If you’ve ever wanted to sew your uppers for sneakers like the pros, but don’t have access to a Strobel sewing machine, don’t give up. Sew your kicks by hand!
How to hand sew “Strobel” construction.
The needle goes all the way in, then pulled back slightly which creates a loop in the thread.
Pick up the loop on the kerf side (very important!)
Pull some thread to make the loop bigger (this pulls the thread from the spool up the grooved side of the needle)
Pull the loop over the insole and upper.
Gently press the needle in to the loop for the next stitch, but don’t cover the eye.
Pull out the slack from the loop to set the stitch.
What exactly is a strobel stitch?
Strobel sewing the insole to the upper is actually a chain stitch. In many types of hand sewing, regardless of double or single needle, you have to measure out the thread ahead of time. With a chain stitch like this, like the Strobel machine itself which has no bobbin, the needle is fed directly off the spool. The good news is you can very likely sew to your heart’s content without running out of thread. The bad news is that if you drop your awl, kick your spool, turn away or pull the thread at the wrong time, you can easily pull the whole thing out. Ok, being able to pull the stitches out easily also means you can easily fix a section that you might have liked to sew differently.
When Strobel sewing an upper with a machine, the fancier models have a differential feed (one feed wheel turns faster than the other) so you can gather the upper at the heel and toe. Sewing by hand, you have to be cognizant of the need to do this and gather as necessary.
To make shoes this way, the perimeter of the upper and the perimeter of the insole have to match exactly. Compared to designing uppers with a lasting allowance, designing uppers for Strobel construction requires a high level of accuracy in locating the feather line and a lot of finesse to deal with the toe and heel. Components are handled differently and the last is typically just stuffed in once the insole is one.
Often there are at least 6 registration marks to make sure the insole and upper align properly in production. I drew a line connecting the center of the heel and toe and eyeballed it as I went. It worked out fine, but it means as I approach the center line, I know how much to gather, but after passing the centerline, the amount needed is ambiguous. Experience with uppers helps, or add all the registration marks.
Ok ok, these boots above aren’t actually sneakers, but the process is the same. One of these days I’ll make some sneakers.
My first pair of 100% orthopedic shoes. I’m not an orthopedic shoemaker, but many of the shoemakers I studied from in the Netherlands are. Why call these orthopedic? I’ve made lots of shoes for people who wear “orthotic inserts.” These boots different. They are a textbook case of how to handle hallux valgus – your basic big bunion and also dealing with foot and ankle instability. The blueprint shows how different the feet are.
On the right foot, there is a significant bunion on the first metatarsal joint (big toe). There is also a bunionette on the little toe ball joint of the right foot. She has had some plantar fasciitis, pain and tenderness on the bottom of the foot. Not a lot of mobility in MT1, the big toe.
The left foot has no such issues, but due to a stroke, my client lost some facility with her left leg creating balance issues and instability with the left ankle and foot. Looking at the print of the left foot, those issues are not visible. The left foot is also a full size longer than the right, and two widths narrower in the standard sense. Her issues have nothing to do with her left foot per se, and yet everything to do with it. Getting to know the client, seeing and feeling the feet first hand is an essential part of making custom shoes. In this regard, the knowledge I got from in person contact is critical to the success of working with her.
For an orthopedic shoemaker, dealing with hallux valgus is really no big deal. Basic beginner stuff. Their daily work is typically with clients that have much more complicated conditions. I have an understanding of these issues, but since I’m not a trained orthopedic specialist. I referred her to one. She said “No.” She really wanted me to make them. I told her that I would take a crack at it, no guarantees.
What to do? I referred to my copy of “Orthopedisch maatschoeisel in de medische praktijk” (1991), by Dr. Klaas Postema. This hand me down from my colleague Rene van den Berg, was the standard textbook that he and many of the shoemakers I met in the Netherlands studied in school. I read through that and Dr. Postema’s latest book, “Pedorthic footwear – assessment and treatment” published (in English!) in 2018. I also thought back on all the discussions I’ve had and shoes I’ve seen at Mischa Bergshoeff’s shop in Gouda. You can look at his work and see how amazing it is and have no idea of what sort of feet go in those shoes.
