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Archive for March, 2010

Monthly Aphorism: On Projections

  • Show me an order of magnitude

Father Vaughn, one of the best managers I ever had, evaluated new project proposals on a simple basis: if you couldn’t demonstrate that the result would be ten times better / faster / bigger / smaller than the existing product, then it wasn’t worth starting the project.

He knew that all benefits are overestimated, all problems underestimated, and that if you couldn’t show an overwhelming advantage right from the start, it’d never actually work.

He was right far more often than he was wrong.

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Ancient CM11A X10 Controller Pinout

I have an X10 CM11A “Two Way Computer Interface” handling the very very very few scheduled events for our house. Basically, it turns the living room lights on in the evening and everything off much later.

As a result, I tend to ignore it for years at a time. A recent power outage killed the regularly scheduled events, which suggested that the backup batteries needed changing… and, yes, they were pretty well corroded.

With that out of the way, I discovered that the last time I’d loaded a program into the thing was so long ago that the heyu config files had either gone missing or were on a system not near the top of my heap. It’s easy enough to configure, so I installed heyu and spun up a new set of config files.

All the doc I can find says the CM11A has an RJ11 modular phone jack, which mates with the standard 6-position 4-conductor dingus found on the end of every phone in this part of the world. My CM11A, however, has a 4P4C jack, the narrower dingus found on phone handsets. Given that heyu reports

Firmware revision Level = 1

I suspect that this thing is slightly older than some of the folks reading this post and the X10 factory switched to a somewhat less bizarre connector in mid-stream.

Anyhow, the DB9 (yeah, it’s a DE9, but nobody calls it that) connector has “X10 Active Home” printed on it in my very own handwriting, with a standard RJ11 plug on the end. A double-jack adapter connects a hank of cable with an RJ11 plug on one end and a 4P4C connector on the other. I have no idea where that cable came from; perhaps I replaced the 4P4C plug with something less bizarre to add that extension so the cable would stretch from PC to wall outlet?

I plugged the thing into a USB-RS232 adapter and heyu had no trouble talking to the CM11A. However, trying to execute

heyu dim n13 10

produced the discouraging report

RI serial line may be stuck.

A bit of deft multimeter work produced this pinout list, which agrees with most of the doc you’ll find elsewhere. Hold the 4P4C connector with the tab down and the cable away from you: the pin numbers are 4 3 2 1 from left to right. The RS-232 pins are printed right on the DB-9 connector.

4P4C   DB9
 1      2 RxD
 2      9 RI
 3      3 TxD
 4      5 Gnd

It’s entirely possible the USB converter doesn’t support RI or it doesn’t do a good job of it. I jammed the cable into the serial port on the back of the PC and shazam it works perfectly.

The x10.conf file, for the next time around

TTY /dev/ttyS0

HOUSECODE N

LATITUDE 	41:40N
LONGITUDE	73:53W

ALIAS MBR_Dresser	N1
ALIAS Front_Hall	N5
ALIAS RV_XCVR		N9
ALIAS Couch		N10
ALIAS Mary_Reading	N11
ALIAS LR_Ceiling	N12
ALIAS Fireplace		N13
ALIAS Kitchen		N14
ALIAS Patio		N15
ALIAS Garage_Spots	N16

START_ENGINE	AUTO

LOG_DIR		/var/log/heyu/

DATE_FORMAT	YMD '-'

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Tailstock Center: Laser Alignment Thereof

Laser spot on tailstock center

Laser spot on tailstock center

I finally made a test bar to line up the (vertically mounted) rotary table and tailstock on the Sherline milling machine. It’s a ground-and-polished 0.500-inch rod from a defunct HP2000C inkjet printer; the print head zipped back and forth along the rod while printing, so you know it’s pretty smooth. You could probably salvage something similar from any dead inkjet printer.

Making the bar is simple: saw off a suitable length, stick it in the lathe, face off the end, chamfer the edge, poke a center drill into it, and it’s all good.

If you’re a tool-and-die jig-boring high-precision kind of machinist, you better stop reading right about now before you catch a heart attack.

Lining the bar up is almost trivially easy with a laser spot coming down the spindle bore. Move the table so the spot grazes the side of the bar and casts a shadow on the table, jog X to the other end of the bar, and tweak the angle for the same picture on the table.

Repeat until satisfied.

The trouble comes at the tailstock end, where the ram extends about 1.5 inches, tops. That’s good enough for the Sherline, but it also means the test bar must be pretty close to the length of whatever you’ll be machining, rather than as long as possible to get the best alignment.

