Wednesday, December 29, 2010
Tuesday, December 14, 2010
a $16 pocket spectrum analyzer
mossmann's blog
Tuesday, March 16, 2010
ShmooCon was, once again, a fantastic experience this year. One of many highlights of this year's event for me was hacking on some radio devices with Travis Goodspeed in the hotel bar for hours on end. This included playing with the IM-Me that he brought. As soon as I got home I ordered one. I found mine for $15.99 and free shipping on eBay.
Since then I've written custom firmware to turn my IM-Me into a pocket spectrum analyzer, shown here displaying activity of a frequency hopping system at a grocery store. The only change I've made to the hardware is the addition of a ribbon cable in order to easily connect to a GoodFET for programming, but this is simply creating a permanent connection to the debug contact points that are already exposed in the battery compartment. I've followed Travis's advice on how to develop for the platform.
The software tunes the IM-Me's radio chip to one frequency at a time, uses the chip's RSSI measurement function, and plots the result as one column on the LCD. It sweeps across the whole screen (132 columns) several times per second, showing a contiguous range of radio frequency activity. The technique works quite well, although there are a few defects. Most notably, harmonics of the IM-Me's 26 MHz crystal show up as spurs on the display.
The frequency ranges supported by my device are 281 - 361, 378 - 481, and 749 - 962 MHz. This is about 50% more than the chip is advertised to support and covers quite a bit of interesting activity in the US including ISM, LMR, television, amateur bands, pagers, and mobile phones. The edges of the bands supported by other batches of chips may differ but probably not by much.
The software supports three bandwidth modes: wide (default), narrow, and ultrawide. Wide mode displays 26.4 MHz of bandwidth in 200 kHz increments. Narrow mode displays 6.6 MHz of bandwidth in 50 kHz increments. Ultrawide mode, shown here with some mobile phone activity, displays 88 MHz of bandwidth in 667 kHz increments.
Sunday, December 12, 2010
Plastic Extruder for Growing Media
Building the Harbor Freight 10x12 Greenhouse
Friday, December 10, 2010
For several months, I’ve been developing a plastic extrusion system that has been able to take virgin HDPE resin pellets, or shredded milk jugs, and properly melt and extrude them into a shape that could be used as a low cost growing media for my Aquaponics system.
There was a lot of trial and error to get to this point. The biggest problem is that the plastic retains little moisture. If the seeds aren’t directly placed in the flood/drain cycle, they won’t get any moisture to germinate. I typically grow in stone and some of the stone above the water line is able to wick and retain enough moisture to provide water to new seeds.
Another issue with HDPE is that it’s extremely smooth (again, works well to repel water). Even adding texture to the media during the cooling process, the media still is smooth, which makes it difficult for bacteria to stick to it. I was also a bit surprised to see that the roots didn’t really care to grow in it and they would grow around the edge of the net pot instead.
On the plus side, the plastic is light, fairly inexpensive, clean, and easy to work with.
I hope some of the info in the video is useful to some of my fellow aquaponic/hydroponic growers in their quest to find a better, more cost effective growing media.
Below is the transcript for the video…no need to read it if you’re going to watch the video… I just included it so some of the search engines could pick up on the keywords. ;-)
Hello Everyone. Today I’m going to show a plastic extruder system that I built. The end result was to produce a synthetic, cost effect growing medium for my Aquaponics system.
The extruder consists of a hopper for high density polyethylene pellets. An auger then forces the pellets through a dual zone heating chamber. The heated material is forced through a small die at the end of the chamber.
The temperature in each zone of the heating chamber is controlled by a Teensy AVR microcontroller which is monitored and adjusted through its USB port connected to a laptop.
The auger is driven by a windshield wiper motor and it is geared-down using an old bicycle sprocket and chain.
The hopper is filled with HDPE pellets where they are slowly forced into the heating chamber. It can also be filled with shredded milk bottles or shredded milk bottle caps to add color.
The heating chamber is covered in some fiberglass insulation to conserve heat. There are two thermal probes mounted near the middle and end which provides accurate readings to the controller as the material is heated. The heating elements draw around 16 amps at 12 volts.
The molten plastic that is extruded from the die is squeezed through a set of rollers which embed a texture into the material. A small tube blows air onto the pressed material to cool it, and to keep the rollers cool.
This is one of the rollers after I turned it on my lathe with a close-up view of the texturing.
And this is a close-up video of the material being extruded and pressed through the rollers.
Here is a close-up view of the finished material once it has been cut to length. There is a waffle pattern embedded into the plastic which provides plenty of surface area for bacterial growth. The media lies flat which helps to retain moisture during a drain cycle. The pieces have plenty of spaces between each other for water and root growth.
Most HDPE plastic is classified as food-grade. However, one problem is that nothing likes to stick to it. Even though a texture has been embossed into the plastic, a small amount of movement can disrupt anything that was clinging on it.
This is a time-lapsed video taken with my PlantCam over a 30 day period. There are 3 bean plants growing. I also planted lettuce seed which didn’t germinate, probably because the top inch of the media doesn’t retain moisture like stone or expanded clay.
After 30 days, I removed the beans from the aquaponic system. I had the net basket wrapped in foil to prevent the roots from wandering into the surrounding stone. The roots seem to have an aversion to growing in the plastic and mainly grew between the basket and foil.
Thanks for watching. If you have any questions or comments, please leave them in the comments section below. Also please subscribe to my YouTube channel to see future videos!
There was a lot of trial and error to get to this point. The biggest problem is that the plastic retains little moisture. If the seeds aren’t directly placed in the flood/drain cycle, they won’t get any moisture to germinate. I typically grow in stone and some of the stone above the water line is able to wick and retain enough moisture to provide water to new seeds.
Another issue with HDPE is that it’s extremely smooth (again, works well to repel water). Even adding texture to the media during the cooling process, the media still is smooth, which makes it difficult for bacteria to stick to it. I was also a bit surprised to see that the roots didn’t really care to grow in it and they would grow around the edge of the net pot instead.
On the plus side, the plastic is light, fairly inexpensive, clean, and easy to work with.
I hope some of the info in the video is useful to some of my fellow aquaponic/hydroponic growers in their quest to find a better, more cost effective growing media.
Below is the transcript for the video…no need to read it if you’re going to watch the video… I just included it so some of the search engines could pick up on the keywords. ;-)
Hello Everyone. Today I’m going to show a plastic extruder system that I built. The end result was to produce a synthetic, cost effect growing medium for my Aquaponics system.
The extruder consists of a hopper for high density polyethylene pellets. An auger then forces the pellets through a dual zone heating chamber. The heated material is forced through a small die at the end of the chamber.
The temperature in each zone of the heating chamber is controlled by a Teensy AVR microcontroller which is monitored and adjusted through its USB port connected to a laptop.
The auger is driven by a windshield wiper motor and it is geared-down using an old bicycle sprocket and chain.
The hopper is filled with HDPE pellets where they are slowly forced into the heating chamber. It can also be filled with shredded milk bottles or shredded milk bottle caps to add color.
The heating chamber is covered in some fiberglass insulation to conserve heat. There are two thermal probes mounted near the middle and end which provides accurate readings to the controller as the material is heated. The heating elements draw around 16 amps at 12 volts.
The molten plastic that is extruded from the die is squeezed through a set of rollers which embed a texture into the material. A small tube blows air onto the pressed material to cool it, and to keep the rollers cool.
This is one of the rollers after I turned it on my lathe with a close-up view of the texturing.
And this is a close-up video of the material being extruded and pressed through the rollers.
Here is a close-up view of the finished material once it has been cut to length. There is a waffle pattern embedded into the plastic which provides plenty of surface area for bacterial growth. The media lies flat which helps to retain moisture during a drain cycle. The pieces have plenty of spaces between each other for water and root growth.
Most HDPE plastic is classified as food-grade. However, one problem is that nothing likes to stick to it. Even though a texture has been embossed into the plastic, a small amount of movement can disrupt anything that was clinging on it.
This is a time-lapsed video taken with my PlantCam over a 30 day period. There are 3 bean plants growing. I also planted lettuce seed which didn’t germinate, probably because the top inch of the media doesn’t retain moisture like stone or expanded clay.
After 30 days, I removed the beans from the aquaponic system. I had the net basket wrapped in foil to prevent the roots from wandering into the surrounding stone. The roots seem to have an aversion to growing in the plastic and mainly grew between the basket and foil.
Thanks for watching. If you have any questions or comments, please leave them in the comments section below. Also please subscribe to my YouTube channel to see future videos!
Thursday, December 9, 2010
Bottle Cutting
- Author: Sean Michael Ragan
- Time required: 30 minutes
- Difficulty: Moderate
There are lots of ways to do this particular trick. You may have seen bottles "cut" using a bucket of ice water, a string soaked in fuel and set alight, a hot narrow gauge resistive wire, or some combination of the above. I've tried all of these ways, at one point or another, with varying degrees of success, and I'm reporting here the method that gives most consistent results for me. But if you're interested in trying some other way, by all means experiment. Glass bottles are freely available just about everywhere, and you can always recycle your mistakes.
Regardless of which of these methods you favor, "bottle cutting" is generally a misnomer, as what's really going on is a process of controlled breakage. (Unless, of course, you're actually using a tile saw or something similar, in which case I'm prepared to agree it's really "cutting.")
Anyway. Glass, molecularly, is mostly silicon dioxide, but it's distinct from crystalline solids like ice or table salt in that the molecules are not well-ordered in space. You may have heard some balderdash about how glass is really a liquid with practically infinite viscosity; generally the swelling of ancient cathedral windows at the bottom is sited as evidence to that effect. Well, it's not true: There is, to my knowledge, no reliable evidence that glass will flow at room temperature regardless of how long you wait. Turns out cathedral glaziers made their windows thicker at the bottom on purpose.
