As built drawings

[Anonymous]

Hi, after a little advice please.

I am relatively new to AutoCAD and I work in the Civil and Marine Engineering sector. I have recently been asked to help out on a project which requires accurate dimensioning for clearances, etc.

I have been using the As-built drawings to gather the required dimensions, by measuring in the CAD drawing. Is this ok to do? As I have been informed, by one of the engineers that we shouldn't measure off the CAD drawings, but to work out the required dimensions using given dimensions for other parts of the drawing. I have checked other dimensions within the drawing and they all match up.

What is best practice please? Any help gratefully received.

[JPomeroy]

Disclaimer: I am not in the Marine Engineering field, so I am not an expert in best practices for that field.

Just for clarification, are the "given dimensions for other parts of the drawing," being taken from the .dwg?  If so, what is the difference between what you are doing (measuring in AutoCAD) and finding other dimensions and working backwards?  At least the measurements have so far all lined up as expected.  That is a nice bonus.

If the "given dimensions" are in text, or a spec sheet or something, those should always (to the best of my knowledge, in light of the disclaimer above!) be given precedence.  

Or am I totally misunderstanding the issue?

[imadHabash]

Hi,

>> I have been using the As-built drawings to gather the required dimensions, by measuring in the CAD drawing. Is this ok to do? <<

since you're working with As-built drawings then it's ok to keep going as you did . you have to take a confirmation from others that those As-built drawings are exactly matching site works . 

Regards,

[dgorsman]

That depends how trustworthy the CAD files are.  Are they real-size or to the stated scale?  Are the dimensions accurate to what the numbers claim?  If so, then you should be able to rely on direct measurements.  It's one of the benefits of CAD, after all- critical features are at the correct (relative) location and correct size.

Note this differs from a hard copy print, or referencing a scanned drawing in AutoCAD - you should be *very* cautious taking a scale to those.  In that case you should be relying only on stated dimensions and anything you measure would be for reference purposes only.

[GrantsPirate]

You asked what the best practice is.  For that you need to take your own field measurements.  Next is to follow the advise given to you by that engineer.  Relying on as-builts is a risk that I don't like to take, if something is messed up it is still on your back.  IMHO

[Anonymous]

All given dimensions within the drawing match up when I dimension them to check if they are correct. The parts I am trying to dimension are part of the same feature, but as has also been explained to me they could just be there to give a visual representation. We have since checked said dimensions between the 2 of us and they do tally. But a a matter of course, he has said it is always worth checking.

Thanks for your reply

[Anonymous]

Thanks for your reply.

We have since carried out some calcs using other drawings to check if they are accurate and they are, but he has re-iterated that they should always be double checked.

[Anonymous]

Thanks for the reply.

The drawings seem to be at a scale of 1:1. I have checked other dimensions that are in the drawing and have been dimensioned and they all seem to tally up. We have just carried out some calculations using other drawings too, gathering all required dimensions and they do all come out the same as the dims from the drawing.

Thanks for highlighting the issue with regards to hardcopy and scanned in drawings for dimensioning and I would never trust dimensioning of those. Thankfully most of the time I am dealing with the actual CAD drawings themselves.

[JPomeroy]

Checking is always good advice!  Sounds like you are on the right track.  Good luck!

[Anonymous]

Thank you for your response.

I had thought of measuring for myself, unfortunately due to the nature and location of the equipment that is unfortunately not feasible.

[imadHabash]

Hi,

>> We have since carried out some calcs using other drawings to check if they are accurate and they are <<

So ... it's accurate As-built drawing , and this is good start . 

>> ... but he has re-iterated that they should always be double checked. <<

Yeeeeh ... i understand that , this words ( double checked ) said to remember your later ( when mistake appeared ) from others that we told you to double check your existing line works .!!!!