So my coin press had been acting up sporadically over the last several months. Usually, the symptom was that it wouldn't complete the ejection cycle. After a coin is stamped, the coin will be lodged tightly in the collar. The ejection is performed when the press pushes up on the lower die to force the struck piece out of the collar. And the last action in a striking cycle is for the lower die to drop back down into the original (lower) position. When it does that, a new planchet can be inserted into the collar for the next striking. The problem was that, more and more often, the lower die would not drop back down at the end. My quick work-around for that was to remove the lower die and repeatedly strike "air" until the lower die dropped back down, But, eventually, I could not get that to work at all. I suspected that it might be related to the "Clutch Valve Failure" fault that I worked on a few weeks ago. It was time to fix the problem once and for all. My biggest challenge was not knowing entirely how some of this worked, or what would be necessary to fix it. After taking off a couple cover plates and looking into some narrow spaces using a bright flashlight, I began to theorize that something was not right in the large shaft that contacts the bottom of the lower die anvil (to push it up). There was only one way to determine for sure what was going on here. I had to remove the large orange-painted metal block (red arrow) and examine the cylinder and bore surface inside it and under it. It took every trick I had to get the large bolts loose, and use wood planks to slide the block out onto a tall cart. The piece weighs over 120 pounds. When I finally got it out, this is what I saw under it (the screws, not the coin shown for scale): One screw was bent a little, but relatively undamaged. The other screw had obviously been caught in the mechanism and destroyed. Since I got the press, I have never been into this area before. The screws were undoubtedly left there by a careless US Mint employee. I would never do that. It wasn't until recently that it managed to cause a noticeable problem. But I believe that the one screw had actually been causing damage for quite a long time. The large steel cylinder that pushes on the bottom of the anvil slides up and down in a heavy brass-lined sleeve. This cylinder also has a flange on the bottom of it that acts as a stop to the sliding. The screw fragment had apparently been smashed between the flange and the bottom end of the brass sleeve. This caused a deformity in the brass sleeve which impinged upon the sliding motion. The impingement was severe enough that I could not push the cylinder through the sleeve. I had to use a sledge hammer to pound the cylinder out of the sleeve. Then I used various sandpaper and stripping tools mounted on my hand drill to "hone" the bore (sort of like what you would do to a cylinder in an engine block. Eventually I got the cylinder to slide freely in the bore. I put things back in place (also very difficult due to the weight). Then I tried striking. I was expecting it to work perfectly. The ejection system never worked as smoothly, quietly, or effortlessly as it did now. However, there remained one big problem. The lower die still would not drop down. And at the point in the striking cycle were it was supposed to do that, there was a loud hissing sound coming from the left side of the press. Full pressure air was being vented, without restriction, into the room. Here is the left side of the press (behind the cover panels): The air control valve that I worked on a few weeks is here (orange arrow, in image below). The main lever that actuates the lower die up or down is the large red-painted metal piece (green arrow, in image below). After trying to figure this out for a day or two, I determined that the pneumatic actuator (purple arrow) is what causes the lower die to move UP to eject the struck piece. Now the question: what gizmo causes the lower die to drop back down, and why is so much air escaping ? Eventually I took both air lines off of the air control valve (orange arrow). I finally determined that, at the time when the lower die was supposed to drop down, the valve was sending air pressure OUT to the upper air line. But the same air pressure was being sent back through the lower air line, and the control valve was simply venting this out to the room. It was as if the two air lines were connected with no hindrance in the flow at all. That shouldn't be. Also, the two air lines wrapped around the red lever and disappeared behind it. What did they do behind there ? The red lever is actually constructed out of two identical and parallel steel plates with about three inches of space between them. After using a mirror and a flashlight, I found that there was another pneumatic cylinder (just like the one indicated with purple arrow) INSIDE the large red lever. The blue arrow points to it. It is mounted diagonally, parallel to the two air lines that are in front of the red lever. Now, how in the hell do I get that damn thing out of there ? The lower end has a cotter-pin type of attachment. So that was not a big problem. The upper end was a mystery - it was very difficult to see in there. Finally I noticed a 1/2-inch diameter pin in the red lever (just out of the picture but located about where the white arrow is pointing to). If I could get that pin out, the pneumatic cylinder would come right out. First I tried pounding the pin through. No matter how hard I pounded with a hammer, it wouldn't budge. But even if it had moved, I realized that there is not enough clearance behind the red lever and the bulkhead for the pin to be removed anyway. And what if the pin had a step-down diameter ? That would prevent the pin from moving forward at all. The pin did have a small threaded hole. So I concluded that, with the right screw inserted, I might be able to use that to PULL the pin out. I went to the local hardware store and "MacGyvere'd" this pun puller tool (sort of like a miniature steering wheel puller, if you know what those are). The small screw goes into the pin. The large bolts are screwed inwards to push against the surface and pull the pin. I deployed my new tool and turned the bolts as hard as I could. I only managed to bend the metal plates in my tool. The pin still did not move, not even a thousandth of an inch. So I began to think that the pin was not designed to be removed. I investigated removing the entire red lever arm, but that appeared to be basically impossible. I had no hope of fixing it unless maybe I could take the pneumatic cylinder apart while it was still in-place, and replace the guts inside it. The only chance of doing that was to remove other items that were in the way. So I took out the blue air pipe (yellow arrow, in image above) and the flywheel brake mechanism (red arrow, in image above). After taking those out, I had a little better view of the upper left end of the pneumatic cylinder. And then I saw it. A small set screw perpendicular to the pin shaft. It was hidden just around the corner behind the front plate of the red lever. Once I removed that set screw, my tool pulled the pin out like butter. The pin actually had a fairly deep groove that the set screw went into. At this point I still wasn't 100% sure, but I was pretty certain that this was the offending part: My theory is that the ejection cylinder was severely pinched in the bore (inside the large orange block). And someone turned up the air pressure to overcome that. The high air pressure eventually blew out the pneumatic cylinder. This is the inside of it. At first, it may look OK. But the rubber diaphragm is supposed to be securely fastened to the brass shaft were the groove is (red arrow). It was torn off of its mounting and also degraded to where it would let air pass right through it. The crate of spare parts that came with the press still provides gifts almost 20 years later. I have two more replacement pneumatic cylinders. Now that I have a replacement installed, when I stamp things the press works perfectly. It is quieter, smoother, and seems to stamp more effortlessly than ever before. I don't feel any vibrations in the floor, even when stamping at 300+ tons. Previously, I would. Now I can get back to doing some real work.
Thanks for sharing. Good thing you had some spare parts, and the skill to repair and replace damaged parts.
Made me miss all the hours underway shipboard down in the engine room and machine shop ... as if! I retired 27 years ago so memories are designed to fade away.
Had to go back and look at the posters name... Nice work Dan, did you Google a YouTube video or have a manual some things you just have to tear into to see if you can get it fixed.
I hope you know by opening that machine up you may have voided your valuable manufacture warranty. James
Your troubles sound frustrating to say the least! But, the accomplishment of fixing the problems makes up for that frustration, right? Right? LOL! YouTube is your friend. You can find out how to do just about anything on YouTube! This, however, I'm not sure there are many videos about. You just need loads of patience and the drive to tear it apart and figure it out! Great job!!!
That was a fascinating read, and a real exercise in problem solving! Thanks for taking the time to post it.
