Archive for category Machine Shop
MOSFET rDS PCB
Posted by Ed in Machine Shop, Electronics Workbench on 23-February-2012
This one came out surprisingly well, apart from the total faceplant with that resistor. With any luck, it’ll measure MOSFET on-state drain resistance over temperature for an upcoming Circuit Cellar column; it’s a honkin’ big Arduino shield, of course.
Drilled holes on the Sherline using the relocated tool height switch:
rDS Tester - drilled PCB
Front copper, after etching & silver plating:
rDS Tester - etched front
Back copper, ditto:
rDS Tester - etched rear
I think I can epoxy the resistor kinda-sorta in the right spot without having to drill through the PCB into the traces. Maybe nobody will notice?
The traces came out fairly well, although I had to do both the top and bottom toner transfer step twice to get good adhesion. Sometimes it works, sometimes it doesn’t, and I can’t pin down any meaningful differences in the process.
And it really does have four distinct ground planes. The upper right carries 8 A PWM Peltier current, the lower right has 3 A drain current, the rectangle in the middle is the analog op-amp circuitry tied to the Analog common, and surrounding that is the usual Arduino bouncy digital ground stuff. The fact that Analog common merges with digital ground on the Arduino PCB is just the way it is…
Basement Safe Humidity: The Trend Continues
Posted by Ed in Home Ec, Machine Shop on 21-February-2012
The desiccant in the basement safe:
Desiccant in safe
Continues to work just fine, much better than the first attempt:
Basement Safe Humidity - 2012-02-06
The paper scrap gives the weight of tray+desiccant, so when the humidity finally starts going up I’ll have some idea of the average leak rate. Most likely, opening the door for the more-or-less monthly logger readout introduces most of the water vapor…
Tweezer Tip Alignment & Shaping
Posted by Ed in Home Ec, Machine Shop on 20-February-2012
During a recent rainstorm I grabbed the fiberglass marker pole at the end of the drain pipe to clear a wad of leaves out of the driveway gutters. Unfortunately, that left me with a finger full of glass fibers; it seems the top of the pole has deteriorated. The first tweezer I plucked from the stash around the pencil-oid tool holder hadn’t had its jaws aligned, so after I plucked (most of) the glass using those tweezers, I did a bit of filing and sandpapering:
Tweezer tips
That’s a millimeter scale in the background: these really are needle-tip tweezers.
A closer view:
Aligned and shaped tweezer tip
It still has a bit of overbite, but it grabs hairs from the bench with no hassle. Given that you can’t get all the glass fibers on the first pass, it’ll come in handy…
Relocated Sherline Tool Length Probe Switch
Posted by Ed in Machine Shop on 17-February-2012
Putting the tool length switch atop the tooling plate has the advantage that it’s higher than most of the workpieces, but it also soaks up a bit of precious real estate. Moving it off the plate to the table puts it nearly level with the top of the plate, but at least now I have room for clamp blocks and suchlike:
Relocated tool length switch
It turns out that Sherline T-nuts protrude just an itsy above the top of the table (which lets them locate the tooling plate to the slot, for example), so I shortened one by filing it down to size:
Original and shortened Sherline T-nuts
Now, I’d like to front as if all that happened in a rational and well-thought-out manner, but the fact of the matter is that I completely used up one 10-32 stainless socket-head cap screw while thinking it was somehow still bottoming out in the slot, before realizing that the T-nut was sticking up. Drat!
KitchenAid Mixer Pivot Shaft Tweak
Posted by Ed in Home Ec, Machine Shop on 16-February-2012
The shaft that tilts the mixer head has started walking sideways out of its hole, which is not to be tolerated. Looking up inside the base column shows a locking screw that’s worked loose:
KitchenAid mixer - pivot shaft and locking screw
I took the thing apart and filed a flat on the shaft:
KitchenAid mixer pivot shaft - added flat
And then a dab of Loctite on the screw will prevent that from happening again:
KitchenAid mixer pivot locking screw
It’s still piddling oil on the countertop. If you have one of these things, always store it with the head tilted upward. That makes the oil run down the column onto the counter, rather than through the planetary gears into the mixing bowl…
Soldering Third Hand Alligator Clip Improvement
Posted by Ed in Electronics Workbench, Machine Shop on 15-February-2012
The third hand grabbers I have all put bare alligator clip ferrules in the adjustable sockets with a thumbscrew to secure them. Over time, that thumbscrew crunches the ferrule and makes the clip hard to adjust. This has become enough of an annoyance that I rummaged around in the brass tubing cutoffs to find some that fit into the ferrules:
Alligator clip with brass tube insert
Given the sorry state of the ferrules, they required quite a bit of squeezing and shaping until that tube fit inside, but after that they rounded up nicely.
I suppose I should solder the tubes in place, but …
Watts 9D-M3 Backflow Preventer Valve: Failure & Aggravation
Posted by Ed in Home Ec, Machine Shop on 14-February-2012
This Watts 9D-M3 Backflow Preventer Valve feeds water into our furnace, provides an overpressure relief, and prevents heating loop water from re-entering the potable water supply.
Watts 9D-M3 Backflow Preventer Valve
The vertical pipe leads downward near the floor, underneath which sits the small plastic bucket I provided to catch the occasional drip. Recently we had an all-hands scramble to soak up a pool of water spreading across the floor from the overflowing bucket, across the aisle, and below the shafts-and-rods-and-tubes-and-pipes storage rack. Evidently the occasional drip became a steady drip while we weren’t watching; not a catastrophic flood, but far more water than we want on the floor.
This is the inlet valve, which is basically a flapper. You can’t see the fine cracks around the central mount, but they’re all over the inner half of the ring.
Watts 9D-M3 - Inlet valve
And this is the outlet valve, which has pretty much disintegrated. Note the outer rim peeled back under my thumb:
Watts 9D-M3 - Outlet valve
A complete new valve is $40, in stock and ready for pickup at Lowe’s, but all I really needed was the failed rubber flapper valves, which they don’t carry. A few minutes of searching reveals the Watts 0886011 Repair Kit, which has all of the interior parts.
Pop Quiz: How much does the repair kit cost?
Answer: Starts at $38 plus shipping and goes up from there. Cheap aftermarket kits run $20 and up, but they’re all out of stock.
Now that, party people, is the sort of thing that ticks me right off.
Perhaps the local HVAC / plumbing supply stores have such kits in stock? To quote: “They may exist, but we don’t have them.”
I don’t see any way to homebrew new flapper valves, so it’s off to Lowe’s we go…
It would seem to me that these things shouldn’t fail after a mere decade of service. I thought that about the CdS flame sensor that crapped out in the middle of a sub-zero January cold snap while I was at Cabin Fever some years ago, too.
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