Posts Tagged Mini-lathe

Printer Filament Millifiori

I finally decommissioned my old Thing-O-Matic, as it’s been far surpassed by the current generation of dirt-cheap Prusa-style 3D printers, and must now figure out what to do with about 10 kg of 3 mm ABS filament. Yes, 3 mm filament from back in the Bad Old Days.

Also back in the day, our Larval Engineer made millifiori creations in glass (at school) and polymer clay, building up the final piece from murrine canes, which suggested a similar technique using filament strands:

Filament Millefiori - 160C pipe - slice detail
Filament Millefiori – 160C pipe – slice detail

Well, maybe it’s not exactly art

Just to see how it might work, I packed a random length of conduit with filament snippets and jammed a thermocouple into the middle:

Filament Millefiori - packed conduit
Filament Millefiori – packed conduit

Which went into the shop’s sacrificial Dutch oven over low heat:

Filament Millefiori - conduit heating
Filament Millefiori – conduit heating

For lack of anything smarter, I slowly heated it to 250 °C, well above what the Thing-O-Matic used for extrusion, let it soak for a few minutes, then let the tube cool on the counter.

Some persuasion with a hammer and drift punch extracted the fused filament:

Filament Millefiori - 250C results
Filament Millefiori – 250C results

Obviously, the concept needs more work, but the bottom side looks promising:

Filament Millefiori - 250C results - bottom
Filament Millefiori – 250C results – bottom

Wrapping the bundle with silicone tape should keep the filament from sticking to the tube and provide uniform compression:

Filament Millefiori - 235C silicone wrap
Filament Millefiori – 235C silicone wrap

I forced it into the tube and wrapped the whole affair with aluminum foil to confine the hot ABS stench:

Filament Millefiori - 235C heating
Filament Millefiori – 235C heating

I held this one at 235 °C for a few minutes, cooled, unwrapped, and discovered the silicone wrap worked as expected:

Filament Millefiori - 235C thermocouple blob
Filament Millefiori – 235C thermocouple blob

OK, the blob on each end wasn’t expected, but at least the thermocouple came out with gentle persuasion. The compressed filament looked like it should be edible:

Filament Millefiori - 235C results
Filament Millefiori – 235C results

The molten filament oozed out of the wrap inside the tube, over there toward the right.

The filament snippets have a distinct curvature, brought on by years spent snuggled around a spool’s core, so I wondered if they could be straightened by application of somewhat less heat. Wikipedia lists the glass transition temperature for various ABS compositions as around 105 °C, so I packed the tube with more snippets and affixed the thermocouple with silicone tape:

Filament Millefiori - 100C setup
Filament Millefiori – 100C setup

Wrap with foil, heat to 100 °C, let cool, and they’re definitely straighter than the unheated white strand at the bottom:

Filament Millefiori - 100C results
Filament Millefiori – 100C results

Having learned my lesson with a thermocouple inside the strands, the straightened strands get a looser silicone wrap with the thermocouple secured to the outside of the bundle:

Filament Millefiori - 160C setup
Filament Millefiori – 160C setup

Heat to 160 °C:

Filament Millefiori - 160C setup
Filament Millefiori – 160C setup

Let cool and (easily!) slide the compressed bundle out of the tube:

Filament Millefiori - 160C cooling
Filament Millefiori – 160C cooling

The silicone wrap definitely mushed the strands together, as shown by the larger diameter on the uncompressed end:

Filament Millefiori - 160C results
Filament Millefiori – 160C results

Bandsawing the bundle reveals nicely fused filaments inside, along with melty ends that stuck out of the wrap:

Filament Millefiori - 160C cut end
Filament Millefiori – 160C cut end

Thinking shorter lengths might pack better without straightening, I faced the ends of a thick aluminum pipe and stuffed as many snippets into it as would fit. This is the point where a real artist would arrange the filaments in a pleasing pattern, if not a picture, but I was content with a random layout:

Filament Millefiori - 160C pipe - cable in pipe
Filament Millefiori – 160C pipe – cable in pipe

That’s what the ends looked like after heating to 160 °C: somewhat glazed, reasonably fused, but certainly not compacted. The other end pointed upward and definitely felt the heat:

