Fred Connell
Student Blacksmith
Power Hammer
Whack Whack Calm
   Notes & Photos:
- Power Hammer closeup
- Anvil
- Frame
- Hammer
- Dies
- Hammer Track
- Dupont Linkage
- Linkage Compressed
- Clutch
- Clutch Assembly
- Clutch Foot Petal
- Crankshaft
- crankshaft assembled
- Motor & mount
- Dupont Linkage Patent
- Operation Conclusions
- Operating Video .ogg
- Back toBlacksmith

   Other Stuff:
- Rose Engine

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Custom fabricated Mechanical Power Hammer


I met Ray Clontz in summer 2011 at a Southern Foothills Blacksmiths group meeting of the North Carolina Chapter of the Artist-Blacksmith's Association of North America [NC-ABANA]. Our area monthly meeting is held in one of the member's very well equipped fabrication shop/smithy.

Around 2000 Ray Clontz built for himself a mechanical power hammer designed similar to a Little Giant mechanical power hammer. Clontz utilized two automotive brake rotors, an automotive clutch plate and automotive clutch throw out bearing as a speed control device and clutch. Ray's hammer works quite well and I like the basic design.

A year or so later, two of Ray's blacksmith friends also wanted to build power hammers, so Ray designed the "Tire Hammer" power hammer. It has since been copied many times all over the word. The first models were built from Ray's notes or photos or visual inspections of a completed machine and all were a little different depending on what materials were at hand. I was able to inspect those first two tire hammers built from Ray Clontz's design. They are still used in North Carolina by Butch Silver and Stuart Willis.

A tire hammer uses a friction drum fastened on the drive motor shaft to contact the running surface of an automobile tire as a clutch or speed control device. By increasing the motor pressure on the tire, the hammer will run faster. Reducing the motor pressure on the tire will allowing the drive drum to slip on the tire surface and reduce the tire hammer speed. The size difference between the drive drum and the tire diameter provide a natural speed reduction. This system works very nicely.

Clay Spencer, a former NASA engineer, has supervised several group builds of Clay's version of the Ray Clontz tire hammer design. Clay's version is designed to be built in a weekend and utilize different tooling for various effects. In a gropu build, a group of blacksmiths build enough tire hammers for each participant to own one. When they are finished, numbers are drawn to determine which hammer belongs to each blacksmith. So due to the time constraint, Clay's design favors simplicity of fabrication. Clay has supervised the fabrication of a lot of tire hammers.

I have access to a metal lathe and milling machine, and I enjoy both designing and fabricating. So, I will take a little different approach to the design of my Power Hammer. The basic design of my Disk Power Hammer will favor the Little Giant Power hammer. Similar to Ray Clontz's personal power hammer, I use two automotive disk brake rotors with clutch friction material between them for clutch and speed control. Included in this publication are some notes and photo's of my Disk Hammer fabrication. This design may not be the easiest to fabricate, but it is the design I wanted to build.

As in most equipment designed for production, all rotating parts except the spring pivots have bronze bushings or ball bearings. Most bushings have grease fittings. Where practical all parts were cleaned and painted. It didn't take a lot longer to make the work look professionally built.

- Initial Design Criteria of the mechanical Power Hammer

  1. Hammer head moving assembly weight of 35 pounds.
  2. Clutch slip control to smoothly deliver from light taps to full force impacts of 3 per second.
  3. Maximum linkage hammer head travel 9.5 inches [neutral to max without crankshaft stroke].
  4. Crankshaft stroke of 4.5 inches [adjustable].
  5. Linkage springs compress at 270 pounds per inch with 4" maximum.
  6. Linkage spring leverage ratio of 37%.
  7. At rest Hammer to anvil height 1.5 inches.
All of these variables can be changed to tune the Disk Power Hammer for maximum hammer impact energy. Since an increase in speed of the hammer results in much more impact energy than an increase in hammer weight, I am attempting to maximize the hammer speed of this power hammer while maintaining an acceptable level of impacts per second.

       Anvil Index

As in traditional hand hammer blacksmith work, the power hammer anvil is very important. Since the Dupont linkage of the power hammer is generating a lot of speed with the heavy hammer, a massive anvil is needed to absorb the excess energy that is not consumed by deforming the hot metal. If the anvil does not have a large enough mass the power hammer will likely move around the Smithy and/or damage the floor.

From the information I've found, the power hammer anvil should weigh from 10 to 18 times the hammer weight. There seems to be a pretty broad range of ratios in the blacksmith community. This calculates to a 350 to 630 pound anvil for a 35 pound hammer. This is a big chunk of steel and was the first acquired item for my Disk Power Hammer. I wanted plenty of mass in the anvil since my Power Hammer will be on a concrete floor which I do not want to damage. My anvil is a 9 5/8" diameter and 32" tall solid steel round and weighs about 660 pounds. It was a drop [waste piece] and is probably some alloy designed for shafting like 1045 or 4140. It will be bolted to a 120 pound 1" thick steel base plate which will effectively add some more to the anvil mass. A rubber horse stall mat will be placed under the Disk Power Hammer base plate to help protect the concrete floor.

Holes are drilled and tapped in the anvil for the post brace, the bottom die and mounting angles to the base. A special fixture was built to support the magnetic base drill.