There is a prescription for hallux valgus, a sort of shoemaking recipe, in the books. Depending on the mobility of the foot, you can squeeze it a bit around the tarsals and that will actually straighten out the bend in MT1 slightly. This should ease the stress of toe-off in walking and possibly give more flex to MT1. Extra room is needed for the bunion and bunionette, but the foot will slip forward to fill that space unless you keep it firmly in the rear 2/3 of the shoe. It’s important to keep the rearfoot firm and secure. It’s a tight fit, but should not be uncomfortably tight. To help keep the ankle and foot in position, the upper is about a hand’s width above the ankles (malleolus). There is a firm heel counter and a rocker bar to assist in toe-off. I made a padded contoured footbed liner with metatarsal bump to helps restore the transverse arch.
Like any recipe, you need to season to taste. Most people don’t want to go to “orthopedic specialists” because they are most famous for making ugly shoes and boots. The difficulty of clinically handling the many foot pathologies orthopedic shoemakers encounter is already extreme. On top of making the most appropriate shoes possible, people also demand they look great. Sometimes there is a real disconnect between the shape and functionality of the client’s feet and what the client wants to see when they look at the shoes. As a custom shoemaker, it’s my job to balance those things. For an orthopedic shoe, it’s no different, just more difficult.
These shoes are EU 39-9(L) and 38-10(R). I wanted to use a Vibram Gumlite unit sole because it’s cushy to walk on and a good all-weather material. Vibram, however, typically only makes huge soles available to the distributors in the US like only men with giant feet need their soles. It’s very hard to get the right size unit sole for a custom shoe, but once the shoe is size 41 or less, you really have to start hacking to make it fit. When I made the trial shoes, I simply made sure the sole covered the shoe. As you can see from the tread pattern, this is not nice. Would anyone even notice? I noticed and I didn’t like it. At the very least, the shoes have to satisfy me.
I had to shorten these to get a passable agreement of the heel and forefoot. If you look closely, you’ll see the word “Gumlite” is gone from the final version. I made a straight cut and then sanded a 1 cm skive for the 39 and 1.5 cm skive for the 38. Previously, I have cut these along the curve of the heel and made an overlap. This time I wanted to try something new. The cut along the curve of the heel looks more finished, but the increased contact area and a transition before the edge of the heel on the straight cut and skive should keep the heel more solidly bonded, at least in theory.
Who doesn’t love a hidden feature? There is one for the wearer and one for shoemakers. For the wearer, there is an embossed inside lace stay. This allows me to use more rust colored thread for not-totally-gratuitous ornamental stitching to sew it in. The embossed stays can only be seen when the shoes are open.
When they are open, look at the back of those speedhooks! Have you ever seen such a clean finish? Thanks many times over to Mischa for this method of setting speed hooks. I want to thank all the shoemakers who helped reach the point where I am able to make shoes like these, and thanks to Dr. Postema. I couldn’t have done it without you.
This is a picture of my first usable 3D scan of a last displayed on my “Mac” using Meshlab. This is a mini progress report of sorts. Back in July, I received a Make|Learn|Build grant from the Oregon Regional Arts & Culture Council (RACC) to explore the ways in which 3D technology might appropriately fit into the custom shoe making process.
While it has never been an area of focus for me, 3D scanning and printing technologies have been a steady companion topic since I took my first shoemaking class back in 2004. My instructor, Alan Zerobnick, created one of the very early 3D foot scanning systems – Digitoe. My reason for learning to make shoes was to get out of technology, not deeper into it, so I have kept the 3D stuff mostly at arm’s length. In 2010, when visiting Ortho Baltic in Lithuania to learn more about the company and the lasts I purchased from them, I had my feet scanned using the Easy foot scanner which they manufacture themselves. It makes an extremely accurate scan of feet or lasts in seconds. Many early studies of using 3D scanners to scan feet focused on whether they actually work. Here’s a meta study of foot scanning from 2010 which mentions that scanner and was published not long after my visit (totally unrelated). Did they accurately record the measurements of the foot? Yes. We know that the scanners, scan quickly and accurately. Interestingly, the paper notes that the actual obtaining of measurements is a bit more nuanced than you might think. There’s more to it than just the the linear circumference of the foot as a cross-section of the mesh.
Over the past 10 years, more scanners for feet have become available. Some new ways of obtaining scans have been developed as well, including different types of structured light, infrared and LIDAR. None currently compare to the old Class 3 red laser for accuracy and speed. It’s clear, however, that this technology is being used extensively now in the development of orthotics and prosthetics. I am wondering, “How useful is this for the custom shoemaker?”
