“Okay. I think I’ve got a lead on the noise we’ve been troubleshooting. The noise is coming from a broadcast RF source between 2200 and 2500 MHz. Let’s check with the FCC and see what is allocated to that spectrum to get an idea of where this interference could be coming from.”
“Right.”
Here’s the full FCC allocation map– or at least a snapshot from 2011.
These terms are all equivalent for most purposes:
metric = ISO metric = ANSI mm
English (US) = imperial (UK) = UTS = ANSI inch
Metric screw sizes are easy to figure out.
M3: The “M” is for metric, and the “3″ is the major (nominal) screw diameter in mm.
English screw sizes are easy for large screw sizes.
1/4-20: 1/4 inch major diameter
For smaller screw sizes, read the next section.
Two common sizes of small machine screws are #4-40 and #8-32. What do these numbers mean? As it says above, the second number refers to the thread pitch, and is reported as the threads per inch. However, the first numbers, the major (nominal) diameters, are a bit more complicated. Here’s how to convert them into inches:
major diameter in inches = 0.060 + (0.013 * N)
Where N is the first number in the name of the screw.
To denote the thread pitch, the two main systems use different measures which are actually the inverse of each other. For metric screws, the pitch is measured in mm per thread. For example, M3 screws are typically 0.5 mm per thread. For English/imperial screws, the thread pitch is measured in threads per inch. For example, 1/4″-20 screws are 20 threads per inch.
UNC, UNF, UNEF
These are from the UTS (Unified Thread Standard). It’s for English/Imperial screw sizes. Each screw size (nominal diameter/major diameter) is available in either a coarse (UNC), fine (UNF), or extra fine (UNEF) thread pitch; e.g., UNC = UNified thread standard Coarse.
BSW, BSF, BSC
BSW stands for British Standard Whitworth. Joseph Whitworth authored the first national screw standard in 1841, and it still carries his namesake. BSF is the variant with fine thread pitch. BSC is a variant used for Cycles (motorcycles and bicycles). UNC is based off of the BSW standard, but with a different shape to the threads. In some applications, UNC and BSW are interoperable. For example, the screw mount at the bottom of SLR cameras for tripod attachement is a BSW 1/4-20 standard, but UNC 1/4-20 screws can often be used in them.
One time in London, I needed a fine pitch tap and die set and the cheapest I could find was a BA set, so I bought that. The BA screw standard isn’t used much any more, but it’s an interesting standard.
The last post was about cage-style optomechanics. This post is about Faraday cages.
In the post about alternative optomechanics, I mentioned 8020.net. They will custom build cages, sending you the cut extruded aluminium pieces, hardware, and fasteners.
Paletti is another source to try. They have a range of extruded aluminum profiles and hardware. They also have CAD files for their products, so you can mock it up yourself. Many of their aluminium extrusion profiles can be cut fairly quickly with just a hacksaw, so you can buy lengths and cut to fit your application.
Cage systems, like optical rails, are platforms for constructing custom optical systems.
Thorlabs’ 16 mm, 30 mm, and 60 mm cage systems are well known (shown above). The numbers refer to the on-center square spacing of the four 6 mm rods that form the backbone of the cages (4 mm rods in the case of the 16 mm cage system). There are some lesser-known cage systems as well.
Edmund Optics recently launched a line of cage system optomechanics. Many of the pieces may fit (or fit with minimal modification) items in the Thorlabs system since they also use 6 mm rods. More broadly, Edmund Optics actually has an excellent line of optomechanics that includes a lot of products that go beyond what Thorlabs offers. For example, these z-axis brackets.
Here is Newport’s impenetrable cage system. Personally, I think it was a brave choice to hire M.C. Escher as an optomechanical engineer.
Formerly known as the infinitely more pronounceable Linos, their Microbench and Nanobench lines are excellent. On paper, they should be compatible with Thorlabs 30 mm and 16 mm cage systems, respectively, but in practice I find that there often needs to be just a little bit of modification– e.g., widening holes slightly. Maybe this is due to English-to-metric round-off errors, or different tolerances.
CVI Melles Griot and Siskiyou both have excellent lines of optomechanics, but no cage systems as far as I can tell.
Elsewhere on Labrigger:
Alternative Optomechanics
I’ve referenced Toolduino before. Now I use Firmata more (upon which Toolduino is based). It turns the Arduino into a simple interface, rather than letting it think at all. I find this handy for prototyping up custom interfaces and checking the low level electronics. It’s cross-platform, of course.
These screw shields make it simple to connect a bunch of stranded wire to an Arduino. This one is available here, or here. It’s a little thing, but it saves a lot of soldering.
GIMP is an open source image editing program. You can use it for a lot of the same things Adobe Photoshop is used for.
They just released version 2.8 (release notes).
In addition to GIMP, be sure to keep up with Inkscape, an open source vector graphics/illustration program. You might be able to do without Adobe Illustrator better than you think.
You can even typeset math equations using TeX. (link)
Both GIMP and Inkscape are available for Windows, Mac OSX, and Linux.
Writing a first draft is almost a completely different sport compared to editing and revising. It’s the most creative part of the writing effort. The work flow incorporates outlines, research notes, references, organization, re-organization, and more. I’ve recently been trying out a new program for writing first drafts: Scrivener.
Scrivener (Win and OSX) is a program designed to seemlessly combine word processing with several other writing tools including note organization, outlining, equation editing, and layout. It can work with EndNote (youtube), too.
It’s great to have all of these other tools right at hand and integrated. There’s less task-switching time.
The only shortcoming I can see is the lack of a “Track Changes” function like Word has. So it’s not great for collaboration, but it might reduce the time until the first draft gets done by reducing the time it takes to refer back to notes and other materials.
