100 Years of Innovation: History of the Electric Drill | Electrical Contractor Magazine
“This year marks the 100th anniversary of the portable electric drill’s invention. A century ago, the Black + Decker Manufacturing Co. (now Stanley Black + Decker) developed and filed a patent application for a ½-inch portable drill that one person could operate. It had a universal electric motor, which could run on alternating current (AC) or direct current (DC) and the pistol-grip handle with a trigger control. Both features have been on electric drills ever since.
The original portable drill, assembled in 1916, is at the National Museum of American History in...”
“In 2004, Makita developed a brushless motor for a fastening tool for the defense and aerospace industries, and, in 2009, Makita introduced an impact driver with a brushless motor. Manufacturers say tools with brushless motors have as much or more power than tools with conventional “brushed” motors. They also operate more efficiently and are more durable.
History of Screws and Screwdrivers
“...In 1798, American David Wilkinson also invented machinery for the mass production of threaded metal screws.
In 1908, square-drive screws were invented by Canadian P. L. Robertson. Twenty-eight years before Henry Phillips patented his Phillips head screws, which are also square-drive screws.The Robertson screw is considered the "first recess-drive type fastener practical for production usage." The design became a North American standard, as published in the sixth edition of Industrial Fasteners Institute Metric and Inch Standards.
A square-drive head on a screw can be better than a slot head because the screwdriver will not slip out of the screw's head during installation. The Model T car made by the Ford Motor Company (one of Robertson's first customers) used over seven hundred Robertson screws.
PHILLIPS HEAD SCREW
In the early 1930s, the Phillips head screw was invented by Henry Phillips. ...”
In 1744, the flat-bladed bit for the carpenter's brace was invented, the precursor to the first simple screwdriver. Handheld screwdrivers first appeared after 1800.
TYPES OF SCREWS
All about screws
“...Here's a rough guide for picking a screw or bolt for a given load:
Start off with the load that needs to be held in tension, call this F. If you have a shear (sideways) load, you should design so that friction or dowell pins will bear the load and not the bolt, but if this isn't an option note that shear strength is 60% of tensile strength in many steels.
We'll use a safety factor of 2.5, so the design load is now 2.5F. Now we need to select a screw with enough strength so that it can withstand the combined external load and pre-load from tightening. Assuming that 80% of the bolt's proof strength is being used up in preload, that leaves 20% to handle 1/3 of the external load. Or in other words, we're looking for a bolt where 60% of its proof strength is greater than the load.
Let's try an example: What size grade 2 bolt is necessary to hold 100 lbs? The proof strength of Grade 2 bolts between .24 and .75 inches is 55 ksi (thousand pounds per square inch), and 60% of this is 34.2 ksi. So, we're looking for a bolt with a tensile area greater than our load (2.5*100 lbs) divided by 33 ksi, or .0076 square inches. A #6 UNC should work. For perspective the diameter of a #6 screw is .138", (1/8 = .125"). If this seems small, keep in mind that the ultimate strength (breaking strength) of a Grade 2 bolt is 74 ksi, so a #6 screw could theoretically hold 672 lbs in pure tension. If you're wondering why bolts you see in cars and weight machines are so large, it's partly to gaurd against loosening and fatigue failure in addition to safety factors.
What about changing loads? According to this Unbrako whitepaper on the Fastener Act, over 85% of failures are due to fatigue and not a simple overloading situation. Think about breaking a paper clip, which is easier: bending it back and forth or out-right pulling it apart? If you have an oscillating load and want a joint to last forever, the best advice we can offer is to multiply the anticipated load by 10 or more, and even this may not be sufficient. Steel can handle about half of its ultimate strength in an alternating load, but add in the pre-load stress and something called a "Stress Concentration Factor" due to the threads and the problem gets more complicated quickly. Here's a good explanation of these effects along with a lot of other great screw information...”
Why is a torque wrench so imprecise? Friction. Some 80+% of applied torque goes into defeating friction, leaving little for actually stretching the bolt. What's worse is that this friction is highly unpredictable and depends heavily on the materials involved and any lubrication that may be present. Most fasteners have a small amount of oil present from the manufacturer to prevent rust. ...”https://www.elexp.com/Images/AllAboutScrews.pdf