Calibration and Gage Block Use

Transcription

1 REHDER DEVELOPMENT COMPANY 2139 Klondike Rd W Lafayette, IN USA Tel: (765) Fax: (765) Web: t.houck@rehder-dev.com Technical Innovations Calibration and Gage Block Use Instruction Manual Jan 1, 2014 Copyright Createch Rehder Development Co 1 of 8

2 ET-3 Electronic Thickness Gauge Calibration Instructions It should be noted that the ET-3 system is very stable and will rarely go out of calibration. However, periodic calibration checks may be necessary to satisfy quality control requirements. It is highly recommend that you follow the Calibration Instructions provided in this manual. Although the ISO standard calls for using shims, that method is not recommended for calibrating the ET-3 Electronic Thickness Gauge. It is not possible to achieve sufficient calibration accuracy by placing shims on the anvil. Shims are not precision ground, flat, accurate enough or traceable for proper calibration of ET-3 instruments. If an attempt is made to calibrate the ET-3 using shims, the result in most cases will be degrading of the calibration accuracy. You may use shims as an indicator for the possible need to calibrate. If the shims indicate an error, precision certified gauge blocks should then be used to confirm or disprove the possible error. If the error is confirmed, the gauge blocks should be used to do the calibration. If the instrument has previously been calibrated properly, errors shown by the shims will most likely be proven false by the gauge blocks. The recommended certified gauge blocks are accurate to 0.1 microns, total cumulative error. The recommended calibration procedure, using these precision gauge blocks, calibrates the instrument to read within one or two microns at any position between Zero and 1000 microns. Room temperature will have a very slight effect on calibration. Five degree C ambient temperature change will typically cause 1 micron calibration shift at 1000 microns. For best accuracy, calibration should always be done at the normal operating temperature of the space in which the ET will be used. Calibration should be performed only after the instrument has been turned on and allowed to warm up for a minimum of 30 minutes so the instrument and gauge blocks can stabilize at the operating temperature. Equipment Needed for Calibration: Certified Type B Grade 0, or better, chromium-carbide precision ground gauge blocks. One each of the following thicknesses: 11.0(13.0)mm, 5.0(3.0)mm, 5.5(3.5)mm, and 6.0(4.0)mm. Approximately 10mm wide x 35mm long. Total cumulative error between any two blocks should be no more than 0.10µm. Two small strips of Scotch Magic Tape", or similar Mylar tape. One small straight screwdriver ~ 2 or 3 mm wide. One 9/64 inch hex key. Copyright Createch Rehder Development Co 2 of 8

3 Calibration Procedure Turn on the instrument for 30 minutes prior to calibrating so the instrument can stabilize at its normal operating temperature. Remove the anvil from it's base and apply a 3mm to 4mm wide strip of tape, roughly parallel and at opposite edges, to the top of the anvil base (fig. 3). If your instrument has been fitted with a Ball Anvil it will be necessary to attach the Calibration Spacer block provided with the instrument to the anvil base. The tape is then attached to the top of the spacer block (fig. 4/ Page 10). The two strips of tape provide a stable, two point base for the 11(13)mm block to rest on (like a pair of saw horses) and keeps the gauge block from being scratched by the anvil base. The 5.0(3.0)mm, 5.5(3.5)mm and 6.0(4.0)mm blocks rest on top of the 11(13)mm block to give precise 000µm, 500µm & 1000µm positions. It is imperative that all oil, dust, fingerprints, etc. are completely removed from the gauge blocks. The smallest speck of dust or a fingerprint on the face of a gauge block can change the reading by several microns. When finished with the calibration apply a film of non-corrosive oil to the gauge blocks to prevent rust. The 1000µm range is adjusted by turning a small screw that is located behind a cover plug in the upper left corner facing the back of the ET-3 electronics. Readings above 1000µm are out of the accurate measuring range of the ET (3.0)mm Block Sensor 11.0(13.0)mm Block fig. 3 Anvil Base Scotch Tape 1. Place the 11(13)mm Gauge block across the two strips of tape (fig. 3). 2. Place the 5.0(3.0)mm block on the 11.0(13)mm block and lower the sensor. Set the digital display to +000 with the Zero knob. If +000 is beyond the range of the Zero adjustment you will need to adjust the position of the Sensor Coil. See page Raise the sensor and replace the 5.0(3.0)mm block with the 6.0(4.0)mm block. This provides a 1000µm step for the sensor and when lowered, the display reading should be 1000µm greater than with the 5(3.0)mm block. If it is not, check for dust, oil, etc. on the blocks and try both blocks again. Only after it is determined beyond any doubt that there is no dust, etc. should the calibration screw be adjusted. If needed, adjust the calibration screw so the 1000µm step gives an exact 1000µm difference in the display readings. Repeat the 5.0(3.0)mm and 6.0(4.0)mm blocks a few times to confirm the display reading consistency. If readings are not consistent check for dust on the blocks and senor tip. Copyright Createch Rehder Development Co 3 of 8

