# do not scale drawing



## ariz (Apr 10, 2010)

time ago I bought the book of 'the motor boys international', which contains a dozen of plans of IC engines
now I wish to build one of them, the apparently simple 'Mate'

I noticed that every page of the book says: 'do not scale drawing, work to dimension'
what it means? I wish to double the measures of the plan, an engine that is 5 cm long is a bit little for my taste

am I misundertsanding something?


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## mklotz (Apr 10, 2010)

I suspect that it means...

Do not determine dimensions by direct measurement of the drawing. Instead, use the dimensions printed on the drawing.

Scaling the dimensions *read from*, not 'measured from' the drawing, should work just fine.


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## GWRdriver (Apr 10, 2010)

ariz,
Marv is absolutely correct. Among other reasons, paper can shrink or expand depending upon the relative humidity, sometimes a great deal. Also some draftsmen, of which I was one for many years, didn't always draw the object to exact scale relying instead upon the dimensions to provide exactness. Thus "Do not scale the print."


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## Tin Falcon (Apr 10, 2010)

Marv and gw are absolutely correct. this is a general rule of building things. 
Sometimes a print will have dimensions but not ones you want or feel you need .This is time to pull out the pencil and paper or calculator, and do the math to determine other dimensions. Do not read them with a scale. If you are really jammed in a corner and need to use a scale as a last ditch no other way to get a measurement check known given dimensions both horizontal and vertical to see what error or distortion is in the print. Even this may not give an exact dimension if the print was not drawn to true scale. 
As far as scaling up you should be fine.
Also be aware that doubling the size of the engine you will have an engine that uses 8 times the material thus weighs 8 times as much will use 8 times the fuel and put out 8 times the power. but going from 5cm to 10 cm should not be a big deal. 
Tin


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## ariz (Apr 10, 2010)

thank you, this is what I had hoped to hear

2 x is the minimum amount that I need to work without a scope, my glasses should be enough ;D

I think that also clearance of the parts would be less restrictive, right?
the original plan is for a 2cc diesel engine, so an 8cc would be equally reasonable I think

because it would became an 8cc, or not? ???


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## Tin Falcon (Apr 10, 2010)

> because it would became an 8cc, or not?  ???



no when you scale up :
linear measurements are proportional ie 2x
area is proportional to the square of the number  2^2= 4x
volume is proportional to the cube    2^3 =8x  
Tin    
Oh and yea a duh doubling a 2 cc motor would give a 16 cc motor where was my head whoops. 
edited to correct mental gas!!!


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## shred (Apr 10, 2010)

That one confused me for a while until an oldster referred to what I call "a 6" ruler" as a "6-inch-scale". Then it clicked

"Do not scale" means "do not slap a ruler on this drawing and attempt to take measurements off it"


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## Tin Falcon (Apr 10, 2010)

The word scale in the English language is a bit ambiguous.
Scale: an instrument for measuring mass. 
Scale: The protective plates on a fish.
Scale : rust crust corrosion on metal such as mill scale. 
Scale the marks on and instrument such as a ruler or scale or a thermometer. 
Scale: The marks on a map representing a stated real distance. 
Scale: ratio of the distance on a map , drawing or model that represent the same distance in the real world object. 
And there are a few others as well. 
Do not scale means do not measure the mass of the drawing :big:
Tin 

Oh and yea a duh doubling a 2 cc motor would give a 16 cc motor where was my head whoops.


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## GWRdriver (Apr 10, 2010)

shred  said:
			
		

> an oldster referred to what I call "a 6" ruler" as a "6-inch-scale".


One shouldn't have to be an oldster to know the difference, especially in model engineering. Members of the engineering, architecture, and science professions always use "scales" although with Cad being the almost universal drafting tool the engineering and architectural scale, like the drafting pen, has become almost obsolete. Scales are now used mostly in design or client meetings to take quick measurements off drawing prints for discussion purposes. The difference is between a scale and a ruler is that a scale is made to a much greater level of linear accuracy than a ruler.


