The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Category: Machine Shop

Mechanical widgetry

Machinable Wax: First Cuts

This is a prototype for the case that will eventually hold a TinyTrak3 GPS-to-APRS encoder, along with a homebrew circuit board that combines the APRS data with voice from the helmet mic. The case slides into the back of our ICOM IC-Z1A and W-32A HTs, replacing the battery case.

It’s the most complex CNC machining I’ve done so far and I figured that was the perfect reason to carve up a block of machinable wax that’s been sitting on the shelf for far too long.

The exterior view shows why you use wax for the first pass… the ugly gash came from not retracting the end mill before the final G30, combined with trying to clamp a bendy shell in the vise. That was, of course, the final operation on that part!

Machinable wax case – exterior

The inside view shows the TinyTrak serial connector cutout (left half), as well as the shoulder to support the audio interface circuit board (right half). The two holes at the upper-right are 4-40 clearance for screws that serve as contacts for the HT’s battery connection and hold the board in place.

Machinable wax case – interior

These survived far too many setups and takedowns as I figured out how to get all the cuts laid out and in what sequence to do everything. Now that I know a bit more about what to do, the plastic version should come out better; I’m sure I’ll also make better mistakes.

2010-06-10
Bell Bicycle Helmet Teardown

Having gotten our new helmets up & running, I decided to tear down my old helmet to see what’s inside. The thin plastic shell was already cracked (and probably brittle from years of sun), so it tore off very easily. The foam structure was in good shape, but I was surprised to see that everything’s held in place by glass filament tape!

Peeled bike helmet

The straps pass through an H-shaped locking clip tucked into a recess in the rear apex (to the left in the picture). The front strap simply loops over the foam shell (to the right of the tape crossing on the right), where it’s held in place on double-sided adhesive foam tape by the glass filament tape.

All in all, a low-cost, low-weight design that works just fine.

2010-06-09
Visor-mounting a Third Eye Hardshell Mirror

Tweaked Third Eye Mirror

The Third Eye Hardshell Mirror was designed back in the day when Bell Helmets had actual hard plastic shells over a foam core, with a lip around the shell’s edge. These days, helmets consist of an elaborate foam structure with a paper-thin plastic covering. Mary’s helmet is like that, but it has a visor and I figured the mounting clamp might grab onto that.

It almost worked, but the edge of the clamp tapered the wrong way: tightening the screw tipped the clamp away from the visor lip.

Solution: chop off the offending part of the clamp, file off the sharp edges, and screw it in place. Works like a champ.

I’m not convinced this mount will survive the test of time, though. We already know that the clever ball joint will eventually lose its griptivity, but that’s fixable.

2010-06-08
CycleAware Mirror Repair

Original CycleAware Attachment

While installing the audio gear on our bike helmets, I found a defunct CycleAware Reflex helmet mirror in the big box o’ bike stuff.

This pic shows that the mirror attaches to the boom through a clever ball joint that allows both rotation around the mirror’s long axis and a slight amount of tilt. Unfortunately, after a few years, the ball stem breaks and at least one of the socket petals snaps. It’s a nice plastic design that’s totally unsuited to a few years of more-or-less daily bicycle travel.

The repair was easy enough, particularly because I think the boom has enough adjustment range to handle the job on its own (and I don’t care about how it looks). I filed off the stem stub and milled a slot for a 2-56 machine screw along the back edge.

Milling slot for screw

Then you just slide a brass tube from the cutoff box over the end of the boom around some JB Weld epoxy, shove the screw into the blob, align the mirror with the boom, and let it cure.

Reinforced attachment

Although it’s not shown here, the helmet attachment is aligned with the mirror at right angles to the helmet bracket. That puts it in roughly the proper position with the boom bent as usual.

I don’t actually plan to use this one for anything, but if I need a somewhat scuffed mirror in a pinch, well, it’s in the box!

2010-06-07
Sherline Tool Table
Having recently converted to EMC 2.4 and switched the tool table to the new format, I took the opportunity to add a few useful drills.

