Quality electric screwdriver

[quantumfall]

I was thinking along the same lines.  But one problem is the diameter of the motor/gearbox is rather large compared to the typical power screwdriver making the ergonomics less than Ideal.  The electronic only (no clutch) torque control I think needs to be fairly sophisticated to account for the inertia of the motor armature and gearbox continuing to dissipate their inertial energy after all current is removed especially at the 1000 rpm typical driver speed.  Think about a screw into a nut at 1000 rpm.  It has virtually no drag torque until the head of the screw hits the nut face.  Even if you de-energized the motor at the exact instant the screw seated against the nut the inertia of the motor/gearbox would have to be dissipated.  My hunch is that even the models that turn off after reaching the set torque have a clutch for this reason.

Yes good point, you need a clutch then.

[SgtRock]

Dear Hacklordsniper:

--I agree with robrenz that a clutch would be a good thing to have. But it seems to me that most lever operated screwdrivers have variable speed and need not be going full tilt at all times. After all, even with a clutch, there is rotational momentum to consider. That is why people often ease up on the RPMs when the screw is almost home. I also think that most of the good ones have clutches. I think eBay is a good source for, if nothing else, information. The question about obtaining extra bits is still pending. Let us know what you find out.

"I were better to be eaten to death with a rust than to be scoured to nothing with perpetual motion."
William Shakespeare 1564 1616

Best Regards
Clear Ether

[robrenz]

Yes good point, you need a clutch then.

I was not considering dynamic braking or even full servo control in my previous statement about the inertial tightening.  Even so with full servo control and an emergency stop of armature the inertial energy would have to be dissipated by accelerating the screwdriver housing (resisted by your hand).  I did see an abstract of an article of a purely electronic torque control so it is doable.

Hacklordsniper here is some pretty good educational info on what you are looking for.  http://www.mountztorque.com/learning-center

[quantumfall]

Yes good point, you need a clutch then.

I was not considering dynamic braking or even full servo control in my previous statement about the inertial tightening.  Even so with full servo control and an emergency stop of armature the inertial energy would have to be dissipated by accelerating the screwdriver housing (resisted by your hand).  I did see an abstract of an article of a purely electronic torque control so it is doable.

Hacklordsniper here is some pretty good educational info on what you are looking for.  http://www.mountztorque.com/learning-center

Yes I see, you can have many ways to achieve a set torque, Its far more complicated than the basic hack I was thinking about to save money though

I suppose if you wanted you could have an electric driver with a whole profile of speed and breaking, even counting the turns of the chuck/bit to have a variable custom speed torque at all parts of the driving process.

You might be able to use a simple tighten to end of thread and a small drop of thread locking compound dipped on the start of the screw,  depending on the application. or a final tighten with a torque wrench /driver.

[EEVblog]

I can second the pro Panasonic cordless screwdriver, they make some of the best in the business.
http://www.justtools.com.au/prod4339.htm
Not cheap though.

Dave.