Author Topic: Drawing interpretation  (Read 412 times)

Offline John Rudd

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Drawing interpretation
« on: January 08, 2021, 10:59:58 AM »
 
Gents,
Opinions needed.....
Study the drawing attached and tell me what you think......

The tapped M5 holesare located as shown, but is the second one located 1/4" + 9/16" or is it located 9/16" from 0" on the bottom right corner?
Then is the 3rd one similar? 1/4"+9/16"+1.0" from 0" from the right hand edge? Or is it 1.0" from the right edge?
Finally the 4th, 1/4"+9/16+1.0"+1-1/2" or is it 1-1/2" from the right?

Thanks from Confused....
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Offline vtsteam

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Re: Drawing interpretation
« Reply #1 on: January 08, 2021, 11:22:58 AM »
John, 9/16" from 0 on the second one, and similarly 1" from right for 3rd and 1-1/2" from right edge for 4th.

Look for the second arrowhead termination on the dimension lines. If there is one, then it's to that base point. If there isn't then it's to the first base point for all. At least in this dwg.

You'll notice that on the other two circular locations (not mentioned) there is a mix. The first dimension (9/32") is from the right edge, the second (1-1/2") is from the center of the first. Check the arrowheads.
I love it when a Plan B comes together!
Steve
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Offline John Rudd

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Re: Drawing interpretation
« Reply #2 on: January 08, 2021, 12:25:40 PM »
Steve,
So to clarify,
All measurements are based on the 0 datum?

i.e  9/16 from 0 rather than the 1/4"?  That would make that hole location 5/16 from the first? ...then the fourth hole would be 1-1/2" from 0?
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Offline Spurry

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Re: Drawing interpretation
« Reply #3 on: January 08, 2021, 12:29:59 PM »
Hi John. Still working in those strange measurements; thought you would have been metricated by now :)
 The drawing looks like it has the datum 0/0 at the bottom right hand corner, and the other measurements are from that point.
Pete

Offline John Rudd

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Re: Drawing interpretation
« Reply #4 on: January 08, 2021, 12:53:46 PM »
Pete,
Although I'm a child of the 50's and was educated between the 60's thru to the mid 70's ( including my apprenticeship)  I still use Imperial fractional measurements...although I do need to use a calculator to go from fractions to decimal for my dro's....
But back to measuring.....

My tech drawing reading skills are a bit below par...So now I know the significance of the datum, something I missed, should be able  to get my holes in the right place...l :dremel:
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Online philf

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Re: Drawing interpretation
« Reply #5 on: January 08, 2021, 01:07:02 PM »
John,

Particularly as you have a DRO, dimensioning with co-ordinates from a corner datum makes life much easier. CNC works this way after all.

Why the drawing has a mix of co-ordinate and chained dimensions (9/32" and 1 1/2")is a bit odd. The 1 1/2" dimension might be critical but if it is it should be toleranced accordingly.

I too am a child of the 50s but always worked in mm. (Working for a Dutch company might have had something to do that.)

I hate fractions with a passion - how many machines have dials with fractions?

Phil.
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Offline vtsteam

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Re: Drawing interpretation
« Reply #6 on: January 08, 2021, 01:29:25 PM »
Steve,
So to clarify,
All measurements are based on the 0 datum?

i.e  9/16 from 0 rather than the 1/4"?  That would make that hole location 5/16 from the first? ...then the fourth hole would be 1-1/2" from 0?

Yes, John. For the holes you asked about.

For the other two holes (double circles) on the drawing that you didn't mention, the first is measured from the right edge, the second is from the first hole.
I love it when a Plan B comes together!
Steve
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Offline John Rudd

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Re: Drawing interpretation
« Reply #7 on: January 08, 2021, 01:54:14 PM »
Thanks guys.....I'll make sure I dont cock up the second piece of plate..., :dremel: :doh: :doh:
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Offline vtsteam

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Re: Drawing interpretation
« Reply #8 on: January 08, 2021, 02:16:58 PM »
oh noooooooooooooo...  :(
I love it when a Plan B comes together!
Steve
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Offline SwarfnStuff

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Re: Drawing interpretation
« Reply #9 on: January 09, 2021, 12:38:52 AM »
I looked at the drawing and surmised that the dimensions were cumulative from 0,0 due to there being no right facing arrow heads between the dimensions. Adding to the confusion I think is that  above the dimensions queried there is a mix of single and double arrow head dimensions.

Anyway, reading further if found that vtsteam offered the solution in the very next post.