But as an analogy, "infinitely viscous liquid" is not a bad way to understand the random molecular ordering of bulk glass. The upshot of this anisotropy is that glass does not cleave in orderly ways: Cracks tend to wander off in random, unpredictable directions, and shattering can easily occur due to internal stresses. There is, therefor, an element of luck involved in the bottle cutting operation, but with a bit of practice and good technique you can make it work most of the time.
Monday, December 6, 2010
Friday, December 3, 2010
Saturday, November 27, 2010
Lurie-Houghton Telescope Design with a Comparison to the Newtonian Telescope
by Rick ScottWhy should I build a telescope? In the spring of 1999, I was reading the telescope design "bible", Telescope Optics by Harrie Rutten and Martin van Venrooij. I was reading it just to learn more about telescopes in general and about Schmidt Cassegrains in particular, because I own an old Celestron 8. In chapter 13, "Other Compound Systems", I read about a design known as the Lurie-Houghton. I found the design to be very intriguing because it seemed to offer an excellent balance between the various trade-offs that need to be made to achieve a great performing telescope. The authors had this to say about the design, "The Lurie instrument seems to be an almost ideal rich field telescope for the demanding amateur". The design they investigated in their book is an 8" f/4 system. After finishing the book, I kept re-reading the section on the Lurie-Houghton and comparing it to the other telescope designs in the book until I decided I needed to build one. The same authors also wrote about this design in the ATM Journal, issue #1, Fall 1992. To derive the particular design I'm currently building, I used the optional software for their book as a starting point and fine tuned it using OSLO LT from Sinclair Optics. OSLO LT is a full blown optical design software tool that performs ray tracing and other optical analysis. Read my review of the program for more details. The idea of building a telescope was not something I had contemplated before. This was a major decision for me, especially in light of the complexities of this particular telescope design. Most amateur astronomers and telescope makers use the Newtonian design, which is the simplest practical form of a reflecting telescope. Refer to the following drawing. The Newtonian telescope uses a paraboloidal mirror at the back end of the telescope tube to reflect and focus the light. A small mirror near the front of the tube and mounted at a 45 degree angle is used to direct the focused light sideways out of the tube to an eyepiece.
The Lurie-Houghton design uses a similar arrangement of mirrors except the main or primary mirror has a spheroidal surface instead of a paraboloid. Also, two full aperture lenses are used at the front of the tube to correct for the aberrations due to the use of the spheroidal mirror. Refer to the following drawing. The two lenses together are referred to as the corrector lens or just the corrector. The addition of the corrector to the telescope adds the complexity of making two large lenses to the design.
Why would anyone add this extra complexity (and cost) to a telescope? I enjoy viewing the planets and other objects through my current telescope, but I really like to look at the various star clusters, nebulas and galaxies the sky has to offer. Many of these are larger than the field of view of the 8" f/10 Schmidt Cassegrain telescope I currently use. A short focal ratio Newtonian like a 10" f/4.5 would offer me wider fields of view, but the trade-off is higher distortion in the stars off axis. The corrector reduces the distortion to negligible levels. I also want to photograph through the telescope and the Newtonian has a curved focal (image) plane, but the Lurie-Houghton has an almost flat focal plane. More details with actual numbers are presented later in this article. Another advantage of having the corrector lens is that it acts as an optical window at the front of the telescope. This controls the air currents in the telescope tube which reduces blurring and contrast reduction of the image. By closing off the tube, the mirrors and interior of the telescope also stay cleaner. How big should it be? The aperture and focal ratio of all telescopes are compromises determined by factors such as cost, weight, size as much as desired optical performance. The telescope I've been using so far is an old Celestron 8 from the early 1970's (Celestron Pacific) that has an 8" aperture. It has been fine from the viewpoint of aperture size, but I wanted something a little bigger. I do have to transport the scope around and a 10" mirror would be reasonable to move. The effect on the image by atmospheric turbulence is also affected by the size of the aperture. As the aperture increases, so does the effects of the atmosphere. My research indicated that a scope around 8" to 10" is at the transition region where the image changes from moving around with some blurring to just becoming blurry, so 10" is the aperture I settled on. The next decision is the focal ratio which determines the focal length of the telescope. The design that Rutten and Venrooij analyzed is an 8" f/4. If I scaled their design, I would have a 10" f/4 which has a focal length of 40". My Celestron 8 has a focal length of 80". This is great for planetary viewing, because it doesn't require extremely short focal length eyepieces for decent views. A 40" focal length would require eyepieces with half the focal length for the same size image. If I made a Lurie-Houghton with an 80" focal length, I would end up with fields of view not larger than my Celestron offers, so I settled on a compromise of 45". This is a very common focal length in amateur telescope, as seen by the large proliferation of 10" f/4.5 telescope in the market. I still need a shorter focal length eyepiece than I currently have or I can use a Barlow lens to magnify the image for planetary work. With my current 1.25" barrel 26mm eyepiece, my Lurie-Houghton telescope will offer me a 1.2 degree field of view. With a low power 2" barrel eyepiece, I'll get field of views greater than 2 degrees. What are the details of this Lurie-Houghton telescope? The following table contains the design parameters for my implementation of the Lurie-Houghton telescope. The parameters for my original design and for the telescope as it actually ended up being built are shown.
