[SOLVED] I need help understanding measurements / dimention markings on a datasheet

[Xenobius]

Hi all,

So I am trying to draw a package for a micro SD card holder from Molex however I cannot quite understand some of the markings.
For example some markings are simple 1.8 meaning 1.8mm however others are for example 2-5.14... or 2-1.0... what does it mean?



https://static6.arrow.com/aropdfconversion/af53f7712567bd056763f4323b2743c483def1df/1040310831_sd.pdf

Thank you

 

[FvM]

Consider that the N-xx.x syntax refers to dimensions occurring multiple times. In case of 2-5.14 this is a bit confusing because 5.14 is also printed separately for the upper pin.


You could also consider that the picture is the copy of a correctly dimensioned CAD drawing. So you can always scale it accordingly and check the dimensions with a ruler, or even convert it to dxf and use it to check your footprint pin placement.

 

[wwfeldman]

i don't think that drawing is correctly dimensioned

the current practice is to measure everything from one reference, usually the lower left
so that tolerances do not build up

the values in the drawing are likely correct, as Molex is reliable, but the drawing does not follow best practices

as for the drawing being a copy, it looks like a small piece of the drawing in the link
there is no reason to believe photocopies and PDFs maintain dimension
if you measure the drawing, start by checking several short dimensions and several long dimension in both directions

 

[FvM]

the current practice is to measure everything from one reference, usually the lower left

Should be so, but incremental dimensions seem to be popular, particularly in Japanese and Chinese data sheets. No reason to assume that the dimensions are wrong.

- - - Updated - - -

You can download a STEP 3D-file from Molex and export it to *.dxf
Should give you exact dimensions.

 

[Xenobius]

Ureka moment! 8-1.1 means qty 8, size 1.1mm

 

[marce]

Better still read the DXF into your cad package and use as a base for the component.