There have been numerous threads in the past asking about how to use the Custom Seam Allowance. It is a very confusing & awkward “feature”. The Dev team is [contemplating] replacing it with something more usable, & is pondering the possibility of completely eliminating it from the codebase if no one uses it anyway.
Does anyone use Custom Seam Allowance? Note that this is not the normal customizable seam allowance, but the subcategory of the internal paths tool.
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Thank you
Contemplating replacing it. 
Thanks Grace! I didn’t look in the right place for the Poll code.
I don’t think I’ve ever used a CSA in a non-experimental pattern, & even if I did, I’m fine with code-editing it out if it ever comes up.
Getting rid of the CSA code also simplfies the Internal path tool… there’s no need for a “type” enum and selection in the dialog.
Hallo, I tried to work with custom seam allowance. Unfortunately I could not figure out how it is working. Once someone of you described how it should work, I was not capable to do it. It would be really useful for folded hem facing. It would make the construction more clear instead of mirroring the curve.
The only way I use the custom seam allowance tool is in creating a fold line (which has no seam allowance) with seam allowance present on the remaining surfaces. I am sure it is possible to have a much simpler way of indicating that a specific line is to be cut on fold.
You can create a foldline by simply setting the After SA to 0 and the Before SA to 0 between 2 node points.
Way easier than dealing with a CSA.
Could you be more specific… Are you saying what I proposed to add new corner angle options would be useful? Or using the CSA is useful?
I think there’s some clarity needed here. creating a Custom Seam Allowance is different to using the Custom Seam Allowance Tool.
I think that we all create a custom seam allowance by editing the points where we want more or less seam allowance for various reasons.
Using the Custom Seam Allowance Tool is totally different and is very complicated (my pea-brain just can’t get a handle on it nicely). It’s found here:
And you need to create the Internal Path and set it as Custom Seam Allowance first:
And then you can try your best to get it to do something nice in this area… Very complicated 
Ok, so I used it completely wrong, but I think you get the idea. It’s a tool all on its own.
To all: When ever I say CSA (Custom Seam Allowance), I’m always referring to the Internal Path → CSA tool. Which is defining a path in draft mode and appending that to some place on a pattern piece between 2 points in Piece mode.
Hem facing, part of the cut piece. Def. CSA is A1#, A15#, Spl_A15x_A8, A23, facing_h
result
It should be like this. Yellow marked part will be the CSA.
Yes… this along with sleeve hems would be the exact situation where my idea of adding new corner angle options would simplify the whole thing. In this case all you would need is your points A15# and A1#… based on a SA width we can determine points A23 and facing_h by using a new 1st edge option at A1# and a new 2nd edge option at A15#, and from that we can mirror those points along the the line A15#_A1# to calculate where the extended corners of the hem SA is located. We don’t need all the convoluted mess of creating a CSA with the Internal path tool and appending to a piece.
I played for like an hour the other night and couldn’t get it to work. And I know how it’s supposed to work. 
Yes. Exactly. BTW… here’s another reason why my idea makes more sense… what if you want a 3" hem? A 2: hem? A 1 " hem? With the CSA it would be a total mess trying to adapt to different SA widths. My way you just simply change the Before and After widths… which could be a formula. 
Just an update on using the CSA… I did some testing and actually got the CSA to work:
My test block:
Working CSA:
What you need to do to get it to work - You need to include the CSA as main path and the start and end points need to be in a clockwise direction:
Including as a Csutom seam allowance never seems to produce a correct result. Plus a big caveat with using the CSA… apparently you can only include 1 CSA in a piece.
Now… while I was able to get the CSA to work with some cases in the Union tool, it had lots of issues.
This worked:
This didn’t:
There’s the issue of which point is which as there can duplicate point names:
Then there’s the issue that the path name is lost for the second path after uniting. In the example for Piece #1 the CSA path was named hem, for Piece #2 it was named hem2… after uniting hem2 name is gone and it’s now Unnamed path:
And again apparently in the Union piece there can only be 1 CSA path even if you try including 2.
Further testing produced more issues… like this one that left the app in an endless loop of throwing this warning as the SA went off the scene. 
My conclusion… this is what a buggy feature that the dev knows how it works, where
your average user won’t, but he puts it in the app anyway.
My vote is to rip it out.
We can re-implement it after the internal path tool is fixed, if we decide we want it. This mirrored seam allowance feature was a real time saver in TMTP to create skirt hems, and especially needed for historical clothing with shaped jacket cuffs and trouser hems that are shorter in front and longer in back.
For future reference, Custom Seam Allowance Tool is a misleading name for this feature.
Mine, too. And @Douglas has some nice ideas for replacing it.
Another thing, I’ve been checking out the Union tool and it’s pretty stable now and also does a very nice job in uniting pieces that can replace this tool, too.
With the exception of how it handles CSA’s as I pointed out above.
Except it doesn’t do what the CSA is meant to do… that is show the whole CSA filled like:
And since you have to add all the extra points in draft mode you might just as well just make a pattern piece including the points that would make up the United piece… like:
Instead of making 2 pieces and using the Union tool that would end up looking the same:
For a little insight into how the Seam Allowance works… depending on the corner “angle” selected for a node - the angle type determines how the app calculates the “projected” corner(s) of the SA (cut) path. With the typical By length it calculates the points in red as such:
Where my idea of simply adding 2 new corner options we can calculate the corners as such:
It’s all just simple geometry instead of the convoluted Internal path->CSA tool.
You can do this - which is how I often feel like with the code:
Or make it simple: 
As long the facing has to mirrored as in your example I do not see any benefit of CSA.
As @Grace mentioned this could be done with the Union tool. Just made a short test. It looks the union tool is improved. It works really well for a folded hem facing .
I would say: Problem solved, CSA can drown in history.
Thank you, @MG2024 . May I ask you to do the poll at the top so that we can have an idea of those who don’t use this nasty tool, please?
