Tour Easy: Chain Drop Pin

Every now and again, an upshift to the large chainring on my Tour Easy would go awry and drop the chain off the outside, where it would sometimes jam between the pedal crank and the spider. In the worst case the flailing chain would also jam in the TerraCycle idler, but I fixed that a while ago.

Contemporary chainrings (i.e., anything made since the trailing decades of the last millennium) generally have a chain drop pin positioned against the crank specifically to prevent such chain jamming.

Making a chain drop pin is no big deal if you’ve got a lathe and an M4 tap:

Tour Easy - DIY Chain Drop pin
Tour Easy – DIY Chain Drop pin

A closer look:

Tour Easy - DIY Chain Drop pin - detail
Tour Easy – DIY Chain Drop pin – detail

That’s a 10 mm length of 5/16 inch brass rod drilled with a recess to fit the head of a 10 mm M4 socket-head cap screw.

The pin should be a micro-smidgen shorter, as it just touches the crank, but, if anything, moving the chainring inward by one micro-smidgen improved the upshifts and I’m inclined to go with the flow.

Should’a done it decades ago …

Mini-Lathe: Adapting a Five Inch Four Jaw Chuck Adapter Plate

The kludge required to trim the coaster rims disturbed the silt enough to reveal a long-lost 5 inch 4 jaw chuck that fit neither the old South Bend lathe nor the new mini-lathe. In any event, the chuck does have an adapter plate on its backside, it’s just not the correct adapter plate for the spindle on my mini-lathe.

Making it fit required enlarging an existing recess to fit the spindle plate, a straightforward lathe job with the plate grabbed in the 3 jaw chuck’s outer jaws:

5 inch 4 jaw chuck - boring spindle recess
5 inch 4 jaw chuck – boring spindle recess

Carbide inserts don’t handle interrupted cuts very well, but sissy cuts saved the day. The plate is kinda-sorta cast iron, so the “chips” are dust and a vacuum snout reduces the mess; you can see some chips inside the bore.

A faceplate for the mini-lathe lathe located three holes matching the spindle plate, after I noticed the amazing coincidence of both parts having 26 mm bores. Making an alignment tool from a scrap of 3/4 inch (!) Schedule 40 PVC pipe was an easy lathe job:

5 inch 4 jaw chuck - adapter plate alignment
5 inch 4 jaw chuck – adapter plate alignment

Transfer-punching those holes produced pips on the chuck side of the adapter plate:

5 inch 4 jaw chuck - spindle bolt spotting
5 inch 4 jaw chuck – spindle bolt spotting

I thought about freehanding the holes, but came to my senses:

5 inch 4 jaw chuck - adapter plate drilling
5 inch 4 jaw chuck – adapter plate drilling

Of course, the Sherline lacks enough throat for the plate, so each hole required clamping / locating / center-drilling / drilling / finish drilling. With all three drilled, hand-tapping the threads was no big deal:

5 inch 4 jaw chuck - rebuIlt adapter plate
5 inch 4 jaw chuck – rebuIlt adapter plate

Those are M8×1.25 studs from LMS (although the ones I got look like the 30 mm version), with the long end sunk in the adapter plate to put the other end flush with the nut on the far side of the spindle plate:

5 inch 4 jaw chuck - installed - spindle nuts
5 inch 4 jaw chuck – installed – spindle nuts

And then it fits just like it grew there, although the jaws don’t have much clearance inside the interlock cover:

5 inch 4 jaw chuck - installed - front view
5 inch 4 jaw chuck – installed – front view

Now I’m ready for the next set of coasters and, if the jaws stick out too far, I can gimmick the interlock switch for the occasion.

If the truth be known, I ordered two sets of those studs along with the 4 inch 4 jaw chuck intended for the mini-lathe, so, if anything, I’m now over-prepared.

The description of the 4 inch chuck seems inconsistent with its listed dimensions, which may be why I ended up with the larger chuck in the first place. You can never have enough chucks: all’s well that ends well.

