Using surfaces to control depth of cut          Author – Derek Mackenzie

The surfaces referred to here are all zero depth flat plane surfaces – they do not really exist in a 3D space as they have no depth. They are very useful for controlling depth of cut in certain areas – just insert the surface as required in your 3D model. For double sided cutting you may need surfaces at different depths for each side.

Depth check for double sided cutting (raster paths only)

            If your toolpath generator produces raster cuts (e.g. MillWizard) you can add a surface that will appear near Y0, X0 when cutting the second side (Ymax, X0 for first side) i.e. at bottom left when viewed from the top. This provides a useful visual check that your cutting depth is correct as the finish cut just removes the surface. Not strictly necessary, but easy to do, and useful confirmation you got the Z settings right.

Surface to prevent cutting too deep

            There may be times when you need to cut deep in some places, but other places would result in the cutter shank colliding with material you do not want cut.

This can be a particular problem when using very small cutters where the shank is larger than the cutter diameter – the cheaper toolpath generators assume that the cutter is the same diameter for its’ entire length.

            Place a surface where you need to prevent collisions – this requires care as it could prevent the model from being cut to the correct depth.

Surfaces in double sided models

            As well as preventing collisions it is sometimes necessary to provide extra support to the part being cut – adding a surface at a suitable depth can achieve this.

Be careful when using surfaces in double sided models as what looks reasonable on the model may actually prevent the cutter from getting close enough to complete the operation, leaving some hand finishing to do. Also make sure that your surfa

Compensating for collet eccentricity            Author – Derek Mackenzie Assumes cutters are truly concentric – if not find a different supply. Commercial collets will probably be OK, but if you have had to make your own, they may be a little eccentric. Check as follows:-  1.                 Cut a shallow slot in a piece of scrap  2.                 Advance the mill twice the nominal cutter width, perpendicular to the first slot – call this distance X.  3.                 Cut a shallow slot  4.                 Measure the width between the slots – call this distance Y.  5.                 The effective cutter diameter is then X –Y. This should be the nominal cutter diameter – the difference is the eccentricity. If slightly eccentric compensate by using the effective cutter diameter (from 5) when specifying the cutter diameter in your toolpath generation program. If significantly out, throw the collet away and make another one! If the collet is more than a few thou out it will make parts of some cutter flutes work harder, creating uneven wear on the cutter. It will also make the finished component narrower than intended if not compensated for – you may not notice until you cut a very narrow component, when a few thou extra off each side could be significant.

ces do not hide areas that must be cut.