C Marshall Fabrication Machinery, Inc.

MG Swing Arms & Parallelism Control Compared to Other Systems

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Below is an example of a machine using linear guides (left) and one using MG swing arm guides (right). Linear guides have been used for hundreds of years so most manufactures take it as a given to use them in their machine design. However, time marches on and so do designs. The MG machine is a engineered machine with no givens.

There are several drawbacks to a linear system which we will show you below. We will show you why the MG system is superior to any other system available. It is apparent the Swing Guide System is more difficult and expensive to make; however, as we shall prove, it totally eliminates parallelism problems.

Let’s now analyze the different technology.

1)     Linear side guide system is accurate when the machine is new and the bronze slides are tightly adjusted between the side rolls support and its guides (the yellow bars of the drawing below). It takes power though to move because of the friction generated; this is why usually all machines like this have a higher installed power requirement.

After a running in period the guides run well and smooth, however, the machine now doesn’t need the extra power needed at the beginning. The machine still absorbs the entire power output. This is a waste of power and money as you have to pay for the power whether you use it or not. After a certain period of time, the bronze slides get worn out and it’s here that the machine looses precision. If you look at the second picture (right) of linear side guides sketch above you can see how the support will soon start to move inside the guides and you’ll loose side rolls precision. At this point maintenance is needed to get back to the initial precision.


MG system use a pivot arm swinging around a center fixed by means of a bearing. It is a proven system working for years without LOSS OF PRECISION. The coupling with shaft and bearing is a very strong and precise fit.  This has given MG a worldwide reputation of precision working for years.

2)   Side rolls parallelism: The basics of electronic parallelism is that one piston – say the left one – moves while the second – the right one – follows it by means of a communication between two encoders (set on each hydraulic piston) and an electronic unit. It’s a continuous adjustment that is moving up and down following the left piston. You may not see it, but this is the way it works. One might think its like press brake system, but while the press brake has a very short stroke the plate roll has a large stroke. The electronic system could be ideal if the oil would not compress, it does though and it gets compressed by 2% every 100 bars. Look at the sketch below:

For this reason, the electronic or hydraulic parallelism control is continuously adjusting the system because one of the pistons, the one that gets more load (when the material is not perfectly on the center of the rolls) drops down because of the oil compression and there is no way to avoid it. This is why this system works on press brakes, which have less stroke, less quantity of oil, and therefore less compression. A plate roll, however, has a large stroke, a larger amount of oil involved and therefore more compression.


MG’s system is based on a massive round torsion bar that connects mechanically to the two hydraulic pistons of the side rolls from left to right. In this way the two pistons become actually one as they are firmly tied together by means of this torsion bar. Also, the oil compression doesn’t matter here because the amount of compression is always the result of the sum of the oil in both pistons. If something moves it is the couple of pistons and never ever one at a time. Due to the lever generated by the side rolls’ arms, we can install smaller pistons and have the same effect but with the great advantage of less oil traveling and so, again, less oil compression. That’s proved to be the most precise and reliable system worldwide and, in addition, it doesn’t need any kind of setting or adjustment for the life of the machine.

3)     The lower roll parallelism control: Also in this case we see a design defect (pic.4). The lower roll of our competitors is directly driven by two hydraulic pistons. Again, because of the oil compression,  there is no way to keep a constant pinch as one side of the rolls will always compress down a little bit making it very difficult to guarantee rolling precision (cone defect) as well as lack of dragging constancy.



The MG system is based on a roll set on two eccentric wheels driven by a torsion bar. See sketch below:

The eccentric is irreversible so there is no way to be compressed under loading. This is why MG can guarantee the best precision even when the machine is pushed to the limit.

4)   Bearings. Below is a comparison between the MG system and the system adapted by some of our competitors:

MG                                                                              OTHERS

MG technology uses a large and heavy bottle bearing calculated to work with a large amount of extra tonnage compared to the machines need,  instead of just two simple bearings that could be overloaded by accident and in a certain circumstances singularly. That’s dangerous and mechanically incorrect. Again, MG can guarantee the bearings’ long life as the load is always distributed on all bearing surface.


To reach the last goal, the smallest possible bending diameter MG focuses on the right point of contact between the bending rolls and the top roll. It isn’t a matter of system; it’s just a matter of knowledge and experience.

If you look at the above sketches you understand how well every system can be adapted to the best geometry. The fact is that MG continuously researches and develops machines while others are still working with machines that have basically been designed 20 years ago.

Above is shown a slide guide system with a fixed geometry.

So it’s a pure matter of geometry? Remember, chose the right partner. MG never uses a given. MG is always trying to find a better way.


MG s.r.l

Cary Marshall, CMF

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C Marshall Fabrication Machinery, Inc.