Watch out for block delete applications

As you know, block delete can be used to give the operator a choice between two conditions. The operator is told to turn the block delete switch on for one of the conditions or off for the other.


With many block delete applications, there are no safety implications. If the switch is set in the wrong position, the machine may not behave in the desired manner, but there is no change in safety.Consider, for example, using block delete to control whether coolant comes on in the program or not. Maybe a given workpiece can be made from two different materials – one requiring coolant and the other not. If the switch is in the wrong position, coolant may come on when it is not required – or it may stay off when it is required.But again, the operator is not placed in any immediate danger.


Now consider a more questionable application. Maybe a turning center programmer has been told that raw material is varying in length. It is supposed to have 0.1 inch of facing stock – and some raw material parts do have this amount of stock. But other shave much more – say up to 0.5 inch facing stock.

The programmer may elect to program a series of additional facing cuts to remove the excess material with block delete codes. The operator is then told to turn on the block delete switch if there is 0.1 inch facing stock on a given workpiece. They are told to turn it off if there is more than 0.1 inch facing stock.


Consider what will happen now if the operator has the block delete switch in the wrong position. There will be no safety issue if the switch is turned off when a workpiece having 0.1 inch facing stock is run. The machine will simply make more passes than necessary. But if the operator has the block delete switch turned on when they run a workpiece having 0.5 inch facing stock, the machine will try to machine all of the facing stock in one pass.


At best, this may stall the spindle. Worse,it’s likely that the workpiece will be pushed out of the chuck – causing damage to the machine and possibly injuring the operator.


So again, before you decide to use the block delete function, always ask the question: “What is the worst thing that can happen if the operator has the switch in the wrong position?” If safety will be compromised in the least, don’t use block delete.


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