This question was asked in a research study commissioned by the EU and published in 2003. In that study, however, the emphasis was really on integrating 3D scanning and customization and large scale custom production of footwear. As you may know by now, almost 20 years later, we are not strolling through the foot scanners and picking up shoes made just for us on the way out. The report from IDEA-Foot (2012) summarizes a pretty comprehensive approach for scan to shoe at smaller scale. Despite a fairly comprehensive understanding of what this might take, the scan to production at any scale has mostly just fizzled. What you see now is more of a digital Brannock device. For roughly $7,000 you can have a system that will match scans of feet with shoes you carry. In theory, that’s why you might organize your shoe inventory by size, but hey, it’s out there. It’s really a system to aggregate demographic information that could be used to inform shoe shapes and sizes, but it’s not scan to shoe customization large or small.
The chatter and hype around 3D scanning and shoes never seems to diminish. It’s like 20+ years of the self-driving car discussion. These are some of my questions:
Are some of these newer scanner types useful?
Can they improve the custom shoe making process as it is?
How and where is this sensible to apply 3D scanning and where is it just a time-wasting exercise in new technologies?
To start with, there is plenty of time wasting. It’s been months of struggle to get one usable scan. Let’s say you’re already a seasoned shoemaker who has previously developed applications for mobile platforms – they taught you that where you studied shoemaking, right? For example, to get this scan I had to complete the following steps.
During this time of pandemic and business closure, when I’ve been unable meet with clients as usual, and trapped inside due to fire and smoke, I have explored some techniques for using new materials to make composite shoe parts. I’m working with basalt fiber and epoxy. Below are my initial trials and some details on how I made them.
Background and Back Burner
I first tried to make carbon fiber parts when making prototypes for a pair of bicycle touring boots requested by a client. 10 years ago when I visited Ortho Baltic (a Lithuanian company where I buy some of my lasts), I was impressed with their ability to produce a wide range of very high quality carbon fiber parts. I contracted Ortho Baltic to make the carbon fiber midsoles for me.
Ortho Baltic can make such high quality parts because they are cured under vacuum in carefully controlled high temperature ovens. Because making custom shoes means never doing the exact same thing twice, I wanted to see if I could develop the facility to make custom carbon parts on par with Ortho Baltic when needed, but with less equipment. The fact remains that carefully controlled heating and cooling is really the only way to produce these kinds of parts.
Without using ovens, I’ve found that the next best thing is to use vacuum resin infusion. I watched videos on this over the years but kept the idea on the back burner because I was never excited about working with epoxy and carbon fiber. Epoxy is considered non-toxic, unless you sand it and inhale the dust. Carbon fiber is very dangerous to work with. When cut or sanded, particles of carbon fiber float into the air and get everywhere. Fibers can become embedded in your skin, eyes and lungs. Carbon fiber’s tiny particle size makes it an inhalation hazard. After carbon fiber has been set with resin, it can make splinters (like fiberglass) which make the parts no fun to handle. The coatings used on the fibers are often toxic as well (OHS Safety Sheet). Yikes. It’s enough already to do all the things needed to make custom shoes without also becoming an expert on plastics and producing custom composite parts. Nonetheless, my curiosity remained.
In the summer of 2019 I visited one of my students at his shop in the Shriner’s Children’s Hospital Orthopedics and Prosthetics lab. There I saw vacuum resin infusion used to fabricate all kinds of prosthetic devices, and that’s where I learned about basalt fiber. Basalt fiber is way less dangerous to work with than carbon fiber.
In August I finally started gathering the basic materials for a vacuum infusion setup. My first goal was to make a midsole which would provide some relief to a stiff big toe and ease toe-off. It is intended to be a combination of rocker bar, spring, and shank – all in one piece. Using the insole with a 1cm inset as a template, I covered the entire area using one basalt fiber braided sleeve. Since it’s a tube, the sleeve is equivalent to two layers of the same type of fabric.
The braided sleeve format means you only need to cut it to length – no fraying edges. It can be shaped easily without coming apart. If you could get a vacuum seal with the upper, the part could be made directly on the last. I was unable get a vacuum seal with this upper. There are a staggering number of places an air leak might occur, but I still think a vacuum seal with the upper on a last is possible.
Maximizing Green Stage
Since getting a good vacuum seal is so difficult, I decided try to keep my setup as simple as possible. I made a flat mold and transferred the part to the last before it has completely cured. If you get it at the right time, the epoxy will be cured enough to keep the part together as a unit, but also sticky enough to make a decent bond to the insole. This is also known as “green stage.” In green stage you can cut the part with scissors or a knife, if needed, which also saves you from sanding a too-big part. This also means I didn’t have to make a matching pair (left and right) of the much more complicated compound curved mold of the last bottom.