This drawing shows the details for the corrector lenses. I'm using AutoCAD Release 14 for all of the design drawings. Besides 2D drawings, I'm also modeling all of the parts using 3D solids. By doing this I can see how the parts fit together and it allows me to create 3D renderings.  How does the Lurie-Houghton compare to an equivalent Newtonian? The following figures compare the performance of the Lurie-Houghton telescope I designed to a Newtonian telescope with the same aperture and focal ratio. The spot diagrams This first set of diagrams are spot diagrams. They show how the light is focused. The small black circle in the center of the spot diagrams represent the diffraction limit for a 9.8" aperture. It is the same size as the airy disc seen using a high power eyepiece. Ideally, all the light entering the telescope should focus within the diffraction limit. This is referred to as being diffraction limited. Most commercial telescope vendors will state their telescopes are diffraction limited, but they don't state over what field of view. The spreading of the light in the Newtonian is mostly due to coma, but there is also some astigmatism. The corrector in the Lurie-Houghton eliminates the coma but leaves some astigmatism that is seen as spreading of the light bundle. Since the Newtonian uses only mirrors and no lenses it doesn't have any chromatic (color) aberrations. That's why the spot diagrams don't show any color effects. Note the scale change for the wider fields in the spot diagrams for the Newtonian. The coma is so bad that a large percentage of the light is far outside of the diffraction limit. 
This second set of diagrams are the Modulation Transfer (MTF) curves. They show how the image contrast is affected by aberrations in the optical system. Each of these graphs have a line that shows the upper limit or maximum contrast possible for a given telescope design. The limit is set by the aperture size and amount of central obstruction due to the secondary mirror. Notice in the MTF curves that the Newtonian with a 5 arc-minute field of view has almost the same amount of contrast degradation as the Lurie-Houghton with a 72 arc-minute or 1.2 degree field of view. The Lurie-Houghton provides a field of view over 14 times wider with the same amount of contrast reduction! Also, the spot diagrams show that the star images away from the center of view will be sharper and brighter in the Lurie-Houghton, because the light is still concentrated within the diffraction limited airy disc. 
The central obstruction that is normally present in reflecting type telescope is there because some type of mirror is needed to reflect the light from the primary mirror to the eyepiece. Because the mirror focuses the light back along its central axis, the secondary mirror must be on that axis, causing it to block the central portion of the light path. If the secondary mirror is no larger than 20 percent of the diameter of the telescope aperture, it causes virtually no degradation to the contrast of the image. Using OSLO LT, I compared the on-axis modulation transfer curve of my Lurie-Houghton telescope to an ideal lens with the same focal length and no central obstruction. I also analyzed different size ideal lenses of the same focal length as my Lurie-Houghton to find the ideal unobstructed telescope that gave the same contrast performance. By performing this exercise, I was able to find the aperture of an ideal telescope, if such a thing could be built, that would give equivalent contrast on objects such as the planets. I did this because in the telescope world, there is the equivalent of a Macintosh vs. PC battle. In this case, the battle is between refracting (unobstructed) and reflecting (obstructed) telescopes. The refracting camp states that no amount of obstruction is tolerable. The results of my analysis, seen in the following figure, shows that an ideal (no aberrations) telescope with no obstruction and a 6.6" aperture would have the same contrast as my telescope for medium resolutions (ie. planetary observing). The graph also shows that the larger aperture with obstruction (in this case 31.6%) has much better contrast at higher resolutions. This is great for observing double stars and various star clusters where the stars are visually very close together.
How about some pretty pictures? Here is a 3D rendering of the corrector lens cell with the two lenses in it. I made this rendering in AutoCAD by making 3D solid models of the parts and assigning colors or material properties to each of them. I removed a quarter section to make the construction clearly visible. The side visible in this drawing is the side facing the primary mirror.  This rendering shows the front of the telescope with half of the tube removed. The secondary mirror assembly is attached through the center hole of the first corrector lens. On the lenses, you can see the reflections of a small light source I placed close to the front of them to add some highlighting to the rendering. You can also see various shadows cast by telescope parts from the many light sources used to make the rendering.  The next rendering shows the details for the primary mirror mount. The mount is basically two pieces, the yoke (triangular plate) that the mirror is bonded to with silicone adhesive, and the ring that is used to attach the assembly to the telescope tube. The push-pull bolt arrangement at each corner of the yoke are used to adjust the collimation of the primary mirror. Also visible are two of the "L" shaped safety brackets used to restrain the mirror if the silicone adhesive should fail.  I looked at many mirror mounts used in other telescopes and found that they all wasted an excessive amount of space behind the mirror. One of my design goals was to have the tube be no longer than necessary, so I designed this mount to be as frugal as possible with the space behind it. In practice, this mount design has worked very well. It is easy to adjust the collimation and it doesn't change at all with transportation in my car. I highly recommend this simple design to other telescope makers. |
Updated: 23 December 2002
Thursday, November 25, 2010
Tuesday, November 9, 2010
introDIY Projects, Communities and Cultures
Instructables
A year or so ago, we invited DIY enthusiasts from Instructables, Ravelry, Adafruit , Craftster, Dorkbot, and Etsy to fill out our survey on DIY communities, projects, and cultures. We received 2600+ responses in just a few weeks. Many many thanks to everyone who contributed!!
