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Posts Tagged Improvements

Power Lift Chair Upholstery Protection

For reasons not relevant here, we have a power lift chair which has been shedding upholstery tufts since the day we got it. After realizing this wasn’t going to stop on its own, I spent a while poking around underneath and discovered the steel struts supporting the leg rest rub along the upholstery during their entire travel:

Lift chair - strut vs upholstery
Lift chair – strut vs upholstery

Apparently, the padding behind the upholstery pushes it a bit further out than the original design could accommodate, letting the raw edges on the steel struts shave off the fuzz.

I put relatively smooth stainless steel tape on all the protrusions and bent it around the rough edges:

Lift chair - strut smoothing
Lift chair – strut smoothing

Those steel folds are smoother than they appear.

It’s not obvious this will solve the problem, but the struts seems to be scraping off much less fuzz than before, so it’s a step in the right direction.

Why is it all of today’s consumer products require 10% more engineering to work in the real world?

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Threaded Brass Inserts: Test to Destruction

With an outmoded LM12UU linear bearing drag knife mount on hand, I threaded an M4 screw into each brass insert, lined it up on a hole in a homebrew (by a long-gone machinist, not me) steel bench block, and applied pressure with the drill press until the insert tore out:

Brass Insert Retention test - A B
Brass Insert Retention test – A B

The retina-burn orange ring is printed in PETG with my usual slicer settings: three perimeter threads, three top and bottom layers, and 15% 3D honeycomb infill. That combination is strong enough and stiff enough for essentially everything I do around here.

The insert on the left came out of its hole carrying its layer of epoxy: the epoxy-to-hole bond failed first. Despite that, punching it out required enough force to convince me it wasn’t going anywhere on its own.

The column of plastic around the insert standing up from the top fits into the central hole (hidden in the picture) in the bench block. Basically, the edge of the hole applied enough shear force to the plastic to break the infill before the epoxy tore free, with me applying enough grunt to the drill press quill handle to suggest I should get a real arbor press if I’m going to keep doing this.

The third insert maintained a similar grip, as seen from the left:

Brass Insert Retention test - C left
Brass Insert Retention test – C left

And the right:

Brass Insert Retention test - C right
Brass Insert Retention test – C right

The perimeter threads around the hole tore away from the infill, with the surface shearing as the plastic column punched through.

Bottom line: a dab of epoxy anchors an insert far better than the 3D printed structure around it can support!

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MPCNC Collet Pen Holder: LM12UU Edition

Encouraged by the smooth running of the LM12UU drag knife mount, I chopped off another length of 12 mm shaft:

LM12UU Collet Pen Holder - sawing shaft
LM12UU Collet Pen Holder – sawing shaft

The MicroMark Cut-off saw was barely up to the task; I must do something about its craptastic “vise”. In any event, the wet rags kept the shaft plenty cool and the ShopVac hose directly behind the motor sucked away all of the flying grit.

The reason I used an abrasive wheel: the shaft is case-hardened and the outer millimeter or two is hard enough to repel a carbide cutter:

LM12UU Collet Pen Holder - drilling shaft
LM12UU Collet Pen Holder – drilling shaft

Fortunately, the middle remains soft enough to drill a hole for the collet pen holder, which I turned down to a uniform 8 mm (-ish) diameter:

LM12UU Collet Pen Holder - turning collet body
LM12UU Collet Pen Holder – turning collet body

Slather JB Kwik epoxy along the threads, insert into the shaft, wipe off the excess, and looks almost like a Real Product:

LM12UU Collet Pen Holder - finished body
LM12UU Collet Pen Holder – finished body

The far end of the shaft recesses the collet a few millimeters to retain the spring around the pen body, which will also require a knurled ring around the outside so you (well, I) can tighten the collet around the pen tip.

Start the ring by center-drilling an absurdly long aluminum rod in the steady rest:

M12UU Collet Pen Holder - center drilling
M12UU Collet Pen Holder – center drilling

Although it’s not obvious, I cleaned up the OD before applying the knurling tool:

LM12UU Collet Pen Holder - knurling
LM12UU Collet Pen Holder – knurling

For some unknown reason, it seemed like a Good Idea to knurl without the steady rest, perhaps to avoid deepening the ring where the jaws slide, but Tiny Lathe™ definitely wasn’t up to the challenge. The knurling wheels aren’t quite concentric on their bores and their shafts have plenty of play, so I got to watch the big live center and tailstock wobbulate as the rod turned.

With the steady rest back in place, drill out the rod to match the shaft’s 12 mm OD:

LM12UU Collet Pen Holder - drilling shaft
LM12UU Collet Pen Holder – drilling shaft

All my “metric” drilling uses hard-inch drills approximating the metric dimensions, of course, because USA.

