It's Hammer Time!
Jim Waldron
Sunday September 4 is the first of 6 Blacksmith Power Hammer Red Tool Sign-off Workshops. Completing this workshop will give you unrestricted access to the Power Hammer in the Blacksmith area.To say it's a Beast would be an understatement. It hits fast and hard.
Andrew McKinney originally proposed the project suggesting an electronic valve control, but after some discussion and research, we opted for an all air pneumatic design
This is a makerspace made tool.
To get started, we salvaged some old big (BIG) I-beam from an old bridge structure, welded it together, and attached pneumatics. As an interesting side note, there was quite a bit of calculation involved in the build. How big should the pneumatic cylinder be? How long a stroke? How much air pressure would be needed and what flow of air in CFM (Cubic Feet per Minute)?
Here is a transcript of a note I sent to Dave Painter just before we started:
OK. Time to get out your pencil and sharpen it up. I need someone to confirm my calculations. Numbers are rounded and/or decimals dropped. I made great use of approximations. (i.e. area of pistion on extend is larger than on retract due to the area of the rod)Assume the hammer weighs in at 80 pounds.
Assume we have 100 psi of pressure.
Assume we use a 2 inch pneumatic cylinder with a 12 inch stroke. Area of piston 3.14 sq inches. Volume of cylinder 38 cubic inches
Assume 1/4 inch nylon tube supplies 11 cfm of air at 100 psi. (The cylinder has 1/4 inlets - I might like larger, but that is what they are)
Target max strokes per second is 3, 2 is acceptable
1 cubic foot of air is 1,728 cubic inches. Cubic inches times supply is (11 x 1728) 19,000 cubic inches
Convert that to seconds (divide by 60) is 317 cubic inches per second
Divide by capacity of cylinder (38 cubic inches) indicates we can fill the cylinder 8 times in 1 second.
Since the cylinder needs 2 fills per stroke (one out and one back), we have enough air for 4 cycles per second.
But it's not instantaneous, so we need to calculate acceleration. Hang on... (gotta convert to metric).
Force on the piston is 100 psi times the area of the piston (3.14 sq inches) of 314 pounds.
This equates to about 2,000,000 Newton's per square meter (100 pounds per square INCH is 890,000 Newton's per square meter, times 3.14 (the number of square inches of the piston)) But that's per square meter - got to convert back to the size of the piston (in metric)
Area of piston in cm is 20 square cm, or 1/50,000 of a square meter
Divide that into the 2 million Newton's gives 40 Newton's
80 pound hammer is about 40 Kg
Divide the Newton's (40) by the mass (40) yields about 1 meter per second squared of acceleration.
This acceleration is about straight line (at least for the distance we are going). 1 meter is about 3 feet, so 1 foot in about 1/3 second.
This would result in 1 and 1/2 cycles (or a little more) per second.
I get about 1.7 full cycles (out and back) per second when I keep the decimals and conversion factors a little tighter and use a perhaps better estimation of the hammer weight)
So, close to the 2 full cycles per second target.
There are probably other losses and gains that I have not considered. For example, there may be other friction losses for the air in the plumbing (I de-rated the numbers - enough?) which would slow operation. Also, the hammer may not operate all the time at full stroke, increasing the number of cycles per second. Air pressure may vary (more pressure=faster, less pressure=slower). I did not take into account any mechanical friction, nor did I take into account the affect of gravity on the down stroke.
The 5 way valve we've chosen has a max rating of 5 cycles per second, so that is not a limiting factor.
Please let me know your interpretation of these (ok, I'll be gusty enough to call them) 'Calculations'.
We could go to a larger diameter cylinder (more force) at the expense of longer fill times due to the increased volume)
We could go to a smaller diameter cylinder, less force but potentially faster cycles.
(But I have to say that I think 2 inches looks like the sweet spot for a hammer of our selected weight).
I'll close with this blurb I found on a pneumatic calculation site: "If either of us remembered our physics, we could calculate the rate of acceleration but we’d have to convert lbs to mass and some other ugly stuff. The easy way to do this is to make sure you can produce double the force needed to balance the load (i.e. 20lb load; provide enough pressure to produce 40lbs force by the cylinder)... Unless you’re talking about a big cylinder being fed by a tiny (or very long) line, the time to extend the cylinder is next to nothing. Most times, you have to put some kind of flow control on the outlet to slow the cylinder down to keep from slamming it too hard."
Conclusion.Our 314 pounds of force working against our 80 pound hammer would seem to satisfy the 'double the force' proposition.
You can read more if you like one the #power-hammer-build channel in Slack.
I sent these calculations to the supplier we were going to use for our cylinder, valves, and plumbing, asking them for a sanity check, but only got back a reply, 'We don't do or comment on any engineering calculations'. Not helpful. But, with faith in our illusions, we went ahead with outbuild.
Some of the materials, beyond the I-Beam, were easy to source, some not so much. We had a lucky find at Winchester Metals - a big circle of 1 inch steel in the scrap bin. This became our anvil sow block. The big piece of 4 inch by 4 inch 2 foot long steel we needed for our 80 pound hammer was another problem. The only local supplier I found with stock was BMG metals who normally only sell a full length of stock. 20 foot long stock. However, they agreed to sell me a 5 foot length. More than we needed, but..... (We have some left over if you need some.)
Assembly was uneventful, just time consuming. Initial trial was....impressive.
The Power Hammer uses a cam design driven by the hammer itself. As the hammer falls it triggers a valve that swaps the airflow to the cylinder to pull the hammer back up. As it travels up, the other end of the cam triggers another valve to send the hammer back down. A foot treadle moves the cam to trigger the first valve. They cycle repeats as long as the treadle is down.
Subsequent tests confirmed the design
Earlier this year we poured a concrete base in the Blacksmith area for the power hammer and a few weeks later moved the beast to its new location. Placing the hammer on its base went well.
The lower building was plumbed for compressed air and the last two tasks, getting the air compressor hooked up to power and the local Power Hammer connections, were completed.
This tool, as suggested above, is a Beast. It hits fast with a lot of power. We actually had to add a pressure regulator to rein it in a bit.
A note from the Red Tool Workshop syllabus:
"NEVER EVER let any part of your body get between the Hammer and the Anvil."
Not to put too fine a point on it, but body parts caught between the hammer and the anvil will be turned into pudding.
Safety Glasses are a must, and you will probably want hearing protection as well. (The impact of the hammer with the anvil makes my ears ring.)
We currently have fullering (rounded) and flat dies for the hammer. And, we can make more for as need arises.
Tool will make drawing out operations much faster and a lot easier on your hammer arm.
We also have a hydraulic press in the Blacksmith area. But it is an automotive type press with an air-over-oil jack to supply the 'push'. This is not ideal for metal fabrication. It could be used, but it's quite slow and requires manual release to get the press ram to retract. Current consideration is to replace the jack with a regular 25 ton cylinder and hydraulic pump. For controls, I'd like to try both a manual and electronic control set-up very similar to the Coal Iron Works presses. And, we'll need some new dies. I feel a new project brewing.
