A fabric shrinkage after washing is
A) Vertical Measurements : 5% B) Horizontal Measurement : 3%
How to update the measurements?
Do I have to calculate all the measurements and enter again?
Are there an attribute for measurements A) Vertical B) Horizontal C) Diagonal
If there is maybe It can be done easily without entering all the measurements from scratch.
Measurements (smis or smms files) are a personâs measurements. People donât shrink afer washing. 
Shrinkage is a property of the pattern, and as such should be included as a âCustom Variableâ that stays wih the pattern file. Custom Variables can be added in the Variabes Table:
Here I added VertShrink and HorzShrink and express them as 1.05 and 1.03
Now you can use them in formulas⌠such as using it to allow for 3% horizontal âshrinkâ of the width of Line_A2_A3:
So now the length of @Chest_Quarter will be 3% longer to allow for shrinkage. You could then load a different personâs measurments into the pattern and @Chest_Quarter will change, but #HorzShrink remains the same where the line resizes to the new personâs @Chest_Quarter plus 3% for shrinkage.
No. Again âmeasurementsâ are a personâs messurements - thatâs it. Custom Variables can be used to modify those measurements⌠such as shrinkage, ease, stretch, etc, and are an atrribute of the pattern not the person. Together the âmeasurementsâ and âcustom variablesâ are used in âformulasâ to calculate a value - length or angle - which determine the geometry of the pattern.
Youâre generally not going to change the âmeasurementsâ once youâve entered them in SeamlyMe - unless someone has lost or gained weight, or a child has grown. But you will need to change the âformulasâ in the pattern to have them shink, stretch, have ease, what ever. Itâs best to draft a pattern with shrinkage in mind from the start if thatâs what you want. That way you can always simply change just the values of the Custom Variables - without changing all the formulas - to change the amount of shrinkage.
Maybe itâs because Iâm a home sewist, but shouldnât you wash the fabric before cutting?
Yes and no. You are not going to want to wash woolens⌠or they will reallly shrink. 
They can still shrink just pressing them. How much depends on the quality of the sponging. Itâs a pain, but we started pre-pressing with steam to shrink woolens (or other assorted fabrics) on custom suits. There was one job we did once making Union soldier uniforms from some bargin wool my partner found. I had already cut liek a dozen jackets & pants, when the sewers found out the wool was shrinking from pressing⌠A LOT! I mean like an X-Large jacket could shrink a much in width to a Medium. Turns out the wool was never sponged. Needless to say we had to find some other fabric, and I had to recut all the uniforms. 
I could give dozens of examples of problems we had over the years with fabrics. You would think after 42 years I saw it all⌠nope. Customers would still send us fabrics that presented new issues to deal with. 
That being said⌠in production, where dozens of layers of garments are cut at once, thereâs no way youâre going to prewash & press all the fabric. Also shrinkage is just one example where you would want to adjust the formulas⌠knits and stretch fabrics come to mind, as well as adding ease. Both of which one could follow the same steps I gave regarding the Custom Variables.
Thanks for the story! It sounds like a very melancholy sort of day.
& I realize I forgot that the title of the thread mentions elasticity. 
Yes, and besides the stretch & the shrinkage, thereâs also the recovery factor in stretch fabrics where, once stretched out, the fabric doesnât go back to its original size. Itâs a very complicated subject. Best handled in the Custom Variables because it changes from fabric to fabric.
Precisely. Me Measurements should only apply to the person, not the pattern. For example⌠in theory we could have a âSeamlyMeâ app for a phone / tablet where say a theatre could take and enter actorsâ measurements, and then email them to a costume shop. They should only be concerned with the personâs measurements and not shrink / stretch ratios, ease, etc⌠these are factors for the designer(s) to figure out in Seamly2D. I know Iâve asked customers âwhat is your waist size?â
Iâve never asked a customer âWhat is the shrink ratio of Melton wool?â⌠kinda like asking âWhat is the air speed velocity of an unlaiden swallow?â 
I totally agree. Anything pattern/fabric specific should go in the Variables Table where they are easily editable without affecting the actual measured measurements of the person, which should only be edited in the event of the person being measured again and differences found.
Question 1) (Iâll also add the shrinkage ratio information for the diagonal fabric line 45 degrees.
Diagonal Measurements : 6%)
Maybe It is more like a Pattern Making question. I donât know. But Iâll ask anyway.
How do we calculate the other lines rather than?
A) Straight Vertical
B) Straight Horizontal
Trousers side seam (A little curvy)
Dresses side seam (A little curvy)
Dresses Back seam (A little curvy(
Shoulder line
V Neck
They are not completely neither straight horizontal nor vertical.
On the curvy lines there are not a specific angle either.
How do we do for the lines like that?
Question 2) Letâs say we also consider Elasticity Ratios How do we handle two different category of variables together?
I share all the ratios here as example
Shrinkage Ratio After Washing
Vertical Measurements : 5% Horizontal Measurements : 3% Diagonal Measurements : 6%
Elasticity Ratio
Vertical Measurements : 1% Horizontal Measurements : 2% Diagonal Measurements : 3%
I donât think that I have the necessary experience to actually reply to you, however, Iâll try to explain what I think.
