The Bulldog is a blacksmith utility air hammer design. It requires the use of a shop compressor.
- All build documents will include a Bill of Materials for both steel and the air circuit components. There are detailed construction and assembly instructions. In addition, there are Operations, Maintenance, Troubleshooting, Frequently Asked Questions and Glossary sections.
The Bulldog 30 build document (PDF) is complete. It is now available on Etsy as a digital download.
The Bulldog 75 will be the next build document available (Estimated spring, 2024)
The build document provides all the information you need to build, maintain, troubleshoot and operate a Bulldog 30. If you accumulate all the specified materials listed in the bill of materials (BOM) …. you will have all the components needed to build an air hammer with the following characteristics…
· Cylinder: 2” Bore, 10” Stroke (Cushions on both ends)
· Ram Weight: 32.9 pounds
· Anvil Height: 20 inches
· Anvil Weight (effective): 208.48. (This includes a significant boost from the base)
· Anvil Ratio: 6.34 to 1
o A 10.74 to 1 ratio would be attained if the anvil diameter is increased to 6.5” and the height to 32”.
· Stroke Range: 9 inches
· Die Overlap: 1 inch (required with a front cushion)
· Total Weight (not including a pedestal): About 520 pounds.
· Height: 87.75” (with a 11.75” pedestal to bring the forging height to 36 inches)
· Height without pedestal: 76”
· Base Footprint: Width: 18”, Depth: 19” (does not include pyramid shaped pedestal or space for a treadle, and/or a foot pedal)
· Air consumption at 80 PSI estimates (using a 2x10 cylinder).
o Hobby use: 4-5 CFM minimum with 30–60 gallon tank for an approximate 50% duty cycle….
o Production use: 8+ CFM with a 60-gallon tank for 75% duty cycle
o A belt driven compressor is recommended.
Estimated cost to build a Bulldog 30.
As indicated earlier, a shop air compressor is required to operate a Bulldog. If you don't already have a compressor, the cost of one has to be considered.
For a production-type shop environment, a 5-HP, single-stage compressor with a 60 gallon tank would meet the need. If the user is a hobby blacksmith, it is expected that a compressor capable of 4-5 CFM at 80 PSI with a 30-gallon (or greater) tank would support a 50% duty cycle. Shop around for prices on new and used compressors. Ebay, craigslist and Facebook marketplace are good shopping grounds... Personally, for shop use, I have a compressor rated at 25 CFM. When I test my machines for environments that don't have a large compressor, I use a compressor I bought off craigslist for $100 that drives the Bulldog 30 at a 50% duty cycle.
Cost to build is going to depend a lot upon your efforts to find inexpensive steel.
Most air circuit component prices in this document are as of Aug, 2023.
· Air circuit
$990 Total estimated cost of a fully featured Bulldog 30 air circuit
§ $420: Basic air circuit, not including the cylinder or advanced features.
§ $30: Consumables you may already have.
§ $300: Recommended cylinder.
§ Advanced features
· $15: Shuttle port flow control
· $25: Governor
· $100: Single-hit
· $100: Ram positioning
· If your hammer is part of a group build, your cost will be about $60 less because extra parts (from buying multi-part packages) could be used on different hammer.
I do not recommend looking for, or buying, use air circuit components.
What does it cost to build a Bulldog 30 if someone is good at finding low-cost steel?
The main question is... what do you have to pay for steel?
I rarely pay retail for steel..... Only when I need small stock, maybe up to 1 inch square for projects not related to power hammers.
I have several steel recycling yards I go to. Not too long ago, I used to be able to buy scrap or drops for as little as 20 cents a pound. Today, the average cost is probably 60-65 cents a pound (75 cents max). I find thick plate (appropriate sizes) for bases. I find heavy walled tubing for backbones. I find 1/2" plate for braces. I find 5/8ths angle iron you see on the hammers I bolt together... I don't remember ever buying new angle iron. I have bought 4140 to make dies for about $1 a pound. I cut recycled forklift tines for most of my dies. A $50 tine will make many sets of dies... and where the tine is too thin for dies, I make tools with it.
Some people are lucky enough to be able to find steel at no cost, or scrap prices (they may have friends at scrap yards, or fab shops that have drops).
A Bulldog 30 only weighs about 520 pounds, so even at 75 cents a pound, recycled steel actually costs less than $400 (for what is actually needed).
Even if you had to buy double the lengths because that's what is available, it would still be less than $800. My average over-length is probably 25% more than I need (cost at 65 cents would be well under $500). In reality, I never buy more than what I use, because I always have another project on the table. Many times, the recycle yard cuts (oxy-acet) the heavy tubing I buy to just over the length I need. Other places may cut and charge you $5-$30 for the cut.
