Possible Condensation Solution? - Test Data

Since I was going to be spending the whole day gluing up slabs for RP doors, which is boring as hell, I decided to try a test of the idea I had about using a light bulb inside of the machine cabinets to ward off condensation and rust. I'm no scientist, having spent my undergraduate years as a lowly philosophy major, so my testing may not be up to snuff - I did the best I could. I figured I'd gather up some data and ask smarter folks what it means.
My shop ain't Dexter's Lab, by a long shot, so I had to work with what was available to me. Since I was going to be using the tablesaw during the day, I decided to run the test using the shaper as a test subject. The tablesaw has a lot less surface area overhanging the cabinet enclosure and would perhaps respond better to the light bulb treatment.
Problem: When a cool/dry air mass is followed by a warm/moist air mass and the transition is somewhat rapid, as sometimes occurs in my area of Pennsylvania in the Spring and the Fall, condensation forms on the cast iron surfaces of the stationary machinery, causing rust.
Proposed Solution: An incandescent light bulb, left on overnight, mounted within the cabinet, may provide enough of a rise in temperature over the ambient temperature/dew point to eliminate condensation and rust.
Test Subject: Delta "Platinum Edition" Cabinet Shop Shaper.     Cabinet Enclosure: Sheet Metal - 19-1/2" x 19-1/2".     Top: Cast iron - 40" x 27".     Note: Cast Iron Top overhangs Cabinet Enclosure by 10-1/4" on each side and by 3-3/4" on front and back.
Heat Source: Sixty Watt Incandescent Bulb in Clip On Fixture, mounted 2" away from under side of cast iron top, within cabinet enclosure.
Test Instruments: (1) Amprobe Digital Sling Psychrometer, Model THWD-1, (2) Unknown Brand Digital Thermometer/Hygrometer (Note: This was not capable of decimal readout, so all numbers for it are whole), (3) Aquarium Thermometer, of the type intended to be applied to the exterior surface of the glass on an aquarium - mounted on the edge of the cast iron top (Note: this was not tested against the other two instruments but was put on in an attempt to gauge the actual surface temperature of the cast iron top - it is only capable of reading out in two degree increments). The instruments (1 and 2) were sat next to each other for one hour and gave the same readings (within their abilities) before the test.
The Test:
The Unknown Brand Thermometer/Hygrometer was left at the workbench and the Digital Sling Psychrometer was used at the Shaper, which was approximately 8' away. True surface temperature of the cast iron top could not be measured with the instruments at hand. The Digital Sling Psychrometer was laid on it's side, with the sensor approximately 1/2" above the cast iron surface.
The Digital Sling Psychrometer was positioned in the approximate center of the area over the cabinet enclosure in Test Position "A" and was positioned approximately 1" from the edge of the overhanging portion of the cast iron top in Test Position "B". The approximate distance between the two test positions was 19". The instrument was moved from position "A" to position "B' at half-hour intervals.
Results:
At Test Position "A" (center of cast iron top, over cabinet enclosure).
Hour    Temperature/Ambient    Temperature/Test Position "A"
0    63f            62.2f 1    63f            67.1f 2    64f            68.2f 3    63f            68.4f 4    63f            68.4f 5    63f            68.7f 6    63f            68.4f 7    62f            67.8f 8    62f            67.2f    
At Test Position "B" (approximately 1" from edge of cast iron top).
Hour    Temperature/Ambient    Temperature/Test Position "B" 0    63f            62.2f 1    63f            63.8f 2    63f            64.3f 3    63f            64.6f 4    63f            64.6f 5    63f            65.0f 6    62f            64.6f 7    62f            63.5f     8    61f            63.9f
NOTE: At the end of the test, the aquarium thermometer, applied to the surface of the cast iron table, read 68f next to Test Position "B", when the Digital Sling Psychrometer read 63.9 at Test Position "B". It read 76f next to Test Position "A" when the Digital Sling Psychrometer read 68f at Test Position "A".
Conclusion: Damned if I know. I'm hoping that some smart person can tell from the data if the light bulb idea will work.         
