Month: September 2012

Reader:  OK, so I need to build a testing setup of some sort, which will be permanent. That means it will sit in my lab and be ready for use, so I can just walk in and make measurements in a few moments, without wasted setup time. It should be permanent for at least a year or more. My boss suggests I use an Optical Breadboard Bench and set up my components on that. Is this the best way to go, in your opinion, Tony?

Tony:  Well OK, in my opinion, NO it’s not the best way to build a permanent testing setup. Unless you need the actual features of a Breadboard Bench, which I discussed in my last post, I recommend you do not use that Breadboard. Why? Several reasons come to mind, which have all happened to me before. First and foremost reason: You just got that testing setup perfected and it works really great. It has been 2 weeks in the lab, left undisturbed and willing and able to help you test stuff. Suddenly, some engineer with way more clout in the company comes in and NEEDS that bench for his testing. Since the boss respects his clout more than yours, your equipment comes off the bench and his goes on. (In companies, clout counts, and not necessarily common sense.)

Second reason, with Breadboards, those evenly spaced 1/4″ x 20 tpi holes seem convenient at first glance, but when you go to install your hardware exactly where you want it, those holes always seem to be in the wrong place. Off by 3/32″ or some other equally dumb amount. Either you have to monkey around with several adapters to get stuff to fit right, or you have to file holes into slots, so they are almost breaking out from the metal surrounding.

Third reason, hardware made for breadboards often rely on post holders and posts to hold components. It’s supposed to be convenient. Well maybe in the university lab it’s convenient to set up some demo or some experiment for teaching principles to students. But in a real-life testing setup, when you’re counting on it to work right every time, not so much. The first time that manager person comes into the lab to show your brilliant test setup to some customers, and bumps the detector (sitting on a post in a post holder) with their elbow, your detector (which took all day to align) is now facing the calendar on the wall instead of the light beam’s axis! Hey, you can easily bump it with your own elbow too.

Reader:  Well what am I supposed to do, Tony?

Tony:  Get yourself a nice thick piece of aluminum tooling plate which will be as long and as wide as you would ever need. Aluminum tooling plate is pretty flat on both sides, too. Attach your optics, adjusters, electronics, detectors, etc. exactly where YOU want them to be, by drilling and tapping that plate for any size screw you think is appropriate for the task. (Does not always have to be 1/4-20 screws.) YOU are making the decision on where those tapped holes shall be, not some mechanical engineer who is just designing a product to sell. For goodness sake, do use machine screws though. Wait, you don’t know how to drill and tap holes in aluminum? For goodness sake, you had better learn how to drill and tap for machine screws, and soon! Unless you have a good technician or a good machinist who is always at your beck and call, you had better get proficient at drilling and tapping, in aluminum, steel, and soft plastic.

One final thing. To support your optics and equipment, do not plan to use posts and post holders, unless there is a compelling technical reason for using them! Learn how to mount stuff on brackets which are firmly bolted in place and can not rotate or move the first time a person (you or the manager) accidentally bumps them with their elbow. You can buy nice construction components or construction kits, with brackets and cubes, etc. If the equipment is shaped weird or is big and heavy, make your own brackets. Learn how to design and make your own brackets and mounting hardware to suit a specific application. Mount components on that tooling plate rigidly, as though it had to go into space.

Reader:  Machine metal? Are you nuts?  Tony, I am terrified of using a drill press, much less a mill or a lathe!

Tony:  OK. Machine tools are dangerous and you should always get proper training on how to use them, safely!  So, in that case, get that good technician or a machinist who is always at your beck and call to fabricate the parts you need. If your company, school, etc. does not have a machine shop and machinist at all, you can design the parts, even if you have to do it on the front of an envelope with a pencil, and take it to a local machine shop in your town, to get a quote. Most machinists can make things like “brackets” to hold optics or components on a plate, without any trouble. By the way, when you find a good machinist and shop you trust, do cultivate their friendship and give them your business. They can be life-savers in industry.

Mount your optical testing stuff on that plate. Do your testing. If that engineer with all the clout comes in and needs the wooden table you have your tooling plate sitting on, (sigh) you and your technician can pick up the plate with its permanently mounted testing setup and equipment, and put it on your desk in your office for a few days, if need be, while that guy does his tests in the lab. Here’s the point my friend:  If that tooling plate and its rigidly mounted components are really put together well, you should be able to pick it up, move it to your desk, then bring it back later, and still have it aligned and working fine!   Do good work!

As the title implies, do I always need one of these, and which one do I need, and why oh why are they so expensive?

