Posts Tagged Improvements
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:
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:
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?
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:
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:
And the 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!
Encouraged by the smooth running of the LM12UU drag knife mount, I chopped off another length of 12 mm 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:
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:
Slather JB Kwik epoxy along the threads, insert into the shaft, wipe off the excess, and looks almost like a Real Product:
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:
Although it’s not obvious, I cleaned up the OD before applying the knurling tool:
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:
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:
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:
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:
Convince all the parts to fly in formation, then measure the spring rate:
Which works out to be 128 g + 54 g/mm:
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:
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.
The OpenSCAD source code as a GitHub Gist:
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:
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:
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:
Reinstall in reverse order, the camera rebooted as it should, and it’s all good out there:
That was easy …
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:
The most recent two batches seem cheapnified:
The tubes show similar changes, going from a stylin’ version to a simple cylindrical cap:
The most recent carton label might lead you to think they’re counterfeits, but it could just be a simple typo:
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.
Homeostasis is a thing:
Having a single spring and a fixed upper plate works much better than the first version:
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:
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:
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:
Even without nyloc nuts, the first test worked fine:
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: