Ahmeek MillIndustry

Last Stamp Standing

&oiDuring the Copper Empire’s peak, over 100 steam stamps were in operation across the peninsula. As mines and their mills succumbed, these massive stamps were quickly sold or scrapped for quick cash. With the arrival of the Second World War any remaining stamps were quickly drafted into the war effort – providing much needed steel and iron for military equipment. By the end of the empire in the 60’s, stamps had become and endangered species. Today only one has managed to survive.

Sitting high atop its massive concrete foundation, the iron monstrosity looking out over Tamarack City is one of eight stamps that once graced the massive Ahmeek Mill. While all of its brothers have been removed,this one has inexplicably managed to survive. As one of the last mills to close down on the peninsula, this stamp represents the best and brightest of Copper Country industrial know-how. Because of this, the Ahmeek stamp is a slightly different breed then what we had been discussing lately.

As far as I can tell, the stamp at Ahmeek is of a steeple-compound design – probably a Nordberg. This stamp is very similar in almost all regards to the Allis stamp featured previously except for the addition of a second driving cylinder powered by low-pressure exhaust steam from the main cylinder. This is known as a compound engine. When the two cylinders work the same shaft (in this case the stamp shaft) and are mounted on top of each other, the engine is then known as a steeple-compound.

To get a better idea of how this type of set-up works, we’ll take a tour of the process along the diagram of a Nordberg stamp seen above. High-pressure steam from the boiler house enters the first cylinder (B) by means of a double-acting valve assemble (A). Here steam is used to both push the stamp shaft (I) down, as well as push it back up (thus the double-acting part). After expanding in the cylinder this steam loses some of its heat and becomes low-pressure steam. The low-pressure steam is exhausted through (C) and enters a holding tank (D). From there the steam is send upwards through a connector pipe (E) before entering the low-pressure cylinder at (F). In this cylinder (G), the low pressure steam is used only to help push the stamp downward, (single-acting) and does not raise the stamp. The steam is then exhausted (H) and the process repeats.

Let’s take a closer look now in practice – using the remains of the Ahmeek stamp as a guide:

Compared to single cylinder stamps such as the Allis, these Nordberg’s are easily identified by the iron box sitting atop of the unit. This box houses the low-pressure cylinder and valve assembly. The high pressure cylinder sits directly below this. Both valve assemblies are controlled by a series of rods and cams, which are powered by the large pulley wheel on the left. This wheel would have been hooked to a belt drive from the ceiling, powered by a steam engine somewhere in the plant. Below the cylinders and valve drive is the stamp shaft and mortar box. You can make out the feed chute in which ore would have entered the mortar on the right.

While the stamp appears to be intact, it is missing the low-pressure storage tank and separator assembly as well as the low-pressure inlet pipe that would have connected that assembly with the upper cylinder. These pieces were probably removed in anticipation of scrapping the stamp, but for some reason the process was never finished.

Here’s a closer look at the upper cylinders and valve eccentrics.

Here’s a closer look of the Mortar assembly. In this view you can clearly make out the stamp shaft, as well as the attached pulley which would have been used to turn the stamp shaft every few cycles. Below the mortar box is the remains of the discharge chute (which appears to still have sand in it since grass can be seen growing out of it). From this chute the copper rock would have been sent on to the next step in the process.

A step we take a closer look at next…

Information and illustrations from “A Textbook of Ore Dressing” by Robert Richards.

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  1. Mike: Slight typo in the description of the stamp diagram near the start of this article. The steam should be exhausted at “H”, not at “E” as indicated. Otherwise, fantastic work! I always wondered how these stamps worked.

  2. Sometimes I wonder how I could have spent 4 years as an undergrad at Tech — visited Hungarian falls plenty of times — and never noticed that giant metal monstrosity standing watch over Tamarack City. The old stamp certain is an amazing piece of work. Thanks for figuring out so much about its workings!

  3. I was actualy just going to ask about this…….. and what mill it was and about it..

    Really funny that you posted it when you did.


  4. I had originally meant to use some of these images to illustrate the last post I did about the stamp technology – until it became clear that this one and the Allis stamp were two different beasts. By luck I happen to come across an edition of the Ore Dressing Textbook that featured the Nordberg Stamp – which was a dead on dupe of this one. Thus I moved those images here and decided to talk about this stamp separately.

    I had heard rumors that the park is very interested in this baby, and has written up plans for its removal and rehabilitation. But I guess its very expensive (that stamp is very heavy I’m sure) and is waiting on funding. Why it had survived relatively intact however, is still a mystery.

