Comparing different brands of acrylic and cement to get the best joints

Getting really clear, bubble-free joints in thick acrylic is not easy. I've done quite a lot of practicing with various methods and eventually did some testing on the materials and cements that I was using. The link below shows the results. Since McMaster plastic is a lot less expensive than TAP plastic, I tend to use McMaster to supply the plastic and I use TAP green label cement on it. I've never tried IPS #3, since I've been told it's identical to TAP green label. I'm not convinced about this and may have to try it some day.


http://www.magconcept.com/acrylic/

Replacing a Honda Civic condenser fan without draining the freon

My 1992 Honda Civic recently developed a strange problem where the engine would idle badly and sometimes stall when the air conditioning was being used. Oddly enough, the problem turned out to be a non-functional condenser fan. Presumably, the compressor would pump the high side of the system up to an abnormally high pressure because the system was unable to dissipate heat from the condenser. Eventually the mechanical load from the compressor was so great it would cause the engine to stall. I would have guessed there was a high pressure limit switch that would deactivate the compressor, but maybe not.

In any case, this is an R12 system, and I did NOT want to open any of the freon lines. It had been working great ever since I bought the car (until this recent problem), and I did not want to mess with it. Luckily, it's possible and not too difficult to change the fan motor without opening the freon lines.
The fan shroud is bolted to the condenser with two 10mm bolts near the top facing into the condenser. There is also a small bracket on your left that has two 10mm bolts to hold the bracket to the condenser and shroud. I removed all four of these bolts, two bolts that held the shroud to the car's frame at the top, a bolt that holds a freon hose to the shroud, and also a bolt that holds a relay to the frame (on your right).



The shroud can be lifted up and out of two pockets that are formed into the metal of the condenser. It cannot be fully removed from the car because there is a freon hose in the way, and the hose cannot be moved. Instead, I removed the plastic rock guard on the underside of the car, and slipped the shroud out through the bottom. There are a few wire-guides and connectors on your right that need to be removed before the shroud will clear the car. I didn't even need to jack the car up.



Once the shroud (and fan) were out of the car, I switched the motor with the new one. Do NOT forget to also move the tiny washer from the old motor to the new one, which tends to stick to the old motor shaft and fits so tightly it almost looks like part of the shaft itself. I made this mistake and it nearly ruined my day. Without the washer in place, tightening the nut will cause the metal hub of the fan to be pushed in a bad way so that it is no longer engaged with the shaft. Since there is no other way to grab hold of the shaft, you are left with trying to get the nut back off and no way to stop the shaft from turning. After fiddling with it for a long time, I remembered my dad recommended the use of a pneumatic impact wrench in situations where a nut must be removed from a free-turning shaft. The idea is that the impact wrench hits the nut so hard and so fast, it is able to back it off while the inertia of the shaft holds the part still. Lo and behold, it zipped the nut right off. Thanks, dad!


The rest of the job was pretty straight-forward, and now my air conditioner works like a champ and doesn't stall the engine.

The old motor appears to have died of old age. There aren't any catastrophic problems, but the brushes and commutator show heavy wear. The motor case was full of carbon dust from the brushes.

Repairing a wireless keyboard

Last night, I sat down to use my home theater (a PC connected to a DLP projector) and had some problems typing in the name of a movie into Netflix. I thought I had mistyped the word, but I soon realized that my wireless keyboard had some non-functional keys on it. The letter 't', numbers 1 and 3 among other keys were not working. Since the failure affected more than one key, and pressing harder did not help the situation, I reasoned the problem was one of the matrix lines in the keyboard's circuit and not a bad connection in the button itself. The rest of the keys worked fine, so the microprocessor and transmitter were probably OK.