The diagonal stretch/shrinkage will be allowed for in the vertical measurements since gravity will pull the fabric downwards and therefore make the garment longer and narrower, as you have probably seen on the test square that was used to test the fabric.
With this in mind, I would only concentrate on the vertical and horizontal stretch factors unless I was cutting the garment on the bias.
You havenât mentioned the type of garments you wish to make, but if there is any wearing ease included in the pattern, this should allow for both the shrinkage which is only 5%, 3% & 6%, so the most shrinkage is only 6cm for every 100cm or 1.8cm on 30cm.
The elasticity ratio is even more miniscule to the point that it most certainly doesnât need to be taken into consideration at all, being 1%, 2% & 3%. Normally you will only start thinking of the stretch factor at about 15% and the norm is to multiply the horizontal and vertical lengths by .98 for fabrics with a stretch up to 25%.
Normally I would only think about stretch factor when working with stretch fabrics such as lycra for dance and swimwear⌠or conversely when taking a leotard pattern and making it out of a non stretch fabric.
Cutting on the bias is a different story. where for example you might take into account how much a fabric stretches on the bias when cutting a circle skirt. With some fabrics if you just cut a circle the hem is going to end up wavy . So I use to do 1 of 2 things⌠flatten the curve on the bias when cutting - something like:
The distance from A4 to A6 and A5 TO A7 takes into account how much the fabric will stertch onthe bias.
Or maybe you do the opposite for a gored skirt, where the seams are on a bias⌠Blue line:
OR make the skirt, put it on a dress form and let it hang overnight - then trim the hem level. Itâs why orginal âpoodle skirtsâ were made of felt, as it has no bias.
Sorry If I did not use the term Stretch Ratio. Previously I had mentioned as Elasticity Ratio.
We have to draw the pattern a little bit smaller than normal If we have a stretchy fabric.
So Iâll ask again
Question 1) How do we handle both on The Variables Tables? Together
Shrinkage Ratios
A) Vertical Measurements : 5% B) Horizontal Measurement : 3% C) Diagonal Measurement : 6%
Stretch Ratios
Vertical Measurements : 1% Horizontal Measurements : 2% Diagonal Measurements : 3%
Question 2) As far as I understand we add those variables according to the way we cut the fabric
Like the length of the neckbands for example
We have to add Cutting On The Bias factor rather than Cutting On The Grainline
Right?
All I could find in my books is this bit:
Perhaps it will help you. I donât have much experience with stretch fabric, but from what I see here, if the stretch is under 25%, then no reduction is necessary.
UnderstoodâŚ
First⌠fabric doesnât really shrink or stretch on the dialogonal⌠it has bias. Even metal screening has bias, but the wire does not stretch. Fabric threads shrink or stretch the width or length of the fabric. How much they shrink or stretch is as you indicated - as a percentage (ratio)⌠therefore Shrinkage can be expressed as values > 1.0 - assuming you need to add to compensate for the loss, where as Stretch can be indicated as < 1.0 to assuming you need to reduce the length.
Just create 2 custom variables⌠something like #VertFractor and #HorzFactor and in your formulas you would use something like bust_circ * #HorzFactor and neck_waist_b * #VertFactor. What ever value you plug into the variables will indicate whether youâre compensating for Shrink or Stretch. Unless of course you want to get into the world of granularity where say you have a stretch fabric that shrinks in the wash, and you want to express the shrinkage AND stretch as seperate factors. In that case use 4 variables like #VertShrink, #VertStretch, #HorzShrink, #HorzStretch⌠and a formula might look like bust_circ * #HorzShrink * #HorzStretch. But to be honest⌠like @Grace mentioned you can get into a crazy area with stretch fabrics⌠because as a fabric shrinks, itâs going to stretch less, so the stretch factor has to be expressed as a ratio of the shrink factor.
Bias is diiferent, and would be a seperate variable you would only use on pattern pieces cut on the bias.
Exactly⌠because close, is close enough. Itâs probably the point of diminshing returns at which someone determined the time spent getting it exact is not worth it.
My method⌠grab a measured length of fabric, stretch it, and say OK 10 inches will stretch to 18 inches so if I use x amount it will fit.
So do you mean;
We write a formula like that
Letâs say;
⢠Stretch = 0.95 (5% Stretch Ratio)
⢠Shrink = 1.03 (3% Shrink Ratio)
EffectiveStretch = 0.95 / 1.03 â 0.922
Am I right?
Yes⌠except in Seamly2D you would define your custom variables something like this:
and then in a tool formula for length you could use something like:
bust_circ * #EffectiveRatio
Now when you want to create a new pattern layout, you can change the measurements (maybe changing bust_circ) and/or one or both #ShrinkRatio, #StretchRatio⌠and the pattern will resize to the new measurements and custom variable values. In other words you can adapt a single pattern to a personâs measurements and/or the fabric being used⌠without changing ALL the tool formulas.
Understood. Thank you very much.
