Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
//-- Read AI channel
// averages several readings to improve noise performance
// returns value in volts assuming known VCC ref voltage
#define NUM_T_SAMPLES 10
float ReadAI(byte PinNum) {
word RawAverage;
digitalWrite(PIN_SYNC,HIGH); // scope sync
RawAverage = (word)analogRead(PinNum); // prime the averaging pump
for (int i=2; i <= NUM_T_SAMPLES; i++) {
RawAverage += (word)analogRead(PinNum);
}
digitalWrite(PIN_SYNC,LOW);
RawAverage /= NUM_T_SAMPLES;
return Vcc * (float)RawAverage / 1024.0;
}
The PIN_SYNC output produces the upper trace, with the LED current in the lower trace at 50 mA/div:
Arduino Analog 10x sample avg – ILED 50 mA-div
In round numbers, ten samples require 1.1 ms and cover about 35 PWM pulses (using 32 kHz PWM, as you really should if you need an actual analog voltage).
Because the samples occur asynchronously with respect to the PWM pulses, the computed average comes out surprisingly close to the actual average. Fewer samples would probably be just as good, but I’m in no hurry.
We hauled 70 pounds of apples back across the river last month:
Apple Ride – 2013-10-20
If only there were a Spackenkill Road bridge across the Hudson…
We laid the bags out on the garage floor, seeing as how they can’t go into the cold cellar with the root crops (apples give off ethylene gas, which doesn’t mix well with long-storage crops). I dropped a Hobo datalogger into one bag to record the temperatures:
Apples and air temperature
The purple trace comes from a data logger in the attic, which is as close as we have to an outside air temperature record.
Those low air temperatures suggest it’s time to move the remaining apples into the basement, as far from the root cellar as possible, as we have more nights in the teens ahead.
Late in the fall, Brown Marmorated Stink Bugs move indoors to spend the winter; they can infiltrate through the smallest of cracks and seem to show up unannounced in the strangest locations. This one magically appeared on my M2 printer while I was starting it up:
Brown Marmorated Stink Bug on M2 Printer
I unceremoniously flushed its contribution to the gene pool…
The Browning Hi-Power magazine case has a 12.5° forward angle with respect to the floor plates:
Browning Hi-Power magazine – components
The natural axes lie parallel and perpendicular to the case axis, which means dimensions parallel and perpendicular to the floor plates (horizontal & vertical, respectively) require a bit of trigonometry. This doodle sketches some of the key values, not all of which are hereby asserted to be correct:
Magazine angle doodles
Name the variables:
Slant angle α
Height H along magazine axis
Length L perpendicular to H
Components of H:
vertical = H cos α
horizontal = H sin α
Components of L:
vertical = L sin α
horizontal = L cos α
Extreme point of the tilt at the edge, relative to center point on axis:
vertical = (L/2) sin α
horizontal= (L/2) cos α
Projection of top parallel to axis onto horizontal:
L / cos α
I suppose one could set up functions for all that, but I tend to just hammer out the trig where it’s needed.
The follower has 15.3 mm long pegs that taper from 8.75 mm to 7 mm, on 14.5 mm centers. The spring compresses down to a little longer than that with 13 rounds atop the follower:
Browning Hi-Power magazine – follower
The top of the follower has a rather complex shape (yes, that’s a crunch toward the front of the ridge):
Browning Hi-Power magazine – follower top
The front view shows more curves:
Browning Hi-Power magazine – follower front
Judging from the online pictures, BHP followers have taken on a wide variety of shapes over the decades, so I’d expect almost anything would work more-or-less well.
The inner floor plate attaches to the spring and has a 5 mm dia x 1 mm tall boss that matches the hole in the outer floor plate:
Browning Hi-Power magazine – base plates
The hole in the outer floor plate is a scant 5.4 mm, just slightly under the head size of a 3.0×0.5 mm socket head cap screw. The OEM Browning magazines have a centered boss, but some aftermarket magazines move it a millimeter or so to the front or rear. The outer plate seems hard enough to be just about spring steel.
