MAKING NICE LOOKING, CALIBRATED DIALS
If you want a real shortcut rather than making a nice custom calibrated dial just use one of the
standard ones above and make a chart mapping the dial values to the actual values. To make a
custom dial, read on.
To make and calibrate your own dial scale, you need a drawing program like Corel Draw [typicaly
vector based - not your average photo retouching program] that will allow you to rotate an object
around a specified center by a specified number of degrees. Use this to create a sunburst
calibration scale with ticks every 90, 10, 5, and 1 degree. Label the 10 degree marks. Or, you can
also just use the sample below.
Temporarily attach the calibration scale to your front panel with masking or clear removable tape
taking care to align it square to the panel and centered about the control shaft. Attach your
pointer/knob and align the min and max positions with the calibration scale. I make my own
pointers by gluing a thin (1/16"), narrow, tapered piece of Plexiglas? or similar material to the
back of a knob. Before gluing it, make a thin black line down the middle of the back side with a
Sharpie? or similar permanent marker and a straight edge and let it dry. Also, clean and rough
up both the dial and the knob surfaces where the glue will be. I use 5 minute epoxy.
Make a calibration chart: For each desired calibration value (frequency, voltage, or whatever) set
the dial so the instrument is generating or reading the desired value verified by whatever standard
you are using (frequency counter, receiver, signal generator, DVM, etc.). Write down the
calibration value and the number of degrees from the calibration scale.
Then use your drawing program to create the actual dial. Create a new drawing and draw
concentric circles for each band or range. I like to make the outer circle/line a bit wider than the
others to form a visual border and allow a little more slop for cutting. I also draw a circle for where
to cut the center hole. At the zero degree line (I usually pick the right horizontal) make a straight
"hash" line between each circle like what you want to mark each value
For each value in your table rotate a copy of the hash mark from zero degrees by the number of
degrees you measured for that point and label it with the value. You can interpolate intermediate
points between the calibration values if the scale is relatively linear in that region. You can trim
the unwanted circle segments with the drawing program, blot them out by drawing a white
rectangle over them or just cut them away after printing.
Save a backup copy periodically and again at this point just in case.. Add any other bells and
whistles (border, colored band markers, wider decade markers, shaded areas, etc.) and print a
test copy on regular paper to check, size, fit, and spot check a couple calibration points. Then
print the final on glossy photo paper if you have an inkjet or some bright white paper for a laserjet.
Cut the dial to the rough shape leaving a little extra all around and apply a piece of thin clear self-
adhesive film (from the office supply store) over the front (and back, to if desired). Smooth down
Carefully trim as precisely as you can around the dial. When done run the edge of a wide black
marker around the outside edge so the white edge of the paper won't show. You might try this om
a scrap first to see how fast/far the black soaks into the paper. Attach a couple small pieces of
masking tape to mark exactly where the calibration dial was before you remove it. Use masking
tape to very lightly hold the new dial in place and check alignment. Then cut 8 or so 1/8" to 1/4"
squares of good, very thin double sided tape. Remove the backing before or after cutting,
whichever is easier and lightly stick the pieces to a sharp corner like on a laminate desktop. Pick
up one of the little pieces with the tip of an Exacto? knife, pin or whatever. Have the knife tip on
top of the tape. Loosen and lift one edge of the dial being careful not to let it slip out of position.
Slip the tiny piece of tape between the dial and panel so it is in past the outer edge by 1/8" or so,
being careful not to let it touch, grab or bunch up. Then set it down against the front panel and lift
the knife away. Verify that the tape is flat before pressing the dial down. Repeat at several other
points around the edge. On a large dial you may need some interior attachment points. In that
case start at the center and work out.
Sample dials below, text on howto follows.