Problems with seam allowance and when exporting pieces

Good afternoon!

I am working on a biker jacket pattern and am experiencing several problems.

The first one, regarding seam allowances. I usually mirror draw the bottom of the garments and when I take the pattern to the “pieces” tab, I remove this seam allowance in the bottom part that is applied simultaneously to all sides of the pattern piece.

Please check this image as an example:

This works for me on the less complicated straight hems, however now I am creating a fake tailored sleeve (taken from the standard sleeve pattern, it has a cut in the back part and a small dart that goes up to the elbow level).

For these sleeve pieces I need the seam allowance to be mirrored, but I don’t get the desired result neither by doing it the usual way I work, nor with the seam allowance panel of the “pieces” tab. It’s as if the corner is too sharp and I cut it off by default.

Here are some additional examples:

How could I solve it? If the pattern looks like this there is no fabric in the margin. What would you recommend?

And on the other hand, I have downloaded the latest version of Seamly to see if I could solve the previous problem and put notches on the seam line (I have not succeeded, but I have solved it by inserting an internal path).

The thing is that now it doesn’t let me export the pieces :scream: it says in the dialog box “Exception: “name of the piece” Doesnt have shape”.

Here I left a link with the measurement file and my pattern:

Thanks for your help, it is much appreciated :slight_smile:


Hello @Esther

I also do my seams like this. It works very well when creating hems on slanted items.

I don’t think that you will get the seam allowances exactly mirrored. I managed something on the side sleeve, but the main sleeve remained the same, no matter which setting I tried:

Here is your file back with the panels that I created with the full seam allowances:
Patrón biker - base prenda holgada 2.val (121.4 KB)

I’m so sorry I can’t help further. Perhaps @Douglas could take a look?



I’ll take a look later.

Just a few notes… an update has been made dealing with zero width seam allowances- it’s in the re-release on Githhub, and I expect it to be available with next Sunday’s release.

Also in fixing the recent issue with the seam allowances, I finally took a look at the “Custom Seam Allowance”… which may be an answer to getting a hem you desire?


In practice this a pain to sew… you have to make sure to line up the corner dots rather than the cut edge. Plus you run the risk of leaving a hole at the corner point as there is no excess past the point. Theoretically the intersection option would be the way to go as that keeps the seam length the same on both parts and removes the excess when pressed open. This also can be one of those issues where which point you start the piece path with can affect the SA… or again the control point angle and length going into a corner can affect the SA.


Ok I took a look at the pattern.

First I can answer this… or at least what’s causing it. There’s an issue with checking “Hide seam line” that making the piece loose the shape of the piece. I got it fixed, just need to push the changes. Until then, unchecking this option will fix the issue… of course the seam line and subsequently the seam allowance will be shown.

As far as the seam allowance on the sleeves I’m not really sure what the problem is.

This is exactly how I’ve been doing an outside sleeve seam for 40+ years. Just added the seam allowance, and used the Angle: by points intersection on the under part.

Which produces this when sewn and pressed open… this is the 2 pieces overlayed: The red line showing how the length from the CanesuEspalda point to the cut line is the same. Assuming the pieces are cut accurately, it’s easy to line up the the 2 seams matching the yellow point of each piece, and just sew the seam. Removing that little triangle automatically establishes the allowance width without knowing what the width is or what marks on the throat plate to follow. Any other corner type requires you to THINK and match up the CanesuEspalda points to be correct.



Thank you very much for your quick response.


Oh perfect! Glad to know I’m doing it like the pros :slight_smile:


Does this change go in the Sunday release? Like the change in the zero width seam allowance you were talking about?

I have only updated Seamly once, so I have a question, on Monday for example do I download the seamly installer again and will the changes already be incorporated?

Perfect, I’m going to start doing it this way too, and I won’t mess up my head :blush:


If I get the changes pushed and Susan is able to review and merge the changes by Sunday evening before the build is automaticly triggered.

Yes… if you download a new release it will install any new changes that may have been made during the week. So I would expect next Sunday’s buikd should fix the hide seam line. Which BTW is mainly there to hide the seamline with cutters as you wouldn’t want to cut on the seam line. Even that is redundant now that the seam and cut line can have different colors, which most cutters now can be set to only cut certain color paths.

Or, you can always download directly from Github a “pre release” during the week. Any time a change is merged with the main repository, a pre-release build is triggered.


Thank you very much :hugs:

1 Like

I’ll build the pre-release then post the link in this thread.


Download the new build from here:


I’ve more or less confirmed I’ve fixed the issue. One of those stupid things where I failed to follow the spaghetti and make a simple change in what is more or less duplicate code that renders the pieces for the layout mode, separate from the piece mode.

Just want to triple check to make sure I didnt miss anything else, and will post changes tomorrow eve.


Well, since the export error was such a simple fix I figured I’d just do it on my phone instead of waiting to use the laptop at home. Job Complete… once Susan merges the PR the export error should be fixed. :slight_smile:


:white_check_mark: Done!



Pre- Release available:


Earlier I read a thread titled “Why do you like Seamly?” and for me it is this forum, the valuable help you provide, thank you @Douglas @slspencer @Grace