  5. Well interestly enough, the Western Museum of Mining and Industry does list an 80 ton Nordberg stamp from the Osceola Mill and they pride themselves in that most of the equipment they have still operates, it doesn’t say the stamp does though

  6. I can verify that they do have the stamp. I have been there a couple times since I am going to school right across the highway from there. They also have a good collection of drills and other mining gear as well as big machinery like a headframe, bucket loader, etc. It is a great museum with a good research library. Anyone who visits Colorad Springs should stop by the museum.

  7. Glad you guys enjoyed, but I’m afraid the stamp itself is as far as I got. Currently the ruins are marked “keep out” (probably due to the playground next door), and I won’t be entering until I get permission. Some day though…

  8. Found this below one of the C&H News and Views about the Ahmeek Mill, this is how they were watching every penny.

    Persons having occasion to climb the many flights of stairs to the head–feeder floor at the Ahmeek Mill has noticed a change of scene there in recent months. In addition to the regular lighting system, there are now rows of blinking lights, both white and colored, which appear to be flashing on and off as far as the eye can see. Closer inspection will reveal that considerable other electrical equipment has been added–counters, relays, more lights and a maze of wiring. The installation looks complicated, but has a very simple assignment.
    The eight Nordberg compound stamps in the mill, which now handle our entire mine rock production, were designed and built to operate with a stamp shaft stroke of about 24″. Operation with a shorter stroke prevents stamping at full capacity, and wastes large quantities of steam. Since each stamp consumes about $100 worth of steam per day, we cannot afford to throw a very large fraction of this away.
    For the first 37 years of mill op-eration there was no way of determining definitely how much of the time the stamps were operating in the proper range of stroke. The elec-trical equipment was installed to get this information.
    The unobtrusive but ever-watchful operator of this assortment of equipment is a small photo-electric” eye, suspended from the upper floor near one leg of the main frame of each stamp. In a corresponding posi-tion near- the opposite leg is a light source; which directs a narrow beam of light at the eye. When the head–feeder feeds rock into the mortar in such a manner as to allow the stamp to make a full stroke, the stamp shaft obstructs the light beam at the bottom this stroke, thus enabling the eye to “see” it.
    Whenever the eye observes that such a low stroke has been made, it immediately flash-es a signal through “blinker” lights, to let the head feeder and mill run-ner know that the stamp is operat-ing in the proper range. Since the eye itself doesn’t have a good mem-ory, it needs assistance in remember-ing how many low strokes were made during each shift. This assis-tance is supplied by a small counter which “kicks” over a number every time the blinker flashes. Thus, the total number of low strokes for any period can be determined by obtain-ing the counter reading at the begin-ning and end of that period. Also, a pen recording set in the mill pump house shows the time distribution of all low strokes made on every shift, by “writing” on a moving chart.
    To date, the information obtained by this equipment has been very en-couraging, indicating that a large majority of the head-feeders are op-erating their stamps in the full stroke range. The headfeeders on Foreman A.W.Grief’s shift have maintained an exceptionally high average stroke score, and the other shifts are improving steadily. The information also indicates that on those shifts which have high average “count” the steam consumption is less than on those with a low aver-age. This and other information in-dicates that the equipment will be a very valuable aid in following mill performance and maintaining top efficiency.

  9. The following info is from the October 19, 1912 Engineering and Mining Journal (E/MJ). The building was 218 x 190 feet. (Not sure which is length and which is width.) The building at it’s highest point was 122 feet above lake level. The trestle was 106 feet above lake level. The boiler house was an integral part of the building. There was also a small “forge shop” and a small machine shop.
    The bins had a capacity of 1000 tons each. These were the largest steel mill bins in the Copper Country. There were two tracks on top of the bins. Coal was delivered using the trestle and dropped by gravity to the bunkers. The boiler house contained six locomotive boilers of 200 horsepower each. The boilers were stoked by hand. (What a fun job!)
    The stamps were Nordberg compound steam stamps, dropping 106 times per minute. (Imagine the noise!) The valve gear was operated by 75-hp motor. The mortar base was 50 feet above lake level. The block is in the shape of a truncated pyramid 40 feet square at the base and 38 feet high.This block rests directly on a slab of concrete 4 feet 6 inches thick. This slab rests on “hardpan.” A mile of steel cable is embedded in each mortar block and slab, “uniting them thoroughly.”
    The two east head’s product of the mill was “treated”in a different method than the product from the two west heads. Once the mill was expanded to eight heads the same method of treatment would be used. There is a two and a half page explanation plus two drawings of how the ore was processed.
    They did not use any method of flotation separation at the time this article was written.
    Also there was 40,000,000 gallon per day Nordberg pump to supply all the water needed to operate the heads currently operating and the four new stamps when they are installed. Also in this pump house was a 300 kw generator.
    In the first half of 1912 the mill produced 7,779,023 pounds of copper at a cost of .73 cents per pound. The rock yielded 24.7 pounds of copper per ton.

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