In this 'Instructable', we share some of our findings. We explore DIY as a broad cultural movement, spanning many domains and materials. This is just one way- and one starting point- for understanding DIY communities, motivations and practices. We would love to hear your feedback!
Please check out our paper . All images are taken from my talk at NordiCHI . Freel free to download the full slide deck as a pdf or a set of images .
Please check out our paper . All images are taken from my talk at NordiCHI . Freel free to download the full slide deck as a pdf or a set of images .
Rise of the Expert Amateur:DIY Projects, Communities, and Cultures
Stacey Kuznetsov & Eric Paulos
Human-Computer Interaction Institute, Carnegie Mellon
5000 Forbes Avenue, Pittsburgh, PA, USA
{stace, paulos}@cs.cmu.edu
Stacey Kuznetsov & Eric Paulos
Human-Computer Interaction Institute, Carnegie Mellon
5000 Forbes Avenue, Pittsburgh, PA, USA
{stace, paulos}@cs.cmu.edu
ABSTRACT
This paper presents a large-scale study of Do-It-Yourself (DIY) communities, cultures and projects. We focus on the adoption and appropriation of human-computer interaction and collaboration technologies and their role in motivating and sustaining communities of builders, crafters and makers. Our survey of over 2600 individuals across a range of DIY communities (Instructables, Dorkbot, Craftster, Ravelry, Etsy, and Adafruit) reveals a unique set of values, emphasizing open sharing, learning, and creativity over profit and social capital. We derive design implications to embed these values into other everyday practices, and hope that our work serves to engage CHI practitioners with DIY expert amateurs.
This paper presents a large-scale study of Do-It-Yourself (DIY) communities, cultures and projects. We focus on the adoption and appropriation of human-computer interaction and collaboration technologies and their role in motivating and sustaining communities of builders, crafters and makers. Our survey of over 2600 individuals across a range of DIY communities (Instructables, Dorkbot, Craftster, Ravelry, Etsy, and Adafruit) reveals a unique set of values, emphasizing open sharing, learning, and creativity over profit and social capital. We derive design implications to embed these values into other everyday practices, and hope that our work serves to engage CHI practitioners with DIY expert amateurs.
Monday, November 8, 2010
Make your own model rocket igniters
Author: Stefan Jones
Time required: 10 to 15 minutes
Difficulty: Easy
Modern commercial igniters can send a rocket soaring with just a touch of current. When inserted properly they're very reliable. Unfortunately, they are fragile, and folks new to the hobby sometimes ruin them by inserting them improperly. Packs of spares are expensive, and not all outlets carry them. There's a cheap alternative: hand-wound nichrome igniters.
Nichrome is a high-resistance alloy. Run a current through it and it glows red hot. Until the mid '60s rocket motors came with a length of the wire, which rocketeers cut and shaped into an igniter. If placed correctly they are very reliable. I enhanced the austere original design with a few tricks picked up from old newsletters and personal experience.
Nichrome igniters can only be used with black powder motors, and have one other drawback: They need a lot of current to work. This isn't a problem if you're using a 12v launch system powered by a car battery. But they'll quickly suck the juice out of the alkaline AA cells or 9 volt batteries used in commercial launch panels. Plan accordingly by bringing extra batteries, or test your Maker chops by making a sturdy 12v launch system!
Tools
- A light-duty paperclip with one "leg" bent outwards.
- A pair of needle nose pliers.
- A pair of scissors.
- A pen.
- A sheet of waxed paper to protect your work table.
Relevant parts
- nichrome wire 3 to 6 feet, 28 to 32 gauge
- Lacquer paint dope or nail polish
- Tissue-type flameproof wadding
- Masking tape (1/4") or mailing labels cut into strips
Step 1 — Make your own model rocket igniters
- Assemble your tools and parts.
- 1/4" masking tape can be hard to find. The freebie mailing labels sent out in charity fundraising letters are a good substitute.
- Nichrome wire is most commonly used as the hot "blade" of electric foam cutters. Costs and lengths vary widely. A big roll of nichrome wire makes a good club purchase; it will take your many years to go through yards of the stuff! Some nichrome alloys include iron; I've heard this makes the wire prone to rust, but I haven't run into that problem myself.