Filament Millefiori - 160C pipe - cable melty end detail
Filament Millefiori – 160C pipe – cable melty end detail

With a PCV pipe “collet” holding the cable / cane / murrina in the chuck, I faced the end:

Filament Millefiori - 160C pipe - cable facing
Filament Millefiori – 160C pipe – cable facing

After taking this picture, I came to my senses and bandsawed the slice instead:

Filament Millefiori - 160C pipe - cutoff tool
Filament Millefiori – 160C pipe – cutoff tool

Parting the slice in the lathe might have worked, but it just seemed like a really really bad idea when I looked at the setup.

A PVC pipe spacer kept the slice lined up in the chuck jaws while facing the bandsawed end:

Filament Millefiori - 160C pipe - slice facing
Filament Millefiori – 160C pipe – slice facing

The slice and the cable:

Filament Millefiori - 160C pipe - slice and cable
Filament Millefiori – 160C pipe – slice and cable

Although the filament snippets fuse together without a silicone tape compression wrap, the gaps collect plenty of swarf during the cutting & facing:

Filament Millefiori - 160C pipe - cable end detail
Filament Millefiori – 160C pipe – cable end detail

The snippets along the outside, closest to the pipe, obviously got hotter than the ones in the middle and fused more solidly.

The pipe has a 35 mm ID for an area 136 times larger than a 3 mm filament. I packed about 100 snippets into the pipe, a 0.73 packing fraction, which looks to be in the right ballpark for the high end of the Circle Packing Problem. If they were straighter, maybe a few more would fit, but twisting the lot into a cable seemed to align them pretty well.

Perhaps filling the gaps with pourable epoxy before cutting the slices would help? A completely filled interior might require pulling a good vacuum on the whole thing.

A hexagonal pipe would produce slices one could tile into a larger sheet.

All in all, a useful exercise, but … it ain’t Art yet!

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NuTone 8663RP Bathroom Vent Fan: Effective Repair

My high hopes for the UHMW bushing supporting the impeller lasted the better part of a day, because direct contact between the impeller and the motor bearing produced an absurdly loud and slowly pulsating rumble:

Bath Vent Fan - bushing installed
Bath Vent Fan – bushing installed

My hope that the UHMW would wear into a quieter configuration lasted a week …

Back in the Basement Shop, some free-air tinkering showed the impeller produced enough suction to pull itself downward along the shaft and jam itself firmly against the motor frame. My initial thought of putting a lock ring around the shaft to support the impeller turned out to be absolutely right.

So, make a small ring:

Bath Vent Fan - small lock ring - c-drill
Bath Vent Fan – small lock ring – c-drill

With a 4-40 setscrew in its side, perched atop the impeller for scale:

Bath Vent Fan - small lock ring - size
Bath Vent Fan – small lock ring – size

It just barely fits between the impeller and the motor frame:

Bath Vent Fan - small lock ring - installed
Bath Vent Fan – small lock ring – installed

This reduced the noise, but the hole in the impeller has worn enough to let it rotate on the shaft and the rumble continued unabated. The correct way to fix this evidently requires a mount clamped to both the shaft and the impeller.

Fast-forward a day …

A careful look at the impeller shows seven radial ribs, probably to reduce the likelihood of harmonic vibrations. After a bit of dithering, I decided not to worry about an off-balance layout, so the screws sit on a 9 mm radius at ±102.9° = 2 × 360°/7 from a screw directly across from the setscrew in another slice from the 1 inch aluminum rod:

Bath Vent Fan - mount ring - tapping
Bath Vent Fan – mount ring – tapping

Centered on the disk and using LinuxCNC’s polar notation, the hole positions are:

G0 @9.0 ^-90
G0 @9.0 ^[-90+102.9]
G0 @9.0 ^[-90-102.9]

As usual, I jogged the drill downward while slobbering cutting fluid. I loves me some good manual CNC action.

Put the mount on a 1/4 inch tube, stick it into the impeller, and transfer-punch the screw holes:

Bath Vent Fan - mount ring - impeller marking
Bath Vent Fan – mount ring – impeller marking

Apparently, some years ago I’d cut three screws to just about exactly the correct length:

Bath Vent Fan - mount ring - test fit - bottom
Bath Vent Fan – mount ring – test fit – bottom

I knew I kept them around for some good reason!

