Saturday, October 31, 2009

Halloween prop: monster in a box

Every Halloween, my dad and I put together a small haunted house on the porch of his house. Most of the props are remotely controlled lights, sound effects, etc. This year, I made a new prop that was inspired by something I saw at this year's Maker Faire. It's a wooden crate with a pneumatic cylinder mounted on the inside facing toward the ground. When the cylinder is filled with air, it violently lifts the crate up an inch or two. When the air pressure is released, the crate comes crashing back down to the ground. I also put a heavy chain on top of the crate for a great visual and audible effect. There is a colored light bulb inside the crate that is illuminated at the same instant the gas cylinder is filled.

The wooden crate came from Michaels craft store ($10), and the chain was from Home Depot. I used the chain previously with a come-along winch and had it in my garage already.

I am using a 5# CO2 tank to supply gas pressure to the valve at about 100 psi. The valve is a Clippard Maximatic 12VDC, direct-acting 3-way valve.

Thursday, October 22, 2009

Stainless steel conical beer fermenter Pt.7

The conical fermenter project is coming along well. Here is what's left to do:
1. Mount stainless cooling coil (chiller) to bottom of lid so that I can quickly chill the hot wort after boiling.

2. Make a silicone seal for the lid

3. Make some beer! Wow, I can't believe this project is almost done... it's taken a long time.

Here's a picture of the lid with a thermowell that I made. The thermowell allows a temperature probe to be inserted deep into the tank without exposing the tank to the outside air. It's basically just a long stainless tube that is welded to the underside of the lid and sealed (welded) on the end.

The peltier heating/cooling module is working pretty well despite the copper block soldering mishap. The thermal conductivity is not nearly as good as it should be, but it still seems to work well enough. My original plan was to use two separate peltier modules, but so far, one seems to be sufficient. Without any insulation on the tank, the device held a 15*F difference from ambient temperature, so this project may not even need much insulation.

The temperature setpoint is 67*F. For actual beer brewing, I'm thinking 64*F will be the target ale brewing temperature. So far, I am just using proportional control with a very high proportional constant. The tank has so much volume, and the heating/cooling power of the peltier is relatively tiny, so there isn't much tendency to oscillate.

Tuesday, October 13, 2009

Flattening parts with glass-backed sandpaper (what to avoid)

In the past, I've used sandpaper that has been glued or double-stick taped to a large piece of glass to flatten small parts. Apparently, this only works well when the sandpaper is stationary and the part is moved. The part will naturally be flattened by the random passes on the sandpaper.
I tried to adapt this technique where the glass was moved and the part was stationary. It didn't work. The part ended up very smooth, but not flat. It's too difficult (apparently) to hold the glass at the same exact orientation for every stroke. I ended up mounting the part back in the mill and using a wide diameter end mill to flatten and smooth the surface in one pass.

Stainless steel conical beer fermenter Pt.6

I decided to scrap the idea of using my ring burner shown in "part 5" of my conical fermenter series of posts. Instead, I started reading about home-built propane burners for use in small metal-working forges.

These sites were very helpful:

I decided to follow Mr.Zoeller's design, for which he was kind enough to post a PDF and provide great instructions.

I used an 1/8" NPT brass cap to seal the end of the 1/8" pipe nipple instead of a Tweco Mig tip. I drilled a .035" hole in the center of the brass cap after machining the sides and face smooth.

I used a 3/4" to 3/4" extender as a flare. I cut out the threads on the lathe, leaving a 1:12 taper on the interior surface. I tested the burner briefly before cutting the taper, and I'm not sure how much it really helped. I never tested it without the flare.

This is really a very good design. It can be built from parts found at any hardware store, and it only requires a couple holes to be drilled. The performance seems to be quite good. I do not have any other burners to compare it to, but I am quite pleased. It doesn't like to run at very low pressures. The flame will be drawn back into the tube, and it starts to sputter (as well as heat up the tube). Above 3 or 4 psi, it runs like a champ, and the adjustable air shutter is a critical piece. Without the air shutter, the flame is very lean and might blow itself out. I kept the shutter half-closed, and this seemed to produce a very neutral flame.

I fitted the conical with its valves and added 1 gallon of tap water. The burner is mounted by simply placing it between two short stainless pipes that I welded onto the frame rail. There is currently nothing holding the burner in place except gravity. I'll probably add a pin or strap to prevent the burner from accidentally falling.