- Sample Suppliers:http://jacobs-online.biz/nichrome_wire.htm http://shop.pitsco.com/store/detail.aspx...
- While the igniter is still wound around the paperclip, use the pliers to pull the legs tight.
- Fold a piece of tape over the legs, leaving about 1/4" below the tape. The tape gives the igniter some structure, keeps the legs from shorting, and reduces tangling in storage.
- Bend about 1/8" of the end of each leg double; this will give your launch pad's microclips a better grip on the narrow wire.
- When you have a dozen or so igniters assembled, dip the tips in the paint or nail polish. You don't need to be neat about it; the coating acts as insulation to keep the coils from shorting out when they're inserted into the nozzle. Lay the igniters on the waxed paper to dry.
- A pill bottle or mint tin makes a handy storage spot for igniters and igniter plugs.
- Pinch a small piece of tissue style flameproof wadding and wad it into a little ball the size of a BB.
- Insert the igniter into the motor nozzle, laying the legs along the "side" of the opening. The coil at the tip should be in direct contact with the black fuel grain.
- Press the ball of wadding into the nozzle and then tamp it firmly into place with the tip of a pen or a paperclip. You should be able to pick up the motor by the leads without the igniter pulling out. (You can also use the colored plastic plugs that come with commercial rocket motors. Lay a little pice of tissue wadding over the nozzle and igniter and insert the plug. Be sure to use the correct color! Thanks to Fred Shecter for this tip.)
Saturday, November 6, 2010
Monday, November 1, 2010
Immaculate Telegraphy
In the summer of 2009, Substitute Materials set out to test if electronic communication could have been built at any time in history, if someone only had the right information. Using no modern tools or materials and relying entirely on material found on the ground in the wilderness, a telegraph switch producing .7 volts of electricity was completed in November. Using the techniques learned during Immaculate Telegraphy, an entire telegraphic network could have been constructed in the stone age.
This project was supported by the Eyebeam Honorary Residency.
View research on deliciousWednesday, October 27, 2010
Tools Used to Cut Plexiglass
- Homeowners and professionals use Plexiglass rather than glass because it doesn't shatter. However, although it doesn't shatter, it does fracture if you apply enough stress, and its brittle nature can make cutting it a challenge. When you do cut Plexiglass, make sure you use the right tool.
- Home Depot recommends the "score and snap" method. Clamp your sheet of Plexiglass between two pieces of wood so that the wood's edge marks the line you wish to cut. Cut the line using a score knife, preferably one with a tungsten carbide tip. Turn the glass over, and score the other side of the glass along the same line. Then unclamp the wood and snap the glass in two using your hands. The problem with this score and snap method is that Plexiglass lacks a defined crystal structure. The glass will likely break if you don't cut it correctly. To avoid cracking it along any line but your cutting route, make sure you apply significant pressure throughout the process, and do not vary this pressure at any point. Also, only score and snap along straight edges.
- When dealing with larger pieces of Plexiglass, it's almost impossible to manually apply even pressure along the entire pane. Use an electrical tool. A table saw cuts straight lines particularly well, but a jigsaw costs less, and you can store it more easily. Use a variable speed jigsaw, and practice on scrap Plexiglass until you determine the correct speed. If the glass cracks randomly, increase the speed. If it melts, reduce the speed. Use an unpainted blade, because coated blades create friction that can melt the glass. Trial and error can help you find the perfect blade, but 32-teeth-per-inch blades usually work well. Wait till the saw has fully sped up to the speed you've chosen before touching it to the Plexiglass.
- You normally want to avoid melting the Plexiglass with your electric tool because you prefer a clean cut to an uneven edge. But if you slowly melt the glass using a soldering iron, you can cut cleanly using the iron's sharp point. Plexiglass melts at 320 degrees F, and soldering irons get hotter than 700 degrees F. Plug in your iron till it heats up fully. Cut your Plexiglass along either a straight edge you've lined with wood or a curved line you've drawn with a wax pencil. The real advantage with a soldering iron is that you can cut any shape without fearing the glass cracking. The process is extremely slow, though, so use this for small intricate work rather than larger jobs.
Score knife
Jigsaw
Soldering Iron
References
Thursday, October 14, 2010
Tuesday, October 12, 2010
Plastic FAQ
Q. There were plastics in 1914?
Q. What about Speeds, Feeds, and Needs?
Ridout Plastics has a library of the proper machining variables you need for cutting, machining, drilling, etc. of all plastics. The single biggest problem is the wrong tool for the wrong job. Email us your request for the type of material and what you need and we will respond quickly by phone or fax! When in doubt, do not call Tim Taylor and do not rewire it.....
