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Harold Hall

Workshop Processes

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An alternative method is to bring the saddle up to the stop but this time without any packing, and again the tip of the boring tool is advanced until it contacts the part being machined. In this case, the saddle is then moved away and the top slide advanced by 18mm. The machining process will then take place in the same way. The method is simpler than using packing but is open to errors due to mistakes in calculating the number of turns and part turns of the top slide leadscrew whilst the packing method is all but foolproof, probably the reason why I prefer this method. As I am invariably, working to metric dimensions on an imperial lathe this prods me in the direction of using packing.

 

If you prefer the packing method then a combination of the two methods can be used for more precise dimensions. Assume a depth of 18.5mm is required, then the lathe could initially be set up for 18mm as above but before commencing machining traversing the top slide by just 0.5mm to give the required result of 18.5mm.

 

Protecting the Faceplate

A frequent operation is to bore a through hole in a part mounted on the faceplate in which case the problem is not getting the depth of the hole just right but to avoid the cutter contacting the faceplate surface. Normally, a thin piece of hard card would be placed between the workpiece and the faceplate surface and the part bored taking care as the tool breaks through, one lapse of concentration though and one has a damaged faceplate, not that serious but it does not look good.

 

In this case, with the saddle against the stop the tip of the boring tool is brought up to touch the faceplate, Photograph 3, after which the top slide will be set back say 0.1mm ensuring that the boring tool stops just short of the faceplate's surface. It would also be advisable to lock the top slide to prevent it being accidentally moved which may result in a damaged faceplate, the very thing that one is attempting to avoid.

 

Machining to a step

A very frequent requirement is to machine a workpiece to a step but having a depth necessitating this being done with a number of passes. The problem is virtually the same as boring a blind hole though the operation is fully visible and therefor much easier. It does though need a degree of concentration at the end of each pass, perhaps having to work to the leadscrew's dial readings. Setting up the saddle stop to set the step's position will therefore make it less demanding.

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