Grew up with imperial, switched to metric (Basically had to for work) and can confirm that grams and decimals thereof are WAY easier to track than Drams, Oz and pounds.
Still visualize stuff in feet and inches though as in someone talks of 75mm, I think (yeah, about 3").
Split personality????   :(
Converting good metal into swarf sometimes ending up with something useful. ;-)

Offline vtsteam

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Re: Drawing interpretation
« Reply #10 on: January 09, 2021, 02:11:51 PM »
Maybe your explanation is clearer for someone.

I also picture metric in translation, multiplying millimeters in my head by 4, and then dropping a couple zeros to get a visual idea of roughly how many inches are being talked about. I'm sure that if I had to do that more often I'd gradually be able to picture metric sizes without that.

Well, I do picture a centimeter as-is and for some reason 6mm, probably because of familiarity with plywood thickness. So I'm a little bit mentally mongrel!
I love it when a Plan B comes together!
Steve
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Offline SwarfnStuff

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Re: Drawing interpretation
« Reply #11 on: January 09, 2021, 11:43:50 PM »
Yep, we all have tricks that help us get the general idea and a lot of drawings seem to come from the USA and therefore imperial rules.

Here in OZ we are metric BUT if I am coming out of a bank for example, there are often markings on the exit 4,5,6,etc with sub marks indicating the 6" bit. My guess is that most still think of a person's height in feet and a half?

Suppose that will fade with younger generations, who knows?

Something else I needed to get my head around is Third Angle Projection (think that's what it is) as I grew up with Plan, Front, Right or Left Elevations where the view was as if you walked around the part or building.
  Until a fellow model engineering club member said to imagine the part in a salad bowl. Looking straight down you see the plan. Slide the part to the right or left and as it slides up the bowl you see the respective view. Similarly sliding the part up the front or rear gives those views.

I was a textile dyer by trade so this modeling caper took me back to my Tech Drawing classes at secondary school. Amazingly I still remembered lots of it.

Hope my above waffle makes sense and helps some.  :mmr:
Converting good metal into swarf sometimes ending up with something useful. ;-)

Offline vtsteam

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Re: Drawing interpretation
« Reply #12 on: January 10, 2021, 09:20:27 AM »
I still think in naval architectural terms: profile, plan and sections for the lines. Often the sections are overlaid onto the profile view at midsection, forward half sections on the left, aft half sections on the right.

Historically, all this came from the early way of designing hulls, carving a half model out of the solid made of plank "lifts" doweled together. When separated the lifts were traced around on paper to yield "waterlines" in the plan view. The flat face of the assembled half model was traced around for the profile. Section lines were erected in plan and profile to get points (offsets) to interpolate the sections, and then these were drawn in with battens (splines), ducks (weights). and curves either on paper or full size on a loft floor. Diagonals were erected to check the offsets. Making sure that all offsets corresponded in all views, with no unwanted humps or hollows was called fairing. The whole thing was a painstaking process. Computers make fairing easier now. But you still need an "eye" to do something pleasing and worthwhile.
I love it when a Plan B comes together!
Steve
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Offline djc

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Re: Drawing interpretation
« Reply #13 on: January 17, 2021, 07:30:53 AM »
I know this is a few days old and you have your answer, but it is possible to use a measuring device on the drawing to confirm or deny your suppositions.

A piece of paper laid over the 3/4" dimension on the left side and marked both ends, then folded in two and marked again will give you 1 1/2". Lay the 1 1/2" over the supposed 1 1/2" on the right side and see if it lines up.

No paper? Use your thumb over the 1" + 3/4" on the left. Same thumb on the right would be slightly longer than zero to 1 1/2" and massively longer than 1 1/2" to 1".

If your supposition of adding the dimensions were correct, the total would be 3 5/16", putting the last hole well over to the left of a part that is only 4" overall long.

Look at the vertical dimensions of the first three holes. They are identical to the horizontal ones.  The third one appears to be in line with the centreline of the material. A straightedge along the three hole centres would show they align, meaning vertical and horizontal  dimensions are identical.

This is not to make excuses for a drawing whose dimensioning leaves a bit to be desired but you can use other features of the drawing you have to sanity check or infer or clarify things as necessary.

Offline John Rudd

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Re: Drawing interpretation
« Reply #14 on: January 17, 2021, 08:59:59 AM »
Yup, all done...
I went with gut instinct and used the tlar rule...

Hopefully have the job finished by the end of this weekend... :dremel:
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