Press Repair

Some of The Presswork We Perform
Fitting A Crankshaft

     We have been in the press construction business for a long time. Fitting in new main bearings into a frame and then fitting a crankshaft into the new main bearings can be a tedious task that requires a lot of effort and patience. There is a lot of measuring involved. The bearings themselves must fit into the main bearing cap and the frame nice and tight without any gaps. Then the cap must fit to the frame perfectly flat without the bronze holding it up. The radius of the bearings must fit the mating radius on the crank. When your bearings are all installed you are ready to begin opening up the bearing I.D. to fit the crank in. You must hone out the I.D. of the main bearings just a few thousandths over the O.D. of the crankshaft all the while making sure that the main's I.D. do not develop an egg shape. Once the crank remotely fits in the bearings, we then cover the journals of the crankshaft in HI-Spot Blue to find our high & low spots. If a high spot is hitting the crank too hard, we take it down with a scraper until the HI-Spot Blue spreads across the bearings and the crank is able to rotate freely by hand. Imagine trying to do all of this on a fully assembled straight side press. Bringing the crankshaft in and out in a repetitive manner. It is a very time consuming process.

Fitting A Pitman

     Pitman bearings follow the same process. In the photos to the right you will notice there is no gap between the pitman itself and the pitman cap. You will also notice there is no gap between the bronze bearing and the pitman & cap. There are no shims to assist the fitting either. Everything in these two photos have been fit tightly together and checked with a .0015 feeler upon completion of assembly. Gaps will cause unnecessary flexing and distortion which will lead to broken bolts, increased wear, damaged crank, etc. Only when that is achieved the honing process can begin. When honing has been completed, you can put in any lateral oil grooves and things of that nature. In the photos you will notice two different styles of pitmans. The one on the left requires an additional ball screw and the one on the right is a complete unit. The pitman on the right is most commonly referred to a knuckle joint. They are normally used on higher tonnage machines that require greater accuracy with a larger ram face. The bottom of the knuckle joint pitman has a hole at the bottom, this is for the wrist pin. Normally this hole will have either one long bearing / bushing press fit into it or it will have two small ones, one for either side. The curved portion at the very bottom traditionally fits into a knuckle seat which is build into the ram or slide adjustment screw.

Fitting a Ballscrew

     In this photograph to the left is a ballscrew, ballscrew nut, & seat. These are three mating surfaces all of which must be carefully fit together before assembly. I cannot not tell you how many times I have seen these improperly installed there have been so many occasions. Many times the customer purchases a new assembly and just blindly installs it into the machine without proper fitting. They just tighten it down as much as they can and begin running. This is absolutely the wrong assumption. First the ball end of the screw gets wiped down with HI-Spot Blue and then the ballscrew seat gets placed on top of it and is gently rolled around the ball. Doing this transfers the surface of the ballscrew to the seat so that you may distinguish the high and low spots. If the seat is has blue spread around evenly across the inner curvature of the seat, then it is making a good, solid contact with it's mating surface. If there is just a couple spots and nothing else, then it is going to require some extra work. The ballscrew nut goes through this exact same process except from the bottom up. It must pass over the screw thread to mate the ball's surface. The top and bottom of the ball are not the same, it is not a perfect sphere so each part must be fitted into the area that they would traditionally mate with. If you have put on bueing and you do not have a good, solid surface contact than the seat/nut will require scraping until the bluing gives you a good spread. Not doing this will give you excessive space between the nut, screw & seat which creates excessive slop in the stack. This causes a hammering effect which can damage parts. Also, the ballscrew will probably squirt oil on the operator.