However, after you get Sherline tailstock aligned to the end of the bar, vertically, horizontally, and angularly, the magic happens

The ram is quite stable, with very little radial play, so the point moves along the X axis (assuming you did a good job aligning the tailstock). Retract the ram a bit, jog X and Y to put the laser spot on the tip of the center (which should correspond to the Y axis coordinate of the center of the bar), and you’ll see a defocused spot on the table (I put a white card on the table to improve the contrast). Jog Z until there’s a nice triangular image of the dead center’s point in that bright round spot.

It turns out that the laser beam in the top picture is about 10 mils wide at the dead center axis, so you can easily see a difference of 1 mil in the Y coordinate. That’s perfectly accurate for the sort of work I do.

Now, remove the test bar, unclamp the tailstock, move it to wherever you need it for the actual thing-to-be-made, snug it down, and jog the table in X (only!) to move the spot over there, too. Move the tailstock around to align the image of the center point in the middle of the laser spot again and you can be sure it’s aligned to the same Y coordinate. Verify that the tailstock has the same angular alignment. Mine is consistent with the T-nuts pressed against the front of the table slots and it’s easy to slide it carefully along the Y axis to get the point in the spot.

Because the bar was parallel to the X axis to start with, the point is now aligned with the axis of the rotary table.

Laser spot focused on tip

Laser spot focused on tip

The minimum spot size depends on the beam width and the lens, but it turns out that for my setup, twiddling the Z position of the lens can shrink the spot down to essentially the width of the dead center point. As nearly as I can tell, the beam width is 3 mils and the point pretty much occludes the beam when it’s properly aligned.

The picture shows that situation; the spot is half-occluded because the point now looks like the side of a barn. It’s difficult to tell, but the lens (on the brass snout in the endmill holder) is lower in this picture.

All that jogging, particularly creeping up on the proper alignment, goes much easier with a joggy thing!

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Bicycle Reflector Adaptor Bushing

Reflector on bushing

Reflector on bushing

After replacing the seat strut screws, I found a Round Tuit lying there on the workbench, right next to the rear reflectors I’ve been meaning to install for a truly embarrassing period.

Recumbents don’t have the usual assortment of standard-sized tubing in the usual road-bike places, making common items like reflectors difficult to attach. The ideal spot on our bikes is at the base of the VHF/UHF antennas, right next to the white blinky LEDs, but, alas, that’s 20 mm in diameter and the reflector clamp barely shrinks down to a bit under 28.

Turns out that a chunk of 1.5 inch PVC pipe has a 4 mm wall thickness, so wrapping a layer of that around the antenna base will do the trick. I whacked off a length of pipe, faced off both ends in the lathe, and put a shallow recess around the middle of the ring to capture the reflector clamp.

By another rare coincidence, 1.5 inch PVC pipe has an ID of exactly 40 mm… so cutting the ring exactly along a diameter produces the right length. The catch is that the pipe isn’t flexible at all, but brandishing a heat gun in a threatening manner solves that problem.

Reshaped bushing on mandrel

Reshaped bushing on mandrel

A random hunk of 3/4-inch aluminum rod is about 19 mm in diameter, so I chucked that in the lathe and shaped the saggy strip around it… wearing thick leather gloves.

It springs out to 20 mm with no problem, slides right on, and grips reasonably well. I may add a strip of tapeless sticky (think double-sided tape without the tape: just the adhesive!) under the bushing if it wants to walk away.

I made two of ’em, of course, and put a reflector on Mary’s bike while I was at it. Our young lady’s bike already has a reflector, although I should upgrade that bushing as well… it’s a layer of self-vulcanizing rubber tape that works perfectly, so this may take a while.

I suppose I should buy a length of gray or black PVC pipe, but that’s in the nature of fine tuning.

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Fractured Tour Easy Seat Strut Screw

Broken bolt

Broken bolt

Straight up: this is about a stainless steel socket head cap screw I installed eight years ago, not the original Easy Racers screw, so this is not their problem.

I rode out for milk-and-eggs at the corner store, a flat one-mile ride, and stopped at the traffic signal. Light goes green, line of cars accelerates, so do I… and there’s a snap and the left side of the seat sags backwards. I am not a powerhouse rider and it’s March, so I’m not doing leg presses while getting up to cruising speed.

I continued the mission by sitting slightly to the right on the seat and pedaling gingerly, then diagnosed the problem in the corner store’s parking lot. If I’d been further away, I’d have done the repair right there, but I figured it’d hold together until I got home. It did.

