Posts Tagged M2

CNC 3018-Pro: Platter Fixtures

Up to this point, the Sherline has been drilling 3.5 inch hard drive platters to serve as as reflecting bases for the vacuum tubes:

LinuxCNC - Sherline Mill - Logitech Gamepad
LinuxCNC – Sherline Mill – Logitech Gamepad

The CNC 3018-Pro has a work envelope large enough for CD / DVD platters, so I mashed the Sherline fixture with dimensions from the vacuum tube code, added the 3018’s T-slot spacing, and conjured a pair of fixtures for a pair of machines.

Because I expect to practice on scrap CDs and DVDs for a while:

Platter Fixtures - CD on 3018
Platter Fixtures – CD on 3018

And a 3.5 inch hard drive platter version:

Platter Fixtures - hard drive platter on 3018
Platter Fixtures – hard drive platter on 3018

The holes sit at half the 3018’s T-slot spacing (45 mm / 2), so you can nudge the fixtures to the front or rear, as you prefer.

The alignment dots & slots should help touch off the XY coordinate system on the Sherline, although it can’t reach all of a CD. Using bCNC’s video alignment on the hub hole will be much easier on the 3018.

After fiddling around with the 3018 for a while, however, the CD fixture doesn’t have many advantages over simply taping the disc to a flat platen. Obviously, you’d want a sacrificial layer for drilling, but it’s not clear the OEM motor / ER11 chuck would be up to that task.

The OpenSCAD source code as a GitHub Gist:

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Tour Easy: Ruggedized Zzipper Fairing Mount

After nigh onto 18 years, the pipe straps holding the Zzipper fairing struts to the handlebars of our Tour Easy recumbents finally shrugged off their plastic wraps:

Tour Easy Zzipper Fairing - OEM mount
Tour Easy Zzipper Fairing – OEM mount

Although they still worked, riding over broken pavement produced distinct rattles; alas, the roads around here feature plenty of broken pavement.

The solution is a rugged plastic block capped with aluminum plates to spread the clamping load:

Tour Easy Zzipper Fairing - block mount
Tour Easy Zzipper Fairing – block mount

The solid model is straightforward:

Zzipper Fairing - Strut Mount - solid model - Show view
Zzipper Fairing – Strut Mount – solid model – Show view

A slight bit of tinkering made the stack exactly the right height for 45 mm screws secured with nyloc nuts. No washers on either end, although that’s definitely in the nature of fine tuning.

The three sections print without support:

Zzipper Fairing - Strut Mount - solid model
Zzipper Fairing – Strut Mount – solid model

I reamed the smaller hole with a 3/8 inch drill to match the fairing strut rod. The as-printed larger hole fit the handlebar perfectly, although the first picture shows the tubing isn’t exactly round on the near side of the block, where it starts the outward bend toward the grips.

The cap plates cried out for CNC, but I simply traced two outlines of the block on 1/8 inch aluminum sheet, bandsawed near the line, introduced them to Mr Disk Sander for finishing & corner rounding, transfer-punched the holes from the plastic blocks, and drilled to suit:

Tour Easy Zzipper Fairing - clamp plates
Tour Easy Zzipper Fairing – clamp plates

Making two pairs of plates by hand counts as Quality Shop Time around here.

The first few rides confirm the fix: no rattles!

The OpenSCAD source code as a GitHub Gist:

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Step2 Garden Seat: Replacement Seat

A pair of Step2 rolling garden seats (they have a new version) served in Mary’s gardens long enough to give their seat panels precarious cracks:

Step2 Seat - OEM seat
Step2 Seat – OEM seat

The underside was giving way, too:

Step2 Seat - cracks
Step2 Seat – cracks

We agreed the new seat could be much simpler, although it must still hinge upward, so I conjured a pair of hinges from the vasty digital deep:

Rolling Cart Hinges - solid model - bottom
Rolling Cart Hinges – solid model – bottom

The woodpile disgorged a slab of 1/4 inch = 6 mm plywood (used in a defunct project) of just about the right size and we agreed a few holes wouldn’t be a problem for its projected ahem use case:

Step2 Seat - assembled
Step2 Seat – assembled

The screw holes on the hinge tops will let me run machine screws all the way through, should that be necessary. So far, a quartet of self-tapping sheet metal (!) screws are holding firm.

Rolling Cart Hinges - solid model - top
Rolling Cart Hinges – solid model – top

A closer look at the hinges in real life:

Step2 Seat - top view
Step2 Seat – top view

The solid model now caps the holes; I can drill them out should the need arise.

From the bottom:

Step2 Seat - bottom view
Step2 Seat – bottom view

Three coats of white exterior paint make it blindingly bright in the sun, although we expect a week or two in the garden will knock the shine right off:

Step2 Seat - painted
Step2 Seat – painted

After the first coat, I conjured a drying rack from a bamboo skewer, a cardboard flap, and some hot-melt glue:

Step2 Seat - drying fixture
Step2 Seat – drying fixture

Three small scars on the seat bottom were deemed acceptable.

The OpenSCAD source code as a GitHub Gist:

This original doodle gives the key dimensions, apart from the rounded rear edge required so the seat can pivot vertically upward:

Cart Hinge - dimension doodle
Cart Hinge – dimension doodle

The second seat looks just like this one, so life is good …

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Drag Knife Blade Ejector Handle

The LM12UU drag knife holder buries the blade ejector pin deep inside the machinery:

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

So a handle with a pin makes sense:

LM12UU Drag Knife Ejector Pin Pusher
LM12UU Drag Knife Ejector Pin Pusher

It’s a variant Sherline tommy bar handle, so there’s not much to say about it.

The dark butt end comes from the traces of the black filament I used for the previous part. Even after flushing half a meter of orange through the hot end, you’ll still see some contamination, even with the same type of plastic. Doesn’t make much difference here, though.

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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 it almost looks 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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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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