Radiometer Demostration Lamp





Introduction: Radiometer Demostration Lamp

About: I like to read all about the creative ideas everyone has here. I love to make "one of" projects, learn something about doing it and then move on to something new. Hope you like my ideas. email me...

Another idea purged from my head an into reality...  I had a radiometer for the longest time on a shelf never really doing anything as it was no where near a light source to make it spin.  That and a few extra meters I had laying around gave me an idea to combine them into a demo box.  I decided to design it with a very clean "test box"   industrial design versus making it victorian elegance.  So is it Steampunk?  No... more industrial punk I guess or is it diesel punk?  You decide and please comment on the style.

Lastly on design, I wanted the lamp to also function as a pseudo night light so I gave it some high intesity LEDs for an underglow.  Let's get started:

Costs:  Hickory $26 for 1" x8' long x6" w
Bulbs: $10 from eBay shipped.
Radiometer:  $12 from Edmunds Scientific
Meters: about  $8 each from a lump sum purchase from eBay.
Leds: $2.69 each x 7 = ~$20
Dimmer & Pushbutton sitches: $12 total.

Step 1:

After designing the lamp, do all the woodworking for the case:

Wood choice is Hickory.  I never worked with it before, so I thought I would try it.  It will probably be my first and last project in hickory too.  It worked like a cross between walnut and very hard oak.  Very oily and a very nice grain structure as in walnut but it is VERY chippy.  I knew this going into the project so I kept all cuts at 90 degrees - no routing edges.  You really need special hook angles to route/shape this kind of wood to prevent chipping which I did not have.  Even then, straight cuts had some small grain chips I had to sand and sand to make it look good.  Also I knew hickory can be a tough wood to stain (blotchiness as in maple is an good comparison).  But that doesn't bother me as much because I think it just shows the character of the wood better.  On a small piece you can get by with this (see the end piece is soooo much lighter than the front).  On a floor it would look terrible.

I finished the hickory first with and oil based Ebony Stain from Minwax.  This stain was jet black and I had it in my stock but I knew the hickory would only really abosrb it very sparingly.  It colored the wood perfectly to what I wanted as a BASE, which I then followed up with a walnut tung oil from Watco.  My feelings on Minwax after using several of their products is that the best place for their finishes is in the can.  I have had several issues on several types of wood with their product and they simply are not a quality stain.  In this case it took FOREVER to dry - even at 72 degrees F and rather dry air.  Here I have my pieces by my air vent to help force the stain to dry.  I have had good luck with the tung oils, only know that they do not do as a good of a job getting the piece dark.  Hence the two step process I used.  In a nutshell, I got the depth of color I wanted but after waiting about three days for the stain to be dry enough to move forward with the tung oil.

Step 2:

Design your circuits.  I used xcel to make sure I wasn't making a mistake on the DC LED circuits and to also help keep me on track for wiring it up.  In fact, when final assembly ocurred, I noticed my voltmeter was not following the dimmer voltage for some reason... Hmmm... had I followed my own drawing, I would have easily noticed I wired it in series versus the required in parallel to the voltage to work.  Doh!  The circuit calculations also helps to protect the LEDs from premature failure so you know you got the right current and voltage drops across them.  Too high and they will work, but not for long.

Then I started to prep for the main devices (Meters and the radiometer).  I used a cut-off wheel on my dremel to carefully cut the pastic base off the glass body pf the radiometer.  It was a very careful process as the base was rather thin nearest the glass neck.  Since the glass is also very thin and to help prevent a possible wheel skip from hitting the glass directly, I wrapped the glass body in duct tape first.  Maybe it wouldn't have helped, but it gave me the confidence to start!  Note I took several passes cutting off small chunks to keep the pressure off the glass as much as possible.  A mistake here is $12 from Edmund's Scientific co.   Whew!  That's done.

Step 3:

Fitting the meters for LEDs is a challenge.  First I used the square - high intesity LEDs for Radio Shack ($2.69 each).  They are very bright and compact and can fit well in a small area.  Open up the meter and look for a location where the led can be superglued or adhered with silicone to a non-functioning area inside the meter.  Be careful to not get glue or place wires where the needle has to swing.  I try to show that here in the second photo. 

Sometimes pulling the meters apart is impossible due to the original manufacturer gluing the outer shell and inside shells together.  This was the case on the 120 VAC meter, so I CAREFULLY used my dremel cut off wheel and cut into the meter wall from the bottom and mounted the LED to shine up through that hole.  Sorry no picture... I forgot to take one.  I then "sealed" up the hole with electrical tape wrapped around the body.  That and the thickness of the face plate holds it perfectly where it will easily stay.  On the DC Ammeter I just siliconed the led right in the direct center of the magnet inside the unit.  After assembly, test the meter function and the LED again or you may find something binding of the needle or not working at all after you placed it in the case and have to start over.  Always check your "tough" work before moving on - it'll save you troubleshooting and disassembly time.  I continue to re-learn this point on every projecct it seems.  UGH!

The underglow LEDS were fitted to a small square of plexiglass (white opaque) that serves as a small bracket to hold and to fasten them to the underside of the case.  They are soldered on the backside then screwed to a relief area cut into the underside piece.  I tested these as well before moving on.

