The Power Hammers

During my apprenticeship with Chuck Fraser, the master smith, I got to use a wide array of tools, including mills, a lathe, rivet guns, and of course, power hammers. This above all else stood out to me as the pinnacle of forging technology as, obviously, it significantly reduces the amount of physical energy and time involved in the brunt of forging work; significantly as in 10x reduction and the added capability of working on much larger material.

As an entrepreneur, I saw this as an excellent way to go from being able to make some money, to having a highly efficient and productive business. I saw myself producing goods much faster and without nearly as much effort at the same level of quality. There was one big hang up though, which is that power hammers are expensive. The cheapest professional hammers on the market are in the five to ten thousand dollar ballpark, and often need significant repair at that mark. Advanced modern pneumatic hammers come in closer to thirty thousand for small ones.

Thus I was out of luck purchasing one since I didn’t have much money at my fingertips. However, the mechanism for a power hammer is rather simple, and I started doing some research into making one. I’m certainly not the only one out there who’s built a working hammer, and I drew much inspiration particularly from Leonardo DaVinci’s design, which uses a conch shell-like wheel to raise and drop something– basically a rotating wedge, like a screw that releases periodically.

That design works well, but relies entirely on gravity for the power, and thus is limited in speed and striking power. This kind of design would work well with an extremely heavy ram that only needs a few strikes per minute to achieve the desired foreign effect. However, my goal was a nuanced machine that could offer hard and soft strikes, not something the DaVinci cam could do, so I looked deeper.

The winning idea is simple–the input shaft attaches directly onto the inside of a cam, offset, and the outside of the cam can move independently of the inside so when the input shaft is spun the whole thing rotates off-center, but if the outside of the cam is fixed in the x and z directions, it simply moves up and down. I build such a cam out of two pieces of pipe, one fitting snugly inside the other, then welding the input shaft onto the inside of the inner piece, and the linkage attachment bracket onto the outside.

To power the input shaft I made a pedal and a belt between a motor on the pedal and a pulley on the input shaft acts as a slip clutch, additionally I attached an adjustable spring maintained tensioner to account for the belt expanding as it heats up with the friction from slipping.

This approach provides a surprising amount for control, and allows for soft and hard strikes. The detail allowing for this is the tensioner. Before adding that, the controls were inconsistent and as the belt heated up I had to press the pedal harder and harder until eventually it would not respond at all. With the tensioner, the pedal pressure stays constant until the belt expands too much at the current tension setting and the hammer stops responding. At that point, I simply tighten the tensioner and it works consistently again. As of now it only has two settings: warm up, and full heat operation.

The next hurdle now that I had a system to provide power was to give it something to power. I used a hinge at the back of a steel bar with a flange plate attached to the end that I can mount dies onto. This allows for interchangeability in the dies so that I can try different designs down the road. It’s controlled in the horizontal direction by steel rails on either side of the bar. I found a heavy piece of steel to serve as the anvil and mounted all of these systems onto a wooden frame and built a corresponding bottom flange plate which also takes interchangeable dies.

The last and most challenging part of a power hammer is connecting the power drive to the hammer or ram. The trick is that this must be done via spring for two reasons. The first reason is that if it is directly attached, when a piece of matel is put between the dies that is too thick to be squashed by the power provided by the motor, the system will jam and the motor will be unable to turn, probably resulting in a burn out of the belt or motor. The first prototype that I ever built demonstrated to me the need for a spring linkage between the power drive and hammer. I built the first one without such a drive and realized that I’d essentially built a glorified potato masher. The second reason is that the spring allows for enough play that the hammer will be “thrown” at high motor speeds, and will be propelled downwards with much more force than gravity can supply, the spring will deform to accommodate for variable thicknesses of steel, and be ready for the next blow, also the spring helps to recover energy spent in each strike and bounce the hammer back up.

The design that I am currently using simply suspends a spring between a U shaped piece of metal attached directly to the outer cam. The spring threads through a pipe welded onto a bracket bolted onto the hammer. The effect is that the hammer is supported and can be raised and lowered by the power drive, but with enough wiggle that if the hammer encounters even a very thick piece of steel, it will continue to spin and hit instead of binding up. Also, the U shaped bracket has numerous attachment points so the resting height of the hammer can be raised and lowered to work optimally at different steel thicknesses.

A different linkage that I built for an overhead hammer that never was functional for production was a complete DuPont style linkage, a more complex style that uses a diamond shape held wide by a spring which can collapse or expand to suspend the overhead ram. This linkage functioned well, and I built it out of used brake pads, a feat that I’m rather proud of, however, the rest of the hammer, the general frame, was too heavy to support the ram I’d created, and I didn’t properly account for the long stroke of the cam I created for that hammer so I got interference with my confinement rails. That project would have required a significantly larger time investment to finish, and I decided to scrap it and redesign the already functional hammer I’d previously built, which is the one that is currently serving as an excellent tool in my blacksmithing shop!