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Interapid IRA2 Hole and Groove Checking Comparator

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. 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.
Interapid IRA2 groove gage
Interapid IRA2 (.375 - 6" / .0005") ordering number 79.108640 … check price and availability

Interapid IRA2 (10 - 150 mm / 0,01mm) ordering number 79.105704 … check price and availability
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) — [manufacturer's note]
Special notes about instrument use:
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.
  • The gage will not repeat if it is allowed to swivel.
  • Measurement must be taken in a vertical position, not in a horizontal position.
  • The gage may malfunction if the arms are spread more than 6 inches.
  • The gage does not require lubrication.
  • Make every effort to stay away from dusty environments. Stay away from grinding machines.
  • Make sure that after the dial is set to zero, you tighten the small set screw on the front of the indicator (upper right). 
  • Contact points should not show signs of wear. You may be using heavily and unevenly worn points. Use rounded points on flat surfaces. Don't use round on round.
  • Use a micrometer to set the gage. If you use a .0001" micrometer you should be fine. If you want, set the mike to a gage block of the right dimension. The parallel faces of the micrometer will give you better readings than the curves of a ring gage.
  • Do not rock the gage left or right. Only up and down.
  • Set the ends of the contact arms as near to parallel with the measuring surface as possible. Do not let them be at angles. The tips of the arms are adjustable for this purpose.
How to calibrate the IRA2:
Use 48 mm (1.9") as the standard reference setting. A micrometer 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.
Setting the tension on the adjusting knob:
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.
Professional repairs:
Repairs are possible on all Interapid gages. With over 40 years of experience in Interapid repairs we are well qualified to perform both repairs and calibrations of these tools.

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Long Island Indicator Service
Long Island Indicator Service was founded in 1960. We provide professional repair service for precision measuring tools and gages with an emphasis on Swiss made test indicators, dial indicators, dial calipers and micrometers. We are pleased to be a recognized service partner for Brown & Sharpe.

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