2. A line segment from the tooth profile is mated
to the face of the spindle shaft. As in real life, this
is a sliding engagement since the tooth component
still has several unconstrained degrees of freedom
in the assembly.
3. Last, a Limit-Distance mate was used to control
how far the jaw is from the drill bit. This does not
mimic the real-world behavior of the chuck. To do
that we could have used interference detection between the bit and jaw during mouse drag. We have
ulterior motives for preferring mates to precisely
Limit-Distance mates are great for a mouse drag
within the limited range of the mate. Such mates
make it easier to pose the model while making various still shots. The limit mates help to goof-proof
the motion during live presentations of the model.
Without a limit mate, a drill bit could pass through a
chuck jaw, for example.
Our work goal according to the original proposed
scenario also includes animations (videos) to go
along with the still shots needed for print. Distance
mates with a single value are handy as controls
when creating animations. Values can be controlled,
whereas limits are beyond the control of certain animation programs.
Now it’s time for the CAD quiz summary. In Figure
2d we see the result of setting the distance mate between the jaw and the bit. This starts a chain reaction in the mates we have set up. The jaw must stay
in contact with both the inside cone of the shell and
with the flat face of the spindle. As the jaw moves to
the specified distance from the bit, the chuck shell
is pushed away from the spindle. The shell drags
the chuck nut along with it. The screw mate with
the spindle and chuck nut causes the chuck nut to
spin about the axis of the spindle and to unscrew
from the chuck nut. Thanks to the frictionless magic
of 3-D CAD, the behavior of the mated parts in the
chuck is visually similar to a real-world machine.
Another product feature is emphasized in Figure
2d: The jaw teeth get closer to the chuck nut as the
distance from the bit is increased. A gap of 0.027
in. is shown in the illustration. As a side note, this
chuck design can almost open up enough to grip a
0.234-in.-diameter bit. We’re looking at a 0.117-in.-
dia. drill bit in Figure 2d.
What happens if that gap between tooth and nut
goes to zero? At that point, the jaws cannot open
any farther, and the chuck will simply unscrew from
The page upon which this article is published presents static illustrations very nicely. If you’re interested in the dynamic details of motion and modeling of this hand drill, we encourage you to download
the SW15 model to study that media also.
Behind the scenes, we’ve used configurations of
the CAD model to display various props and modes
of operation. We also use configurations to toggle
the model from drag mode to movie mode.
The objective behind our mate management
plot is to suppress limit mates that were useful for
mouse drag and unsuppress mates that rigidly lock
the model in position—perfect for a Motion Study, a
brand name for animations.
A Motion Study will then be used to change the
value of various distance mates over time. This creates repeatable animation. This is a topic for a separate article, but these types of animations use key
points in time to set a value. For example, at time
1:00, the mated distance is 0.234 in., while at time
2:00 the distance is 0.117 in. When the animation is
played, the Motion Study varies the mated distance
within the specified key points.
Here are a couple of links to example videos that
show how our chain of mates behaves when the distance to the drill bit and jaw tooth is varied: https://
youtu.be/66ey6lNiyvw and https://youtu.be/JBseb
RuQCEU. We also added some motors to make things
turn, added a camera, and flew around the model.
Creation vs. Show and Tell
The CAD tools demonstrated in this article are well-suited for engineering, design, and development
of mechanisms. The mates constrain the model to
behave in a controllable and predictive way. Sometimes the required chain of mates gets exotic. Nonetheless, these are outstanding tools for designing
tools, gear-driven hand drills, for example.
What if you just need documentation for assembly and ownership of a tool like a hand drill? Is all
of this mastery of mates required? Stay composed.
We’ll be looking at other tools that use 3-D CAD
models to prepare documentation.
Gerald Davis uses CAD software to design and develop products for his clients at www.glddesigns.
com. From 1984 to 2004 he owned and operated a
job shop. Gerald would love for you to send him
your comments and questions. You are not alone,
and the problems you face often are shared by others. Please send your questions and comments to
The jaws are about to clamp. The challenge is keeping
the jaws away from the bit. Jaws are separated by spring
pressure and trapped by the inside cone of the chuck.
The jaws are clamping. The challenge now is keeping the
jaws equally spaced and in contact with the cone and in
contact with the face of the spindle.
Sketch elements are used for mating the jaw to the bit,
to the cone, and to the spindle. A parallel mate between
plane in jaw and plane in casting keeps the jaw moving
nicely for illustration purposes.
The mate scheme used to position the chuck tooth is
shown to the left. Note the measured gap (0.027 in.) between the teeth and chuck nut. At a 0-in. gap, the jaws
open to accept almost 0.25 in. diameter. This image is
an example of how function follows form and how one
might reveal the consequences for design review.
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