Posts Tagged Sewing

Kenmore 158 Foot Pedal: Fine Tuning

After a week of use, Mary decided the single additional graphite disk in each stack produced a too-high initial speed when the sewing machine started up; this being a matter of how it feels injects some of trial-and-error into the repair.

Shaving a graphite disk down from 0.8 to 0.4 mm seemed entirely too messy, so I snipped squares from 0.40 mm = 16 mil brass shim stock, nibbled the edges into a polygon, and filed the resulting vertexes to produce a (rough) circle:

Kenmore 158 Foot Pedal - 0.40 mm brass shims

Kenmore 158 Foot Pedal – 0.40 mm brass shims

Each stack looks like this:

  • 1.5 mm graphite disk (double-thick)
  • 0.30 mm brass (original part)
  • 0.79 mm graphite disk
  • 0.40 brass (new part)
  • The rest of the stack

Protip: dump those shards onto a strip of wide masking tape, fold gently until it’s all corners, and drop in the trash. Otherwise, you’ll pull those things out of your shoes and fingers for months…

You can get cheaper nibbling tools nowadays; I’ve had mine for decades.

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Kenmore 158: Presser Foot Tweak

After watching Mary fiddle with the shrunken presser foot screw, I tapered the tip as a guide into the hole:

Presser Foot Screw - tapered tip

Presser Foot Screw – tapered tip

A hint-and-tip (which I cannot, alas, find again) suggested making bushings to simplify trimming screws in the lathe. A rim on the bushing aligns it with the front of the jaws, the screw threads into the central hole with a jam nut locking it in place, then you can turn / shape / file the end of the screw just beyond bushing with great support and a total lack of drama.

For the moment, I just aligned the screw in the tailstock drill chuck, crunched the three-jaw spindle chuck on the screw head, backed off the tailstock, took unsupported sissy cuts, and it was all good:

Presser Foot Screw - chuck alignment

Presser Foot Screw – chuck alignment

Gotta make those bushings!

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Kenmore 158 Sewing Machine: Another Foot Pedal Rebuild

The pedal on Mary’s most recent Kenmore 158 lost its low-speed control, which meant I must add a few more graphite / carbon disks to the stacks:

Kenmore 158 - carbon disks

Kenmore 158 – carbon disks

The contacts needed a bit of attention, too:

Kenmore 158 - carbon contact plates - detail

Kenmore 158 – carbon contact plates – detail

Contrary to what I found in the previous rheostats, these stacks end with a double-thick graphite disk backed up by a disk of brass shimstock, all of which needed cleaning, too. No broken disks, none severely eroded, no debris, just a general shortening of the stacks; I think the disks gradually turn into carbon dioxide.

Each stack has 42 graphite disks that average 0.79 mm thick, the double-thick disks measure 1.5 mm, and the brass shims are 0.30 mm = 12 mil. The punched contacts on those brass plates stand 0.95 mm proud of the surface.

With the big graphite plugs in place, the ceramic housing had 37 mm deep holes for the disk stacks. Subtracting the 0.95 mm contact leaves about 36 mm and, seeing as how the stacks add up to just under 36 mm overall, there’s barely room for one additional disk. I added one to each stack, buttoned the pedal up, and it works perfectly again.

Good thing I have a bag of those disks from the crash test dummy machine!

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Respooling Stainless Steel Thread: The Knack

The comments on my previous stainless-steel thread respooling attempt suggested that I was entirely too much of a sissy, so, when another empty spool appeared, I tried again with more vigor:

Stainless steel thread - second spool

Stainless steel thread – second spool

As before, I put the larger spool on the floor under the lathe and let the thread spill straight off the top toward the smaller spool. This time, I didn’t have a twist accumulating in the loose thread between the two spools:

  • Grab longer lengths of the loose thread
  • Absolutely no slippage between the fingers!
  • Put more tension on the thread at the takeup spool

As nearly as I can tell, the thread still has a slight twist coming off the larger spool, but grabbing longer lengths captures the twist and more tension lays it on the smaller spool. After cutting the thread, what was left had maybe three turns of twist, which was no big deal and obviously hadn’t accumulated.

Seems better: thanks for all the comments!

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Quilt Blocks: Scan and Montage

Mary has been working on the Splendid Sampler project, with 56 completed blocks (*) stacked on her sewing table. We agreed that those blocks would make a nice background for our Christmas Letter, but the labor involved to photograph all the fabric squares and turn them into a page seemed daunting.

Turned out it wasn’t all that hard, at least after we eliminated all the photography and hand-editing.

The 6½x6½ inch blocks include a ¼ inch seam allowance on all sides and, Mary being fussy about such things, they’re all just about perfect. I taped a template around one block on the scanner glass:

Quilt block in scanner template

Quilt block in scanner template

Then set XSane to scan at 150 dpi and save sequentially numbered files, position a square scan area over the middle of the template, and turn off all the image enhancements to preserve a flat color balance.

With “picture taking” reduced to laying each square face-down on the glass, closing the lid, and clicking Scan, the scanner’s throughput became the limiting factor. She scanned the blocks in the order of their release, while tinkering the auto-incremented file number across the (few) gaps in her collection, to produce 56 files with unimaginative auto-generated names along the lines of Block 19.jpg, thusly:

Block 19

Block 19

The “square” images were 923×933 pixels, just slightly larger than the ideal finished size of 6 inch × 150 dpi = 900 pixel you’d expect, because we allowed a wee bit (call it 1/16 inch) on all sides to avoid cutting away the sharp points and, hey, I didn’t get the scan area exactly square.

