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[Tug-Kenny RIP]

I have a problem with the mathematics of scale conversion.

I need to convert sizes drawn in 1:400 scale (or other scale sizes)  to their correct sizes in 1:200 scale.

I need to know the formula please.    ie:  multiply or divide a length by a number to 2 decimal places.

For example..... if converting from  1:200 to scale 1:100,  is it multiply the length by 2.

Hope you can point me in the right direction.

ken

[Bob K]

I have a problem with the mathematics of scale conversion.

I need to convert sizes drawn in 1:400 scale (or other scale sizes)  to their correct sizes in 1:200 scale.

  is it multiply the length by 2.

Yes, that's it.  multiply the length by 2

Bob K

[Tug-Kenny RIP]

Thanks Bob.  Looking back , it seemed a silly question but I've been using the calculator to transpose between real sizes in feet and inches and converting to metric sizes in my model Queen Mary scale of 1:200. 

Problems come in when I find another plan where the measurements are in 1:190 or 1:175 scale  (and worst still even 1:1400 scale )   purporting to be exact scaling of the real object and then trying to convert them down (or up)  to my chosen scale of 1:200.

Does this sound confusing enough.  I have sought out scale conversion charts on the web.  Some you pay for, some are free but they do not give the formula or the scale required for any future calculations.

My reasons for writing for advice is I have been measuring twice and cutting once and I'm still getting errors.  They may be small, but they do  'stick out' when viewed overall and I do so want it to be right.

Regards, one lonely modeller in a cold shed.

ken

[Bob K]

Following your Queen Mary build with great interest.


Scale you've got plans for
------------------------------    =   factor to multiply measurements by.
Scale you want to build

ie 400
   ----   =  2.0
   200

[Tug-Kenny RIP]

Thank goodness for ModelboatMayhem.   

Takes the loneliness out of being alone.

Cheers

ken

[Brian60]

Or because you are getting old you need to save the braincells Use this page to take all the hassle out of it..........


http://jbwid.com/scalcalc.htm, if you search the interweb you can also download an app for your phone

[Tug-Kenny RIP]

Thanks for the  'heads up'  Brian.

Onwards and upwards.     

ken

[Baldrick]

Or if your feeling as lazy as me get a cheap pair of engineers proportional dividers off ebay.


http://www.ebay.co.uk/itm/ACCURASEE-ARTISTS-PROPORTIONAL-DIVIDER-DRAWING-PAINTING-TOOLS-/271845800968?hash=item3f4b45bc08:m:mnBoxoMtdzCGKEYTyy_rCuA

set the scale change to 1:2 , then dimensions taken off the plans from the narrow end points will  be set on the wide end points . Fastest way of doing scale change

[ChrisF]

Am I right in thinking that it doesn't matter whether you are working in metric or imperial?.

Whichever is used will provide the same size for a given scale.

[malcolmfrary]

Provided that both ends of the calculation are in the same type of unit (both metric or both imperial) it works by giving you the right number.  Its when you mix them that problems creep in.

[Colin Bishop]

Its when you mix them that problems creep in

Which is what happened with one of the NASA Mars probes I believe!

Colin

[dreadnought72]

Mars Climate Orbiter. September 1999.

'The primary cause of this discrepancy was that one piece of ground software supplied by Lockheed Martin produced results in a United States customary unit, contrary to its Software Interface Specification (SIS), while a second system, supplied by NASA, expected those results to be in SI units, in accordance with the SIS. Specifically, software that calculated the total impulse produced by thruster firings calculated results in pound-seconds. The trajectory calculation software then used these results - expected to be in newton-seconds - to update the predicted position of the spacecraft.

The discrepancy between calculated and measured position, resulting in the discrepancy between desired and actual orbit insertion altitude, had been noticed earlier by at least two navigators, whose concerns were dismissed. A meeting of trajectory software engineers, trajectory software operators (navigators), propulsion engineers and managers, was convened to consider the possibility of executing Trajectory Correction Maneuver-5, which was in the schedule. Attendees of the meeting recall an agreement to conduct TCM-5, but it was ultimately not done.'

Dear old Lockheed Martin. $200 million burned to a crisp.

Andy

[RAAArtyGunner]

Or if your feeling as lazy as me get a cheap pair of engineers proportional dividers off ebay.


http://www.ebay.co.uk/itm/ACCURASEE-ARTISTS-PROPORTIONAL-DIVIDER-DRAWING-PAINTING-TOOLS-/271845800968?hash=item3f4b45bc08:m:mnBoxoMtdzCGKEYTyy_rCuA

set the scale change to 1:2 , then dimensions taken off the plans from the narrow end points will  be set on the wide end points . Fastest way of doing scale change

Good call.

Have one of these for years, work very well, even useful when constructing to check measurements.

[roycv]

Hi dreadnought 72 the reference you made to pound / seconds was that called a Poundal? 
I vaguely remember my physics done in S I units, found it difficult to visualise the webers and Neuton seconds and kilometers, after that as I already had a nice cozy relationship with fractions!

Do not laugh they can be very useful and often provide a quick ball park answer.
I still work in fractions, millimeters and ounces and cubic inches, it works for me!  (hate kilometers)
regards Roy

[SailorGreg]

Am I right in thinking that it doesn't matter whether you are working in metric or imperial?.

Whichever is used will provide the same size for a given scale.

Yes, you are quite right.  The figure describing the scale is a ratio and therefore dimensionless. It doesn't matter if you make your measurements in inches, millimetres or cricket pitches. The scale calculation doesn't care.