I achieved a full rolling boil in 20 minutes (1 gallon of water). I started out fairly low with the gas pressure, and gradually increased it, as I saw nothing bad happening.

Sunday, October 11, 2009

Stainless steel conical beer fermenter Pt.5

I found a 0-10 psi adjustable propane regulator at Home Depot. It was a closeout item with a price of $4.99! I built a circular burner from 5/8" copper tubing and soldered in some "jet burners" from the ubiquitous 23-jet wok burner.

The 23-jet burner is available in natural gas and propane versions. I ordered the propane version from (it was on sale for $20.03 a few weeks ago), but they might have sent me the natural gas version. I suspec this might be the case because the burner runs very rich. Take a look:

The yellow tips on the flames show that there is a lot of excess fuel. The flames are jumping off the burners probably because the mixture is too rich to start combustion inside the burner tube.

I ordered some hypodermic tubing from McMaster and made the jets smaller by press-fitting the hypodermic tubing into the existing jets. This changed the jet size from about .023" to .012". Now, the jets seem to burn too lean, and have a very hard time staying lit. The slightest breeze blows the flame out. When the burner was running too rich, it also could be blown out by slight breezes. I think the burners are not designed very well. The original orientation in the 23-jet burner caused a lot of turbulence to be generated -- it positioned the jets to aim into each other's path. This might have been a required design element to prevent the flames from being blown out.

Anyway, I'm considering a different propane burner design. More later.

Stainless steel conical beer fermenter Pt.4

Today I built a three-legged support structure to hold the beer fermenter. My original design called for welding three square cross-section tubes to the sides of the conical tank. I decided against this method because I wanted to ability to remove the tank from the stand, and I was also a little worried about having inadequate argon coverage on the weld backside (in the tank).

The three legs are only held together by the welds near the ground. The tank just rests on top of the legs. I may add some strapping to prevent the legs from splaying outward from the conical tank, but so far, this doesn't seem to be much of a problem. The legs are all 304 stainless steel - same as the tank.

I was surprised how little filler rod I needed for these welds. Next time, I will make my tack welds much smaller, because the weld bead itself was very tight, and the globs of filler from the tack welds were annoyingly large.

I welded some stainless nuts to small sheet metal structures, then welded the assemblies to either side of the copper heat block. The two nuts will allow me to sandwhich the Peltier between a large heatsink and the copper block. I'll use nylon screws to prevent heat transfer and also to make the compression on the Peltier more gentle and balanced.

Thursday, October 1, 2009

Quickly tapping (threading) holes in plastic

For my day job, I often have to tap (cut threads into) holes in plastic that will receive screws. This can be done by hand with a standard tap wrench, but it's also possible to do with a hand drill. I bought a small 3/8" square drive adapter that has a 1/4" hex shank. This was intended for use in cordless screwdrivers which accept hex shanks, but a drill chuck will grab the hexagon just fine. I also bought a set of adjustable tap chucks that have a 3/8" square drive hole.
The smaller chuck goes from #2 taps up to about #10, and the larger for #10 up to 3/8".

For plastic, I use lots of distilled water as coolant. If I am tapping a blind hole, I usually just fill it up with water. The nice thing about using distilled water is that it leaves no residue after being blown clean with compressed air.

Tapping a hole with the hand drill works best for a certain range of sizes:

In ABS, I would use the drill for any size #2 through 1/4"

In acrylic or Delrin, I would probably only use the drill for #6 through 1/4"

The really small taps sometimes clog up, even with coolant, and the drill doesn't provide enough sensitivity to avoid snapping the tap. ABS is so soft, a clog would just be pushed away, whereas in acrylic or Delrin, it might jam.

For sizes larger than 1/4", I would probably use a tap wrench because they take a lot of torque, and it's difficult to keep the drill straight and have it deliver enough torque to spin the tap.

I like using the chrome-plated taps because the finish will not rust (a concern since I use water as a coolant), and the chrome is supposed to have a lower friction coefficient than bare high-speed steel.

For sizes smaller than 1/4", I would only use a bottoming tap in plastic. There is no reason to use a plug or taper tap because the bottoming tap makes a cleaner cut, and actually produces less friction and heat than plug or taper taps. In harder materials it makes sense to cut gradually, but plastic is so soft, it will just melt if the tap keeps making light passes that rub against the surface.