Across the Bench: One-Man Solution

Several years ago when I was employed for another company, I was working second shift when a multicavity monster mold with way too many inserts landed on my bench. The inserts buried inside of this old forty-eight-cavity mold, required removal for routine cleaning. The standard technique was to use a sized nylon punch and a small brass hammer. Holding the punch with my left hand and the hammer with the other, the challenge was to tap the inserts out of the bore, just far enough to loosen them without anything falling onto the bench and risking damage. Since I was the only one working this shift and I could not find another set of hands, I could only attempt to tap out the inserts to a point that would allow me to lay the hammer down, push them out the rest of the way with the punch in my right hand while grabbing them with my left. Invariably, some of the inserts fell out. Lying the plate down was not an option because some of the inserts were loose enough to drop out, risking even more dings. I could have removed all of the loose ones, then lay the plate on parallels and punch out the rest, but I have never felt comfortable with that method either, since it is impossible to control tooling as it falls from the plate. I pondered the situation in front of me.

 

Tooling Solution

The solution was to design a tool that would allow me to remove tooling quickly and safely using only two hands. It would serve as both hammer and punch that would allow a controlled weight to be used with one hand and without fear of costly miss-hits.

The tool, a spring-load slide hammer, looks and works somewhat like a standard slide hammer, with a couple of important differences. The weight on most slide hammers is used to pull out pressed-in components. The weight on this hammer is used to push out components and the shaft is lightly spring loaded to return the sliding weight back to the end of the rod. This spring pressure also keeps the punch end of the tool in constant contact with the components being removed regardless of the speed used during repetitive blows. This eliminates rebounding and allows for better control of the exact amount of force, or length of stroke, needed to move the insert. Since the punch does not retract from the inserts during use, aiming the tool is not necessary, eliminating miss-hits.

In addition, for this particular application, I fashioned the lead end of the nylon punch to extend all the way through the three inserts, which kept them together during removal. After tapping them out, I placed each set of three inserts on a board that was outfitted with thirty-two wooden dowels that prevents the inserts from banging around during handling and cleaning.

 

Maintaining Control

Now, I have a spring-load slide hammer that allows complete control over where and how much force is applied to the inserts, freeing up one hand to maintain control of the tooling as it is being removed from the plate. It couldn't get any easier and better yet, safer.

Over the next few months, I will discuss the typical run/repair cycle of a standard thirty-two cavity unscrewing cap mold. I will discuss the necessary documentation and how a mold repair plan should be developed and used as we progress through the seven stages of a mold repair. Next month's topic will discuss clean/repair (C/R) preparation. Stay tuned.

 

Easy to Make

The spring-load slide hammer can be made by a "C" class machinist or higher, and from most steels commonly found in any toolroom. A few helpful tips when fabricating a slide hammer for your shop are: First determine the weight of the hammer that you use most often during the disassembly stage of a repair. Multicavity molds weighing 6,000 lbs or less normally have tooling that can be removed easily with a 24-oz. hammer. Notice the length of swing required (normally three to twelve inches) with your hammer to remove the tooling. This gives you an approximate stroke distance for the slide hammer (see Figure 1). When fabricating the weight of the slide hammer, I chose aluminum bronze because it wears better than brass, but stainless works great too and it resists rusting from the perspiration off your hands. Apply a light knurl and a few finger grooves to the O.D. of the sliding weight. This keeps it from slipping through your hand during use. The rod should be made from 0-1 or any prehardened and ground tool steel. Most shops have 0-1 in-house and it comes preground to size. Various configurations of punches can be made to fit the slide hammer, depending on what you need. Use nylon to make the punches if removing tooling with a highly polished finish or fragile edges, otherwise brass, copper or aluminum works fine. I threaded the punches for attachment to the slide rod, although you could easily fabricate a quick disconnect, use a setscrew against a flat or develop another means. The spring should only be heavy enough to return the weight to the back of the rod. The slide-hammer spring in Figure 1 is 0.035 dia. Make sure the punch stops the travel and not the spring. If the plunger's spring is collapsed completely and repeatedly, it will fatigue and break.