Back to the work order:

work order oah

OAH stands for overall height.  Overall means when you measure the depth of the head you include the thickness of the material.  This head is supposed to be approximately 14 and 1/4 inches deep.  There is a reason the order reads 14.2456.  While the rest of humanity measures everything in metrics, we here in the backward ASU still measure everything the old way, whatever it’s called.  Inches, feet, yards, miles, pints, quarts, gallons, etc., etc., etc.  No one else uses these measurements anymore.  So when orders come in from the real world, the measurements are converted from meters.  That’s why we get such screwy numbers to work with.

Be that as it may, by ASME code we are allowed to be deep 1 and 1/4 per cent or shallow 5/8 per cent of the diameter.  In this case the diameter of the head is 90 inches.  That means this head can be 1 and 1/8 inch deep or 9/16 inch shallow.  So the overall height can be between 13 and 11/16 inches and 15 and 3/8 inches.  That is what the ASME code allows.  Of course, customers can order a tighter OAH, and they do.  The most common hold on the OAH is plus or minus 1/4 inch.  But it can get tighter.  Plus 1/4 inch and minus 0.  Plus or minus 1/8 inch.  I’ve even seen plus 1/16 inch minus 0.  The common rule is if there is a hold on the OAH, then the length of the SF must be a reference (which means it will be as long as whatever remains after machining the head to the requested OAH).  But many customers put a minimum requirement on the straight flange also, and one customer (who orders a lot of heads) demands an OAH of plus 0 minus 1/8 inch, while demanding the SF to be plus 0 minus 1/4 inch.  These are very difficult to do.

Sometimes if we will need to cut off too much SF in order to machine to the OAH, then we’ll send the head back to the press to be shallowed up.  This usually causes a disturbance in the force (press operators whine a lot).  But (sh)it happens.  What also happens way too frequently is you machine a head down to the OAH, then bevel, or double bevel, and/or taper the edge, only to find when you inspect the head that you are still deep.  So after you stop cursing and throwing things around, you have to machine off all this detail as you machine the head to the OAH you thought you’d had it to, then you have to machine back all the stuff you just cut off.  Very wearisome.

Sometimes heads get warped.  Which is okay, you are allowed a certain amount of out of round, by ASME code 1 per cent of the diameter.  That would be 7/8 inch with the 90 inch diameter head on this order.  Heads are hardly ever more than 1/4 inch out of round, most of the time only 1/8 inch or 1/16 inch.  But a head can be warped and still be okay as long as it’s not more than 1 per cent of the diameter out of round.  The problem is the OAH of a warped head will read differently in different places.  So I’ve learned to take at least two readings of OAH on heads with tight tolerances.  I learned the hard way, after a number of heads were shipped back because I hadn’t realized they were warped enough to effect the OAH.  Geoff L. was upset over this, there were a lot of heads on that order.  As you would expect, Brighton has to eat the shipping costs of returned heads, both coming back and going out to the customer for the second time.

Bill R., the inspector with the chalk (that I put) in the finger of his glove that didn’t have a finger in it, used to climb inside heads to measure the OAH.  Once when I caught him doing this I asked him if he had heard the joke about how do you make a hillbilly dizzy?  He said no.  I spun the head.  And he sat there in the middle of the head as it went around and around.  Cussing at me every time he came around.  Because there was no way he was getting out of that head while it was spinning without breaking his neck.  Whether he got dizzy or not, I don’t know.  He probably did.


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