The 9 mm radius just barely fits the screw heads between the ribs:

Bath Vent Fan - mount ring - test fit - top
Bath Vent Fan – mount ring – test fit – top

Some Dremel cutoff wheel action extended the motor shaft flat to let the setscrew rest on the bottom end:

Bath Vent Fan - mount ring - shaft flat
Bath Vent Fan – mount ring – shaft flat

Then it all fit together:

Bath Vent Fan - mount ring - installed
Bath Vent Fan – mount ring – installed

The fan now emits a constant whoosh, rather than a pulsating rumble, minus all the annoying overtones. It could be quieter, but it never was, so we can declare victory and move on.

Dropping fifty bucks on a replacement fan + impeller unit would might also solve the problem, but it just seems wrong to throw all that hardware in the trash.

And, despite making two passes at the problem before coming up with a workable solution, I think that’s the only way (for me, anyhow) to get from “not working” to “good as it ever was”, given that I didn’t quite understand the whole problem or believe the solution at the start.

But it should be painfully obvious why I don’t do Repair Cafe gigs …

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Shower Curtain Magnet Anchors

Back in the day, bathtubs had a porcelain coating over a cast-iron carcass, so embedding little magnets in shower curtains worked perfectly to keep the loose ends from billowing out of the tub. Surprisingly, even here in the future, with plastic bathtubs ruling the land, some shower curtains still have magnets. The mud-job tile walls of shower stall in the Black Bathroom have nary a trace of iron, but we though I could add ferrous targets for a new shower curtain, thusly:

Shower Curtain Anchor - installed
Shower Curtain Anchor – installed

The magnet lives inside a heat-sealed disk, so it’s (more-or-less) isolated from the water. As you’d expect, it’s a cheap ceramic magnet, not a high-performance neodymium super magnet, with no more strength than absolutely necessary to work under the most ideal of conditions.

My anchors must also be waterproof, firmly attached, non-marking, easily removable, and no more ugly than absolutely necessary. The general idea is to slice the bottom from a pill bottle, entomb a thin steel disk in epoxy, and attach to the tile with a patch of outdoor-rated foam tape.

So, we begin …

Cutting a narrow ring from a pill bottle requires a collet around the whole circumference, which started life as some sort of stout aluminum pole:

Shower Curtain Anchor - cutting tube stock
Shower Curtain Anchor – cutting tube stock

Bore out the inside, with a small step to locate the bottle:

Shower Curtain Anchor - boring fixture
Shower Curtain Anchor – boring fixture

Clean up the outside, just for pretty:

Shower Curtain Anchor - turning fixture OD
Shower Curtain Anchor – turning fixture OD

Slit the fixture to let it collapse around the bottle, then chuck up the first victim with support from a conveniently sized drill chuck in the tailstock:

Shower Curtain Anchor - cutting bottle
Shower Curtain Anchor – cutting bottle

I did a better job of cutting the second bottle to the proper length:

Shower Curtain Anchor - parting base
Shower Curtain Anchor – parting base

Nibble disks from sheet metal, half-fill the bottle bottoms with steel-filled (and, thus, magnetic!) JB Weld epoxy, insert disks, add sufficient epoxy to cover the evidence:

Shower Curtain Anchor - epoxy curing
Shower Curtain Anchor – epoxy curing

Fast-forward to the next day, punch out two disks of double-sided foam tape:

Shower Curtain Anchor - adhesive foam
Shower Curtain Anchor – adhesive foam

Affix, install, and it’s all good.

Actually, it’s not. The ceramic magnets are so weak they don’t hold the curtain nearly well enough to satisfy me. The next anchor iteration should have embedded neodymium magnets to attract the curtain’s crappy ceramic magnets, but this is Good Enough™ for now.