A tab on the front of the inner floor plate (to the left in this picture captures the spring:
Browning Hi-Power magazine – spring inside base plate
The inner plate is 0.75 mm mild steel and may be removable, depending on how tightly the tab got crunched during manufacturing. The tab extends a millimeter or so beyond the spring on the inside of the curve and is about 2 mm tall at that point.
The boss on the inner plate and the hole on the outer plate locate the spring at the proper position and also ensure the outer plate doesn’t accidentally slide off; you must push the boss inward to release the outer plate before sliding it forward. Using a rounded rod lets you push the inner plate far enough inward to release the spring pressure on the outer plate, making it much easier to slide; in fact, for my fingers, I can’t move the outer plate without inserting a rod in the hole.
The case is a seamless 0.7 mm thick high-carbon-steel tube with complex curves:
Browning Hi-Power magazine – case on grid paper
The “high carbon” part means that it’s not in the least bendy; a few operations on large presses mashed it into that shape and it’s not going to take on anything else by accident. The feed lips on the top can get bent if you abuse the thing, but that’s about it.
The case is 20.5 x 31.7 mm from the base to the latch hole, 99 mm long in front and 109 mm long in the back. The latch hole is 4.2 x 7.3 mm with a 2.7 mm notch in the front side, 67.2 mm from the base and 27.7 mm from the top. The angle of the case axis with respect to the bottom (on the right) is 12.5°.
Inside measurements at the base: 30.5 x 18.7 mm. The rear corners are essentially right angles and the front curves fit 1/4 inch = 6.3 mm or 9/32 inch = 7.1 mm drills.
The lower flutes are 26 x 6.5 mm, centered on the side (even though it doesn’t look that way), and compress the outside of the case to 16.2 mm and the inside to 14.7 mm. The tabs engaging the outer floor plate are 23 mm edge-to-edge, 10.5 mm and 6.0 mm long, and protrude 1.5 mm from the outside of the case:
Browning Hi-Power magazine – bottom
The top of the case is 10.5 mm wide at the rear of the feed lips, with the sharp bend 17.0 mm from the outside of the rear face:
Browning Hi-Power magazine – top
The spring is 1.25 mm = 49 mil wire, 143 mm flat-to-flat high, about 15.1 mm turn-to-turn, 13/32 inch = 10.3 mm ID at the ends, 13.2 mm outside width, 25 mm inside length, and 27 mm outside length. Those don’t quite add up, but the whole thing is, well, springy.
The spring exerts these crudely measured forces:
1 round = 1.1 kg
10 rounds = 2.5 kg
The follower moves 5.3 mm, so the spring constant is very roughly 0.26 kg/mm = 14.8 pound/inch. Aftermarket springs tout their stiffness and come in 5% increments of additional force, so that’s probably not a critical number.
Limiting the capacity of a magazine so that it cannot be “readily” converted back to a higher capacity seems difficult, particularly if you allow disassembling the magazine for proper cleaning and maintenance. If operator safety and proper function isn’t a concern, then many things become possible.
I’ve been doing a lot of fiddly gluing lately and, despite my best efforts, some adhesive collects in the lid’s screw threads. The gummy residue makes it really hard to unscrew the lid without a strap wrench after a few days.
Wrapping two turns of silicone tape around the cap helps tremendously:
According to Wikipedia, Polylactic acid, a.k.a. PLA “is soluble in chlorinated solvents, hot benzene, tetrahydrofuran, and dioxane” and is not soluble in acetone, alcohol, or water.
Just to see what happens, I dunked a pair of those 3D printed dummy bullets in Shooter’s Choice Gun Solvent (which has since gone obsolete) and Hoppe’s No. 9 Gun Bore Cleaner (which seems to have been reformulated several times), then let them air-dry in those background puddles:
PLA dummy bullets after solvent bath
Nothing much happened: they’re not soft or gummy, haven’t slumped, and seem undaunted.
That’s in contrast to ABS plastic, which isreadily soluble in acetone and the aromatic hydrocarbons commonly found in solvents used around firearms. Apart from that, ABS would be a slightly better choice on mechanical grounds. I’m not sure the difference really matters for most purposes, given the very wide tolerances on 3D printed objects.
The Smell of Molten Projects in the Morning 