The Use of Computer-Aided Design (CAD) in Clockmaking - part 1

 

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The Use of Computer-Aided Design (CAD) in Clockmaking 

By David J. LaBounty, CMC  FBHI 

 
 
21

st

 century clockmaking uses an interesting mix of antique and modern tools.  And, 

being constantly tool-poor, clockmakers are always on the lookout for that rare utensil 
which will speed up the restoration process.  One of the modern tools that fit that 
category is the computer.  Using a program called computer-aided design or CAD

1

, 

clockmakers can design, alter, and manipulate a clock part, working out the bugs long 
before the actual piece is made.  The uses for CAD in clockmaking are limited only by 
one’s imagination! 
 
 

Drawing an Escapement:

  

 
As an exercise in the capabilities of a CAD program, let’s walk through laying out a dead 
beat escapement as described by Ward L. Goodrich in his book, The Modern Clock 

2

. 

  
To get started, Goodrich says:  “Draw a line, AB,… to serve as a basis for 
measurements.”  (fig. 1)    Then, “…draw from some point C on this line a circle to 
represent the diameter of our escape wheel.”  (fig. 2) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
To follow Goodrich’s example, we will draw the pallets for a 30 tooth escape wheel 
spanning 7 ½ teeth at a 90

0

 angle.  “We now take 90

0

 and, dividing it, set off 45

0

 each 

side of our center line and draw radii, R from the center to the circumference of our 
circle;  this marks the beginnings of our pallets.”  (Fig. 3) 
 
 

Fig. 1:  Step one in drawing 
Goodrich’s dead beat escapement.  
Line AB.

 

Fig. 2:  Circle P representing the 
circumference of a two inch diameter 
escape wheel.  

 

2

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
“Now to find our pallet center distance we draw tangents, T (at right angles), from the 
ends of these radii toward the line of centers.  The point where they intersect on the line 
of centers is the pallet center.”  (Fig. 4) 
 
Giving each pallet two degrees of lift, “we draw a line two degrees inside the tangent, T 
(towards the escape wheel center), from our pallet center on the entering pallet side and 
another line from the pallet center two degrees outside of the tangent, T, on the exit pallet 
side.”  (Fig. 5) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Fig. 3:  Radii R, 45

0

 away from line AB, 

showing the amount of escape wheel the 
pallets will span. 

Fig. 4:  Tangents T showing the pallet center 
distance  at their intersection. 

Fig. 5:  Lines representing two degrees of lift on 
the entrance and exit pallets.

 

Fig. 6:  A circle, centered at the intersection of the tangents, T, 
and meeting the point of intersection between tangents, T, and 
radii, R.  This circle represents the lock faces of the entrance 
and exit pallets. 

 

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Next, from the pallet center we draw a circle “cutting the tangents, T, and the radii, R, 
where they intersect;  this gives us the locking planes on which the teeth of the escape 
wheel “run” (slide) during the excursions of the pendulum, if the escapement is to have 
unequal lockings…”  (Fig. 6) 
 
Following Goodrich’s example gets a little fuzzy here, but sticking with an escapement of 
unequal arm length, we can draw the lifting planes “at an angle of 60

0

 from the radii, 

R…”  to determine the pallet thickness. (Fig. 7)  Finishing the outline of the pallets can 
be done by drawing an arc from where the lifting plane intersects the lift reference line on 
the entrance pallet and another where the lifting plane intersects the tangent line, T, on 
the exit pallet.  (Fig. 8)  This completes the escapement drawing and all that’s left is to 
attach them to arms. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The accuracy of the CAD program makes laying out a set of pallets quick and easy.  The 
finished design can be printed to scale and used as a pattern for roughing out a set of 
pallets.  (Fig. 9) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Fig. 7:  The lift planes of pallets of unequal length, 
drawn at an angle of 60

0

 from radii, R. 

Fig. 8:  The edges of the pallets can be drawn from the 
intersections of the lift planes with the reference lines.

 

Fig. 9:  The completed pallet design can be printed to scale and used as a 
template.

    

 

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Another pallet design has the pallet arms the same length.   The layout proceeds exactly 
as before; producing line AB, circle P with center C for a 2” diameter 30 tooth escape 
wheel,  radii R, tangents T, and the two 2

0

 lift lines.   The circle from the pallet center 

now represents the mid-point of the pallets instead of the lock face.  (Fig. 10) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
“If the pallet arms are to be of equal length,” Goodrich continues, “the arc for the 
entering pallet is drawn three degrees below (outside) the radius, R, while that on the exit 
pallet is drawn three degrees above (inside) the exit radius.”  (Fig 11)  Goodrich errs here 
since this will produce pallets which have an overall thickness of 6

0

 and wouldn’t leave 

any room for drops or tooth tips.  (6

0

 x 2 pallets x 30 spaces = 360

0

) I suspect Goodrich 

means for the total pallet thickness to be only 3

0

 

which would necessitate drawing arcs 

1.5

0

 below and 1.5

0

 above the radius, R.   (Fig. 12) 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Fig. 10: 

 

A circle, centered at the intersection of the 

tangents, T, and meeting the point of intersection 
between tangents, T, and radii, R.  This circle 
represents the mid-point of pallets with equal arm 
length.

 

Fig. 11:  Two circles representing the lock faces of the 
pallets, offset 3

0

 from radii, R.  This will produce 

pallets which are too wide for the escape wheel, 
however.

 

Fig. 12:  Two circles representing the lock faces of the pallets, offset 1.5

0

 from radii, R.  This 

will produce pallets which are the proper thickness for the escape wheel and leave room for 
drops and tooth tips.