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 Enclosu 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