Using rubber cork, I made a mold for the part on a rigid piece of ABS plastic (4mm thick was the minimum). The base has to be rigid enough or it will bend under vacuum if the bagging film pulls on the perimeter.
With the film applied and tubing to pull the vacuum and let the resin in, it only takes a minute to actually infuse the fabric with epoxy and make the part.
So little resin is used to infuse the part that the vacuum changes hardly at all. The resin trap provides enough of a stored vacuum that you don’t need to have the vacuum pump connected to complete the infusion. It takes hardly 2 minutes to infuse. On the second run, I infused it much more slowly. Here’s about 13 minutes sped up to about a minute and a half.
Infusion – The Movie
Sped up version of infusing the part slowly.
3 hours after I first mixed the epoxy, here’s the transfer to the shoe.
Recap and Plastic Waste
To revisit the pieces pictured at the top of this article, different vacuum levels, or none at all, produce very different results. Looking at the four pieces above, and starting from the left:
Using a two part mold to squeeze out the extra resin made a very nice looking part that felt good to handle and was quite strong. The extra resin provides a lot of strength, but adds extra thickness and weight.
This part had a leaky vacuum seal, which is similar to using very low vacuum. More resin is allowed in and the whole assemblage is allowed more space for both air and resin. The resin saturation and thickness is not very consistent, but it is strong and functional
The product notes for basalt fiber will tell you that 30in/Hg vacuum will result in a part that’s a bit too dry, or “starved.” 20 – 24in/Hg is recommended. I wanted to see what “starved” looks like. The part is very thin and light, but brittle. There is not enough resin for the part to maintain integrity and it can easily be broken.
20in/Hg worked well for me, and I would consider even 15in/Hg. In making this last part, I tried a two-step infusion – first infusing under full vacuum (30in/Hg), then releasing more resin with the vacuum set to 20in/Hg. The fabric is fully saturated, strong, light, and not breakable.
Sometimes you want a stiff part, sometimes you want something flexible. Sometimes you want a bit of both. Using a braided sleeve, the irregularity of the insole shape naturally creates stiffness in the shank and flexibility in the forefoot. It does this simply by narrowing and condensing the material in the shank area and spreading it out in the forefoot. More fabric can be added as needed to make the part stiffer overall or stiffer in places.
I’m already able to make parts without the need for flanges or other fabrication artifacts to be cut, sanded or otherwise discarded. My biggest challenge right now is trying to figure out how to develop ways to reuse the molds and setup materials.
When working with plastics and composites, I’m always shocked at the prevalence of single-use materials. For example, the plastic film that covers the mold is thrown away after one use. It’s difficult to remove it without destroying it, even though it’s quite tough. Bleeder cloth and infusion mesh are also not easy to re-use. A failed part is a genuine failure – there’s literally nothing other than the experience to be recovered and reused.
I was given a sample cordovan shell from a tannery in Argentina called Lis Royal. The line of cordovan leather is called Rocinante and the color is “Dark Brown.” It is a lovely dark brown. I’ve written about cordovan before, but this sample was my first opportunity to make a pair of cordovan shoes for myself. The representative for the tannery told me that the horses in Argentina are kind of small, so I should expect the cordovan shell to be on the small side as well. Indeed it was a very tight fit to get a complete shoe pattern on a single shell. To do so, I had to forego any skiving allowance on the quarters.
This is on an Alvin 24″x36″ cutting mat. I think you can get the idea that this is not a lot of material. No mistakes in cutting or marking allowed!
The leather arrived with a very glossy classic cordovan finish. This makes it challenging to sew because there is so much glare it’s hard to see. I used a contrasting rust colored thread and vegetable tanned liner embossed with a leaf pattern.
The embossing is quite deep, but the cordovan is also ~2mm thick, so there was no visible trace of the embossing from the outside, as you can see above.
I have heard from others who have worked with it, that cordovan is very stretchy. In lasting you can pull and pull and keep pulling. I did not find this to be the case for this shell. I was actually stressing about the back height as I felt that my pattern came up short in length from the heel seat to the top line. I was hoping to have some stretch there, but it definitely didn’t want to. Ok, to be fair this is the first time I made a pair of shoes on this particular last and the volume of the heel seemed to be a bit bigger than I expected. I’ll take responsibility for a pattern error on that. There was very little lasting allowance. In the end, it fit, but it was a close shave.
