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.

Tag: Improvements

Making the world a better place, one piece at a time

Plastic Wrap Plastic Cutter Blade: FAIL

OK, somebody decided that the classic metal blade used on all plastic wrap boxes since the dawn of time cost too much, so they decreed that it be replaced with a plastic blade that costs essentially nothing:

Walmart plastic wrap – plastic cutter

Unfortunately, a thin plastic blade also bends easily and, after a few uses, cracks along the midline. After that, it simply doesn’t work; there’s no way to actually tear the plastic off the roll.

It turns out that a common hacksaw blade is exactly the right length and, oriented with the teeth pointing to the left, will rip through plastic wrap like, uh, a hacksaw through plastic:

Walmart plastic wrap – real cutter

That this hack should not be necessary goes without saying…

There’s a layer of double-stick foam tape between the box and blade. It’s probably removable, but I was in a hurry.

2013-09-20

Devilspie2: Lua Scripts

Prompted by that suggestion, here’s the current collection of Devilspie2 scripts (in ~/.config/devilspie2/) that make my dual-monitor setup (left: 2560×1440 landscape, right: 1050×1680 portrait) usable with a single X session in Xubuntu 12.10. The window manager understands about the monitor layout, so maximizing a window will fill whatever monitor it’s currently occupying.

acroread.lua — maximized on portrait

if (get_window_name()=="Adobe Reader") then
      unmaximize();
      set_window_geometry(0,0,1000,100);
      set_window_geometry(2561,0,1000,100);
      maximize();
end

chromium.lua — right half of landscape

if (get_application_name()=="Chromium" and get_window_name() ~= "Print") then
   set_window_geometry(1400,0,1150,1200);
   maximize_vertically();
end

debugging.lua — handy with –debug option

debug_print("Window Name: " .. get_window_name());
debug_print("Application name: " .. get_application_name());

digikam.lua — right half of landscape, force large Search dialog, dammit

if (get_application_name() == "Digikam") then
	debug_print("DigiKam conditional - top");
	if (get_window_name() == "Advanced Search") then
		debug_print("Digikam - Adv Search");
		set_window_geometry(750,100,1000,1300);
	else
		debug_print("Main DigiKam window");
		set_window_geometry(0,0,1400,1000);
		maximize_vertically();
	end
end

firefox.lua — left half of landscape, enlarge dialogs

if (get_application_name()=="Firefox") then
	debug_print("FF conditional - top");
	if (get_window_name() == "Print") then
		set_window_position(700,350);
	elseif (0 == string.find(get_window_name(),"Password")) then
		set_window_position(0,0);
		maximize_vertically();
	end
end

gimp.lua — force Gutenprint dialog to the top, dammit

if (get_application_name() == "GNU Image Manipulation Program") then
	debug_print("GIMP conditional - top");
	if (string.find(get_window_name(),"Print")) then
		debug_print("GIMP - GutenPrint")
		set_window_position(700,350);
		make_always_on_top();
	else
		debug_print("GIMP - Main window");
	end
end

passwords.lua — put password dialogs in mid-screen

if (get_window_name()=="Password Required") then
	debug_print("Password");
	set_window_position(700,350);
end

pronterface.lua — force to middle-ish of Desktop 2

if (get_window_name()=="Printer Interface") then
   set_window_workspace(2);
   set_window_position(1200,750);
end

slic3r.lua — force to right side of Desktop 2

if (get_window_name()=="Slic3r") then
   set_window_workspace(2);
   set_window_geometry(1600,0,700,700);
end

terminal.lua — maximized on portrait

if (get_window_name()=="Terminal") then
   set_window_position(2561,0);
   maximize();
end

thunderbird.lua — left half of landscape, force big dialogs

if (get_application_name() == "Thunderbird") then
	debug_print("TBird conditional - top");
	if (1 == string.find(get_window_name(),"Print")) then
		debug_print("TBird - print...");
		set_window_position(700,350);
	elseif (string.find(get_window_name(),"Sending") or
			string.find(get_window_name(),"Confirm") or
			string.find(get_window_name(),"Processing")) then
		debug_print("TBird - generic dialog");
		set_window_position(200,600);
	elseif (string.find(get_window_name(),"Write:")) then
		debug_print("TBird - writing");
		set_window_geometry(1300,0,900,600);
		maximize_vertically();
	elseif (0 == string.find(get_window_name(),"Password")) then
		debug_print("Main TBird window?");
		debug_print(" name: ",get_window_name());
		set_window_geometry(0,0,1300,1200);
		maximize_vertically();
	end
end

2013-09-12

Improved M2 Heated Build Platform: First Light

Although the M2’s heated build platform works well enough, somebody who knows what he’s doing (you know who you are: thanks!) sent me an improved version. It’s a PCB heater, laid out to compensate for the usual edge cooling, firmly attached to a tempered glass plate with genuine 3M thermally conductive tape:

Improved M2 HBP – test setup

They designed the heater around the 30 VDC power supply used in their other equipment. Although I had ~~high~~ moderate hopes that a boost power supply would convert the 24 V supply I already had for the stepper driver bricks into the 30 V for the heater, it was not to be. So there’s a 36 V 9.7 A 350 W supply arcing around the planet that (I think) should work better: adjust the voltage down as far as it’ll go, soak up another few volts in the solid-state relay, and Things Should Be Close Enough to 30 V. One can buy a genuine 30 V supply, but it costs surprisingly more than either 24 V or 36 V supplies on the surplus / eBay market and won’t really provide the proper voltage without upward tweaking anyway.

