Saturday, May 18, 2013

What are Stamp MIll "Shoes"

Stamp mill shoes are the consumable attachment “shoes” on the lower end of the stamp shafts that crush the ore down to the consistency of sand. The stamp is made up of the stem, tappet, boss and the shoe which is attached to the end of the stamp stem. The drawing below shows the location of each of the components of the stamp. You can see the holes in the boss that allow removal of the shoe and the stem from the boss. The unusual thing is that all of the components associated with the stamp are press fit together, not screwed or threaded. The shoes are attached to the boss with hard wood shims. Shoes are frequently replaced since they do wear down by crushing the ore that is sometimes quartz which is very hard. The shoes start out about 6” to 9” of steel pad that will wear with use. The rule of thumb is if the shoe pad gets down to less than 2” thick then it needs to be replaced.  The shoe is removed by placing a drift pin in the lower hole of the boss and forcing the cone on the shoe out of the boss. Once the new shoe is placed in the mortar box, the stamp is dropped on to the shimmed cone of the shoe and presses itself to the stamp.
During a previous stamp mill restoration, we got to the stage when we needed to install shoes for a 10-stamp mill project, but there were no shoes with the artifacts for the mill. The shoes were classically made from steel castings, so I tried to find a foundry and there were no foundries in Arizona that would cast the shoes. I went to three other foundries out of state and was surprised with the cost of casting shoes. I contacted the Star Foundry and Machine Company in Salt Lake City, Utah; Kit’s Foundry & Machine Inc. in Shelley, Idaho and  AFFCO in Anaconda, Montana and their quotes for the shoes was more than the museum had figured into their budget. Part of the cost is that you have to pay for the manufacture of the casting that the shoes will be poured into. That ran from $125 to $350 for the casting. The cost of the metal ran around $3500 for 10 Stamps. This was for shoes that included some manganese “hardener” in the castings.
The decision was made to make the shoes from 9 ½” bar stock. We found a supplier that had some used hydraulic piston shafting that had manganese hardener and we got the material for $600 for the 10’ of 9 ½” shafting. The more expensive part of the process was the machining of the cone on the shoe. That came to about $2,000. We saved over $1,000 plus we had some very hard shoes and did not have to pay for shipping.

I found a bill of sale for steel shoes (below) for a stamp mill back in 1912. Joshua Hendy was an important producer of stamp mills back in the late 1800’s. The cost back then seemed to be inexpensive at $21.00. I did a study on mining prices in 1915 as compared to 2012 and found that back then the stamps were actually more expensive in comparison to today’s prices. The quote I received on the cost of the shoes would have come to $3,850. The Consumer Price Index (CPI) for 1915 is equal to $1 = $23 in 2012 using the formula on the Website The 1915 cost with the CPI came to $4,830 in today’s money. That was $1,000 in today’s money more for the 1915 prices.

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