David

Wearing my SCISS Ltd hat to answer this.

We are Abrasive waterjet profile cutters and cut a fair amount of model
engineering parts.

Our preferred format is .dxf and preferably from a single layer 2D drawing.
3D to .dxf can cause some problems with some details mirrored. Probably due to
picking up different sides of the drawing.

We probably have less problems with the lower cost programs, than we do with
full blown AutoCAD.
From memory some of the ok programs are AutoCADLT, AutoSketch, TurboCad,
FastCad and probably many more.

We do use the .dxf as part of the programming, so it would need to be correct
and clean.
We do not need all the dimensions, just one to check scaling as this can vary
depending on the units used. We use mm.

All the drawing should be drawn to size required, our machine program off-sets
the cut to suit the material and thickness.
Generally we cut to +/- 0.127mm / 0.005" and can reduce this on small parts.
Positioning is +/- 0.001".
For tapped holes, draw to the size you require, or a bit smaller if you want to
run a drill through.
For reamed holes, draw .010" - .020" undersize. You can then just run the reamer
through.
Unlike laser, Waterjets do not harden the edge as there is no heat involved, so
can be tapped or reamed or machined direct.
We can also vary the quality of the cut, in any part of the drawing. There are 5
qualities of which, we mainly use No.3 as standard.
If there are areas that will be machined afterwards, then using a lower quality
cut would help to reduce costs as it is faster.
If you do require a lower or higher quality of cut, just indicate on the drawing
or email.

For those without Cad we also copy from printed drawings, or backs of envelopes,
providing that all the dimensions are there.

These guide points will apply to pretty much all of the Waterjet industry, not
just to SCISS, apart from the tolerances which may vary depending on the
machines used.

I can't speak for lasers, so if there are any laser cutters out there, would you
like to give the model engineers, some of your guide lines.


Ian
www.sciss.co.uk


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