The quick answer is NO, you do not always need to use an Optical Rail or a Breadboard. For example, many good opticians do excellent work in their shop using very simple testing aids, such as lots of wooden blocks. I’ve seen opticians test large mirrors which were supported on wooden stands and blocks. It really depends on the type of testing you need to do.

When do you really need an Optical Rail?  When you have a bunch of optics hardware which is made specifically to reside and slide on a rail, and these are what you need to use, you probably ought to have that rail. Sounds kind of dumb, I know. But I have been faced with that problem in a lab. We had a bunch of really nice rail-mounted testing hardware, but no rail to be seen anywhere within 3 miles. That is just frustrating. If you need to slide one or more optical elements or detectors, etc. so that they move (smoothly) relative to one another, and then can be locked down where you want them to stay, you probably ought to have that rail so you can do your work. If you want to keep some optics fairly aligned to one axis, it might work. If you cannot afford to purchase a full-on Breadboard, or you do not have a crane to pick it up and move it around your building, there are some inexpensive Optical Rails with various attachments and hardware mounts which can be obtained from optical supply houses. If you must do your testing on a wooden bench, etc., then the Rail might be a helpful aid.

When do you really need an Optical Breadboard Bench? If you need to mount lots of optics and components all spread out on a 2-dimensional surface, and you want to be able to attach them to it (breadboard style) with all the same fasteners (usually 1/4-20 machine screws in the USA) then you probably will love a Breadboard Bench. They have a matrix of accurately spaced 1/4-20 tapped holes all over the flat surface, which by the way, can be quite flat! What usually happens is a lab is set up with a comfortable budget, so they buy a couple of massive 4 ft x 8 ft benches with super good support legs. (These wind up being heavy enough to use as anchors for the Queen Mary I.) Then 90% of the time, the optical setups they do require a tiny fraction of the space available on them. Oh well; I should not fret about stuff like that. These benches can be obtained in many styles, including some which have clever internal mechanical structures which reduce vibrations a lot, at least over certain frequencies!  In case you simply do not have the budget, or perhaps do not have enough space for a ship anchor in your lab, you can also buy small Breadboards which are made to order, and are thin and light weight, which can be better than other options. I once had one I could pick up and move myself. If you plan to do serious interferometry where you will be counting fringes or using software to analyze the fringes and patterns, you are going to wish you had a good, heavy, monster bench, and have it mounted on an air piston isolation suspension. Unless you are working inside a subterranean cave, you will probably experience nasty vibration problems with any flimsy support table for your interferometer setups.

Why are they so expensive?  Cause they are complex to build. If you don’t believe that, try making one yourself. And because the manufacturers have a captive audience.

OK, I have to do a test on a lens I have. I have this gadget called a lens holder which looks like a large open clamp, with an adjustment screw, which when turned tightens the rubber covered clamp tines around the edge of a lens.  It kind of reminds me of a clamp I used in chemistry lab to hold some glassware equipment? Is this thing the right way to hold my lens? Do I need a more sophisticated holder?

Well, we older folks have all been there at some time.  The true answer is, it really depends on what you are trying to do or measure regarding that lens. If you intend to make a quick and dirty measurement of the focal length of the lens and you are going to use a wooden desk ruler and a 3″ x 5″ index card to see the “image” etc., well then that clamp they gave you, which might be designed to hold an Erlenmeyer flask in the chemistry lab, could be good enough. You might have a budget of zero. We would understand.

But, if you are trying to do a sophisticated test or measurement, you will benefit from having a more sophisticated holder. There are so many what-ifs to answer.

Do you need to hold a bare glass lens or a lens in a barrel or housing? Do you need to tilt it around some axes in order to align its optical axis with something? Are you going to measure its image in air with some kind of measuring microscope? Are you going to try to “focus” that lens’s image to a fixed focal plane in space or on a detector you have? Or, (good grief) are you going to have to do interferometry using that lens? The Erlenmeyer flask clamp may not work at all in these cases. This post will get horribly long if I try to consider all of these possibilities in detail. So, to keep this one short, let’s say:

There are many kinds of opto-mechanical lens holders available. If you expect to make very small angular adjustments or very small linear movements with that lens assembly in order to make really accurate (or repeatable) focusing, or (good grief) interferometric measurements, then you are going to need a good, sturdy, stable, adjustable, lens holder, which may cost much more than that lens you have to work with! Even when the boss tells you that your measurement budget is “zero,” the fact is that your time spent in the lab is costing way more than zero. Time wasted on making a “serious” measurement or a “go/no-go test” on a lens will be worse than wasted, if your results of the test are erroneous because they gave you a cheap clamp to use.  Do good work!