Posts Tagged Mini-lathe
Primitive Screwheads
Posted by Ed in Home Ec, Machine Shop on 2019-06-24
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:
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:
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:
Thread the end, starting in the lathe and ending with a die turned just barely enough to accept the nut:
Epoxy the nut in place and sand it to rough up the surface finish enough to hold the primer:
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:
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:
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:
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!
MPCNC Drag Knife: Ground Shaft in LM12UU Bearing
Posted by Ed in Machine Shop, Software on 2019-06-18
The 12 mm drag knife holder on the left slides nicely in an LM12UU bearing:
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:
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:
The ground shaft started as a pen holder:
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:
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:
Which gets an LM12UU bearing rammed into place:
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:
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:
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:
MPCNC Drag Knife: PETG Linear Bearing
Posted by Ed in Machine Shop, Science on 2019-05-24
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:
The 11.5 mm body is long enough to justify making a longer holder with more bearing surface:
Slicing with four perimeter threads lays down enough reasonably solid plastic to bore the central hole to a nice sliding fit:
The top disk gets bored to a snug press fit around the flange and upper body:
Assemble with springs and it pretty much works:
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 …
Improved Shoelace Ferrule Aglets
Posted by Ed in Home Ec, Machine Shop on 2019-03-20
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:
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:
I snipped another half inch off each end of the laces and crimped on the prepared ferrules:
Which were definitely too jaggy, so they now sport an 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.
Minilathe MT3 Spindle Collet Fitting
Posted by Ed in Machine Shop, Oddities on 2019-01-16
I’ve used the LMS set of inch-size MT3 spindle collets on occasion, but releasing them required an unseemly amount of drawbar battering. It recently occurred to me to check their fit in the spindle taper:
Minilathe – MT3 collet – taper test
Huh.
The only place they touch the spindle is right around the base, so it’s no wonder they clamp poorly and release grudgingly. I tried several others with the same result.
Cross-checking shows a much closer fit along the entire length of the dead center, so it’s not the spindle’s fault:
Minilathe – Dead Center – MT3 taper check
Stipulated: we’re not talking toolroom precision here
I set the collets on centers:
Minilathe – MT3 collet – drive setup
And proceeded to file away the offending section to move the clamping force closer to the business end of the collet:
Minilathe – MT3 collet – filed result
I did the small collets, the ones I’m most likely to need, and left the big ones for another rainy day.
They don’t have much clamping range and seem good only for exact-inch-size rods.
I should lay in a stock of ER16 and maybe ER32 collets for small stuff.
Bird Feeder Unbending
Posted by Ed in Home Ec, Machine Shop, Science on 2018-11-13
At some point in its history, the left rail holding the wood perch on our industrial-strength “squirrel proof” seed feeder took a hit, most likely from being dropped:
Squirrel on bird feeder
I finally got a Round Tuit and un-bent the poor thing:
Bird feeder – rail un-bending
Because the bend happened at the base of the vertical strut holding the shutter, I clamped a Genuine Vise-Grip sheet metal pliers along the straight section. The Craftsman knock-off Vise-Grip then applied torque at the bend, rather than just making things worse, and some two-axis tweakage lined up the rail pretty well.
With the bend taken care of, I clamped the rail in the bench vise with some scrap wood around the strut:
Bird feeder – warped rail
A percussive adjustment jam session flattened the top flange, leaving both sections as flat as they’re gonna get.
While I was at it, I turned a pair of stepped aluminum washers for the new wood rod:
Bird feeder – parting off washer
Which looked about like you’d expect, including a little chatter from the cut off tool:
Bird feeder – perch hardware
Yeah, I drilled the wood rod on the lathe, too; I loves me some simple lathe action.
Reassemble in reverse order and it’s all good:
Bird feeder – perch installed
We’re supposed to bleach the feeder every week to kill off the bacteria causing House Finch Eye Disease and, while I can’t promise a weekly schedule, we’ll (try to) reduce the amount of crud on the feeder this year.
If you’ve got a feeder, sign up for Project Feederwatch and do some citizen science!
Kenmore Progressive Vacuum Tool Adapters: Third Failure
Posted by Ed in Home Ec, Machine Shop, Software on 2018-11-08
The adapter for an old Electrolux crevice tool (not the dust brush) snapped at the usual stress concentration after about three years:
Crevice tool adapter – broken vs PVC pipe
The lower adapter is the new version, made from a length of 1 inch PVC pipe (that’s the ID, kinda-sorta) epoxied into a revised Kenmore adapter fitting.
The original OpenSCAD model provided the taper dimensions:
Electrolux Crevice Tool Adapter – PVC taper doodles
The taper isn’t quite as critical as it seems, because the crevice tool is an ancient molded plastic part, but a smidge over half a degree seemed like a good target.
Start by boring out the pipe ID until it’s Big Enough (or, equally, the walls aren’t Scary Thin) at 28 mm:
Crevice tool adapter – boring PVC
Alas, the mini-lathe’s craptastic compound has 2° graduations:
Minilathe compound angle scale
So I set the angle using a somewhat less craptastic protractor and angle gauge:
Crevice tool adapter – compound angle
The little wedge of daylight near the gauge pivot is the difference between the normal perpendicular-to-the-spindle axis setting and half-a-degree-ish.
Turning PVC produces remarkably tenacious swarf:
Crevice tool adapter – PVC swarf
The gash along the top comes from a utility knife; just pulling the swarf off didn’t work well at all.
The column of figures down the right side of the doodles shows successive approximations to the target angle, mostly achieved by percussive adjustment, eventually converging to about the right taper with the proper dimensions.
Cutting off the finished product with the (newly angled) cutoff bit:
Crevice tool adapter – cutoff
And then It Just Worked™.
The OpenSCAD source code for all the adapters as a GitHub Gist:
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