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Harold Hall

Workshop Processes

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The simplest approach to this method is to used thin film double adhesive tape a method that I have used a number of times, Photograph 14 showing one application where a steam chest cover casting is being machined. Of course, the rear of the workpiece must be reasonably flat so as to make good contact with the adhesive tape over much of its surface and this was achieved by lapping the back on a sheet of abrasive paper, about 100 grit. Providing the tool being used is sharp and only light cuts are taken then the procedure should be problem free. Having machined the first side it can then be reversed and the second side machined similarly. The photograph shows that the part is additionally supported by strips being placed around the four sides. However, these were added just to illustrate the principle as the part would have been adequately held even without them.

 

There are two situations when the system being employed requires heat to be applied, in one the heat is only needed to break the bond after machining has taken place with the part having initially been assembled cold. Typically, bond the workpiece to the faceplate using a two part resin adhesive and allow to cure. Using the tailstock may make a good method of holding the part against the faceplate whilst the adhesive is setting.

 

With that done, machining can take place as required after which the part can be separated from the faceplate by applying heat. Tubal Cain in his "Model Engineer's Handbook" quotes a temperature of 120C to break the bond. I have  seen both Locktite and Super glues mentioned for this purpose, if the viewer wishes to adopt the method I would recommend further reading on the subject and a few trial runs before applying it to an important workpiece.

 

In the second method heat is required both to melt the adhesive so as to make the bond and then to release the part after machining. Just using hot melt adhesives as used in woodworking is not practical as it would rapidly cool as soon as it was applied to either the faceplate or the workpiece and to overcome this both parts have to be pre heated. With that done there would still be the problem of ensuring that the adhesive coating was of an even thickness, if not, then this could have a detrimental effect on the part being machined.

 

This problem can be easily overcome by using adhesive supplied in the form of a film as used extensively in industry. However, this to my knowledge is only obtainable in large quantities and is therefor a non starter. One material that is easier to obtain in practical quantities is "Gluefilm" that is used in woodworking for applying veneer to the base timber below.

Small Solid Faceplate for use with adhesive
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