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Harold Hall

Next stage is to mount the workpiece for machining and is the most demanding aspect of working with a vertical slide. As a general rule I can only stress that the workpiece must be securely fixed using sufficient clamps and supporting pieces to achieve this aim. For an example at this stage, Photograph 14 is a variation on the arrangement in  Photograph 8. However, the supporting piece on the right also acts as a stop so that a number of parts can easily be finished to the same length. Note how the rotation of the cutter will be attempting to force the workpiece onto the lower support, rather than raising it if as in Photograph 15. The setup in this photograph should only be used for light cuts unless of course the workpiece is large enough for two clamps.

 

As the setup is a vital part of carrying out milling on the lathe I would suggest that you go to my index of pages for the lathe only workshop and select a few of the projects there, You can then study the setups I am illustrating, even if you have no intention of making the item.

 

A suitable cutter also has to be chosen and this is probably more crucial than is the case when working on a robust vertical milling machine. For this reason, I have chosen to go into some detail as this should help with the understanding and therefore the choice of cutter.

 

Consider an end mill being used to produce a narrow (W) and shallow (D) step on the edge of a piece of material as illustrated in Sk. 1/1. From this it can be seen that the thickness of cut is dependent on the feed rate and not the width of the step being cut. Sk 1/2 shows that for a wider step the thickness does not change appreciably only the duration (A) of the cut increases. It can be seen that in both cases the cut starts very thin and increases towards the amount of the feed per tooth, (FR) Therefore, within limits, the width of the step will not greatly effect the load presented to the machine, only the power consumed. If though the depth of the step is increased,  SK1/3 , the amount cut will increase accordingly, comparing a surface skim of 1/64" with a definite step of 1/8" the load on the machine will increase approximately 8 times.

 

Considering further width, as this approaches half the diameter of the cutter other factors come into play, a subject that is beyond the scope of these pages. As a result, when cutting steps, even if  very shallow for surfacing, width of cut is best limited to no more than 1/3 rd of the cutter's diameter. This though is not a hard and fast rule as cutting at the full diameter will be necessary when machining a groove. In this case and when using a slot drill depth of cut and feed rate will need to be kept lower.

Metalworking

Workshop Processes

Milling on the Lathe
Milling on the Lathe
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14

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15

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