Being a “hard goods” kinda guy, I’m familiar with dimensional control as it relates to fitting parts together.
But I’m curious, what are the tolerances, and other “controls” used in the footwear industry? Given that the human body is truly unique, how are the various “sizes” and “widths” determined? i.e., are there universal standards (templates) within the industry, or does each company develop it’s own set of lasts? And how are these “controls” maintained in production?
I bring this up because I bought a pair of Converse Hikers a month ago, and they are still tearing me up. The right foot is well fitted, but the left one pinches my outer toes, but the insole on the right foot tends to bunch up after wearing for about five minutes. On both boots the laces (“parachute cord”) are already unlaying themselves and must be replaced (again, due to eyelet design (hard edges)).
Other boots and shoes that I own fit differently. i.e., some cramp my right foot, won’t lace up to the last eyelet, the laces wear prematurely because of the eyelet design, the heel “cup” of one foot fits looser than the other, etc.
Like I said, just curious…
It’s pretty complicated, but I’ll try to share some light on the subject from my own experiences (concept is still the same, but processes may vary in a larger company with more dedicated teams working on the subject).
Yes, each company makes their own lasts (or develops/“copies” lasts based on another product). not only does each company have their own but normally each model is different as well. There are several key measurements on a last that will determine the fit/look of the shoe, such as toe spring, ball girth, stick length, last length, heel cuboid shape, etc. the initial fit of the last is normally checked with fit samples made from the last. At this point, the company will have some standards in place that determine overall fit (ie. size). for example a last that is 273mm in length might be a size 9US. This also varies by company and there is only loose guidelines (that’s why you might be a size 9 in one brand but size 10 in another).
From there, there is the grading process. This determines how the last is scaled up or down for different sizes and which dimensions change an how much. For example, one last or company may change the length by 4.2mm per 1/2 size, and the ball width by 1.06mm per 1/2 size, etc.
Then there is the whole production process and the variations that come with it along with the QC. As footwear is essentially made by hand, by countless different works from different parts, materials, and processes, there is naturally some variation there. It’s not like it’s something that is just injection molded, popped out of the mold and done. A worker is literally on a sewing machine sewing every stitch, and add to it some materials also have variances (such as leather where every piece has a different grain and varies in thickness (for example most leather is spec’d in a thickness range to account for this, such as 1.2-1.4mm)). The QC is responsible for checking various things and of course QC quality can vary with the fty and price point (you wouldn’t expect as thorough of a job for $20 wal-mart sneakers as $200 running shoes).
QC and specs normally involve visual inspection and also material specs or product testing. Without getting into too much detail there might be abrasion resistance specs which can be checked by a machine that rubs a part on sandpaper while checking for the breaking point, or UV fastness, humidity handling, durometer, etc. In any shipment, there are usually 20 or so things they are checking either visually or by testing a certain % of product with categorization of # of major or minor defects and some acceptable rate it’s judged against. If the shipment passes at a level above the acceptable rate, it’s good to go, with perhaps some specific major defects pulled, or is rejected outright if more than an acceptable rate fail.
That, I think pretty much sums it up, but if anyone has any corrections or stuff to add, by all means…
hope this helps.
PS> also don’t forget your feet are likely different sizes/shapes while the L/R shoes are not (in theory).
As Richard says, every company has their own quality control standards for last fitting.
For instance I cannot wear certain brands due to the fit. Also depending on where the brand is from, the fit will be different too. An African foot has a very wide heel, many European lasts will not fit. French lasts tend to be narrow and not at all curved. Japanese feet are flat and wide at the forepart.
I work with people worldwide and it’s quite common to hear complaints, for instance I worked with a factory that manufactured mainly for Australia - the fit was no good for us in the UK! Sounds mad but it’s quite a common gripe.
Add to that the different sizing standards for footwear and their different tolerances and you can see it’s a nightmare. See the attached bata size chart, you can see the different sizing sytems don’t grade against each other evenly.
So, if you are a technologist working with a factory and they only have American sized lasts and you have to grade them for the Uk market, because no one does half sizes anymore, you’re going to have a problem when you grade the shoe for the UK. A USA 6, should you call it a 5 or a 6? What about a European size 39? Most UK stores call it a 6, but it’s not , it’s actually closer to a 5 1/2. It’s a nightmare to be fair, when I worked for Skechers, we had a hellish time fitting things for the UK - especially for home shopping (where a true fit is vital, otherwise you get too many returns), because they just did not grade into UK sizes properly.
Actual fitting of the product is a black art. Technologists that I work with (I use a freelance) takes the sample and fits it on various people who are about that size. he has measured their feet so he knows that they are a near perfect 6, for instance. He has to go on his own judgement and what they say to determine whether the shoe is a good fit or not. Its no good for me to know that it fitted in the factory. It needs to fit a British foot.
As far as testing is concerned, big factories tend to have their own testing labs, to do flex and abrasion tests for instance. Also we tend to use third party labs, such as Satra or Intertek for testing. I still rely on a book I have for the (now defunct) British Shoe Corportaion for quality control standards, if I’m working with a small business and they haven’t set any standards up. Alot of it is common sense, for example I would never use a zip on a ladies fashion boot that wasn’t Optilon or YKK branded and I would always ensure it was double stitched in, with a gap left between the edge of the zip and the stitching, loads of stuff like that, I’ve just picked it up over the years from working with technologists. Also if a client is a Satra member and we are developing a new technical outsole they will be able to advise me on compounds for the outsole, stuff like that that I just wouldn’t know as a designer concerned mostly with the auesthetics of a product.
I’ve been told that shoes in the UK are the worst for ‘customer destruction’, thats when people deliberately damage them and return them to the store for a refund. Satra have develped tests to determine whether stitching has been deliberately unpicked or not, seriously. I have to be aware that any hardware used on the shoe has to be very firmly attached and not just by pins like alot of Spanish or Italian footwear might be.
Sounds like there was something awry in the qc process for the OP’s boots!
Finally, I develop lasts with a last maker and the other dark art is developing a new fashion last with a funky toe shape and then trying to get it to fit! They never fit to start with! Unbelievably difficult, the compromise between fashion and fit!