I have used cordovan from a few other tanneries and usually the finish goes to matte quite quickly after wetting and lasting. The Rocinante from Lis Royal held its finish pretty well. I have questions about the nature of the finish. The top side of cordovan is in fact the flesh side of the skin. Creating the finished “top grain” means shaving away everything until you get just the callus that is cordovan. Lis Royal did a really good job as it still remained quite smooth when wet and pulled. With a sample size of one, it’s hard to tell what was a property of this particular shell and what was part of their process. In any case, we’re off to a good start! I’m looking forward to seeing how this beautiful material performs in wear testing.
This pair of cordovan derby shoes is sewn with an English welt to a J.R. Rendenbach vegetable tanned leather sole. They have stacked leather heels capped with a Vibram heel lift. The stitching on the welt is dark brown and the welt is dyed dark brown. The welt thread color and dye treatment were not my first choice, but that’s a different story. Note that this last has a bit of a bulldog toe. On the subtle side, but a bulldog toe nonetheless. The bulldog toe shape, which rises and then drops as you look at the profile from the side was very popular in the years 1910 – 1920.
Beginning with an overview of women’s fashion from 1905 to 1925, this portion of the presentation will explore how tango influenced mainstream fashion, with particular focus on the easing of strict Victorian social mores and the increasing need for freedom of movement. Original apparel, shoes and hats from the era will be modeled and discussed.
Learn the anatomy of tango shoes. This portion of the presentation will cover how women’s tango shoes were made – from the early days through the present. Discover how innovations in shoemaking during the 1930s are still with us today. There will be real-time shoe deconstruction!
I made these two tone cordovan wingtips for a client who really wanted dress shoes, but he has wider than average feet, and much wider than average heels. He had never found a dress shoe that fit.
The uppers feature quite a bit of broguing. Broguing is often done with a tool that has a combination of punches at fixed distances for consistent hole spacing. Brogue punches have one big hole punch and two or four little hole punches on either side. If you punch it freehand with individual large and small hole punches as I did, you can make whatever combination you want.
I made assembled this pair using welted construction and hand stitched the welt to the leather outsole. The upper is vegetable tanned shell cordovan.
When I first read the book Handmade Shoes for Men, I saw this picture: Der Leistenbauer (the last maker). I was struck at the time, and for many years to come, by the utter otherworldliness of the man, the tool and the activity. How was it that such a refined and beautiful shape was crudely hacked out of a piece of what appeared to be basically firewood?
While visiting the shop of Berluti in Les Rosiers-sur-Loire in April, I unexpectedly received a paroir (aka stock knife) as gift from Anthony Delos. (A famous shoemaker in his own right who’s business was purchased by Berluti.) Stunned, I thought about that picture and I really wanted to find out what it is like to make a last using this tool. It was pretty rusty and I have no idea when it was used last, or when it was made. Using one of the polishing wheels on my finisher, I cleaned it up and sharpened it.
First I had to make a handle. Thanks to my friend Greg, I learned a bit about how to turn a piece of wood on a lathe and how to make a T handle. We used maple for the shaft and T, and copper pipe for the front of the haft. The T was fitted to the shaft in much the same way that a leg or spindle is fitted to a Windsor chair – tapered shaft to tapered hole. It was pinned, but also set with epoxy.
I decided to copy a last that I already had. Using rough outlines of the profile and the bottom pattern as guides. Going primarily by eye, I chopped away. After 2 days and about 10 hours of chopping, I was totally wiped out and figured I had gone about as far as someone would with that tool.
Throughout the carving process, I used my existing last to compare the shape and size, length and width, toe and heel spring. I did not use a profile gauge or take the dimensions too seriously.
My guess is that a last maker would put it in a vise and clean it up with a file and spoke shave. I sanded and did the final shaping on my finisher.
The heel height and toe spring looks right and the lengths are the same. I could have spent days working on it to get it exactly right. Ok, I did spent 3 days on it. I’m just going to stop and call it good.
Learning which cuts were hard and which were easy was very interesting. I would definitely mount the paroir on a lower table next time. I managed not to cut or otherwise injure myself. While my right hand was really tired and sore, I did not get any blisters. I’m quite happy with the shape of the handle, and ultimately with the last I carved totally from scratch.