Q. What are the Working Temperatures of Plastics?
The correct definition for the "working" temperature of a plastic is how hot it can become and still function normally. Most plastics can go -40 F and retain their physical properties without becoming overly brittle (except flexible vinyl convertible windows). There are special cryogenic grades of plastic(G10,UHMWPE) that will go below -400 F ! For the most part, most plastics will soften or lose their structural properties around 200 F. The chart below list a few of the most popular plastics and their maximum continuous working temperatures:
Acrylic 180 F Polycarbonate 240 F Styrene 150 F
ABS 175 F Nylon 220 F Acetal 220 F
Noryl 265 F PEEK 480 F UHMWPE 160 F
Canvas Phenolic 250 F Linen Phenolic 250 F Teflon 500 F
G10 Epoxy/Glass 300 F G7 Silicon/Glas 480 F
Q. Can I Glue Plastic?One of the really great properties of some plastics are their resistance to chemicals. Plastics that can be dissolved by a chemical are generally glueable, while those that are not dissolved, cannot be glued.
A quick test you can do at home: Find some nail-polish remover (acetone) and test a very small area on the plastic you would like to glue. If it gets sticky, then Ridout Plastics has a solvent adhesive that will work! If the acetone simply dries up, you have a problem. Your choices will be: mechanically fasten the plastic, ultra-sonic welding, or hot-air welding. Most chemical tanks are made of polypropylene or polyethylene and will not glue. PVC and ABS will glue (like your sprinkler pipes). Engineering plastics for the most part cannot be glued with adhesive, unless a contact adhesive is acceptable for your application. Please the Adhesive Cross-Reference chart that will help you select the right adhesive for your application!
Q. Is 1/4" Plastic Really 1/4" Thick?
Depends on what kind of plastic you buy. Most engineering plastics (Nylon, Delrin, Teflon, etc.)are sold "thick" - standard tolerances are -0.0", +5% because the machinist needs the extra material for exactness. This is also true of the rod and tube in these grades. However, there are many plastics that are sold in metric thicknesses with english width and length! Yikes!
Acrylic, such as Plexiglas, is sold this way. The table below should help you be more informed about what you are getting. Please be aware that some plastic companies in the U.S. may substitute .098" for .118" and .220" for .236". If you receive a price quote substantially lower than ours, you may want to measure the sheet they are selling...
1/10" = .098" 1/4" = .220 to .236" 3/4" = .708"
1/8" = .118" 3/8" = .354" 1" = .944"
3/16" = .177" 1/2" = .472"
Q. Does acrylic (Plexiglass, Lucite) yellow in the sun?Since the beginning of the creation of plastics, many myths have been perpetuated about the longevity of plastics, especially outside in the elements. All plastics come from petroleum and natural gas. Sunlight, especially ultraviolet radiation, has a disastrous effect on most plastics. Some plastics, like polyethylene (PE) milk jugs, degrade quickly in the sun - in a matter of months. PE can easily be recycled. Many children's toys are made from PE and get brittle and crack when left outside.
Acrylic (Plexiglass, Lucite,and Acrylite) comes from natural gas and is completely inert when in solid form. American-made acrylic does NOT yellow in the sunlight. Witness the protective canopies and bubbles in the World War II bombers - they are still clear after 50 years in the sun! There are three other clear plastics that do yellow in the sun and get confused with acrylic - Styrene, PETG, and Polycarbonate. They have their respective qualities that make this an acceptable trade-off. Ask your Ridout Plastics salesperson for information on all of these plastic solutions.
Q. What about Expansion & Contraction of Plexiglas?
Thermal Expansion and Contraction - All materials expand and contract to a greater or lesser degree due to changes in temperature and humidity. Allowances must be made for these changes in the construction and fabrication of products; for example, the expansion joints in cement sidewalks and on steel bridges. Acrylic sheet is subject to greater dimensional change, due to thermal expansion and contraction, than other materials with which it is used in construction.
Comparison of Co-Efficient of Thermal Expansion Acrylic Sheet vs. Other Materials Inches/Inch/F Acrylic Sheet .0000410 Aluminum .0000129 Plate Glass .0000050For indoor applications where temperature normally remain the same (+/- 20 degrees F), acrylic sheet does not generally require special considerations for expansion and contraction other than providing for a snug rather than tight fit since its movement is approximately .00984" per foot length for each 20 degrees of temperature change.
Degree of Size of Temperature Change for Plexiglass
10 15 20 30 40 50 60
12" 1/16 1/16 1/16 1/16 1/16 1/8 1/8
24" 1/16 1/16 1/16 1/16 1/8 1/8 1/8
36" 1/16 1/16 1/16 3/8 1/8 3/16 1/4
48" 1/16 1/16 1/8 1/8 3/16 1/4 1/4
60" 1/16 1/16 1/8 1/8 1/4 1/4 3/8
72" 1/16 1/8 1/8 1/8 1/4 5/16 3/8
84" 1/8 1/8 3/16 3/16 5/16 5/16 1/2
96" 1/8 1/8 3/16 1/4 5/16 3/8 1/2
PLEXIGLAS® SHEET ASSEMBLY METHODS: THROUGH-FASTENING Drill holes larger than the fastener, allowing at least 1/16" more per running foot of Plexiglas® sheet. Holes should be located at least the diameter of the hole size from the edge of the sheet. Smoothing the hole surface with a round file should provide maximum breakage resistance. Tighten the screw just snugly and back off a 1/4 of a turn to provide free expansion or contraction movement of the Plexiglas® sheet. Do not use counter-sunk holes for flush mounting, but use a counter-bored hole. Q. Help....My Plastic Is Scratched!!?