The problem turned out to be a broken screw holding the left-side seat strut to the threaded eyelet on the rear dropout. The top picture shows the way I have it set up: seat strut clamp outboard, rack strut inboard, with a socket head cap screw extending all the way through, and secured with a pair of stainless nuts that went missing along with the broken screw end.

Screw fracture closeup

Screw fracture closeup

Here’s the fracture across the end of the screw, which shows no evidence of foul play. As nearly as I can tell, the whole thing snapped off in one event, with none of the crud that would indicate a progressive crack. Compared with that wheel stud, this is in pristine condition.

So it’s time to replace the right-side screw, as well, which means a trip to the Bike Repair Wing of the Basement Laboratory. While I had the bike up in the repair stand, I decided to reshape the head on the right-side screw for better chain clearance.

As nearly as I can tell, the usual practice puts both the seat strut and the rack strut outboard of the threaded eyelet on the dropout, but that seems wrong to me. The seat strut puts a tremendous amount of stress on the screw, so you really want that lever arm as short as possible: put the clamp against the eyelet. While the rack isn’t as heavily loaded, cantilevering it outboard of the clamp just doesn’t look right.

But putting the rack strut inboard of the eyelet means the screw head sticks out rather more than I’d like. Very rarely, the chain will snick against the head and even more rarely it jams between the head and the freewheel. Nothing much happens (it’s a freewheel, after all), but I think reducing the head thickness ought to help.

Reshaped socket head cap screw

Reshaped socket head cap screw

So I chucked the screw in the lathe, shortened the socket by about half, and put a taper on the head. If I had a stock of round-head cap screws, one of those would be even better.

The shortened socket makes it a bit tricky to get enough bite with the hex key, but this isn’t something that requires much attention after it’s installed… and I get to do all that in the shop.

Dabs of Loctite in the eyelet and nuts, for sure!

By a truly rare coincidence, a standard 1-1/2 inch cap screw is exactly the right length.

Right-side mount

Right-side mount

Here’s a view of the installed right-side screw, looking rearward along the upper rear triangle tube. Seat strut to the outside, rack strut to the inside, and reshaped head above the cluster.

Took the bike out for a 16 mile spin today and it’s all good.

A note for the weight weenies in the crowd: a rack on the back of the seat adds a redundant support structure. Without that, a failed seat strut can be a real showstopper. Even if you don’t use your bike as a pack mule, maybe you should add a rack.

Memo to Self: add more nuts to the tool kit!

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Too Many Deer

Five-deer herd

Five-deer herd

This herd, a family unit that’s been traveling around the neighborhood in recent weeks, paused for morning brunch in our neighbor’s yard. They generally cross the road at a dead run, but haven’t gotten themselves or anyone else killed. Yet.

They and their ilk are why our vegetable gardens must have ten-foot fences with robust supports. There are no understory plants left in the wooded areas and precious few young trees; the deer population is literally eating everything in sight.

Vassar College recently culled 60-odd deer on their preserve in about ten hours, much to the dismay of the local animal huggers. It wasn’t a hunt; professional sharpshooters took ’em out.

We have a proposal: if you like deer so much, adopt ’em, haul ’em home, and take care of the things. Let them eat your shrubbery, crap all over your lawn, and infect your children, but keep them off the streets and out of your neighbor’s yards. Fair enough?

And let’s not get started about deer ticks. Dutchess County is the epicenter of Lyme Disease infections, for well and good reason.

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X10 PHC02 Maxi Controller: Green LED

PHC02 Circuit Board

PHC02 Circuit Board

Got the replacement X10 controller from the usual eBay source and it works fine, except it has a red LED that’s on unless it’s sending an X10 command.

That’d be OK, except that I’ve spent the last few months associating a red LED at that spot on the dresser with a jammed X10 controller.

Not to mention that red LEDs are sooo 20th Century…

Four screws hold the baseplate in place; it takes a bit of prying to release the stiffening collars around the front screws and remove the baseplate. One more screw holds the circuit board in place.

Surprisingly, they used the same metal-dome switch plates!

Anyhow, with the board out, it’s easy to unsolder the red LED and replace it with a green one from my bag o’ mixed LEDs. It’s not quite the same shape and doesn’t have a big shoulder to keep it in place, but it’s good enough for me.

New green LED

New green LED

The heat of soldering melted the thermoplastic glue that held the original LED in place. The new one isn’t quite as firmly bonded, but I don’t intend to jam a paperclip into the hole after shoving the LED out of the way.

That was easy…

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