A Quick Overview On Rams

     Sometimes you have to pull the ram. Either you are working on the ram or you have to pull a crank or a die cushion. I think the ram is the most labor intensive parts of the machine. The ram also contains multiple systems, it has a lot of working surfaces and just also happens to be the business end of the press. The ram is also a giant pendulum whether it has one pitman or two or four. Gravity is always pulling on it, so take that into mind when you are leveling you're machine. It contains the slide adjust, it is part of the oil recirculation system (most of the time) it opposes the counterbalance, initially driven from the crank, and punching parts out all at the same time while staying perfectly square in three dimensions. The wear strips on the ram's gibbing must be perfectly perpendicular to the ram's face within a couple of thousandths (length depending) all the while running perfectly parallel with one another within the same tolerance. Gibbing is a loaded subject for the stamping industry. Many manufactures do not know why they cannot hold a good repeatable tolerance on the ram face and its gibbing! I'm sure they may know why but, they don't want to. It can be a long and expensive process to properly address the issue and sometimes it involves a lot of down time. The face of the ram should be free from burrs, knicks and slug marks at all times. Imperfections in the ram's face hinder the ability to properly measure the shut height side to side & front to back. It also creates an insufficient mounting surface for the die which will turn into excessive deflection. Setting a ram in another one of those extremely tedious jobs, there are many things to take into consideration. As far as wear strips & gibbs are concerned, this another one of those things where you cannot just purchase replacement parts, install them on the machine and assume that everything is just going to work case closed. It may be great in theory but bad in practice.



Seals & Bushings

     Rubber seals go out all of the time for a variety of reasons. Most of the time it is due to age & wear. Other times are due to something that could have been avoided to begin with such as catastrophic failure. I prefer to avoid "wait and see moments". When you hear a leak or see some excess fluid the time has come to perform some maintenance. If you take to much time beyond that you risk damaging the working surfaces that the seal comes into contact with which can end up costing additional cash to repair. 

     The photo in the upper left hand corner is the die cushion from an 800 Ton Minster. While the ram was pulled out to have some work done the management decided to pull the die cushions for maintenance. The decision paid off because the seals in the cushions were all shot. If you look at the picture the outer edge of the seal is wavy. There is no way in the world that holds back air in an efficient manner. In the photo just beneath that one, there is another bad seal that was in the same cushion. The gland bushing was in okay shape but it was decided to just change it while it was out anyway.

    The lower right hand photo is the gland of a hydraulic cylinder. It is for the mandrel that expands and contracts on the I.D. of a steel coil on a decoiler unit. This particular job was a little distressful because we could no longer find a parts manufacturer for this particular piece of equipment. We had to make our own O-rings and fabricate out own gland bushing. The photo shows a new, unfinished gland bushing being fitted for the back end of the hydraulic cylinder.


     Counterbalance Cylinders are a little more tricky, we rebuild these very frequently. It is normally not the machine at fault for damaged and worn out cylinders. Counterbalance cylinders are just traditional air cylinders mounted to a press with the intent purpose of counterbalancing the weight of the ram. The reason the seals go out and the cylinder walls get damaged is due to alignment issues. The counterbalance cylinder gets mounted stationary to the press, it is not able to move front to back or side to side. When the ram of the press is adjusted one way or the other, the counterbalance cylinder is unable to compensate. When this happens the counterbalance rod is operating in a slight angle not noticeable to the naked eye in most cases. This causes the seals in the cylinder, the counterbalance rod and the gland in the bottom of the cylinder to wear out in an accelerated rate. This problem can be easily avoided by installing a slip joint coupling on all of your counterbalance rods. This allows for gib adjustments without having to worry about counterbalance cylinder alignment.

     Clutch and brake air bladders contain seals as well. Not all clutch and brake units are crated equal. Some are all in one unit and some are independent units such as a brake on one side of the crankshaft and the clutch on the other. The photo to the left is the brake hub that goes over the clutch on a 100 Ton Minster. It has a round doughnut shaped air chamber with an inner and outer air seal. There is a plate on it's backside that specially mates up to the back of the hub with large O-rings and sandwiched in between the two plates is a large brake ring that the rotation of the crankshaft stops on. On occasion these O-rings wear out and must be changed. The clutch will normally have an audible air leak accompanied with a slow reaction time at the beginning of the stroke due in part to the brake having a hard time letting go. Also on this particular air bladder you will notice two quick air release valves that are notorious for getting caught on themselves when they have inadequate lube in the cylinder or the seal is worn out. Basically what happens when you hit the palm buttons to cycle the press, air gets sent to the clutch and will sometimes immediately escape from the air bladder through the quick air release. This sometimes is mistaken for a blown air bladder seal and is not anywhere near severe to repair.

Chris's Machine Repair LLC Welcome to the Rust Belt!

© 2017 by Chris's Machine Repair LLC.

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