Scale in Drawings

[Anonymous]

I was always taught to make drawings to a specific scale as per the size the sheet. So when we send a drawing for construction, does the contractor carry a scale with him to read some of the dimension that are not mentioned in the drawing because i would not like to fill the drawing with dimensions everywhere.

[Alfred.NESWADBA]

Hi,

>> I was always taught to make drawings to a specific

>> scale as per the size the sheet

The model has always be drawn 1:1 in it's units.

A scaling on the sheet means the content will be prepared to fit on the paper, the output is scaled then, but not the model itself!

E.g. if you have a table with 1m x 1.5m you draw the rectangle with

• 1x1.5 if your drawing is set to UNITS = Meter
• 1000x1500 if your drawing is set to UNITS = Millimeter

If you want to plot that table now 1:10 or 1:20 has nothing to do with the model itself, it's a question of paper format and viewport scale.

- alfred -

[Anonymous]

Yes, I am aware of that but my question is how is the drawing read on site. We scale the drawings to fit a specific paper size. So how does the person in-charge of reading the drawings determines the dimensions that are not given in the drawing.

[Alfred.NESWADBA]

Hi,

>> We scale the drawings to fit a specific paper size

Maybe I'm not clear, excuse me for my limited English ... a drawing is not scaled, just the plot (better the viewport to plot) is scaled.

>> So how does the person in-charge of reading the drawings

>> determines the dimensions that are not given in the drawing.

The dimensions should always show the value of the distance (or angle) of the model, so the values have to be the correct modelsize. If the model is 1.2m in length, then it shows the value 1.2 independet of the plot scale.

Hope that makes it more clear.

- alfred -

[cadffm]

Are you talk about PAPER?

regardless of how you draw and how you print.

you are responsible for displaying the correct scale on the plan (or proper text in the titleblock).

Then it can measure on paper with special hardware or the client can math and calculate it.

https://goo.gl/images/qHTvEV

[Anonymous]

Yes, that's what i wanted to know. They would have to use a Metric ruler to determine a certain dimension(which is not mention).

But where im from, every contractor doesn't carry a metric ruler with them, so in that case do i have to mention every dimension in the drawing?

[TheCADnoob · Accepted solution]

Generally just create the drawing in the fashion described in the contract. There are also given assumptions on what should be scaled in different trades. It helps to know or have an idea how the item you are drawing is being constructed. This will give you a good idea of where dimensions will be needed. If a part of an assembly will come as a uniform standard prefab, don't dimension it.

When it comes to them scaling in the field, I've known contractors who only look at 11X17 regardless of scale. That not to say its unimportant, but to say that how they use the drawings will differ. 

I've never seen one running around with a scale, but i have seen scales pulled in PDF readers. I've also seen drawings revved to provide the proper information. The idea is that you have already provided all the information needed and if they have to pull a dimension you haven't given them enough data. 

[ian.mag]

Hey,

I believe that would be correct. The people on site more often than not always have a scale rule, to enable them measure the dimensions that may have been missed out, or which they require and haven't been shown. A good practice would be to always have a scale indicated for each drawing or detail that goes to site.

[jordan.kay]

I am a Journeyman Carpenter, and I was taught that if I was missing a dimension on the plans, I could make up a ratio to come up with the information I needed.

You simply take a measuring tape, find the largest dimension on the plan (for the greatest accuracy) and measure what it reads on your tape. Divide this dimension on the plan, by the number on your tape. The answer is your ratio; that you can store in your calculator's memory. Then measure what the missing dimension reads on your tape, and multiply it by the ratio you came up with, and voila! So I wouldn't worry about showing every dimension; as a contractor I would prefer this.

[dgorsman]

Field procedures can differ based on industry.  For example, in residential construction it would be common to "make it work", either through scaling or "guestimating" because minor variances rarely make a difference in the finished product.  In more rigorous engineered jobs though, they won't scale off a drawing.  They'll file an RFI (request for information) or similar document to get missing values.  That can impact schedules (the fabricator/constructor doesn't want to bill that to the client, so they pass it on to the engineering company) so you want to avoid that.  Similarly putting too many dimensions can also result in an RFI, as a collection of end-to-end dimensions may not agree with an overall dimension value (now they need to confirm which one is right), or a dimension may not precisely agree with what they are physically measuring.

While you don't need to dimension *everything*, all critical values necessary for fabrication and/or assembly (depending on the type of drawing) should be included so there are no such questions from the field.  That means taking steps such as letting non-critical dimensions "float" inside an overall dimension so there cannot be any conflicts, notes to ensure parts that need to fit existing spaces/objects are field measured prior to construction, and so on.