Step 4:

After all the sub assembllies are complete, I laid them out to plan my assembly steps.  This is because I designed my case to have minimal screws showing on the most viewed surfaces like the top.  So the case assembles with added difficulty to getting the wiring done.  I made a new base for the radiometer with a pvc conduit connector and a dowel - epoxy holds it together.

I also had to cut the dimmer's mounting ears off for a closer fit in the width of the case dimension.  It still had two rivet holes I mounted a small wood screw in to the rear of the face plate.

Also prewire as much as you can with long leads then cut to length on final assembly.  Wire is fairly cheap and it will help you get a good fit / space saving when it goes together instead of having to resolder connecctions or have a rat's nest of too much wire in the case.

Step 5:

Finish assembly by using wax on the screws before driving them into hickory.  I broke two stainless #8 screws off that I had to unthread via a vise grip, even with what I thought to be a large pilot hole!  In my design, I had routed out the back of the faceplate to allow for thickness of the switches and dimmer fit up.  Routing this out to 5/16 inch thickness remaining looked good but then I cracked the first faceplate lengthwise when I first test fitted it before staining.  So after a second fabrication of faceplate number two, I left a little more thickness and was very careful to have oversized holes for final assembly to eliminate all stresses as much as possible.  Live and learn.



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    Skycraft Parts and Surplus has Volt Meter and Amp Meter with blue leds built in.

    That is beautiful Sir. Excellent project and very inspiring.


    Very nice! The idea with the bulbs in combination with the radiometer is really great!! Thanks for the inspiration.

    Maybe I am missing something but what are the specs on the meters?
    This is really nice looking, how hot do the bulbs get? Would a class cover of some sort be in order for long term usage to protect from little fingers?

    1 reply

    The voltmeter is 0 -150 VAC, the ammeter is 0-15 mA. The Edison replica bulbs do not get searing hot at all as they are coated with some kind of an amber coating and the filiment is very large and throws off a lot of light at low voltages. I imagine one could get some glass or certainly some plexiglass tubing and slide over a sleeve over them for safety but allow for a gap at the bottom for convection to flow thorugh

    If the hickory is that hard why not drill ,tap & use machine screws ? Sheet metal screws are not designed for a lot of holding power/ torque. Really like your work ! Very pro looking ...

    1 reply

    Thanks! I never tried tapping wood. I would think it would need to be a very coarse thread to deal with the grain. Then the coarser the thread the diameter has to go up so...
    I hear your comment on the sheet metal screw's holding power. If i were to try again I might be inclined to try a concrete screw. Bottom line - what worked was a very generous pilot hole, just enough to grip the sccrew and still hold the cover onto the box.

    Excellent work! This would be a nice addition to any home. I've found screws don't seem to be as strong as they used to be - a result of a throw-away society? Now, probably like you, I predrill and add a touch of grease to the screw. So now it's easier to get the screw in or later when you need to out.

    6 replies

    I always pre-drill to prevent the possibility of splitting, but this hickory was way too hard. I agree with the quality comment. I specifically used stainless for the look as well as the strength yet, I twisted 2 of them off.

    Are you using the right type of screw? Notably:
    * Philips and Pozidrive screws look very similar, yet using the wrong type of bit will rapidly destroy the heads.
    * Pozidrive screws are designed to resist torque; Philips ones are specifically designed to "cam out" when there is too much torque (to resist over-tightening)... and are therefore much easier to strip.

    Actually the screws I used are stainless sheet metal screws with Phillips heads. The heads didn't strip, the body sheared off with the body sheared off almost flush with the case and the head in great shape. Thankfully I was able to use a vise grip and back them out. I then re-drilled the pilot hole out even more, then more wax on the threads. That did the trick. So in short - the phillips held up fine the body material was weak as a sheet metal screw is quite thin all the way down the body versus a true wood screw.

    Actually, you have to be careful with stainless (like brass). Bolt Depot says:
    "It is a common misconception that stainless steel is stronger than regular steel. In fact, due to the low carbon content, stainless steel cannot be hardened."

    Whomever "Bolt Depot" is they are very wrong and should look up the numbers in a metalurgical engineering handbook such as CRC. 304 Stainless Steel is 46,000 psi in Shear, Brass is 31,000 psi, mild steel is 34,800. Stainless steel is way tougher that mild steel because of the carbon atoms fitting inside of the crystalline lattice of the iron atoms. I don't recall if stainless is body centered cubic or face centered cubic lattice, but the bottom line is mild steel will shear more easily because the lattice will slide in sheets, whereas the carbon prevents that from happening. Brass is simply too soft and its lattice is not nearly as locked as in stainless. Engineer here, so whomever Bolt Depot is, please relay the message. :o)

    Engineer? Me, too! Steel screws are made from high carbon steel (not mild) and are heat-treated (which goes to your point about carbon atoms). While it's not impossible to snap a steel screw, in my experience it's certainly easier to snap a stainless one.

    Probably but I'm always wanting to see them with my hands so I can get an idea how things will fit / work out versus buying blind on the internet. Maybe I could do so now looking towards the future!

    I really love the way this looks! Great work. As for the style, I wouldn't classify it as any of the above, as it would most definitely be Atom Punk. As in, this would seem right at home in a 1950's laboratory.

    By the way, what is the name of that particular bulb style? I've been looking to get some of those.