Introduction: Manual Fire Alarm

About: My name is Troy. I'm a Mechatronics and Aerospace Engineer. I make things out of wood and electronics and spend time outdoors (especially SCUBA diving).

Whether you are trying to get someone's attention, signaling danger, or getting a sporting event started, this manual bell will do the trick.

This manual trip bell features a lever activated clapper arm with a spring reset. This project was inspired by Measured Workshop's Boxing Bell YouTube video.

This is a simple metalworking project that can be done with limited tools.

Step 1: Tools and Materials



Step 2: Rough Cut Parts

Cut out and attach the templates to your steel. Cut out the pieces for the bell mechanism.

Step 3: Shape Pieces

Using a bench grinder, clean up the edges of each piece. Using a center punch, mark the center of each hole from the template.

Step 4: Shape Striker

Cut the outside of the tabs and bend them using a vise. Bend the end of the striker slightly. This angle can be changed later.

Step 5: Drill Holes

Drill 1/4 in. clearance holes for each piece. Shape the tabs round using a bench grinder.

Step 6: Bend Catch Tab

Attach the catch to the lever arm. Mark the edge of the lever arm on the catch. Bend at that point and verify it fits correctly on the lever arm. Mark and cut off the excess tab.

Step 7: Finish Mechanism

You can finish the mechanism anyway you like. I opted for a brushed metal look. I sanded each piece up to 180 grit sandpaper.

Step 8: Create Standoffs

Mount the 3/8 in. bar in your lathe. Drill and tap 1/4 - 20 in. threads. Be sure to cover the bed of your lathe to protect it from metal shavings. Sand and finish to your liking.

Cut standoffs to 7/8 and 5/8 in.

Step 9: Finish Bolt Heads

All the bolts should be finished to your liking. All of the bolts were mounted on the lathe to have the marking removed and to be shined up.

Step 10: Attach Catch

The bolt for the catch needs to retain some of the square carriage bolt profile. Remove a small amount of it until it only has the thickness of the catch. Finish the head of the bolt as shown in the previous step.

Using small files, cut the hole in the catch square. Attach the catch to the lever arm with a lock nut. This will allow the tension on the catch to remain constant. Cut off the excess bolt.

Step 11: Create Stops

You will need to create two stops for this mechanism. One 3/4 in. long and one 1 in. long both with 1/4 - 20 in threads tapped.

Mount the 5/8 in. rod in the lathe and file the end round. Finish to your liking and cut to length with a hacksaw. Turn the stop around and drill and tap the other end.

Step 12: Create Brass Striker

Turn a 7/8 in. long striker from 3/4 in. brass on the lathe using the same techniques as before. The brass was polished to a high gloss using buffing compound.

Step 13: Drill Spring Holes

Drill two spring holes in the top of the striker bar. One spring hole in the edge of the catch and next to the catch in the lever arm.

Step 14: Mounting Board

Using the attached template, mark and drill corresponding holes. All holes are 1/4 in. except the main hole in the middle for the bell is 5/16 in. Use edge banding to cover up the plywood edges and spray with lacquer. The corresponding holes for springs were just eyeballed based on spring tension.

Step 15: Assemble

Assemble the bell by fist attaching the stoppers (longer stopper on top). The lever arm assembly and springs are next followed by the striker arm. Finally attach the bell with a 5/16 in. carriage bolt.

Step 16: Attach Pull

I braided some black paracord with the traditional circle boondoggle stitching.

With that, your bell is complete! You can now hand it up anywhere you want to get some attention.

Audio Contest 2018

Participated in the
Audio Contest 2018