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## Tin Falcon (Apr 10, 2010)

Drafting scales are still available mostly used by students most commonly in a trianglular shape with 6 to 12 scales on it. I have three different ones:
 metric for engineering or architectural use 
architectural imperial fractions. ie 1" to the foot scale or 3" to the foot scale
and engineering in decimal inches. 
I am still one of those old timers that leanred drafting in Jr high and high school on paper before the heavy use of computer drafting. The first release of auto cad was fall of 1982. 
Tin


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## capjak (Apr 11, 2010)

I took two years of mechanical drawing in high school in 1955 and 1956. One of my classmates was female and that was considered so unusual that she was mentioned in the local newspaper. The time in the class that the tension was highest was when we had to use pens with India ink to complete the drawings. No errors were tolerated.

Jack


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## Lew Hartswick (Apr 11, 2010)

Rulers are made of plastic or wood, scales are metal or in a few old rare cases 
a triangular device with ivory faces. 
  ...lew...


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## Brian Rupnow (Apr 11, 2010)

Lew---Triangular scales were also available in cheap, white plastic. I know, because as a starving drafting apprentice in 1965, making $53 for a fourty hour week, that was all I could afford. I couldn't afford one of the "nice" triangular scales untill I'd been working 5 years. ;D ;D We worked on a lot of large gold mining projects, self unloading ships (grain carriers on the Great Lakes) and on the Athabaska tar sands project. Most of our General Arrangements were done at 1/4"=12", detail work was done at 1"=12" scale, and "blow ups" were done at 1.5" and 3" to the foot scale. We HAD to draw everything to scale, but we had to calculate every dimension. This was in the pre calculator days, when everything was done with "Smoleys Four Combined Tables of Logarithmic Functions". The "Checker" (Most hated man in the drafting office) would check your drawing for scale, and your calculations with a slide rule, and if things were out of scale, you would be looking at a complete redraw. Too many "redraws", and you were taken aside by the chief engineer for a "Little Talk" and it would be suggested that perhaps your talents lay in a field other than mechanical drafting.---And God help the machinist/fabricator who was caught scaling anything off a drawing. His career change would be immediate and irrevocable. Now in the wonderfull world of computers, when one of the printing options is "Scale to fit paper size when printing" it would be an even worse option to consider scaling a drawing.----Brian


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## steamboatmodel (Apr 11, 2010)

To save time when a product is revised and a dimension is changed just the written dimension would be changed rather than redrawing the drawing. ie it was found that a hole should be drilled 3.5" from an edge, where originally it was 3.6", the dimension would be changed but the hole would still be drawn at 3.6" from the edge.
Regards,
Gerald.


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## Brian Rupnow (Apr 11, 2010)

Steamboatmodel---That may have worked in the horse and buggy days when I started out. Now however, the customer will ask for the cad file of the drawing as a .dxf file to be sent to the burning table or the cnc shop. And when ya get old like me, you can no longer remember which dimensions you "fudged" and which ones you didn't, so you pretty well have to make it a blanket policy to never fudge any dimensions. Nothing is uglier than a fabricator who had just made a $2000 cnc part and then finds out that some of the math data in the cad file was DIFFERENT than what the dimension said.


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## steamboatmodel (Apr 12, 2010)

Hi Brian,
It was mostly work that was done in house that the drafting dept. didn't have time to redraw the drawing. It was quite common for us in the shop to get drawings/prints that would have changes done to dimensions in red ink with initials and a date, and be told they needed the parts yesterday and proper drawings will come latter. It got to the point that I would photocopy all the drawings that came in like that and file them with a copy of the workorder and a printout of the cnc program. It was much better once we got to the point that all the drawings were done in cad, but I always had a fight to have them keep the drawings current with changes on the production floor.
Regards,
Gerald.


