We had an opportunity to recalibrate a customer-supplied EN 12223 cal block no. 1 this week and noticed something interesting that I wanted to get some feedback on. The zero point slot (on the 100mm radius centerline) is specified as 4.0mm deep x 0.5mm wide x 30.0mm long. No end view of this slot is provided in the EN. BS 2704 includes an end view of this feature and clearly indicates that the slot depth is to be uniform over the length except for the inboard ends which are radiussed (to allow conventional machining using a slitting saw.) PH Tool opts to machine the slots this way. The block in question was clearly machined via wire EDM as was evidenced by a cast replica. As a result, the observed slot was angled or tapered from 0.0 to 4.0mm deep over its length. In addition, rather than having square-cornered features, the slot exhibited a corner radius of .25mm, typical of wire EDM. My question is this: Is the angled slot with radiussed corners in compliance with EN 12223 and would a reflector machined in this manner function as intended? Considerable time would be saved machining it via wire, but in my estimation, an inferior product will result. Any comments would be greatly appreciated.
Re: 0.5mm reflector on V1 and EN 12223 Cal blocksIn Reply to Phil Herman at 17:14 May-27-2009 (Opening).
As you had, presumably, both types of block to hand you could have answered your own question about functionality with some side by side comparisons.
As the purpose of the slot is to allow repeats from the 100mm radius I would guess that the actual form of the slot is not critical so long as it works.
As for the spec then a question to the relevant working group at ISO would clear that up.
I have had problems with these blocks before where units with imperial and metric dimensions exist side by side with no marking to differentiate. I had to go and sort them out and hard stamp myself to avoid mix ups with the inspectors.
23:19 May-28-2009 Roger Duwe NDT Inspector, API-510, 570, 653 MISTRAS, USA, Joined Jan 2009 148
Re: 0.5mm reflector on V1 and EN 12223 Cal blocksIn Reply to Dave Davies at 10:18 May-28-2009 .
Concurr with Dave D. -- the slots are just to lobtain a 200 mm reflection to go with the 100 mm reflection. The lack of parallelism [specifically, not parallel to the 100 mm radius] hurts the quantity & quality of sound to generate the 200 peak. The radius at the bottom of this slot on the corner closest to the 100 radius also decreases the available surface parallel to the radisused end, giving more loss of sound. The 'implied tolerance' is 4.0 +/- 0.1 mm of flat face parallel to the radiused end of the block. Since that tolerance is not expressed in EN 12223, it falls under 'workmanship', and is not mandatory.
In short, Phil is right. Poor workmanship to cut the block and leave a tapered draft and radiused bottom corners. However, it meets the strict interpretation of the EN 12223 dwg's and will work as a cal block. Second peak will just be smaller, broader, and 'fuzzier'.
And I will continue to buy my reference blocks from PH Tool. What's a little more money for a prime reference that will still be useable in 2-3 more generations? 'First Rate' always has cost a little more.