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Within the bounds of safety, a billet can be any size provided it can be fixed securely to the mill table and the end of a tool can traverse in free air above it. The panels at the left and right hand ends of the swarf tray can be removed to accommodate a long billet. If these panels are removed, great care must be taken to ensure that safety is not compromised.

Working Envelope
The amount of a large billet on which machining can be done is determined by the working envelope of the mill: the maximum mill table movement in X is 200mm and in Y is 100mm. (Note: a very small number of the last of the F1 mills / WoodWorkers have a maximum Y movement of 125mm. If your machine is one of these, please take this into account when reading the following text.)

What Moves
While it is the mill table which actually moves in X and Y and the milling head stays still, on a CNC mill you need to learn to think of the table staying still while the head moves in X and Y. The four cursor keys which control manual X and Y movement expect this understanding. For example, hold down the right cursor key and the milling head moves to the right. OK the table actually moved left but that is not the point. The point is that the head, and therefore any tool, has made a positive X movement.

Machining Limits

                              

Pocketing: Potentially, a 20mm diameter slot drill can cut a rectangular pocket, with 10mm radiused corners, to the dimensions X=220mm and Y=120mm. The centre line of the cutter moves 200mm in X and 100mm in Y but, of course, the periphery of the cutter goes 10mm (ie cutter radius) beyond the working envelope at each of the four boundary lines. However, as explained below, it is asking for trouble if the tool centre line is taken right up to an envelope boundary.

Perimeter: Care must be taken in the choice of tool diameter when it is necessary to trim round the perimeter of a part. You cannot trim round the perimeter of a part which is 200mm long in X and 100mm wide in Y, ie, the same as the working envelope. This is because the centre line of any cutter would have to go outside the working envelope.

                              

The maximum size part for which, for example, a 10mm diameter slot drill can do a perimeter trim is 190mm in X and 90mm in Y. To actually achieve this, the centre line of the cutter would have to exactly follow the boundary of the working envelope and the billet would need to be perfectly symmetrically placed within the working envelope.

Such a tool centre line path and billet placing are not practical. If attempted, the mill table is virtually certain to hit one or more of the four end stops as it traverses.

Notice that the bigger the cutter diameter the smaller the X and Y dimensions of the billet have to be if the cutter is to trim round the billet perimeter.

End Stop Danger

                              

The picture shows a billet placed badly relative to the working envelope. It may be that the code contains a move which would take the tool centre line outside the working envelope. This move will be attempted but the mill table will hit an end stop. The controlling PC will continue to send movement information but the table or milling head will not move and the drive system will be put under great strain. As there is no overrun cut-out or positional feedback from the mill to the PC, no corrective action can be taken and thereafter there will be a mismatch between where the PC

the tool is and its actual position. The job is ruined and material is wasted. It is up to you, the user, to avoid this situation.

                              

The picture shows a billet placed symmetrically within the working envelope. This is the ideal situation, particularly if the billet X and Y dimensions are approaching those of the envelope.

General Rules
If machining has to involve working close to the boundary of the mill