RAPID ECONOMY STAMP MILL
I received a copy of a letter from Curator, Richard Sauers of the Western Museum of Mining & Industry in Colorado Springs. It was a letter from the RAPID ECONOMY STAMP MILL COMPANY, San Francisco, CA, dated January 3, 1905, touting their 3-Stamp Mill. He found this letter in their files while doing research and figured that I would be interested. He was not wrong. This was not your common run-of-the-mill stamp mill as they said in their letter.
I actually found one of these stamp mills while touring California. It was at the Ironstone Vineyards near Mariposa, CA. At the time I was very impressed with the difference in the construction of that stamp mill. It had three separate mortar boxes that was not that uncommon, but the real difference was the cams. This was not your common cam, but a three-throw crank shaft, that intrigued me at the time. The mill at the Vineyard was falling down and I could not get a good view of this crank mechanism. The picture below shows the stamp mill at the Ironstone Vineyards as I saw it a couple years ago:
I read through the letter that Richard sent to me and found some very unusual characteristics of this Rapid Economy Stamp Mill (RESM) machine. The following information is what I found in the letter touting this machine:
Speed of the machine A normal gravity stamp mill can produce about 95 to 105 drops per minute. The RESM speed can be set from 150 to 250 drops per minute, depending on the material being crushed. This is due to the crank mechanism. I will quote the letters author, “Our mill has a 3-throw crank shaft, to which is attached a rocker arm on a fulcrum shaft. The cross-head of this arm holds the stem, very much as the hand holds a churn dasher, and brings the stem down with the first hammer blow.” As already stated, this can produce 150 to 250 strikes per minute.
Springs The springs add additional energy to the dropping stamps. With the standard gravity stamp mills you just have the weight of the stamp plus gravity to act on the ore. The RESM has two heavy duty steel locomotive spring. These springs take up the jar and recoil of the blow from the stem and prevent rapid crystallization of the stem. The rapid blows add energy to the stamp on the downward action and produces twice or more to the stamp quantity crushed by the gravity mill. This RESM will produce 8 tons through a 40 mesh screen against 3 to 4 tons in the gravity mill.
Production The extra screen area allows more pulp to be processed. This added round screen surface of 440 sq. inches for each stamp or 1320 sq., inches for the battery of 3-stamps. This is larger than any gravity mill built.
Hp Requirement The Hp requirement for this mill is much less than the gravity mills. The size of the present mill is 800 pound stamps and 8” hoes and dies. This mill will operate on 3 Hp or 1 Hp per stamp as against 2 ½ to 3 ½ for the gravity mill with the same size and weight stamps.
Operation Costs The cost savings of this mill speaks for itself. RESM can operate a 40 stamp mill on 40 to 50 Hp were as a 40 stamp gravity mill require a least 125 Hp. In other words RESM gives double the output of crushed ore with 1/3 Hp required.
Transportability The RESM is very much lighter in construction and particularly adapted to transportation to out-of-the-way places. The heaviest part of the RESM is the mortar bases that weigh about 700 pounds each and other parts weighing325 pounds or less. The total weight of the mill is about 15,000 pounds.
The Rapid Economy Mill with (3) stamps with 8” shoe and die can crush a minimum of 5 tons to the stamp through 40 mesh screen of ore fed to the stamps broken down to 1 ½” to 2” ring size, and crushing 8 tons to the stamp through 40 mesh screen of ore fed to the stamps broken to ¾” ring size.
It will crush daily through a 20 mesh screen 10 to 15 tons to the stamp, according as the material fed to stamps is broken coarse or fine.
It crushes this quantity of ore with one-half the Hp required by gravity mill of the same size.
The actual crushing cost for mill power is less than five cents per ton. Think about it for you who have gravity mills and are paying from 15 cents per ton and up for power.