I replaced their standard 0.156 inch square terminals with Anderson Powerpoles, soldered a length of shielded cable to the 100 kΩ thermistor pads, and gimmicked up a connection to the 24 V supply; it delivered 23.7 V at the PCB terminals. The thermistor is 100 kΩ at 25 °C and 11.4 kΩ at 77 °C. The PCB heater is 5.9 Ω at 25 °C and 7.3 Ω at 77 °C; it dissipates 77 W at 77 °C (no, that’s not a typo).

The ultimate temperature looks to be about 90 °C with a 24 V supply, which isn’t quite enough for ABS (which I’m not using in the M2 right now, but probably will eventually). The time constant, assuming the 1-e^-1 point is 66 °C, works out to about 9 minutes; it’ll be up to final temperature in half an hour. Those numbers aren’t quite as accurate as one might wish, because the heater power drops as the temperature rises and the copper resistance increases.

A 30 V supply would dissipate 120 W at 77 °C and rumor has it that the ultimate temperature is around 125 °C, which would be fine for ABS. Goosing the power a bit would produce more heat, but I’v been running the Thing-O-Matic at 110 °C and that’s good enough. More power, of course, gets it to the temperature setpoint faster, which is probably a Very Good Thing.

Obviously, you need PWM to control the temperature; given a 9 minute time constant, a bang-bang controller will work perfectly well.

The original data, including the thermistor resistance after I got my act together, plus a cute little temperature-vs-time graph:

Improved M2 HBP – 24 V supply

The colored flyspecks are part of the paper; I salvaged a stack of fancy menu cards from a trash can and padded them up as geek scratch paper.

2013-09-05
Basement Safe: Foam Door Seal

A bit of rummaging in the Big Box o’ Weatherstripping produced the stub end of a spool bearing 1/4 x 1/8 foam tape that exactly fills the gap between the Basement Safe’s door and liner:

Basement Safe – Foam door seal – latch side

The hinge side of the door has tape between the door liner and the safe wall, because that closes in compression rather than shear:

Basement Safe – Foam door seal – hinge side

There should be a big bump in the humidity record marking that installation, but I don’t expect any immediate difference. If the silica gel lasts more than two months, I’ll consider it a win.

2013-08-26
Public Facilities Maintenance: Progress

A day or so after kvetching about that informal DCRT vehicle entrance to the head planner developing the Dutchess County Master Plan for bicycle & pedestrian facilities, this appeared:

DCRT Overocker Crossing – block on informal entrance

Notice the blue electrical junction box on the right? That can’t possibly be a Good Thing… but, so far, it doesn’t seem to bother anybody enough to repair it.

Those missing ADA strips at Grand have been swept out, converting them into rough-bottomed trenches across the trail. At least they’re not quite so slip-prone, even if they’re still a tripping hazard.

2013-08-24

Air-gapped Ferrite Toroid Data

For an upcoming Circuit Cellar column on Hall effect current sensing, I slit another pair of toroids:

Then wound them with grossly excessive amounts of wire (the up-armored core on the right appeared earlier):

The smaller toroid is an FT37-43 that barely covers the active area of an SS49-style Hall effect sensor, but experience with the FT50 toroid suggests that’ll be entirely enough:

slit FT37 toroid trial fit to SS48-style Hall effect sensor

Data on the uncut toroids:

Property	FT50-61	FT37-43
Outer diameter (OD) – inch	0.50	0.375
Inner diameter (ID) – inch	0.281	0.187
Length – inch	0.188	0.125
Cross section area – cm²	0.133	0.133
Mean path length (MPL) – cm	3.02	2.15
Volume – cm³	0.401	0.163
Relative Permeability (μ_r )	125	850
Saturation flux G @ 10 Oe	2350	2750
Inductance factor (A_L) – nH/turn²	68.0	420

Those overstuffed windings improved the sensitivity, but increased the winding resistance far beyond what’s reasonable.

Data on the slit toroids:

Toroid ID	FT50-61	FT37-43	FT50-61
Measured air gap – cm	0.15	0.15	0.17

Winding data
Turns	120	80	25
Wire gauge – AWG	28	32	26
Winding resistance – mΩ	530	920	100
Predicted B field – G/A	872	660	163

Hall effect sensor @ 1.9 mV/G
Predicted output – mV/mA	1.7	1.3	0.31
Actual output – mV/mA	1.9	1.9	0.37
Actual/predicted ratio – %	+12	+46	+19

The last few lines in that table show the transimpedance (transresistance, really, but …) based on the winding current to Hall sensor output voltage ratio (in either mV/mA or V/A, both dimensionally equivalent to ohms), which is why the toroid’s internal magnetic flux doesn’t matter as long as it’s well below saturation.

Gnawing the 80 turn winding off the FT37-43 toroid and rewinding it with 15 turns of 24 AWG wire dropped the winding resistance to 23 mΩ and the transimpedance to 0.36 mV/mA:

FT37-43 with 15 turns 24 AWG - Hall sensor — FT37-43 with 15 turns 24 AWG – Hall sensor

However, applying a voltage gain of about 28 (after removing the sensor’s V_CC/2 bias) will produce a 0-to-5 V output from 500 mA input, which seems reasonable.

2013-08-08

Precision Wrench Rebuild

Decades ago, one jaw on my little 1/4 inch wrench that fits 4-40 nuts broke off. I brazed it back on, fully aware that one day it would break off again, because brazing isn’t really a suitable repair technique for a wrench, even one labeled as “Precision” in that time-honored manner of all low-cost tools.

Time passes, I’m tightening screws against 4-40 nuts, and the jaw gives way:

Precision wrench – broken jaw

So I sawed off a strip of bedframe steel that fit the nuts better than the original stamped steel, did a bit of hand filing, and came up with a reasonable replacement:

Precision wrench – detail

I rammed it into the handle, just as they’d done with the original stamped steel shape:

Precision wrench – rebuilt

That should last approximately forever…

2013-07-31