With the files in hand, turning them into a single page background image requires a single Imagemagick incantation:

montage -verbose B*jpg -density 150 -geometry "171x173+0+0" -tile "7x" Page.jpg

I figured the -geometry value to fill the 8 inch page width at 150 dpi, which is good enough for a subdued background image: 8 inch × 150 dpi / 7 images = 171 pixels. Imagemagick preserves the aspect ratio of the incoming images during the resize, so, because these images are slightly higher than they are wide, the height must be slightly larger to avoid thin white borders in the unused space. With all that figured, you get a 1197×1384 output image.

Bumping the contrast makes the colors pop, even if they’re not quite photo-realistic:

Quilt block montage - contrast

Quilt block montage – contrast

I’ll lighten that image to make the Christmas Letter text (in the foreground, atop the “quilt”) readable, which is all in the nature of fine tuning.

She has 40-odd blocks to go before she can piece them together and begin quilting, with a few other projects remaining to be finished:

Mary quilting

Mary quilting

(*) She’s a bit behind the block schedule, having had a year of gardening, bicycling, and other quilting projects, plus whatever else happens around here. Not a problem, as we see it.

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Wearable Electronics: Connections

Although I’m not the type of guy who thinks twinkly LEDs will enhance his apparel, one of Mary’s quilting thread sources had a closeout deal on their “wearable electronics”, including a large cone of stainless steel thread / yarn:

Stainless steel thread

Stainless steel thread

… CR2032 lithium cells & holders, plus assorted LEDs on small PCBs.

The usual advice for connecting the thread seems to involve knotting it through the PCB holes, then sewing it to the backing fabric. Alas, I’m bad with knots and the stainless steel yarn isn’t all that cohesive:

Emerald LED - Stainless steel thread - knotted

Emerald LED – Stainless steel thread – knotted

The holder has an even smaller hole, but Mary gave me a needle threader that helped:

CR2032 - Stainless steel thread - knotted

CR2032 – Stainless steel thread – knotted

Some advice found on The InterTubes suggests using copper crimp beads (perhaps with solder) to prevent the thread from completely unraveling and keep the thread loop tight around the PCB hole:

Rose LED - Stainless steel thread - Crimp bead - Wire Glue

Rose LED – Stainless steel thread – Crimp bead – Wire Glue

Beadworkers use crimping pliers that leave a tidy dent; I mashed the beads with a needlenose pliers and called it good.

The LEDs seem to be white LEDs with filters or, perhaps, blue / violet LEDs with different phosphors: their forward voltages look more blue than red or green. Everybody in this field depends on the minor miracle that lithium cell voltages match blue LED forward drops closely enough that you can get away without a ballast resistor.; the cell’s 20-ish Ω internal resistance doesn’t hurt in the least. An interesting white paper (SWRA349) from TI explores the effect of current on cell capacity and how to size a parallel capacitor that reduces the peak battery current.

The black gunk is Wire Glue, which costs about five bucks for a lifetime supply in a small jar (or nigh onto 15 bucks via Amazon Prime) and is basically carbon powder in a water-based binder. Apply a dab to the connection and the water evaporates to leave the carbon + binder behind.

That works better on joints that don’t move, which is precisely what you don’t have in a wearable electronic situation. You can see the crumbling Wire Glue after the trip back from a Squidwrench meeting:

CR2032 - Stainless steel thread - Crimp bead - Wire Glue

CR2032 – Stainless steel thread – Crimp bead – Wire Glue

I also picked up a Permatext Rear Window Defogger repair kit (09117, if you’re looking) that seems to be a staggeringly expensive way to get a tenacious high-current conductive adhesive. More on that later.

The yarn runs 3.5 Ω/ft, much lower than Adafruit’s three-ply yarn (10 Ω /ft), and suggests itself for flexible connections, EMI gaskets, and suchlike.

Those LEDs are taped to the kitchen window, where they cast a cool light over the table, with the battery holders sitting on the sash. I’d just replaced some data logger CR2032 cells, so they’re running from nearly dead lithium batteries.

For future reference: 2.77 V and falling, pushing less than 2 mA through the LEDs.

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Pencil Guides for Ruler Quilting

Mary has been doing Ruler Quilting and wanted a pencil guide (similar to the machine’s ruler foot) to let her sketch layouts before committing stitches to fabric. The general idea is to offset the pencil by 1/4 inch from the edge of the ruler:

Ruler Adapter - solid model

Ruler Adapter – solid model

That was easy.

Print three to provide a bit of cooling time and let her pass ’em around at her next quilting bee:

Ruler Adapter - Slic3r preview

Ruler Adapter – Slic3r preview

Her favorite doodling pencil shoves a 0.9 mm lead through a 2 mm ferrule, so ream the center hole with a #44 drill (86 mil = 2.1 mm) to suit:

Ruler quilting pencil guides

Ruler quilting pencil guides

The outer perimeters have 64 facets, an unusually high number for my models, so they’re nice & smooth on the ruler. Even though I didn’t build them sequentially, they had zero perimeter zits and the OD came out 0.500 inch on the dot.

The chamfers guide the pencil point into the hole and provide a bit of relief for the pencil’s snout.

If I had a laser cutter, I could make special rulers for her, too …

The OpenSCAD source code as a GitHub Gist:

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