Generally speaking, "industrial" equipment has a larger head and is powered by electricity. My 1929 Singer 31-15 is a perfect example. So is the 1943 Willcox&Gibbs rotary take-up(have 2 and love them!). Both techinically have "treadles". But the treadles are not the primary means of powering them. Of course, "treadle" machines were used commercially before electricity; I'm not THAT dumb, after all... ;) I was merely pointing out the difficulty "treadle" presents as a descriptive term. My brand new Juki 9010 has a "treadle", but it's simply an antiquated monniker, in no way indicative of the computerized motor/control box that operates the machine head.

Great answer about your grandchild, Joan. She must really be something. I have multiple machines, most are task specific (serger, blindstitch, button sewer, walking foot, needle feed, and rotary take-up), all but one are industrial models; many are now termed "vintage". I would say I tend to clean them (on average) once a month, but that depends on what I've been sewing, too. Sometimes I do really dirty/gritty awning repairs, sometimes I'm working with clean, new product, sometimes with really "linty" fabric. If one of my machines hasn't been used in a long time, the first thing I do is give it a dusting, a thorough oiling, and check the stitch length and thread tension. As a matter of habit, the first thing I do when I start a new job is check the needle size and condition. Always! I am a stickler about oiling, too. Many of my machines are quite old (50-100 yrs.) and require very regular oiling. That's very common in elderly industrial equipment. The manual for my Willcox & Gibbs industrial rotary take up (c.1943) recommends a complete oiling every 4 hrs.! My brand new Juki sits in a pan of oil and never requires it.

Mastering the use of a scroll hemmer on the bias is no easy feat. I have an old Willcox&Gibbs rotary take up machine from the '40s. It came with a very unusual assortment of specialty feet (scroll hemmers, folders, shirring feet, etc.). It had come from a lingerie factory (rotary take up permits exceptionally fine tension adjustment). I love the machine, but the idea of using a 1/8" scroll hemmer to finish the bottom of a bias cut slip makes me sweat!

I learned to sew at 38 as well :) Taking private lessons with a lovely lady who helped me make my DH a bunch of silk pillows and a crazy quilt. She's an amazing person :) and had many first timers who were well over my age. Her studio was in the basement, and much smaller than yours, and yet she'd have 4 women in there at a time and occasionaly a man would take a lesson as well. I learned curtains with a wonderful guy trying to suprise his future wife with a redecoration of their wedding home. She did instill one bad thing in my little mind. I just couldn't go home to the manual brother machine I purchased at wally world for a couple hundred dollars. She had all bernina's, all computerized and she also had babylock sergers. Now I can't live without the best machine I can afford. Six years ago I didn't sew a seam and now I think it would be nice to upgrade my 3500 machine LOL what a machine snob!!! That's loretta's fault entirely :) But she also gave me a hobby I love, and that I've used to raise thousands of dollars for charity, so take that as a small hint to not forget the old people like you and me when you're giving lessons :) (And put the old people on really cheesy machines) LOL my husband asked me to add that.