Clean up the ring face, file a chamfer on the edge, and part it off:

LM12UU Collet Pen Holder - parting ring
LM12UU Collet Pen Holder – parting ring

Turn some PVC pipe to a suitable length, slit one side so it can collapse to match the ring OD, wrap shimstock to protect those lovely knurls, and face off all the ugly:

LM12UU Collet Pen Holder - knurled ring facing
LM12UU Collet Pen Holder – knurled ring facing

Tweak the drag knife’s solid model for a different spring from the collection and up the hole OD in the plate to clear the largest pen cartridge in the current collection:

Collet Holder - LM12UU - solid model
Collet Holder – LM12UU – solid model

Convince all the parts to fly in formation, then measure the spring rate:

LM12UU Collet Pen Holder - spring rate test
LM12UU Collet Pen Holder – spring rate test

Which works out to be 128 g + 54 g/mm:

LM12UU Collet Pen Holder - test plot - overview
LM12UU Collet Pen Holder – test plot – overview

I forgot the knurled ring must clear the screws and, ideally, the nyloc nuts. Which it does, after I carefully aligned each nut with a flat exactly tangent to the ring. Whew!

A closer look at the business end:

LM12UU Collet Pen Holder - test plot - detail
LM12UU Collet Pen Holder – test plot – detail

The shaft has 5 mm of travel, far more than enough for the MPCNC’s platform. Plotting at -1 mm applies 180 g of downforce; the test pattern shown above varies the depth from 0.0 mm in steps of -0.1 mm; anything beyond -0.2 mm gets plenty of ink.

Now I have a pen holder, a diamond scribe, and a drag knife with (almost) exactly the same “tool offset” from the alignment camera, thereby eliminating an opportunity to screw up.

The OpenSCAD source code as a GitHub Gist:

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Weatherproof Outlet Cover Re-Chaining

The yard camera now resides outdoors and plugs into one of three outlets on the patio, all of which have weatherproof covers attached by a bead chain to the trim plate:

Patio Outlet - new chain installed
Patio Outlet – new chain installed

That’s the after-repair condition, as two of the three chains were broken when we bought the house.

Stipulated: the covers needed scrubbing, but sometimes ya gotta stay focused on the Main Goal.

Two feet of 3.4 mm brass bead chain (because spares: ya gotta have stuff) arrived from eBay, I dismounted all three covers, and discovered the bell-shaped brass caps on the old chains were perfectly serviceable after six decades:

Patio Outlet - chain retainers
Patio Outlet – chain retainers

The outlets are wired to circuit breaker 28, of course.

Having enough chain to go around, each cover now sports a slightly longer leash than before:

Patio Outlet - chain assembly
Patio Outlet – chain assembly

Reinstall in reverse order, the camera rebooted as it should, and it’s all good out there:

Pressure-washing Patio Railing
Pressure-washing Patio Railing

That was easy …

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KEDSUM LED Shop Lights: Cheapnification Thereof

As the basement’s fluorescent fixtures and lamps gradually die, I’ve been rewiring the fixtures for LED tubes, all bought from KEDSUM through Amazon. The first few batches looked like this:

Kedsum - good LED lamp
Kedsum – good LED lamp

The most recent two batches seem cheapnified:

Kedsum - poor LED lamp
Kedsum – poor LED lamp

The tubes show similar changes, going from a stylin’ version to a simple cylindrical cap:

Kedsum vs Kedsun - tube end caps
Kedsum vs Kedsun – tube end caps

The most recent carton label might lead you to think they’re counterfeits, but it could just be a simple typo:

Kedsum vs Kedsun - LED lamp carton
Kedsum vs Kedsun – LED lamp carton

There’s absolutely no way to tell what you’re going to get from any vendor on Amazon (or anywhere else, for that matter), so there’s no point in returning them, but I’d hoped buying “the same thing” from “the same seller” would produce a consistent result.

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Monthly Science: Weight

Homeostasis is a thing:

Weight Chart 2019-06 - Ed
Weight Chart 2019-06 – Ed

On the other paw, the eyeballometric trend line since mid-April slopes at -1 lb/month and arrives at just over 150 lb in December, so progress continues apace.

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MPCNC Diamond Engraver: LM3UU Bearings, Second Pass

Having a single spring and a fixed upper plate works much better than the first version:

Diamond Scribe - LM3UU Rev 2 - overview
Diamond Scribe – LM3UU Rev 2 – overview

The (lubricated!) nyloc nuts under the plate provide a little friction and stabilize the whole affair.

The solid model has the same stylin’ tapered snout as the LM12UU drag knife mount:

Diamond Scribe - LM3UU bearings
Diamond Scribe – LM3UU bearings

The spring seats in the plate recess, with the 3 mm shank passing through the hole as the tool holder presses the tip against the workpiece.

I diamond-filed a broken carbide end mill to make a slotting tool:

Diamond Scribe - LM3UU - Rev 2 - carbide notch tool
Diamond Scribe – LM3UU – Rev 2 – carbide notch tool

Lacking any better method (“a tiny clip spreader tool”), I rammed the Jesus clip the length of the shank with a (loose-fitting) chuck in the tailstock:

Diamond Scribe - LM3UU - Rev 2 - clip installation
Diamond Scribe – LM3UU – Rev 2 – clip installation

Even without nyloc nuts, the first test worked fine:

Diamond Scribe - LM3UU - Rev 2 - first light
Diamond Scribe – LM3UU – Rev 2 – first light

The 53 g/mm spring rate may be too low for serious engraving, but it suffices for subtle Guilloché patterns on scrap platters.

The OpenSCAD source code as a GitHub Gist:

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