Waterjet Jeweler/Coping Saws

Jewelers/Coping Saws

For my last project at Cal Poly's machine shops, I wanted to make a set of nice jewelers and coping saws so I could use them to make projects after graduating college. These saws represent the culmination of all my skills in design and manufacturing that I learned in college. The designing and fabrication of these three saws was done in my last two weeks of college.

For all of these saws, I designed the saw frames using topology optimization to make the saw frames very lightweight but still stiff. I used the waterjet to cut out the saw frames and powder coated them. I then used a mill and lathe to create the saw blade holders. I also 3D printed the tensioning mechanism and the saw handle.

Finished Jewelers/Coping Saws

5 inch Jewelers Saw

7 inch Coping Saw

7 inch Jewelers Saw

Design Process for Topology Optimization

In order to run the topology optimization on my saw frames, I needed to first determine the forces on the saw frame. The most extreme load case that will happen on the saw frame is when the jeweler saw blades snap. Jeweler saw blades are very thin and often snap, this is why it is important to have saw frame that can properly tension these blades along with making them very easy to replace when they do snap. To figure out this load case, I first started by modeling when the saw blade breaks and using it to get estimates of the forces on the blade and saw frame.

For my saw blade, I assumed the blade would have around 25 lbs of tension due to that being a comparable amount of tension to other types of hand saws. I then applied a cutting force acting along the saw blade, sideways cutting force, and a vertical upwards cutting force. I assumed the vertical cutting force was 20% of the primary cutting force along the blade and the sideways cutting force was around 10% of the cutting force along the blade. I then used the ultimate tensile strength of the blade's steel to get estimates for the cutting force that would break the blade.

Created free body diagram for saw blade

Created shear and moment diagrams for the saw blade

Derived equation to determine cutting forces on blade

Used excel to calculate cutting forces

Drew FBD of the saw frame with calculated cutting forces

Modeled the base saw frame design in Fusion 360

Ran the topology optimization and checked saw frame's deflection

Meshed topology optimization results and fixed the meshed model

Blade Tensioning Mechanism

To tension the blade, I designed a tensioning mechanism on the front of the saw. I designed a blade holder that would be machined using a manual lathe and mill. This blade holder is tensioned by having a thumb screw thread into the back of the blade holder. This thumb screw is then tightened to provide initial tension in the saw blade. To fine tune the tension, a cam lever mechanism is also used. The thumb screw's head rests against this cam. As this cam lever is flipped upwards, it pushes the thumb screw further to the left, applying more tension to the saw blade. This allows for a quick way to increase and release tension in the blade.