A lesson on tolerances...

[ChadV]

Preface: not quite a structural topic but a construction one so it seems like it fits here...

http://seattletimes.nwsource.com/html/localnews/2009599889_portmistake05m.html

As a side note, somebody on another forum points out that 2.52" is 64.008mm which means someone quite possibly converted from metric and dropped a bit of precision...

 

[Teguci]

Something is not right with this story.
- If this was important the cable could have been procurred in less time.
- 2/100th of an inch =slightly more than 1/64th of an inch off. To mitigate the problem its hard to believe they couldn't have made use of the larger cable.
- Its a quasi government job ie results not as important as process

These, of course, are opinion, but this story has me slightly upset.

 

[ChadV]

As pointed out in one of the comments... this story needs a followup written by someone who knows the right questions to ask.

 

[JAE]

I think the federal government should step in and bail them out.

 

[Ron]

A prime example of measuring with a micrometer, marking with a crayon, and cutting with an axe.

Incompatible tolerances. Absurd.

 

[msquared48]

You do that too?

Mike McCann
MMC Engineering

 

[Ron]

Mike...you've had almost as much to drink as I have!....you still have a couple of hours to make it up...go Brother.

 

[lsmfse]

When Cadd first got started years ago, we had dimensoned drawings from architects showing something like 32'-6 27/32". Personally, I have a hard time reading a 1/16" on a tape measure. Agree with Ron

 

[Grahammachin]

Why on earth would you cut a trench/groove to that tight a tolerance. Wouldn't you just cut a 3" trench/groove and be done with it.

It's a cable at the end of the day.

 

[hokie66]

The article said the "trench" was lined with steel. Sounds like a fabricated steel tray rather than a trench. But the journalist wouldn't know the difference.

 

[NomLaser]

Either way it's a construction job and not a precise machined component. .02 is closer to 1/64th.

 

[BAretired]

Maybe they should have used a grinder on the trench. Sounds like too tight a tolerance.

BA

 

[BridgeBuilder88]

If the trench is lined with steel, isn't it the trench manufacturers fault for providing an inside diameter of 2.50" instead of 2.52".

Unless of course this is cast in place steel... ;-)

Anthony Deramo
American Bridge Company

 

[Teguci]

If I told you to give me a 2 1/2" wide trench and you gave me a 2.48" wide trench, I wouldn't have a leg to stand on unless I said a 2 1/2" min.

If the company said a 64 mm trench and I gave them a 63.5 mm trench, do they have an argument? (Perhaps 64 mm, min)

 

[MechEng2005]

Ron said, "A prime example of measuring with a micrometer, marking with a crayon, and cutting with an axe."

Can't those problems usually be fixed with a big hammer? (Particularly in this case!)

-- MechEng2005

 

[yakpol]

I guess it is hard to push 2.52" O.D. cable through 2.5" I.D pipe.

 

[aayjaber]

There is a lot of journalistic fluff in the article and very tiny or no science in it.

This is what happened when engineers/scientists read the news.