So, next.... what does the air circuit cost? The fully-featured Bulldog air circuit would cost about $1350, including a new cylinder. About $60 of that is extra parts (multi-part packaging... which you can sell to friends building their own Bulldog).
It isn't necessary to spend that much. You easily start with a basic air circuit (about $400), and use an old new-stock or used cylinder (often less than $100 shipped on eBay). All my advanced features, although they increase the usefulness of an air hammer, are not necessary for what 95% of blacksmiths currently do with a power hammer (they don't yet know how useful my advanced features are).
Soooo.... here's the deal... If you are lucky enough to be able to scrounge steel for free, you can build a Bulldog 30, with a basic air circuit for about $500, and (I believe) it will perform better than almost all home-built hammers out there. You will still want the advanced features, but you can put them on later when you are rolling in dough.
If you are reasonably competent at finding recycled steel, it would cost from $400 to $800 (max).
If you fall into the "I can get steel free" category, you can build a Bulldog 30 for about $500.
If you have to pay the average used steel prices out there, the steel cost would be from about $340 to double that ($680). Remember my average oversize is only about 25%.
The Bulldog 75 will cost more because it weighs about 800 pounds and the air circuit needs to be more robust (larger air cylinder). The build Bulldog 75 document will list a 32-inch anvil. The Bulldog 30 has a 20" anvil, and a wood stump for a pedestal.
Both hammers will require some shop materials to make jigs and clamps for construction, but I would expect you would have those materials on hand. You will need to buy a digital level ($35 on Amazon), if you don't have one.
If you can weld and have basic metalworking tools, you should be able to build a Bulldog 30 for well under $1200 (and have steel left for other projects).
Every Bulldog will have equal basic features and capabilities, which can be enhanced by adding advanced features such as a rich singe-hit mode, governors to limit the upper speed and ram behavior during cycling, the ability to raise and lower the ram independent of cycling and
a special die mounting system.
All advanced features, individually, can be installed during the initial build, or added later at any time with minimal replacement parts.
· Ram weight and Stock Size... Stock as small as a paper clip could be forged on the smaller hammers (I did on the Mini). Larger stock sizes are limited by ram weight and PSI setting.
Upper stock sizes that can reasonably be forged. Upper stock sizes estimated for Bulldogs with rams 50# and up.
I believe larger cross-sections could be forged with patience.
· Dies... The shape of dies is a personal preference, with styles varying tremendously. This document describes combination dies in the Construction Section. Obviously, the builder determines how his/her dies are dressed.
o Upper dies are bolted (from above) to the upper die holder.
o Lower dies are welded to a base plate, which is bolted to the anvil.
o Alternate die holders can be fabricated for supporting specialty dies.
· Cycling Speed... Cycle speed can be varied dynamically, from very slow to up to 300+ cycles per minute.
Upper cycle speeds will vary by ram weight.
o Control points.
§ A treadle or foot pedal is used to initiate and control the speed of cycling.
§ A foot pedal is required for the single-hit feature.
§ Advanced features can be installed to set upper speed limits.
· A flow control valve on the 4-way valve shuttle port can be set to slow cycling.
· Governor(s)... A maximum cycling speed and impact force can be established by setting a governor.
When this feature is in play, cycling speed will not exceed a set upper limit regardless of how far down the treadle is pressed.
The primary governor (a butterfly) valve works well, but if you want to really dial into a specific low-speed setting, or save a slow setting, you may want to add a needle valve as a governor (it would installed parallel) with the butterfly valve..
· Slow-Rise valve... This valve restricts the rate the ram will rise without affecting the speed of the falling ram. It is always in use while in single-hit mode, and may also be used during cycling to create desired cycling behavior.
You must always (partially) close this valve when in single-hit mode to eliminate the potential of the piston in the cylinder violently striking the end cap during heavy single-hit impacts.
§ Roller valve role... The roller valve interacts with the ram, determining when the air circuit should initiate reversing the direction the ram is traveling. Its position determines the (nominal) center of the stroke, which can be moved up or down to accommodate top tooling or forging various thickness of stock (paper clip to maximum size).
· Stroke Length... The Stroke length is defined by the upper and lower boundaries of the ram during cycling. It is very dynamic and varies with the cycling speed, the maximum volume of air being allowed to pass through the air circuit (control at the exhaust valve and/or governor limit) and the PSI the regulator (on the FRL) is set to. It can involve very little movement, or at the highest cycling speed, approach the stroke range. The operator generally controls it using the treadle or foot pedal.