In what became the follow up to my visit to Texprocess, I visited the Pfaff industrial machine showroom in Kaiserslautern, Germany. For years I have wanted to go there. You can’t see it from this picture, but all of the postbeds are just to the left of this view.
At the trade shows, you can often spend some time on the machines and speak with a sales rep who may or may not be able to answer some of your questions. Texprocess was totally secondary in priority for my visit to Europe this year, but since it was happening around the same time, I went to check it out. I learned a lot there. Still, the industrial showroom was what I was after. This is what Pfaff has to say about the showroom on their site:
Are you looking for information on the latest state of the arts?
Do you wish to consult one of our specialists, or perhaps just talk shop?
Experienced consultants, sewing mechanics, technical engineers, application engineers and organisation specialists are all ready to help you.
Yes, please! The representative from Pfaff who coordinated my visit, Axel Zangerle, has been with Pfaff for almost 50 years. To say he is knowledgeable about their machines is a bit of an understatement. Only recently returned to Kaiserslautern, where he grew up, Axel has spent a lot of his career working for Pfaff in various parts of Asia. As I had confirmed with Axel previously by email, if you want some time to yourself and also get some personal attention, make the effort to go to the showroom.
He set me up with Julia Weigerding-Domic, who worked with me while I went through a pile of samples that I had prepared. We tried different needles, different thread, and different machines. We didn’t go through all of the zillions of settings that are available these days, but I did learn some very important things about how these machines work and how much influence the speed of factory production and the repetition of mass production influences their character.
Making custom shoes, it’s unlikely I will ever get to make the same piece twice, let alone the same pair of shoes. On one pair of shoes, the left and right uppers are typically not two of the same, they are mirror images. These machines can stitch up to 3,500 stitches per minute! Sewing through leather at high speeds can really heat the needle and thus melt the thread. Most seams on shoes are short, and very curvy. We’re not making jeans, awnings or sails. Sewing one-of-a-kind uppers, we’re not sewing quite so fast or as long. Even so, if you put the pedal to the metal, look out! Turning down the max sewing speed was the first adjustment I made on each of these machine’s control panels. This is such a far cry from the old 3-phase 380V clutch motor days that used to characterize “industrial” machines.
Until very recently, all the moving parts on industrial postbed sewing machines were mechanically linked together and driven by one motor. Functions like presser foot lifting were handled with compressed air. Like the various CNC machines, there are now stepper motors everywhere. The latest postbed machines have dedicated electric motors for almost every moving thing – roller foot, roller feed wheel, presser foot lifter, stitch length, etc. This allows easier control of the speeds of all of those things. It’s not a change in the mechanics of sewing, but it is a change in the adjustment of it. The 878 from Durkopp/Adler even has an electronic motor and cam for thread tension. That is a new thing. Thread tension was always mechanical, never linked to a motor or compressed air. Adjusting the thread tension is always a bit fussy.
As I learned at the show, Durkopp/Adler and Pfaff are all part of the same company now, along with a few others. This means at the Pfaff industrial showroom, you can also try out the Durkopp/Adler machines. I found it very educational to have these machines side by side and discuss them with someone who has been in the business for a long time.
I’m not going to write up a review of the machines or make a buyer’s guide, but I will emphasize that I have read tons of spec sheets, spent time on the phone with reps, looked at the websites and videos and did not discover on my own what I was able to learn with Axel in the first hour of my visit. To be fair, much of what I learned really is in the brochures, but it doesn’t resonate until you sit down and do it yourself.
I will wrap up with an example of the different speed settings for top and bottom feeds. Why would anyone ever use this? I have seen reference to this even in the service manual for the old Pfaff 491/471 series which were discontinued in 2000. It’s an idea that been around for a while. Nobody I knew seemed to have any idea how this might be useful.
I learned from Axel that it’s a gathering function which creates additional curves, or distortion, depending on how you look at it. Julia showed me that it can also help mediate stitch length distortions on tight inside and outside curves. On oxford patterns, for example, where the quarters meet the vamp, it’s not completely flat and a bit of gathering is what you want. When flattened it out, the quarter facings overlap. The line where the quarters meet the vamp can be tricky. A lot depends on the shape of the last and the design of the pattern. A skilled person can get the shape they want at the time it’s sewn together even if the pattern wasn’t designed that way. Different top and bottom feed speeds can greatly facilitate this. With electronic controls, it’s very simple to set and switch to and from.
Thank you Axel, and Julia for making my visit worth the journey!