When your beautiful piece of Lucite acrylic scratches, you can fix it quickly! If you can't feel the scratch with your fingernail, then Novus#2 or #3 should restore the finish. Otherwise, you will need to sand and buff the area that is scratched to return the shine (see next paragraph). It's the same way we polish the edges of thick pieces of acrylic here at Ridout Plastics - it works! This procedure ONLY works on acrylic. It does not work on styrene (like the colored boxes we sell) or on polycarbonate (Lexan, Tuffak, Cyrolon). They both look clear, but they cannot be restored. Ask about our Abrasion Resistant coatings...
Solution: Sand the affected area with 400 Wet/Dry, then 600 Wet/Dry. Use a buffing wheel on your drill with the Plastic Buffing Compound or White Diamond as Rouge is too fine, to restore the shine. Let the compound do the work - do not press hard or you will "burn" the compound into the plastic. Ask a salesperson to show you the helpful products on our shelves.
Q. What adhesives work with Plastics?
One of the really great properties of some plastics are their resistance to chemicals. Plastics that can be dissolved by a chemical are generally glueable, while those that are not dissolved cannot be glued.
A quick test you can do at home: Find some nail-polish remover (acetone) and test a very small area on the plastic you would like to glue. If it gets sticky, then Ridout Plastics has a solvent adhesive that will work! If the acetone simply dries up, you have a problem. Your choices will be: mechanically fasten the plastic, ultra-sonic welding, or hot-air welding. Most chemical tanks are made of polypropylene or polyethylene and will not glue. PVC and ABS will glue (like your sprinkler pipes). Engineering plastics for the most part cannot be glued with adhesive, unless a contact adhesive is acceptable for your application.
Please check the Adhesive Cross-Reference chart that will help you select the right adhesive for your application!
Q. Hey - This Sticker/Masking Paper Won't Come Off My Plastic!?
Don't you just hate it when those price tags don't come off a plastic item? The problem is that the adhesive either dries out or the wrong kind of adhesive on the price tag was used.. In any case, you need to find a way to get the darn thing off your plastic!
Solution: The simple way to lift a "tight" sticker off of plastic is by moistening the price tag with Lighter Fluid or WD-40 - which is actually a very refined grade of kerosene! This will not bother Acrylic, Styrene or Polycarbonate plastics which will be 90% of the types you will be dealing with. If in doubt, test the fluid on a small part of the plastic. Look at it in 24 hrs. OK? Remember that you could scratch the plastic when rubbing the price tag loose. Easy does it.... for larger areas we sell "Mask OFF" in the Accessories section.
Q. I am worried about Junior falling through railing!?
One of most appealing plastic solutions around the home is the installation of Plexiglas or Lucite along railings and fences to prevent small children and pets from passing through the railing uprights. Remember, Plexiglass is 50% lighter than glass of equal thickness. In 1/8" thickness, it is 17 times stronger. If Plexiglass breaks, you will find only large, rather blunt pieces that you can handle with your bare hands. You will not find shards of material scattered like a mine field!
Installation of Plexiglas is incredibly simple. Using a special drill bit, you can drill small holes on either side of the railing in strategic places and use plastic cable ties. If you are renting, or simply don't want a permanent installation - it's quick and effective.
Q. Are The Edges of Your Plexiglass Too Sharp?
Our saws and routers leave nice chip-free edges on the pieces of Plexiglas we cut. They can be quite sharp if the edge will be exposed to the touch. While this edge is not sharp like glass, if you run your hand down the edge quickly, and with pressure, you may get a "paper-cut" type of injury.
Solution : Use 100 grit sandpaper and a sanding block. Just pass the sandpaper over the edges at a 45 angle a few times. Use your fingers to test the edge. When it feels good, stop!
Q. There's a crack in my plastic window! What do I do?
There is nothing more frustrating than a crack in a piece of Plexiglas or Lexan. Both of these materials are "notch sensitive". By the way, so is glass! That's why you can scribe and break glass (and Plexiglas) along the scribe. These materials have no grain and therefore cracks can travel as they please. However, cracks can be stopped with a simple procedure. Using a very small drill bit, 1/16" or so, drill a hole through the material at the end of the crack. That's it. If it is a long crack, you might be able to inject some IPS WeldOn #3 (methylene chloride) into the crack to partially seal it. If this is a boat window or skylight, we recommend clear silicone sealant on both sides of the crack to seal it up. If the plastic is on a sign, and therefore most likely opaque, you should glue a 1" strip of 3/16" Plexiglas to the back side to reinforce the cracked area.
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