Regards, Tom Thomas J. Watson-Cabinetmaker Gulph Mills, Pennsylvania http://users.snip.net/~tjwatson
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Hi Tom,
Here's a couple of observations regarding the condensation:
1. A 60 watt bulb will generate quite a bit of heat. It will also die an early death IF you run it at full voltage. Try a 100 watt bulb, but instead of connecting it directly to the line, install a 3-amp, 200 volt diode (Radio Shack P/N 276-1143, $1.39) will work just fine) in series with the hot (black wire or brass screw) lead. What this does, is only allow 1/2 the voltage to flow through the bulb. The bulb burns a bit less than 1/2 bright, and much more red in the spectrum. It also REALLY lengthens life. Had a yard light that would blow a bulb everytime I hit the post mowing the lawn, or even if the paper delivery person kinda bumped it with their sack of papers. I was getting 2 weeks max on a bulb. Installed the diode, bulb was going for over two years (may still be going, we sold that house and moved). By moving from a 60 watt bulb to a 1/2 lit 100 watt bulb, you are losing just a little bit of heating, but the bulb will last longer.
2. Condensation is a problem in many areas. One difficult area was on the radar indicator on several different classes of Coast Guard Cutters and small boats. The "old" equipment was full of tubes, and never had a bit of a problem, but the new solid state radar indicators (well, except for the cathode ray display) had severe condensation problems. First attempt was to seal the indicator up ... which fails because when you heat the sealed box, it's pressure goes up and will blow past the door seals. When it cools back down ... yep, creates a vacuum which draws in damp air, and the effect is a very nicely sealed box full of water.
The answer there was to install a heater strip ... looked all the world like a power resistor, but was designed to conduct heat both to the chassis where it was mounted, and to the surrounding air. If the light bulb test works and you want to eliminate the dangers of a broken bulb, you may want to look further into this possibility.
3. The simplest answer may simply be to get one of those double jointed drafting table lamps, and simply turn the lamp on and put it close to the top surface of the equipment you're working to protect. Put a fairly small bulb (25 watt) and move the lamp real close ... and you'll heat the top surface. Might need two lamps, but I think they're what ... $8.95 each ( http://www.draftingequipment.com/DEW/products/suppliespaper/Lamps/combo&swing.htm ) ... that's the name ... swing arm lamp. This has several benefits ... first, it's cheap. Second, you can use the lamps in the shop for spot illumination when needed. Third, you won't forget that you left a lamp on that's buried inside the cabinet. Fourth, it's cheap. Fifth, you'll be able to adjust the lamp position for optimal heating (without overheating) ... so you don't dry out the lubrication on the trunion and tilt assemblages. Sixth, it's CHEAP!
It sounds like you were measuring the air temperature immediately above the table, and not the table surface temperature. An infared pyrometer is just the ticket, but at about $300.00 for a good one ... probably more than you'd like to spend for a one-shot deal. If you have an electronic thermometer ... one for cooking (it has a nice wide range as opposed to a digital oral/rectal thermometer (1) that has a very narrow temperature range) you can make direct contact with the surface and read the temperature. Mark several spots on the table surface by circling the area with a pencil, and measure the temperature at all of these points everytime you need a sample. Averaging the temperatures will give you an overall indicator ... likewise, mapping the temperatures will give you a reasonable temperature gradient to help determine if you are heating a localized spot, or diffusing the heat throughout.
HTH
Rick
Who will get back making sawdust "Real Soon Now"
(1) I don't EVEN need to go there!

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Thanks, Rick. You gave me some interesting things to think about.
Regards, Tom Thomas J. Watson-Cabinetmaker Gulph Mills, Pennsylvania http://users.snip.net/~tjwatson
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Damned right rapid. One fall day I had the garage door open under those circumstances. Cool from the last couple of days, then a farm front with high humidity. I could see the rust forming on the table top from front to back right before my eyes. I grabbed nearby paper towels and could not stop it.
That is the day I decided to change from wax to Top Cote. Ed
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