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Die Keys for Little Giant Power Hammers

contributed by:Carl Sharp, Iron Phoenix Forge, Chino Hills, CA
written by: Sid Suedmeier, Little Giant/Mayer Bros, Nebraska City, NE: 402 873-6603

Before I get started into this subject, I want to make one thing very clear. What I am going to share with you is not, nor ever will be, the final word on die keys, but we have to start someplace. This information has been accumulated from working with Fred Caylor, practical experience, and from talking with many of you that work with these machines. All of my experience has been with Mayer Bros/Little Giant but will still pertain to many other brands of power hammers.

To begin with, the old key and die need to have been removed. This in itself can present some real problems, depending on what previous methods have been used to keep the die in place. We will discuss only the standard single key as all the alternatives that have been tried is a whole story in itself.

To remove a standard key that is not all battered up, we use a long chisel that has been ground thin to reach behind the die, The end needs to be squared off to present a good contact for the driving area. After you have the chisel ground to suit you, give the small end of the key a good hit with a medium sized hammer, two to three pounds. Do not tap with a small hammer, as this tends to swell the end. The use of penetrating oil and heat can also be very helpful. I have seen some dies that defy all methods and have to be literally blown out with a cutting torch. Once the key and die have been removed we are ready to check the dovetail and die for any repairs or modifications that may have to be made to insure proper fit.

At this point we need to check the condition of the dovetail and floor the die sets on. The floor needs to be flat. Many times the die will be hammered into the bottom; this needs to be corrected. For minor erosion, flat filing will take care of it. For major damage, other methods will be needed which can include welding and machining.

The sides of the dovetail can generally stand some shaping up; again, a good flat file can be utilized. Care should be taken not to modify the angle of the dovetail. You want to achieve a good, straight, smooth surface so as much contact as possible can be obtained between die, dovetail, and key.

At this point we need to measure the dovetail to check for taper from end to end. The factory machined 1/8 inch per foot of taper into the dovetails. It is generally set up with the small end to the left and the large to the right. It needs to be checked and verified. The sow block could have been turned on models, so equipped, causing it to be the opposite. The dovetail in the rams is generally not tapered from side to side. The die also needs to be checked for the same taper, On the new dies that we make, the ends are marked "W" for wide and "N" for narrow. Set the die into the dovetail with narrow end into the wide end. This creates a natural taper into which the die key will be fit.

The die is usually positioned to the front of the dovetail with the key going into the rear. Variations of this are found on some machines. It can also be changed in order to position some dies for proper relationships to each other.

Check the corner of the die for proper radius so it does not keep the die from seating squarely. The angle at the point where the die contacts the front of the dovetail should be compared with the angle of the die (they should be the same). This creates two parallel surfaces that should contact each other squarely. Minor corrections can be made with the file or a small grinder. Proceed slowly with corrections. This fit is very important.

Move the die to the key side and check for the same fit. The angles should be the same, or a little wider, at the bottom. It can not be wider at the top as this will cause the key to "squirt" up out of the dovetail as it is driven in.

Once you are satisfied that you checked all the above, we are now ready to start on the key itself.

There is a controversy over the material the keys are made of. The factory keys seem to be made out of mild steel. Tool steels and spring steels have been used with equal success.

Measure the opening the key will fit into. Let's say the small end is 3/8 inch and the large end is 5/8 inch. Start with material at least 5/8 inch thick and with enough width to cover the dovetail/die face. I always make it at least twice as long as needed, trimming later. Shape the taper to the key using a belt grinder with a 50 grit belt. They can be forged to a rough shape before grinding. Once you get enough taper to start fitting, coat the two surfaces the key will be contacting with Prussion Blue. This is used in many close tolerance fitting applications in machine shops and garages. The Permatex brand is part number 35V. Most auto parts stores should be able to order it for you if they do not have it on hand.

Insert the key into the opening and tap in lightly. Drive the key back out with the chisel and notice the contact area as indicated by the blue left of the key. These are the high areas that need to be removed by grinding. Make corrections in both the long taper and the top to bottom dimension. The goal is to achieve at least a 70% to 80% overall contact area. Take it slow and stop to check often. I always mark my key so it is certain that the same side is always up. This is also good for later reference when changing dies.

Continue to check and grind until the key will extend to at least the far end of the die. Watch the contact area closely. I have seen dovetails broken because of small contact areas exerting all the force into a very concentrated spot. Extra time here can save you time later.

Trim the key to length, leaving some extra on the large end to allow the key to be driven in as the key conforms. Chamfer the end generously, especially the small end, so it does not swell up when driven.

Drive the key in, again using a two to three pound hammer. If properly fit, it should drive to a certain spot and you should get a definite solid sound when striking the key. Hit it solid, but don't overdo it. It isn't necessary if all things are right. Run the hammer for a few blows, and tap the key occasionally to check. After a few minutes of operation the key should be seated and need very little attention for quite some time.

Another little trick if the sides of the dovetail are not in real good condition is to use a soft brass or copper shim. This is made of .030 or .040 thick soft material which is placed between the die and the side of the dovetail on the side away from the key. This softer material gives additional contact on an irregular surface.

I hope this will ease any problems you may have had keeping dies from moving while in use. From some of the conglomerated methods I have seen on machines moving through the shop, it has been a problem for a long time. No need to weld, double wedge, bolt, pin, use witchcraft or many of the other methods if the time is taken to do it right the first time.

One little afterthought: The key on the upper 25 lb. Little Giant is a double taper key, meaning it not only tapers from left to right, but also across the width. This presents no special problems; it still has to fit carefully for good contact. All above procedures still apply.

You will notice the words generally and usually have been used, The reason for this is that about the time you think you have seen it all and have found a fix for them all, a variation pops up that you had never thought about. Keep an open mind, think it through, and try to do it right the first time.