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| Slip gauges - gage blocks - Johansson gauges |
Slip gauges (also known as Gage blocks, Johansson gauges) are precision ground and lapped measuring standards. They are used as references for the setting of measuring equipment such as micrometers, gap gauges, sine bars, dial indicators (when used in an inspection role).
Slip gauges Grades:
They are available in various grades depending on their intended use.
- Calibration (AA) - (tolerance +0.00010 mm to -0.00005 mm)
- Reference (AAA) -high tolerance (± 0.00005 mm or 0.000002 in)
- Inspection (A) - (tolerance +0.00015 mm to -0.00005 mm)
- workshop (B) - low tolerance (tolerance +0.00025 mm to -0.00015mm
Slip gauges are wrung together to give a stack of the required dimension. In order to achieve the maximum accuracy the following precautions must be preserved.
- Use the minimum number of blocks.
- Wipe the measuring faces clean using soft clean chamois leather.
- Wring the individual blocks together.
In use, the blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and wrung together to form a stack of the required dimension, with the minimum number of blocks. Gauge blocks are calibrated to be accurate at 68 °F (20 °C) and should be kept at this temperature when taking measurements. This mitigates the effects of thermal expansion. The wear blocks, made of a harder substance like tungsten carbide, are included at each end of the stack, whenever possible, to protect the gauge blocks from being damaged in use.
- Use the minimum number of blocks.
- Wipe the measuring faces clean using soft clean chamois leather.
- Wring the individual blocks together.
Description:
Each gauge block consists of a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart. Standard grade blocks are made of a hardened steel alloy, while calibration grade blocks are often made of tungsten carbide or chromium carbide because it is harder and wears less. Gauge blocks come in sets of blocks of various lengths, along with two wear blocks, to allow a wide variety of standard lengths to be made up by stacking them. The length of each block is actually slightly shorter than the nominal length stamped on it, because the stamped length includes the length of one wring film, a film of lubricant which separates adjacent block faces in normal use. This nominal length is known as the interferometric length. In use, the blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and wrung together to form a stack of the required dimension, with the minimum number of blocks. Gauge blocks are calibrated to be accurate at 68 °F (20 °C) and should be kept at this temperature when taking measurements. This mitigates the effects of thermal expansion. The wear blocks, made of a harder substance like tungsten carbide, are included at each end of the stack, whenever possible, to protect the gauge blocks from being damaged in use.
Gauge Block Metric Set
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| Gauge block interferometric length |