Low numbers are random end mills & suchlike. Number drills run from 100 to 180, and I’ll add more as I need ’em. Fraction drills run from 201 through 264, although it’s highly unlikely I’ll ever fit a 64/64-inch drill in a chuck that also fits in the Sherline spindle.

All the Z lengths are exactly 1, because I now have a tool length probe that is absolutely wonderful.

In practice, I use the tool table mostly to tell Axis how to draw the tool cylinder in the backplot, because I feed in most diameters directly in the G-Code. The Axis “manual toolchanger” routine prompt will now serve as a mnemonic for the actual size, but I write the G-Code to emit a (debug, #Drill_Size) message for clarity.

The Sherline.ini file references the tool table with the line:
```
 TOOL_TABLE = Sherline.tbl
```
Herewith, Sherline.tbl:
```
; Common end mills
T1 P1 Z1 D0.1225    ; 1/8
T2 P2 Z1 D0.1535    ; 5/32
T3 P3 Z1 D0.187        ; 3/16
T4 P4 Z1 D0.25        ; 1/4
T5 P5 Z1 D0.3122    ; 5/16
T6 P6 Z1 D0.374        ; 3/8
T7 P7 Z1 D0.4374    ; 7/16
T8 P8 Z1 D0.4720    ; 1/2
T20 P20 Z1 D0.09787 ;  2 mm
; Number drills
T107 P107 Z1 D0.201 ;  7     5.11    10-32 clear
T109 P109 Z1 D0.196 ;  9     4.98    10-32 clear
T118 P118 Z1 D0.170 ; 18     4.32     8-32 clear
T121 P121 Z1 D0.159 ; 21     4.04    10-32 tap
T127 P127 Z1 D0.144 ; 27     3.66     6-32 clear
T129 P129 Z1 D0.136 ; 29     3.45     8-32 tap
T136 P136 Z1 D0.107 ; 36     2.72     6-32 tap
T132 P132 Z1 D0.116 ; 32     2.95     4-40 clear
T143 P143 Z1 D0.089 ; 43     2.26     4-40 tap
T141 P141 Z1 D0.096    ; 41     2.44     2-56 clear
T148 P148 Z1 D0.076 ; 48     1.93     1-72 clear
T150 P150 Z1 D0.070    ; 50     1.78     2-56 tap 0-80 clear
T152 P152 Z1 D0.064 ; 52     1.63     0-80 clear
T153 P153 Z1 D0.060 ; 53     1.52     1-72 tap
; Letter drills
T203 P203 Z1 D0.047 ;  3/64     1.2     0-80 tap
```
It turns out that the tool table has an undocumented limit of 50-some-odd entries, at least in EMC2 2.4.1. That puts the kibosh on my plans to add a bunch of entries to cover all the drill sizes Eagle might require for a PCB. More on that in a while …
2010-06-01
New Tires for the Van: Overtightened Lug Nuts

The shop spec says the lug nut torque shall be 104 newton·meter or an equally odd 77 lb·ft. Let’s not get into quibbles about the differences between lb·ft and ft·lb here, OK?

Anyhow, based on the wildly differing and grossly excessive tire pressures left by the guys who installed the new tires, I figured the lug nuts would be over-torqued… as, indeed, they were. My bending-beam torque wrench goes up to 140 n·m and didn’t even come close to breaking those puppies loose.

So I deployed a manly breaker bar and applied most of my weight to the far end. A back of the envelope guesstimate says they were well over 200 n·m, with a few grunt outliers.

Yes, the breakaway torque can be higher than the tightening torque, but they were far beyond even that level.

Lubed the threads, tightened to spec, and it’s all good. I’ll check them next week just to be sure, but sheesh if we had to fix a flat on the road, it would have gotten ugly.

2010-05-30
Turning Off Gnome Desktop Tooltips
This probably isn’t applicable to the Latest and Greatest, but for the Ubuntu 8.04 version used by EMC…
```
gconftool -s --type=bool /apps/panel/global/tooltips -enabled false
```
2010-05-28