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Primitive Screwheads

Painting the patio railing required removing the short section on the garage, which stalled with a thoroughly galled / corroded nut on the 2 inch bolt going through the wall. Deploying a Dremel slitting wheel and bashing the slit open with a cold chisel saved the day, as shown in this staged reenactment:

Patio railing - square head bolt - extraction
Patio railing – square head bolt – extraction

It seems square head bolts have gone out of fashion, at least in the 3/8-16 size seen here, over the last half century:

Patio railing - square head bolts
Patio railing – square head bolts

I reused the lag screw with no qualms at all.

The local fastener emporium had square bolts ranging upward from 3/4-10, which wasn’t much help. Amazon has ’em, if you spend enough time rummaging around in the debris from its search engine, at a buck apiece in lots of ten. Fortunately, a local big-box home repair store had 3/8-16 hex head steel bolts and square nuts, so I needn’t start from scratch.

Start by turning off the hex head:

Patio railing - square head bolt - removing hex head
Patio railing – square head bolt – removing hex head

Thread the end, starting in the lathe and ending with a die turned just barely enough to accept the nut:

Patio railing - square head bolt - threading
Patio railing – square head bolt – threading

Epoxy the nut in place and sand it to rough up the surface finish enough to hold the primer:

Patio railing - square head bolt - lineup
Patio railing – square head bolt – lineup

Yeah, that’s a nasty little zit. Fortunately, nobody will ever notice.

Prime & paint the railing, affix it to the garage wall, then prime & paint the bolt:

Patio railing - square head bolt - installed
Patio railing – square head bolt – installed

Thing looks like it grew there; tell nobody about the zit.

The yellow blotches decorating the shiny black paint come from the pine trees across the driveway. The first day of pine pollen season corresponded to the second day I intended to paint; the dust clouds were a wonder to behold.

Bonus Quality Shop Time!

The far end of the railing around the patio has a bracket against the house siding with a hole intended for a 1/4 inch bolt they never installed, perhaps because there’s no way to maneuver a bolt into the space available.

The threads on the 3/8-16 bolt may be wrecked, but turning the shank down to 1/4 inch isn’t any big deal:

Patio railing - fake bolt - thinning shank
Patio railing – fake bolt – thinning shank

Part off the head with a stub just long enough to fit into the bracket, epoxy that sucker into the hole, and paint it black:

Patio railing - fake bolt - installed
Patio railing – fake bolt – installed

The square post on the left goes down to an anchor in the concrete patio, the railing is welded to a 4 inch column a foot away, and the end of the railing isn’t going anywhere; the fake bolt is purely for show.

And, yes, the dust atop the railing is more pollen from the pine trees responsible for the weird green-yellow reflections on the vertical surfaces.

No boomstick required!

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MPCNC Drag Knife: Ground Shaft in LM12UU Bearing

The 12 mm drag knife holder on the left slides nicely in an LM12UU bearing:

Drag Knife holders - detail
Drag Knife holders – detail

However, its aluminum body isn’t really intended as a bearing surface and it extends only halfway through the LM12UU, so I finally got around to modifying the 11.5 mm body on the right to fit into a section of 12 mm ground shaft:

Drag Knife - turning 11.5 mm body to 10 mm
Drag Knife – turning 11.5 mm body to 10 mm

The general idea is to turn the body down to 10 mm OD; the picture shows the first pass over the nose after turning the far end down and removing the flange in the process. Exact concentricity of both ends isn’t important (it gets epoxied into a 10 mm hole through the 12 mm ground shaft), but it came out rather pretty:

Drag Knife - 11.5 mm body - turned to 10 mm
Drag Knife – 11.5 mm body – turned to 10 mm

The ground shaft started as a pen holder:

DW660 Pen Holder - ground shaft
DW660 Pen Holder – ground shaft

I knocked off the ring and bored the interior to fit the 10 mm knife body. The large end of the existing bore came from a 25/64 inch = 9.92 mm drill, so it was just shy of 10.0 mm, and I drilled the small end upward from 0.33 inch = 8.4 mm.

The smallest trio of a new set of cheap carbide boring bars allegedly went into a 5/16 inch = 7.9 mm bore, but I had to file the bar body down and diamond-file more end relief into the carbide for clearance inside the drilled hole:

Modified boring bar vs original
Modified boring bar vs original

I blued the bit, kissed it against the drilled bore, filed off whatever wasn’t blued, and iterated until the carbide edge started cutting. Sissy cuts all the way, with no pix to show for all the flailing around.