· Stroke Range... The stroke range defines the upper and lower boundaries (location) a stroke can occur within. In most cases, this range is the length of the cylinder stroke minus the die overlap (sometimes, the entire stroke length of a cylinder is not used). Generally, the active ram stroke length during cycling will be much less than the stroke range. It would be rare for the stroke length to fully use the stroke range during cycling. Think of the range as a playground, with strokes only using part of it at any given time.
- Stroke Position... The position of the stroke is established by the position of the roller valve. The roller valve assembly, using a lever, allows the operator to reposition the roller valve up or down. When you are forging small stock, the roller valve would be low, and the stroke would occur in the lower part of the stroke range. When you are forging larger stock, or using top tools, the roller valve would be moved up and your stroke would occur higher. ·
- Impact Force... When the upper die hits its target, the bore of the cylinder, the PSI the regulator is set to and speed the ram is moving are factors that determine the impact force when the ram hits its target. The operator has controls that allow her to produce a tiny-tiny hit to the most forceful hit possible by the hammer. Generally (during cycling), the operator uses the treadle to control the impact force. The position of the roller valve also comes into play. When the roller valve is low, it facilitates little impact... When the roller valve is positioned higher, the stroke can be longer and facilitates higher impact. Also, using other features that affect ram position and cycle speed can impact ram speed at impact (single-hit, slow ram-rise, flow control at the shuttle port, exhaust valve lever position setting, governor settings... and more).
Another force factor is the performance boost that occurs when the direction the ram is moving changes.
Read “How does the performance boost work?” in the Frequently Asked Questions section to understand what the performance boost is and how it works.
· Use of Tooling... All types of tooling can be used on the Bulldog 30.... from simple hand-held tools (such as a flatter), to taller tools (punches, chisels, repousse type tooling) and lower tools held by a harness clamped to the lower die (hardy hole type and bent-base tooling).
The stroke range of the Bulldog and movement capability of the roller valve allows the stroke to be positioned appropriately to accommodate using tooling during normal cycling.
· Single-Hits... The Bulldog 30 can deliver single-hits in both cycling and single-hit modes.
Single-hits during Cycle Mode... A fairly well-controlled single-hit can be accomplished when the ram is sitting idle in cycling mode.... by just tapping quickly on the treadle... then quickly backing your foot off the treadle. Force can be controlled by how far down the treadle is pressed. Of course, when in cycling mode with the ram idle, the ram will be sitting at, or just above, the roller valve. This limits the height of the tooling you can use and may result in less force than you would have available if you were in single-hit mode.
Single-hits while in single-hit mode... When the Bulldog is put in single-hit mode, the ram will rise to its upper-most position, and wait for a single-hit to be initiated via the single-hit pedal.
o True, repeatable, controlled (impact force) single hits are possible when in single-hit mode.
o A single-hit pedal is used to initiate a single-hit.
§ The pedal may be separate from, or mounted on, the treadle.
. § A maximum impact-force can be set.... using a governor.
§ A consistent impact-force can be established by removing linkage from the exhaust valve lever and setting the exhaust valve lever position.... or setting a governor to limit upper end air flow through the air circuit.
§ The impact force can also be dynamically controlled by using the treadle.
o One foot would be used to press on the treadle to establish the force of the hit.
o The other foot would press on the single-hit pedal to initiate the hit.
This, unless you can levitate, would be done sitting on a stool.
· Ram Positioning Feature... A joy-stick can be used (while in cycling or single-hit mode) to raise or lower the ram to any position.
The ram will stop moving when the joy-stick is released and will hold at any position.
Proper action of this feature requires the shop air being delivered to the Bulldog to be at least 20 PSI higher than the FRL is set to on your Bulldog.
· Clamping... If the treadle is held all the way down in single-hit mode, the object between the dies will be clamped, using the air circuit regulator PSI.
If, when using the ram positioning (ram-rise) feature, the ram is lowered all the way down onto an object, clamping will occur using the PSI setting of the rise-ram regulator.
The clamping force can be determined using the bore of the cylinder and the PSI setting of the ram-rise regulator (area times pressure).
· Pressure Release Valve... This valve is used (after the input air valve is closed) to release all pressurized air from the input side of the air circuit during shutdown.
Pressurized air is released from the exhaust side by pressing on the treadle.
· Repoussé Capable... If the lower die is removed, the operator could use the Bulldog 30 for repousse.
§ All the features described above could be used to provide required control of the ram behavior.
§ The front cushion on the cylinder (critical for repousse) will prevent the ram from going as low as the anvil if there is a mis-hit using a repousse tool. If the anvil was set up with a sow block, that stop could be as high above the anvil as you want it to be.