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Harold Hall

Workshop Processes

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The design of the tilting head feature varies considerably from machine to machine and some just maybe easier to reset to the all important position for milling operations. If your machine permits, it may be possible to drill, ream and fit a locating dowel but if this is entering into a blind hole then do remember to drill and tap the end of the dowel so that it can be jacked out when it is required to set the head at an angle. Without such a provision I would be reluctant to move the head once set and find some other way of carrying out the task in hand.

 

A few related thoughts.

Above, I have illustrated an end mill cutting over its full width but this is only acceptable with a small overlap and for very shallow finishing cuts. The surface will though be made up of a series of furrows as is illustrated by Sk. 11. As the amount is very small this situation is more of a theoretical interest in most cases than of actual importance. Even so, it is worth considering that the effect is greater with larger cutters. For example, do be aware of the condition if you are attempting to finish a block of cast iron to make a surface plate using a large fly cutter.

What however if the error in the machine's spindle is across the line of the workpiece's traverse?

 

In this case the surface produced will be a shallow saw tooth as Sk. 12 shows. As with the furrows produced when the error is in line this will rarely be a problem, but again the larger the cutter being used the more likely that the result may be unacceptable.

 

Also take note that when machining a surface that both edges of the cutter should pass the edge of the workpiece as you may end up with a raised edge if the trailing edge of the cutter requires to machine the workpiece at the edge. This can easily be seen on the left hand edge of Sk. 12.

 

When surfacing do use a sharp cutter, especially if there is no option and back cutting has to be allowed. Alternatively, using a blunt cutter will certainly make the effect of the trailing edge more apparent resulting in a poor finish. See next page