       Frame Index

The base is a 1" thick by 16" wide by 30 inches long piece of hot rolled steel plate. It was drilled and tapped 1/2"-13 UNC for fastening the anvil and the post. A piece of 3/8"x4"x4" steel tube was found for the vertical post. It weighs 100 pounds without the top and bottom plates, thus adding considerably to the mass of the machine. The 3/4" thick steel plates were welded to the top and bottom of the vertical post. The 3/4"x8"x"8 bottom plate was drilled for mounting the post assembly to the Power Hammer bottom plate. The 3/4"x8"x10.2" top plate was drilled and tapped 3/8-24 UNF for mounting the crankshaft pillar block bearings. In the sides of the vertical post, 3/8-24 UNF holes were drilled and tapped in appropriate locations for mounting the anvil brace, hammer track, clutch linkage, motor mount, accessory rack and foot control.

       Hammer & Dies Index

The impact weight of a power hammer includes the weight of all materials attached to the hammer head such as the weight of the top die, slide, slide spacer, bolts and about half of the weight of the lower swing arms. This totals 35 pounds for this Disk Hammer. The dies are 4140 alloy steel and can be oil hardened and tempered. The 1.5"x1.5"x3" die and 1" thick mounting plate are attached with four 3/8" bolts. All parts of the hammer assembly are bolted together to simplify adjusting the total hammer weight if desired.

The hammer, spacer and hammer slide plate were keyed and bolted together. This hammer assembly would have been really nice to have been cast in one piece.

       Hammer Track Index

The hammer track or guide assembly is bolted to the frame. The hammer movement is constrained by the "U" shaped 1"x3/4" Ultra High Molecular Weight Polyethylene [UHMW-PE] bearing material. The "U" shaped UHMW-PE is almost as slick as Teflon and is available from McMaster-Carr.

       Linkage Index

P. D. Dupont registered a patent for a Power Hammer Spring on June 10, 1890. The Dupont design is very interesting. It will cause the hammer to travel a greater distance than the stroke of the crankshaft. I am designing my Disk Power Hammer so that all of the variables controlling the hammer head speed can be varied. I want the hammer head energy to be as high as possible within the basic design limitations.

The highest energy will be obtained with the largest head weight that can be utilized while still maintaining the maximum hammer head stroke at the desired impacts per second. The energy delivered by the hammer-blow is equivalent to one half the mass of the head times the square of the head's speed at the time of impact (E={MV^2/2}). The impact energy increases linearly with an increase in mass, it increases geometrically with an increase in speed. Doubling the head weigh will double the head impact energy. Doubling the head speed will increase the head impact energy four [4] times. If one wants more energy from a power hammer, it seems logical to try and increase the head speed per revolution and the number of revolutions per second as much as possible. This should be a familiar concept to a blacksmith.

This Dupont linkage is designed such that adjustment of the length of the lower toggle linkage arms will adjust the total travel of the hammer and at the same time adjust the spring pre-load tension. As we lengthen the lower toggle linkage arms and thus the hammer head stroke we are also reducing the spring preset at the same time. If a power hammer with a Dupont linkage is not producing a long enough hammer travel then lengthening the lower toggle linkage arms will give more travel and at the same time reduce the spring pressure and thus allow more hammer travel. This ability to easily tune the power hammer is a very handy design feature to incorporate into the Power Hammer design.

Like the Little Giant, both ends of the Disk Hammer lower toggle linkage arm connectors are offset to allow maximum vertical travel of the hammer head before mechanically binding with the hammer and main linkage arms. The lower toggle linkage arms can fold almost parallel to the upper linkage arms. This Mechanical Power Hammer linkage is designed such that at the maximum head travel limit, everything crashes at the same time. That is, the hammer will hit the spring at the same time the hammer lower toggle linkage arms bind together with the hammer and upper linkage arms. If our spring is sized correctly, the Disk Power Hammer design will almost, but not quite reach this crash condition at full speed operation. We would then have the most head travel per revolution of the crankshaft and thus the maximum hammer head speed and impact power possible with constraints of this particular Dupont linkage.

       Clutch Index

The drive line is similar to the Little Giant power hammer. The 1.375" drive shaft rotates in "off the shelf" pillar block ball bearings and is driven by a rear mounted clutch assembly. The crank shaft arm is fabricated from aluminum and drilled and tapped to allow for adjustment of the counterbalance weights. The counterbalance weight is difficult to calculate and easier to balance statically. The initial crank throw is a 2.25" radius.

The clutch is made up of two automotive brake disk rotors bolted to aluminum hubs. The front one is keyed to the crank shaft. The rear one rotates and slides with a bronze bushing on the shaft. The rear disk rotor has a V-belt grove cut in the outside edge to make it a pulley and is driven by a V-belt directly from the 1140 RMP motor. A 7.5"x7.5" square of low coefficient of friction material 3/8" thick freely rotates between the two disk rotors. This is providing a total of 40 square inches of friction contact. A Chevrolet small block V8 clutch throw-out bearing presses the two disk rotors together to engage the clutch mechanism and control the speed of the crankshaft. Foot petal pressure is transferred by linkage to the throwout bearing by a bell crank mechanism.

The clutch mechanism requires 120 pounds of force on the throwout bearing for positive clutch engagement. Leverage in the foot petal system reduces this to 20 pounds for full clutch engagement. With lesser pressure the clutch smoothly reduces the number of hammer to light impacts.

       Electric Motor Index

A 1.5 horsepower 1140 RPM three phase Baldor motor was found to power the Disk Hammer. This is a little more power than necessary but delivers the lower RPM needed.

To keep things simple, I did not want to use a jack shaft to reduce the motor output speed. So, a 1/2" V-belt grove was cut in the outside of the 10.8" diameter rotating rotor disk so it could be used as the driven pulley. This was a noisy interrupted cut on the gear head metal lathe because of the brake disc cooling fins. For the initial setup a 1.75" motor pulley was used, full speed produces about 3 hammer impacts per second. Later, I may install a larger drive pulley on the motor to achieve a faster rate of impacts.

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