A Crap load for small screws. Start gentle.
 
I used to love my big impact screwdriver for working on old Japanese motorcycles previously worked on by people that never heard of JIS screwdrivers...... As you say, they work great on big stuff, but are useless on anything small. For those, I've always had good results simply tapping on the handle of a screw driver as I push down and turn. I don't have any of the fancy through handle screwdrivers made for that, but I've never broke a screwdriver yet. Not saying it's not a possibility, but usually for smaller screws, you're not tapping very hard anyway. Just enough to impart some jarring force to hopefully get things moving. With smaller screws you need to "feel" them more, and I doubt with a scaled down impact tool, or other power tool you could ever feel them as good as you could simply by tapping on the back end of a driver as you turn.

Of course, I'm not trying to talk anyone out of buying new tools either lol.
 
I have a little Chinese Hitachi mini grinder, the same one Metabo now sells. It was cheap. I bought because I needed something I wouldn't be afraid to to toss. The company was closing down and I wouldn't get replacement for my Walter. That was 10 years ago ! And it's still going.
 
Susquatch said:
At first, I was puzzled by your question Chazz. I'm not speaking for Wira. But I think that's not what they meant. I believe it refers to the fact that the driver column is solid. So any impact applied via the hammer is purely translated into both vertical and torsion without any losses in plastic or rubber energy absorbing materials as would occur in a regular screwdriver.
Click to expand...
That may be what they meant: for my own enlightenment I'm going to ask them.

Susquatch said:
Fundamentally, such a mechanism cannot convert the hammer force into 100% torque. But it can be translated into thrust plus torque.
Click to expand...
Agree.

Susquatch said:
NOTE that 30Nm is 22 ftlbf. A Crap load for small screws. Start gentle.
Click to expand...
Yes, and the un-adjustable 20 N-m = 14.75 ft-lbf: still more than you would want to apply to small screws or screws in "delicate" mounts.

In my experience, unless you wap the head of an impact driver pretty hard, you don't get much rotation (needs to be enough to overcome the internal friction and ride the bit holder up the ramp. Wera must have a better mechanism to justify the 3x price: I'll ask about that, also.

Since the Bosch 21PS has two speeds and 20 (+1, which I assume is direct-coupled), I'm assuming that which ever end of the adjustment is lowest torque will be significantly lower than 30 N-m. Once I'm able, I'll try to get a set of torque readings (on my list).

EDIT: I forgot to include this info from a (very) recent post on a Southern Forum. iFixIt did not recommend subjecting any of their hardened 4mm hex bits to 4.2 N-m @ 220 RPM, without impact; they were also hesitant to give me an upper limit for torque, although as noted in the last sentence of linked post their electric screw driver only develops 0.15 N-m and they recommend using the driver in manual mode (~1 N-m) for loosening & final tightening.


@Mcgyver : Have you tried using a light hammer (hard plastic mallet?) to tap the end a well-fitting screwdriver while applying CCW torque by hand? That may be enough to break the screw loose, without damaging the housing. This is basically what you do with one of the hammer-driven impact drivers – pre-load the driver in the direction you want it to turn, then whack it.
 
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ChazzC said:
Wera miusy have a better mechanism to justify the 3x price: I'll ask about that, also.
Click to expand...

It is an amazing driver and in my opinion worth the price.

ChazzC said:
Since the Bosch 21PS has two speeds and 20 (+1, which I assume is direct-coupled), I'm assuming that which ever end of the adjustment is lowest torque will be significantly lower than 30 N-m.
Click to expand...

I can say with some experience that 30Nm will break most small screws. It is the upper limit of the driver, not the in-use torque. Power drivers often have adjustable torque but only in increments and even the lowest is too much for the smallest screws. But because it is manual, the applied torque with the Wera can be as low as needed. That's why I recommended starting very low and tap tap tap tap.
 
ChazzC said:
@Mcgyver : Have you tried using a light hammer (hard plastic mallet?) to tap the end a well-fitting screwdriver while applying CCW torque by hand? That may be enough to break the screw loose, without damaging the housing. This is basically what you do with one of the hammer-driven impact drivers – pre-load the driver in the direction you want it to turn, then whack it.
Click to expand...

Won't have the chance on this one, I got it done with my Klein impact screwdriver. The task just make me pine for something a little less brute force-ish. Wera on order.

I agree some impact straight down can help release a stuck screw, and it's a good suggestion that it might loosen things up. However for the really difficult ones it's a different thing happening than what an impact screwdriver does, i.e. very high torque but only at the moment of impact.
 
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