Part of Lesson Plan: **Broken Bolt Extraction Methods Part 2 (updated) by Robert Thayer
Activity Overview / Details
Background -- Safe Shop Attire
Before I allow students to perform lab work, I ask them to form a line standing shoulder to shoulder in the shop. This is called "lining-up". During the line-up, I visually inspect all students to make sure they are following all required safety rules, in terms of appropriate dress and personal protective equipment. Each student must display the following:
- OSHA approved safety glasses covering their eyes
- Loose clothing or jewelry removed or tucked in
- Long hair tied back and out of the way
- No open-toed footwear
Once students pass inspection in the line-up, they are free to begin working.
Background -- Activity Stations
In my shop, I have created one or two activity stations for each skill in which I expect my students to become proficient. During lab time, students work individually or in groups at a particular station until the student or students and I feel that proficiency has been achieved. This strategy accomplishes two important goals. First, students can work at their own pace. Second, by having one to two stations for each required skill, limited shop space and funds are maximized.
Background -- Shop Card
At the beginning of the course, give each student an 8 1/2" by 11" piece of card stock on which you print all the of the skills in which you require them to become proficient. Place the cards in alphabetical order by student name in document organizer in the shop. Each time students achieve proficiency in a given shop task, they will retrieve their shop card from the organizer, and ask you to punch a hole with a scissor style hole punch next to the name of that skill. Each student's goal is to have you punch a hole next to each skill on the shop card by the end of the course.
Background -- Laminated Instructions
Next to each activity station, attach a set of laminated instruction sheets for the activity the students are about to practice. You should also include any additional guidelines, hints and cautions of which you want students to be aware, while performing the task.
Tools and Equipment
- A cylinder head or small engine block which contains several broken bolts or studs. I recommend studs/bolts with an 8 mm diameter.
- Penetrating oil
- A small hand-held grinder or cut-off wheel
- A centering block
- An air powered or electric drill
- A small to medium size center punch
- A ball peen hammer
- A set of mechanic's right-hand drill bits
- Cutting oil
- A set of easy-outs with a T-handle included
Instructions for Students
- Lightly spray the broken bolt with the penetrating oil.
- Grind or cut the bolt flush with the surface of the engine/head, being careful not to grind or cut into the engine/head.
- Make a center punch mark directly in the center of the bolt. Use the centering block, if necessary.
- Choose a 1/8th inch drill bit (or similar), lubricate the bit with a small amount of cutting oil, and begin drilling into the bolt. Drill straight and on center. Use the centering block if necessary. Use low to moderate speed and moderate pressure. Drill down about 1/4th of an inch. Re-apply the cutting oil as needed.
- Place an appropriate size easy-out in the T-handle. The tip of the easy-out should be slightly smaller than the size of the drill bit used, in this case smaller than 1/8th inch.
- With moderate downward pressure, twist the easy-out counterclockwise until the bolt is removed. If the bolt does not come out, increase the downward pressure.
- If the bolt still won't come out, drill in with the next size larger bit. Then, try the next size larger easy-out. Use incrementally larger diameter bits and easy-outs until the bolt comes out. If the bolt still won't come out, drill in with incrementally larger diameter bits, until all that remains of the bolt is the threads. Then, use a pick and small needle nose pliers, or the correct size tap, and remove the remaining threads.
- Once the bolt comes out, show the broken piece to the instructor. Show the threads to the instructor, if that is all that remains.
Instructions for Teacher
Walk around and observe students working. (Remember, using the shop model I have described, you will be observing only one student or a small group of students practicing at the broken bolt extraction station; the remaining students will be working at stations performing tasks other than broken bolt extraction.) Modify instruction for students who are struggling with any step in the procedure. Model best practices, and let students work until the bolt is removed.