Material: Tool Steel, Wood
Cambridge, MA
January 2025
helloI learned how to hand-forge and heat treat a hammer at MIT.
We started with a block of tool steel. The process had 7 main steps:
- Form the center hole for the handle to fit into.
- Indent each side of the hammer head to isolate the start of the peen.
- Form the peen.
- Grind the hammer head.
- Heat treat the hammer head.
- Shape the wooden handle.
- Insert the handle into the hammer head.
The images and captions below walk through these steps in more detail.
helloI started with a block of tool steel and milled out 3 holes in the center as a starting point for the center hole into which the handle would be inserted. Alternatively, this could be formed by using a punch and hammering it into the block from both sides until the material falls through, but this would take signficantly more time.
Then, I worked with a partner to sledge hammer a parallel drift through the hole to widen it uniformly. Once the parallel section of the drift was reached, I switched to a tapered drift to refine the shape of the hole. A slight hourglass geometry was formed inside the hole to better secure the handle. This means that the hole was slightly wider at the top and bottom surfaces and narrowest at half the depth.
Figure 1: Early stages of center hole formation
helloI used a power hammer to carefully indent each end of the hammer head to mark the start of the peen. While forging the center hole in Step 1, the drift moves the material outward, causing a buldge to form at the center. The indentations were made near the start and end of this buldge.
Figure 2: Center hole is to size and indents have been formed on each side to start the peen.
Like the previous steps, the head needed to be forged while hot, typically between 810 - 1050°C.
Step 4: Grinding
helloOnce the desired shape was achieved, I used a belt sander to clean up the surfaces and refine the shape. For example, the faces of the peen needed to be grinded flat since a fish-mouth profile was formed as material was squished out by the power hammer.
Figure 3: Power hammer
Figure 4A: Top view of hammer head with forged peen.
Figure 4B: Side view of hammer head with forged peen.
Figure 5A: Top view of hammer head after grining.
Figure 5B: Side view of hammer head after grinding.
For the final step of heat treatment, I used a blow torch to apply heat to the center of the head. Gradually, the color changed from light yellow to golden to brown to red to purple to blue to light parrot blue. Thorugh conduction, the heat from the middle gradually moved out toward the ends, creating a color gradient. Once the tips were golden and the center was parrot blue, I immediately quenched the head in water. This final step is done to harden the ends of the head will making the center softer.
Figure 6: Salmon-like glow for 1st step of heat treatment.
Figure 7: Head after being quenched in oil. A residual oil layer remains.
Figure 8: Color gradient from final step of heat treatment.
helloI need to shape the top of the handle to fit securely into the hammer head. To do so, I first traced the perimeter of the center hole of the head onto the handle. Using a belt sander, I removed material until I reached the trace. Then, I iteratively pressed the handle into the head and sanded off more material until the handle fit snuggly through. Each time the handle was pressed into the head, a black mark would be left from the dried oil, indicating where to remove more wood for the handle to be inserted further. I also ground down the bottom of the handle until I was able to achieve an ergonomic fit for my hand.
Step 7: Insert the Handle
helloTo insert the handle I used a mallet to push the handle into the head until it stopped moving. I used a hacksaw to cut off the excess wood at the top of the handle. Then I applied glue to a wooden shim and malleted that into a slit at the top of the handle. This causes the top to expand in one direction until it compresses against the metal hammer head. Lastly, I malleted a metal shim perpendicular to the wooden one to extend the top of the handle in the opposite direction, achieving a compression fit along the full circumference.
Figure 9: Side view of finished hammer.
Figure 10: Top view of assembled hammer showing the wood and metal shims inserted at the top of the handle to expand the material and create a reliable compression fit.
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