Blade micrometers are designed for outside diameter groove measurement and undercuts on lathe work.
Old-school fully analog Mitutoyo high resolution blade micrometers have a steel blade thickness of .030" and blade length .250". All blade micrometers have non rotating spindles. Storage case and manufacturer's certificate of calibration is included. They are far superior in construction to the inexpensive Chinese versions available in catalogs and online.
Avoid getting ripped off by imitation Mitutoyo gages. If you buy from Amazon, verify that it "ships from and [is] sold by Amazon.com" or buy your gages through an authorized Mitutoyo dealer, such as Long Island Indicator Service.
Mitutoyo model 122-135 has Type B extra thin blade thickness of .016", and blade length .118" (see diagram)
Mitutoyo model 122-151 has Type D carbide blades with blade thickness .016", and blade length .157" (see diagram)
A note about carbide blades: although they won't wear down like steel blades, thin carbide blades are brittle and sooner or later they will break off, usually when you inadvertently "twist" the micrometer while it's in a groove, and usually while you're in the middle of an important project. Repairs are possible but quite expensive when the carbide needs to be replaced. The moral: don't buy carbide unless you have a good reason.
(diagram courtesy of Mitutoyo America)
|Range||Graduations||Accuracy||Blade Style||Mitutoyo No.||Price US$|
|0 - 1"||.0001"||± .00015"||Type A||122-125||check price and availability|
|0 - 1"||.0001"||± .00015"||Type B||122-135||check price and availability|
|0 - 1"||.0001"||± .00015"||Type D||122-151||check price and availability|
|1 - 2"||.0001"||± .00015"||Type A||122-126||189.00 (while supply lasts)|
|2 - 3"||.0001"||± .00015"||Type A||122-127||check price and availabiltiy|
|3 - 4"||.0001"||± .0002"||Type A||122-128||check price and availabiltiy|
Blade micrometers can be calibrated with square or rectangular gage blocks when the blades are still flat and parallel. After much use, these blades will develop worn areas, particularly if you measure slots or grooves on cylindrical parts. In this case, use a pin gage to establish the correct readings on the good portion of the blade. The pin gage you use must be of a diameter which is smaller than the curvature of the worn area. Then take a measurement with the same pin gage in the worn area. (To find the worn areas, close the blades and hold them up to a light. You'll see the spots where the blades no longer meet.) The mathematical difference between the two readings will give you a correction factor which you add to any readings you now take in that worn area. Repeat this calibration often, because the correction factor will change with additional wear. When the damage is out of control, then you can return the blade mike to us for grinding and lapping. The blades will be returned to factory specs. If the blades chip or break, they can also be replaced.
Caution if buying from Amazon: their product images sometimes do not match the product description. Read carefully!
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