Acrylic Coasters: Edge Finishing, Round 4

Lacking a 4-jaw chuck for the lathe, this should suffice:

Coaster Epoxy Rim - chuck-in-chuck setup
Coaster Epoxy Rim – chuck-in-chuck setup

Which is just the Sherline 4-jaw chuck chucked in the lathe’s 3-jaw chuck, with both chuck Jaw 1 positions lined up and marked on the acrylic disk fixture. The picture is a recreation set up after the fact, because I lack a good picture of the overall scene.

Now it’s easy enough to center the fixture, stick the coaster in place with reasonable accuracy, then tweak the Sherline chuck to center the coaster:

Coaster Epoxy Rim - turning setup
Coaster Epoxy Rim – turning setup

Because the bottom layer is a laser-cut disk, eyeballometrically aligning its edge to a simple pointer worked surprisingly well:

Coaster Epoxy Rim - locating mirror edge
Coaster Epoxy Rim – locating mirror edge

Turning the OD down to match the bottom disk meant I could finally get decent results with zero drama:

Coaster Epoxy Rim - turned samples
Coaster Epoxy Rim – turned samples

From the bottom, this one has a 3 mm mirror, the 3 mm fluorescent green frame + petals, and a 1.6 mm top sheet:

Coaster Epoxy Rim - turned 6 petal mirror
Coaster Epoxy Rim – turned 6 petal mirror

This one has a 3M double-sided tape with low-surface-energy adhesive layers between the mirror and the fluorescent blue frame + petal, with epoxy between the top layer and the frame.

Coaster Epoxy Rim - turned 4 petal
Coaster Epoxy Rim – turned 4 petal

If I never tell anybody, they’ll think the slightly granular look if the tape was deliberate; it looks OK to me.

And, for completeness, the crash test dummy from the start of this adventure:

Coaster Epoxy Rim - turned 6 petal black
Coaster Epoxy Rim – turned 6 petal black

I don’t know how to avoid the bubbles, as the usual torch-the-top and pull-a-vacuum techniques pop bubbles at the epoxy-air interface. These bubbles are trapped under the top acrylic sheet, even though I was rather painstaking about easing the layer down from one side to the other while chasing bubbles along.

Maybe I can define bubbles as Part of the Art?

Definitely fancier than chipboard, although not nearly as absorbent.

OMTech 60 W Laser: Mirror Cleaning

While I was puttering around inside the laser cabinet, I figured it was time to check the mirrors for cleanliness. The first two mirrors looked fine, but Mirror 3 needed help:

OMTech 60W laser mirror 3 cleaning - before
OMTech 60W laser mirror 3 cleaning – before

It turns out OMTech used molybdenum rather than gold-plated silicon or copper, trading off some reflectivity to reduce damage from over-enthusiastic cleaning with a vigorous circular motion.

A first pass with an optical wipe removed most of the crud:

OMTech 60W laser mirror 3 cleaning - during
OMTech 60W laser mirror 3 cleaning – during

Gentle touch-up with a little more isopropyl alcohol cleared the rest:

OMTech 60W laser mirror 3 cleaning - after
OMTech 60W laser mirror 3 cleaning – after

The focus lens required similar attention, but there is no way to get meaningful pictures of a transparent lens.

Realigning the mirrors went well (top before, middle during, lower after):

Beam Alignment Targets- 2022-08-06
Beam Alignment Targets- 2022-08-06

The diagonal results at Mirror 3 show the XY axes aren’t quite square, but AFAICT it’s close enough. The rightmost tape shows good beam centering in the nozzle and the Focus target shows excellent Z alignment over about 50 mm of travel.

Done!

OMTech 60W Laser: Repurposing the HV Power Supply Water Protect Input

For reference, the input terminals on the OMTech anonymous 60 W HV laser power supply:

OMTech 60W HV power supply - terminals
OMTech 60W HV power supply – terminals

AFAICT, that’s the default layout for all similar power supplies.

The H and L pins are the High- and Low-active enable inputs that, when it’s working right, control the laser output. The KT332 controller (and, most likely, all RuiDa controllers) produce a low-active output, so you just wire the controller’s output to the L input and you’re done.

