Tag Archives: science

Building better trousers with SCIENCE

I’m still very much in sewing mode rather than knitting mode these days. I’ve decided I need new work trousers and the only way forward is to sew them myself.

Unfortunately making trousers that fit well is a high-level challenge. All those intersecting topographies at the crotch! Once you’ve got that bit right the rest will follow. I’ve not found a satisfactory crotch-seam drafting tutorial on the internet and I’ve watched my own mum have limited success with the Palmer & Alto tissue-fitting method. Frankly, everyone seems to be relying on standard crotch seam templates and blind trial and error, which just isn’t good enough for a professional woman of science such as myself.

The best advice I ever got as a Physics undergraduate was this: YOU CAN SOLVE ANYTHING WITH LASERS

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This is the Bosch PLR15 Laser Measure. It can measure distances to an accuracy of ±3 mm, which is the highest acceptable accuracy I was willing to pay for.

So what I did this weekend was measure the profile of my crotch to an accuracy of ±3 mm. Yes, I genuinely believe the findings are worth a blog post on their own! Let me detail the method: I marked up the centre of an A3 piece of paper with 1cm increments, and stood in my knickers with my feet either side of the paper, whilst my incredibly good-humoured boyfriend moved the laser measure along the marks, noting the distance measured. He also noted the ideal inseam placement.

So we ended up with a piece of paper like this:

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Which I translated into the following x-z plot. Not well, mind you, I had to redraw a few points.

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There’s some variation here, which we will have to chalk up to measurement uncertainties and also any movements I made whilst standing. Nonetheless I think it shows a fairly clear profile. Two things immediately jump out: the lowest part of the crotch is slightly behind the inseam, making it almost dead centre of the profile, and the front crotch is very long.

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I then added error bars and a generously deep line of best fit. I had to think about that line. How closely should a crotch fit before it starts to highlight the er, “topography” a bit too well? I then cut the curve out of the paper and holding it against myself, the backside seemed to fit absolutely fine, but I had been skittish about the front and the resulting curve had too much depth. The overall length of the crotch profile was fairly spot on.

Compare the seams though, against the Palmer/Pleutsch trouser pattern, McCalls 6361.

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The curve of my backside starts later, and is shallower than any of the suggested sewing lines the pattern has helpfully marked out. You can see my inseam marking through the paper here. It’s clear I really need to move the inseam if I’m going to make this pattern. The front crotch on the other hand…

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Completely different to the pattern! Even moving the card back to compensate for hypothetical inseam movement, I can see that I need a very long front crotch. It explains a lot though. In shops, I always find trousers pull at the front crotch (the Palmer book calls them ‘smile lines’), or I get that oh-so-flattering camel toe, or both. At the back, I occasionally find some odd folding under the butt-cheeks but not very often. Incidentally I really hate shopping for trousers.

Redrafting the crotch seam to the extent I need it will take some doing, but hopefully my scientific hubris will pay off. At any rate, I feel like I’ve figured out an awful lot of trouser problems without doing any actual sewing.

Updates to follow when I have something wearable!

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This post is dedicated to the lovely man in my life, and any other S.O. that, on hearing the question “Can you point this laser up my butt?”, says yes first, asks why second, and starts worrying about centering methods third.

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