The Swiss-made Interapid Hole and Groove Checking Comparator Gage model IRA2 has the advantage of an extended range, up to six inches, so that one gage will perform the function of many. It is a superior tool and comes at a premium price. The gage is complex. Be sure to read all of the information on this page so that you understand the tool's limitations. The hardened steel measuring anvils are exchangeable and optional accessories allow for 3-point contact measurement. The dial scale reads in .0005" or 0,01mm and the accuracy is ±1 graduation.
The manufacturer provides the following statement:
"The IRA2 gauge is an instrument with many application possibilities. Thanks to its design as well as a variety of standard accessories, the IRA2 is suited for the measuring of blind and through bores, grooves and undercuts as well as form errors such as conicity, ovality and parallelism. Due to its light weight and form, the IRA2 is easy to handle. Because of the angular adjustment of its measuring arms it has a large measuring range, going from 10 to 150 mm (0.4 to 6 inches)"
The complete Interapid IRA2 set includes:
comparator gage (.0005" or 0,01mm)
three measuring inserts (hardened steel) with 2.2 mm length and 3 mm diameter (metric part 105667; inch part 105697)
three measuring inserts (hardened steel) with 2.5 mm length and 1 mm diameter (metric part 105668; inch part 105698)
three measuring inserts (hardened steel) with 5 mm length and 1.4 mm diameter (metric part 105669; inch part 105699)
two adjustable flat bottom contact arms for measuring diameters larger than 6 mm (The installed tip can be removed - note the black screws in the photo above - and replaced with this pair of contact arms. The flat bottom allows you to go to the bottom of a blind hole.)
bridge attachment (small probe) for 3-point measurement
bridge attachment (large probe) for 3-point measurement
custom probe wrench
centering device for diameters 15 - 30 mm (.6 - 1.2 inches)
centering device for diameters 30 - 150 mm (1.2 - 6 inches)
instructions for inspection of a cylindrical bore, 3-point inspection of a groove, and control of the cylindricity of a bore.
plastic holding case
Repairs are possible on all Interapid gages. With over 50 years of experience in Interapid repairs we are well qualified to perform repairs of these tools. Additionally, we can provide spare parts to qualified repair shops and dealers.
This style of measuring gage is available in every conceivable cost range from cheap throw-aways out of China, to flimsy Japanese models, to sturdy and recently improved German Intertest, all the way up to these high end Interapid gages.
On the back of the gage, just below the adjustment knob, you'll find a black screw which can be turned in or out to set the amount of tension on the adjustment knob. If you don't like the factory preset, or if someone's fiddled with this screw, you can easily make changes.
First and foremost, remember that this is a comparator gage. You will not be taking direct readings beyond the range of the dial (±.008 inches). From the charts above, you will also notice that a linearity error exists as you go above or below 1.9 inches (48 mm). Furthermore, the repeatability lessens as you approach the upper range of 6 inches. At that point, one graduation of repeatability is expected.
If you're having problems try these steps:
Use 48 mm as a standard setting (1.9"). A micrometer which has been set to 48 mm will give you best results. Repeatability must be .0003" (about half a graduation on the inch models).
Keeping the dial locked in place, use a micrometer of .0001" accuracy to check the movement of the hand on the dial. As you close the micrometer .008" and then .016" you will see the dial hand move correspondingly. At that range, there is no error of linearity and your dial hand should move the full .016".
If you repeat this procedure at other settings (it would be a good idea to do it at or near the settings you normally use) you will have to take repeatability and linearity errors into consideration. See the charts above.
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