That was the original failure that got me to this point: the power supply ignored its L input and turned the beam on at whatever power the PWM signal on the IN terminal called for. Having that happen was surprising, having it happen with the cabinet lid open was … disturbing.

The P input is intended for the Water Protect signal from the flow sensor on the laser cooling plumbing. When the water is flowing, the IN terminal will be low and the power supply will pay attention to the L input.

The power supply arrived with a jumper between the P input and the G ground / common terminal:

OMTech 60W HV power supply - Water Protect jumper
OMTech 60W HV power supply – Water Protect jumper

The jumper holds the P input low = active, meaning the power supply thinks the water is always flowing.

It turns out that the Water Protect signal goes only to the controller. When it’s inactive = no water flowing, the controller will refuse to fire the laser and also sound an alarm. Running the signal directly to the power supply would result in a puzzling failure-to-fire with no diagnostic from the controller.

I removed that jumper and added a (green) wire from the Lid Interlock signal at the controller:

OMTech KT332 controller - Lid Interlock input - added wire
OMTech KT332 controller – Lid Interlock input – added wire

To the power supply’s P input:

OMTech 60W HV power supply - Water Protect as Lid Interlock
OMTech 60W HV power supply – Water Protect as Lid Interlock

In principle, if this power supply fails the same way as the previous one (with its L input always active), then at least it won’t fire with the lid up.

Believing that may display a childish naivety, but at least the thing seems marginally safer than it was before.

High Impact Art: Smashed Glass Coaster Meniscus Removal

After using the smashed glass coaster for a while, the beveled epoxy meniscus around the perimeter proved itself more annoying than expected:

Glass Coaster - second test
Glass Coaster – second test

So I clamped it to the Sherline’s tooling plate and milled off the rim:

Smashed Glass Coaster - meniscus removal
Smashed Glass Coaster – meniscus removal

Given the Sherline’s cramped work envelope, all the action took place along the rearmost edge, requiring eight reclampings indexed parallel to the table with a step clamp.

The cutter cleared off everything more than 0.3 mm above the surface of the glass chunks. I could probably have gone another 0.1 mm lower, but chopping the bit into the edge of a shattered glass fragment surely wouldn’t end well.

Polishing the dark gray milled surface might improve it slightly, at the risk of scuffing whatever poured epoxy stands slightly proud of the glass:

Smashed Glass Coaster - leveled edge
Smashed Glass Coaster – leveled edge

Perhaps if I define it to be a border, everybody will think it was intentional.

Rounded Petal Acrylic Coaster

Having gotten the rounded-petal pattern generator working, applying it to acrylic sheets seemed reasonable:

Cut Acrylic Coaster - top cleaned
Cut Acrylic Coaster – top cleaned

The petals stand slightly proud of the black top frame, as the colored sheets were marginally thicker than the black sheet, but it looks OK in person. They’re all epoxied to a transparent base plate, so the bottom view is pretty much the same:

Cut Acrylic Coaster - bottom
Cut Acrylic Coaster – bottom

Because the bottom is perfectly smooth, I think it looks better than the top, which shows irregularities around the petals where the epoxy didn’t quite fill the gaps. There is one small bubble you won’t notice if I don’t tell you about it.

I laid a small bead of epoxy around the perimeter of the base, laid the black frame in place, ran a bead along the midline of each petal shape plus a drop in the round part, laid the petals in place, and hoped I didn’t use too much epoxy. It turned out all right, with only a few dribbles down the edge that wiped off easily enough.

I peeled the protective plastic off the top while the epoxy was still tacky, which pulled far too many fine filaments across the surface:

Cut Acrylic Coaster - frayed top
Cut Acrylic Coaster – frayed top

After the final cure, I managed to scrape most of them off with a thumbnail; I hope to never make that mistake again.

As you might expect, acrylic plastic’s pure saturated colors wipe the floor with Sharpie-scribbled white chipboard:

Chipboard coaster - rounded petals - front vs back cut
Chipboard coaster – rounded petals – front vs back cut

The black frame makes the whole thing overly dark, so the next attempt should use white or perhaps a transparent layer atop a mirror base.