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## Dan Rowe (Apr 12, 2010)

Gerald,
I work from copies of original Lima Locomotive Works drawings and it is very common to have changes noted on the drawings or even several different mods to castings for different applications. I think some of this might have been done in a different color but I only have B&W copies. I always double check any note in a different hand writting as it was not done by the original draftsman.

There have been times when a dimension is not specified, so I like the original pattern maker have to use my best judgement as how to make the part. If I have to use a scale on the drawing I always check near dimensions both vertical and horizontal to check for paper stretch or scan error.

Errors In Lima drawings are fairly rare but they do exist and each one I find takes more research to figure out how to deal with conflicting information.

Cheers Dan


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## steamboatmodel (Apr 12, 2010)

I enjoy Drawings much more since I am retired and don't have to worry about Bosses, Customers, and deadlines. When I was working drawings were sometimes a real Pita.
Regards
Gerald.


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## Brian Rupnow (Apr 12, 2010)

Steamboat---Yeah, in the pre-computer days, I used to do it all the time too. As long as it was marked up as a "Revision" and a date and reason were included, we felt pretty safe with it. On a lot of our repeat orders that were "almost" the same it was not uncommon to make a sepia or mylar, change half the dimensions on a sheet, put a big note on it "NOT TO SCALE" and issue it to the shop floor. Time was money.---Still is!!! ;D ;D ;D


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## tornitore45 (Apr 12, 2010)

I have never seen a "Diesel" model engine larger than 5cc, however 10cc glow plug are popular.
There must be a reason for it.
A 16cc "Diesel" may be a bear to start by flicking the prop, and if it bites it may take the finger out.
Mauro


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## rleete (Apr 12, 2010)

"Drawing not to scale, dimensions omitted for clarity." One of my favorite notes.


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## ariz (Apr 12, 2010)

tornitore45  said:
			
		

> I have never seen a "Diesel" model engine larger than 5cc, however 10cc glow plug are popular.
> There must be a reason for it.
> A 16cc "Diesel" may be a bear to start by flicking the prop, and if it bites it may take the finger out.
> Mauro



thank you Mauro (forse possiamo parlare italiano? Mauro è un nome italiano, tornitore è un sostantivo italiano...)

anyway, your answer make me to think more about it... perhaps 2 x is a bit too much, maybe 1,5 x is a better option?
or I have to be patient and meticulous and afford it following the original specs
but I have to work always with my 'scope' on the head :-\


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## tornitore45 (Apr 12, 2010)

Ariz, we coud talk Italian but this forum is read all around the world and english seems to be to common language.
I am Italian, but leaved in the US for the last 38 years.
If you have visual acquity problem you are probably in my age group.

I have mounted a lens on a homede adjustable arm just over the chuck.

Now, precision is more of a technique (which I lack) than good eyesight.
If you can read the micrometer and the machine dials, you can hold a dimension.

I have learned a lot about precision set up on this board and also on the excellent

http://www.chaski.org/homemachinist/


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## GailInNM (Apr 12, 2010)

Ariz,
Bob (Maryak) built a 10cc compression ignition (Diesel) engine a while back. The complete build thread is at 
http://www.homemodelenginemachinist.com/index.php?topic=3712.msg37577#msg37577
and the video of it's first run is in post 400 of the thread.
Gail in NM


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## Lew Hartswick (Apr 12, 2010)

Brian Rupnow  said:
			
		

> Lew---Triangular scales were also available in cheap, white plastic.---Brian


Hummmm. I wonder does that make them Architect/Drafting RULERS ?? 
  ...lew...


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## Brian Rupnow (Apr 12, 2010)

Lew---I never heard them caled a ruler.---Brian


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## ariz (Apr 13, 2010)

Thank you Mauro and Gail (and Maryak too)

now I'm more relaxed and can afford it, the thread of Maryak's build will be very helpful too

thanks again


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