4 4. When the 1000µm range has been properly adjusted place the 5.5(3.5)mm block in place. The reading should be 500µm ± 2µm greater than with the 5.0mm block. If not check for dust etc. on all blocks and recheck. This routine should be repeated until 000µm and 1000µm readings are exact and the 500µm reading is within ± 2µm. A few sequences of the three gauge blocks should then be repeated to ensure accuracy and repeatability. If there is inconsistency of the readings additional cleaning of the gauge blocks is probably needed. After the calibration has been completed, replace the calibration screw cover plug and the anvil on the anvil base. Make sure that the anvil is centered under the sensor. This can be done by lowering the sensor to the top of the anvil and then sighting across the top of the anvil from two positions approximately 90 apart. When the sensor appears to be centered on the apex of the anvil from the two positions, tighten the screw that holds the anvil in place. Adjust the position of the sensor coil so the Zero adjustment is mid range, approximately -015 to +015 microns. (See Sensor Coil Adjustment on page 15). Copyright Createch Rehder Development Co 4 of 8

5 Calibrating the ET-3 with the Ball Anvil Adaptor MICRONS Serial Number Sensor at Zero microns ET-3 ZERO 5.00(3.00) mm Gauge Block 11.00(13.00) mm Gauge Block SENSOR C ALIBRAT S/N xxx Two strips of Tape on top of Spacer Block Calibration Spacer Block fig. 4 # 8-32 Mounting Screw Important: Do not discard the Calibration Spacer Block that has been supplied with the Ball Anvil Adapter. It will be required when calibrating the ET. Each Spacer Block is unique and has been hand lapped to be the precise length required for that particular Ball Anvil Adapter. Each Spacer Block and Ball Anvil Adapter have serial numbers on them that match that of the ET to which they have been fitted. Calibration Procedure: 1. Remove the Ball Anvil Adapter from the anvil base of the ET and install the Calibration Spacer Block that is supplied with the Ball Anvil Adapter. (fig. 4) 2. Follow the normal Calibration Instructions provided in this manual. Copyright Createch Rehder Development Co 5 of 8