I took the keyboard apart and located the matrix lines between the microprocessor and the array of buttons. I used an oscilloscope to see which lines were pulsed (outgoing from the microprocessor) and which were switched (incoming to the microprocessor). I also compared the signals from the working "2" key to the broken "1" key. The signal was present but weak for "1". I tested the total circuit resistance for "1" and "2". "2" (working) was a couple hundred ohms, but "1" was 10k ohms. The circuit had a bad connection somewhere.
I used my meter to trace the bad connection to this spot on the flexible circuit board beneath the keys. It looks fine visually, but there is an electrical discontinuity right in the very center of this photo where the trace becomes narrow and passes above the middle rectangular cutout.

I used some conductive paint (marketed for repairing automotive defrost grids) to cover the bad area of the trace.

I was tempted to use conductive epoxy for the repair, but it can be very brittle and has low adhesion qualities. We'll see how the defroster repair product holds up.

Woodworking with a piece of raw tree trunk

My friend recently had a tree die and fall over on his property. He cut it up with a chainsaw, and offered a few of the pieces to me for use in woodworking. I have never started a project with just a raw log, so I figured it would be a fun learning experience. The tree died in the winter, and it was soaked with rain water, so I put the pieces on a few bricks to keep it off the ground and covered it with plastic on rainy days, leaving it uncovered on dry days. After the rainy season was over, I removed the plastic, and left it sitting in the sun for few months. It's dry now, but badly cracked. I have a feeling it may have been cracked even before the tree even fell over, but I would be interested in hearing from anyone who has experience drying logs.

I chose one of the smaller logs and sliced off a piece with the bandsaw.


Next, I clamped a 4x4 to the bandsaw table to act as a crude fence. It's set to a little over 1" of thickness from the blade.

I jointed the exposed log face before cutting each 1" slice with the bandsaw. I then jointed the other side of each board, and also jointed one edge. I then planed each board to exactly 1" and used a table saw to square up the other side. I now have flat, square stock ready for the project. The wood had lots of cracks, but the figure was really pretty. I think this was an almond tree.


I ended up cutting the boards into 1"x1" x 12" long strips. I decided to make a napkin holder, since it was something that I could build with a small amount of wood, and would be useful. I used standard yellow wood glue and only used tape while drying -- no clamps.


I used a 1/8" radius round-over bit in my router table to smooth the edges, then sanded with 150 grit on a random orbital sander, and also did some hand sanding. I applied a Tung oil finish (my favorite finish) in a few heavily-rubbed coats.

Improving guitar cable connections

This weekend, my band played a gig on Saturday and Sunday in Monterey. On the third-to-last song on Sunday, I started to have problems with the sound coming out of my bass guitar. The sound cut in and out and had some distortion and static. I managed to get through the last few songs by wiggling the cable and standing very still (to prevent jostling the connection). After I unpacked my gear, I set about finding and correcting the problem. I found two separate problems:

1. The bass->amp cable had an intermittent short in one end caused by a strand of the shield coming into contact with the signal conductor. I've seen this failure mode many times in guitar cables. The constant motion and bending causes the shield wires to fray and migrate around inside the connector. The fix was to cut off the stray strands, and wrap some tape around the center conductor in the connector.

2. The 1/4" phone jack in the bass guitar itself would fail if the plug was pushed in just the right direction. This bass uses active pickups and senses when the ring of the phone jack is connected to the sleeve (ie a mono plug is inserted into the jack) to supply power to the active pickups. This way, the bass will not run down the battery when it's not plugged into the amp. I am not sure which contact was failing intermittently, but it was probably the sleeve or ring. I replaced the phone jack with a 4-pin "mobile radio" connector. These connectors are very rugged and have a threaded ring to secure the plug into the socket. No amount of twisting or pushing will cause it to break contact. I used three of the pins (two are shorted inside the plug to provide the battery-saving feature). I made a special cable that converts the 4-pin connector on the guitar to a standard 1/4" phone jack on the amp. The only downside to this setup is that the plug cannot rotate, which is one benefit of the 1/4" phone jack -- it helps to get kinks and twists out of the cable while walking around or moving the bass around stage.

Anyway, I'll post about this again if it turns out to be a really bad or really great idea.