Epoxying the turned-down drag knife body into the shaft: anticlimactic.

The solid model features a stylin’ tapered snout:

Drag Knife LM12UU holder - tapered end
Drag Knife LM12UU holder – tapered end

Which gets an LM12UU bearing rammed into place:

Drag Knife - LM12UU holder - inserting bearing
Drag Knife – LM12UU holder – inserting bearing

The steel block leaves the bearing flush with the plastic surface, rather than having it continue onward and indent itself into the wood; I can learn from my mistakes.

The new idea: a single spring pressing the knife holder downward, reacting against a fixed plastic plate:

Drag Knife - LM12UU ground shaft - assembled
Drag Knife – LM12UU ground shaft – assembled

Unlike the previous design, the upper plate doesn’t move, so there’s no problem caused by sliding along the screw threads. I should run nylock nuts up against the plate to keep it in place, stiffen the structure, and provide some friction to keep the screws from loosening.

The top of the knife holder now has a boss anchoring the spring:

Drag Knife - turning spring recess
Drag Knife – turning spring recess

As you’d expect, the ground shaft slides wonderfully in the bearing, because that’s what it’s designed to do, and the knife has essentially zero stiction and friction at any point along the bearing, which is exactly what I wanted.

The spring, from the same assortment as all the others, has a 48 g/mm rate.

The OpenSCAD source code as a GitHub Gist:

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MPCNC Drag Knife: PETG Linear Bearing

Having reasonable success using a 12 mm hole bored in a 3D printed mount for the nice drag knife holder on the left, I thought I’d try the same trick for the raw aluminum holder on the right side:

Drag Knife holders - detail
Drag Knife holders – detail

The 11.5 mm body is long enough to justify making a longer holder with more bearing surface:

Drag Knife Holder - 11.5 mm body - Slic3r preview
Drag Knife Holder – 11.5 mm body – Slic3r preview

Slicing with four perimeter threads lays down enough reasonably solid plastic to bore the central hole to a nice sliding fit:

Drag Knife - 11.5 mm body - boring
Drag Knife – 11.5 mm body – boring

The top disk gets bored to a snug press fit around the flange and upper body:

Drag Knife - 11.5 mm body - flange boring
Drag Knife – 11.5 mm body – flange boring

Assemble with springs and it pretty much works:

Drag Knife - hexagon depth setting
Drag Knife – hexagon depth setting

Unfortunately, it doesn’t work particularly well, because the two screws tightening the MPCNC’s DW660 tool holder (the black band) can apply enough force to deform the PETG mount and lock the drag knife body in the bore, while not being quite tight enough to prevent the mount from moving.

I think the holder for the black knife (on the left) worked better, because:

  • The anodized surface is much smoother & slipperier
  • The body is shorter, so less friction

In any event, I reached a sufficiently happy compromise for some heavy paper / light cardboard test shapes, but a PETG bearing won’t suffice for dependable drag knife cuttery.

Back to the laboratory …

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Improved Shoelace Ferrule Aglets

After considerable evaluation, the Customer decided the shoelaces were still too long and said the hex-crimped ferrules were entirely too rough and tended to snag on things. This time, I prepared the ferrules by chucking them in the lathe:

Ferrule - original flange
Ferrule – original flange

The steel rod inside the ferrule encourages it to remain round and not collapse while I’m filing off the flange that normally holds the plastic strain-relief doodad:

Ferrule - reshaped flange
Ferrule – reshaped flange

I snipped another half inch off each end of the laces and crimped on the prepared ferrules:

Shoelace ferrule aglets
Shoelace ferrule aglets

Which were definitely too jaggy, so they now sport an epoxy coat:

Ferrule aglets - epoxy coat
Ferrule aglets – epoxy coat

Alas, JB Kwik epoxy has a pot life measured in minutes, so the last ferrule looks a bit lumpy. They seem to work fine and the Customer is happy with the results.

Memo to Self: Next time, dunk the ferrules in a pot of slow-curing JB Weld and let them drain overnight.

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