6 Gage Blocks Gage blocks were developed as a length standard evolving from the need to be able to have comparative measurements. Hundreds of years ago there were many different units of measure that were not based upon any agreed upon standard. The arguments that arose made obvious the need for accepted standards. Metrologists have used gage blocks for almost one hundred years and their basic design has remained the same for almost the same amount of time. Gage blocks typically come in two styles, square or rectangular and in three types of material. Steel, Tungsten Carbide or Ceramic. While steel are the leas expensive, they are the least durable. Tungsten Carbide are more expensive but have far greater wear characteristics. Ceramic Gage Blocks are the most expensive however they will not rust and have excellent wear characteristics. Unfortunately, Ceramic Gage Blocks are more brittle than Steel or Tungsten Carbide. When specifying gage blocks, please take these characteristics into consideration. Most companies use gage blocks as their masters thru which they obtain traceability to NIST. Please see our traceability section for details on traceability. Gage blocks are manufactured to the US Standard B or the formerly applicable Federal Standard GGG-G-15-C. The new B standard became effective in January of While it may seem that the new B specification has a significant wider tolerance, there is an important difference in the standards. The size tolerances of the new B standard applies to all the points on the gage surface not just to the reference point. The new B gage block grades are as follows: Grade 00, Grade 0, Grade AS1 and Grade AS2. Many people still use the even older Federal specification grades of AA and A whose use has been discontinued. Please see the Table One and Table Two for the old and new tolerance comparisons. TABLE ONE Copyright Createch Rehder Development Co 6 of 8

7 TABLE TWO Notes on Old or Other Standards While GGG-G-15C has been superseded, it is expected that industry will probably continue to use those specifications for some time. GGG-G-15C was originally effective March 20, Federal Specification GGG-G-15B was effective from November 6, 1970 thru 1975 and GGG-G-15A was used from 1964 thru The 15B and 15C Grades used the same nomenclature. However, the 15A Specification had the following grades specified: Grade AAA, AA, A+, A and B. It is also not uncommon today to see the reference grade of "Toolroom" which typically means the gage blocks tolerances are + / - Fifty millionths ( "). Note on Gage Block Usage Gage blocks are precision measuring tools and need to be kept clean. Gage blocks are stacked, or wrung together to obtain a specific size. A common 81 piece gage block set is designed so that you can stack any size from.1000 thru In increments of.0001" by stacking no more than four blocks together. The trick to selecting blocks from the box is to eliminate the right hand figure or digit of the size you are looking for and then work your way to the left. An example would be like this: Target size First eliminate the 9 by choosing the.1009 block Balance = Second eliminate the 4 by choosing the.1340 block Balance = Third eliminate the 5 (yes I know, it originally was an eight but your options for second digit are 0 or five so you work it out that way, it really isn't hard. Or you can buy a simple piece of software to figure it for you) by choosing the.5500 block. Balance = Fourth eliminate the 1 by choosing the block and you get: = Wringing gage blocks together can best be accomplished by practice and using this procedure: 1. Clean with mineral spirits and lint free rag. 2. Place another clean dry lint free rag on a flat surface like a surface plate and drop two small drops of very light oil (like a CRC 3-36 Technical Grade Oil) on one area of the cloth. 3. Rub the clean block's measuring surface on the oil and then on a clean area of the rag using a figure 8 motion to clean off any excess oil. Slide the Gage Block on to the other Gage Block (or wringing block) similarly prepared and rotate the top block 90 degrees and then back to the matched position. Copyright Createch Rehder Development Co 7 of 8

8 Note that dropping or abusing gage blocks is bad. If a burr raises on the surface of the block there are Gage Block conditioning stones that may be very gently used to remove the burr. Temperature Gage Blocks grow as temperature increases. The amount this will affect your measurements is contingent on the type of Gage Blocks and amount of temperature change. Gage Steel that is made of steel has a coefficient of expansion of 6.4 micro inches per degree F increase in size. Other materials have different expansion rates. Standard Gaging temperature is 20 C or 68 deg F. While these amounts seem small, they can grow quickly depending on the size of the part you are measuring. Don't forget to consider temperature because some materials, like aluminum have extremely large coefficients of expansion. Recalibration While each company specifies their own periods for recalibration a guideline that many companies use was stated in the GGG-G-15C standard as Grade 0.5 and Grade 1 as Annually Grade 2 as Monthly to Semiannually and Grade 3 as Monthly to Quarterly. ASME B appendix B has the following suggested replacement grade table: Copyright Createch Rehder Development Co 8 of 8