Hold the crank with the left hand, turn the knob with the right hand to make the distance between the measuring rod and the measuring rod slightly larger than the measured object, then put the measured object in, turn the protective knob to clamp the measured object, and after the ratchet makes a sound, turn the fixed knob to fix the measuring rod and read the reading.
Screw micrometer, also known as micrometer, screw micrometer and micrometer clamp, is a tool for measuring length more accurately than vernier caliper. It can accurately measure the length to 0.0 1 mm, and the measuring range is several centimeters.
Part of it is processed into a thread with a pitch of 0.5 mm. When it rotates in the screw sleeve of the fixed sleeve B, it will move forward or backward. The movable sleeve C is connected with the screw as a whole, and its periphery is divided into 50 squares. The complete number of turns of the screw is measured by the scribed lines on the fixed sleeve with an interval of 0.5 mm, and the part less than one turn is measured by the scribed lines around the movable sleeve, and the final measurement result is estimated to one decimal point.
The first such measuring tool was patented by French inventor Jean Laurent Palmer at 1848, and it is called "caliper with circular vernier". Today, we still use this typical feature to manufacture outside micrometer. Micrometers were introduced into the mechanical world when two American engineers, Joseph R Brown and Lucian Sharp, visited the Paris exhibition in 1867. Their attention was attracted by Palmer's invention and they were very interested.
After improving Palmer's design, the products were manufactured in large quantities and successfully promoted by two partners in the market. When TESA Company of Switzerland decided to manufacture the outside micrometer, they repeated the story that happened in the past, making it the first product of the company. Except for a few cases (such as a micrometer for measuring gears), the micrometer we use follows the Abbe principle, just like a comparator.
Micrometer spindle is machined by modern grinder, with high thread profile accuracy and negligible pitch deviation. The processing conditions ensure that the micrometer has extremely low measurement uncertainty.