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Cover Sheet for Exemplary Lessons/Units Project

Faculty Member Name: D. BARNHOUSE Date: 5/24/06

Organization: SolidWorks

Title of Lesson/Unit: Bolt Circle Pattern – From Design to Construct – Engineering to
Manufacturing – Drawing for Construction

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Science, Technology, Engineering and Math) STEM Concepts Addressed: This
lesson provides an overview for the design process of creating a bolt circle pattern to be
manufactured on a steel plate. It involves the basics of creating the geometry (drawing)
in Solid Works and then retrieving the information (X and Y centers) necessary for the
machinist to construct the part. Understanding the needed information that the
machinist needs in order to engineer a production part is essential in the design process
for accuracy and efficiency.

The drawing will give information based on the lower left hand corner of the part as the
datum point. All bolt hole centers will be based upon their X and Y relationship to the
lower left hand corner of the plate.

Length of Instruction period: 50 minutes

How many periods needed to implement lesson unit: 1

Objectives:
1. Creating a steel plate with a bolt circle pattern
utilizing Line, Circle, Circular Step and Repeat,
and Extruded Boss/Base commands on Solid
Works.
2. Calculating X and Y coordinates for CNC
(Computer Numerical Control) or Manual
Machining.
3. Understanding the need for location points in
Engineering for industry.

A bolt circle pattern is the diagram that indicates a series of holes drilled in a polar
fashion around a point that are equally spaced both by degrees and by the radius
indicating the centers of each drilled hole. This is used quite frequently by industry as a
means of fastening housings over shafts, gear boxes, etc.
For a CNC machinist or programmer to be able to program the milling machine to drill
this series of holes, that machinist will have to have the X and Y center locations for
each hole. This location point is essential because the machines that drill these holes
base the location upon the center of the drill.
Some programmers choose to locate the centers according to the center of the part,
(especially if the part is circular). Other programmers choose to locate the centers
according to a datum point located on a specific edge of the part.
In this exercise, we will develop a 6” x 6” x 1” steel plate with a bolt circle pattern.
We will then retrieve the data necessary for the CNC Programmer to program this part to
be drilled by an origin being located at the lower left corner of the plate.

Materials: SolidWorks, paper and pencil

Procedures:
 Create a new part on SolidWorks using the front view as your starting view.
 Sketch a rectangle using the origin for the lower left corner as 0, 0 (0 on X axis
and 0 on Y axis).
 Dimension the rectangle to be 6.00 by 6.00 square.
 Sketch a vertical and a horizontal center line through the middle of the part.
 Sketch a circle with a 2 inch radius or 4 inch diameter at the intersection of the 2
centerlines. This will be the center of the bolt circle.
 Sketch a circle with a .375 diameter at the intersecting point of the top quadrant
of the 4 inch diameter and the vertical centerline.
 Under Tools, then Sketch Tools, select Circular Step and Repeat.
 Under Arc Radius type in 2 inches. Under Center for X type in 3. Under Center
for Y type in 3. Under Step Number type in 8. Then Under Item to repeat, left
click inside this box and then select the small circle from the part.
Then select OK.
 Under the Features tool, select Extruded Base/Boss. Under selected contours
select any area outside the bolt circle and then also select an area inside the bolt
circle (not a small circle). Under Depth type in 1 inch. Then select OK.
 To find the X, Y, and even Z coordinates of each small circle on this plate, just
click on a small circle. When it turns green, this information and the diameter of
the hole will be displayed in the lower right hand area of the screen.
 Then determine these coordinates for each hole in the same manner by selecting
them.
 A drawing from the part can be made to indicate each of these with dimensions
originating from the lower left corner to the center of each hole can also be made
to show this information.

Assessment: On their own, have the students to create a plate that is 5.50 inches wide
by 5.50 inches tall by .50 inch thick. Then draw a bolt circle diameter of 2.50 inches with
6 equally spaced drilled holes with the diameter of .25 inches each. Have the students
to determine the center location (X and Y coordinates from the lower left hand corner of
plate) for each drilled hole. Have the students to prepare a drawing sheet (Sheet1) with
a front view, a side view and an isometric view and the correlating dimensions all located
from the lower left hand corner of the plate. Include the overall width, depth and height
dimensions. Also include the feature dimensions (ie Diameters, etc).

* Optional Synthesis Assessment: On their own, have student to create a second
sheet (Sheet2) with the same views and overall dimensions. But on this sheet have the
students to dimension all drilled holes (X and Y coordinates) from the center of the bolt
circle pattern.

Resources Used: N/A

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