By Joerg Hugel 

M4. C4n

The slide ways of machine tools are very sensitive components and should always be clean and free from any debris. The machines for industrial production are carefully designed today with protective elements, not only to keep the slide, slide ways and sensors clean but also avoid any pollution of the environment. However, in the enthusiasts' workshops this is not the standard. Most lathes and milling machines the author has seen have no or at best very rudimentary devices for the protection of the slide ways or lead screws. Clearly any protective cover needs some space and reduces the usable travelling distances of the carriages, slides or work heads. As long, as the machines are operated manually the operator may be responsible for removing the swarf. For CNC controlled machines another solution is necessary. For grinding equipment an effective slide protection is a must because the dust of abrasives together with the lubricant of the slides is a very efficient lapping paste.

Photo 1: A Sherline CNC mill with bellows

There are different solutions to protect the sensitive components of a lathe, milling or grinding machine. One very simple answer are bellows and this short article will show, how they can be made. In Photo 1 is my Sherline milling machine, converted into a CNC machine. The slide and lead screw of X-axis are protected from swarf in the design of the machine but not the respective components for the Y-axis. Therefore, two bellows were installed. One end is mounted to the cross slide, the other ends are held by two flanges, fixed to the base plate by a spring loaded ball detent. So the bellows can be easily lifted for cleaning and lubricating the slide ways, no tool is necessary. In Photo 2 the bellows for a Stent tool grinder is seen.

Photo 2: Bellows for a Stent tool grinder

Figure 1 shows the folding scheme for bellows. It is a simple matter to make this from a sheet of paper. But with other materials, e.g. leather or fabrics this would be difficult or even impossible. Paper has the necessary stiffness and if folded becomes flexible at the edges.

Figure 1: The folding scheme for bellows

The bellows in Photo 3 were commercially manufactured. To make these from different materials, even from sheet metal, very special jigs are used. I would not go into the details. But please notice, the folding scheme is different from Figure 1. This has the property that the side parts of stretched bellows move together, opposite to the behaviour of the bellows of Figure 1. In the experience of the author these features are not really essential.

Photo 3: An example of commercially manufactured bellows

Clearly bellows from paper wouldn't be suitable for the purpose regarded here. But a combination of paper, more precisely, polyester paper, and a  protective layer could be the solution. By accident the author received a somewhat worn out protective cover for an ironing board. This is a compound of a thin foam layer and a fabric which has a metalized surface. The foam was easily scraped off. he metalized fabric together with the polyester paper has proved to be the perfect material for bellows for milling and grinding machines.

Manufacturing Details

First it is necessary to make the design, a drawing with the folding lines. In the compressed state the folding angles are zero, for the maximum length a folding angle of 45 Deg. is recommended, however not more than 60 Deg. To avoid errors the lines should show the folding direction by different line pattern or colours. An example is seen in Figure 2.

Figure 2: Drawing for the folding lines

Photo 4: Polyester paper and metalized fabric

The materials for the bellows can be seen in Photo 4. The drawing for the folding lines is now transferred to a sheet of polyester paper as seen in Photo 4a. Recommended grade is  120 to 180 g/mm2, equivalent to 0,1 to 0,15 mm thickness. In this case the drawing was made with an inkjet printer. However, to dry the drawing takes several hours if not a day. A laser printer cannot be used, because the polyester paper becomes warped by the heat. But as seen in Photo 4b the polyester paper is available with a millimetre grid and then a manual drawing of the folding lines is really a simple matter. In Photo 4 c the metalized fabric is shown from the rear side.

Photo 5: Two folding legs

Now the polyester paper is folded in several steps. Here the bookbinder's traditional tool, the folding leg, comes into its own; two examples are shown in Photo 5. The folded paper bellows are seen in Photo 6.

Photo 6: The bellows from polyester paper

Then the fabric and paper bellows are put together with white PVAC glue as seen in Photo 7. The completed bellows are shown in Photo 8.

Photo 7: The metalized fabric glued to the paper

Photo 8: The bellows completed.

Joerg Hugel is a Member of the Society of Model & Experimental Engineers and this article first appeared in the SMEE Journal in February 2014.