(no subject)

From: Jon Hunwick (Delcam  International PLC)
To: Gregory Pettengill (Cote Art & Engineering)
Date: Friday, July 29, 1994
Forwarded to RP-ML by Greg, 94 08 03
Greg, hello again! (This has the makings of a beautiful friendship!).

O.K. I stand corrected, the knife is a sharp one!.

By re-entrant features I mean those that are not mouldable in line-of-draw 
of the tool itself, e.g. undercuts, side pockets etc. for which a multi-part 
tool with side cores is necessary.

Yes, I know that it is possible (and not too onerous) to design the FFFF 
model so it looks **exactly** like the conventional tool. We (advert coming 
up), that is Delcam, produce a CADCAM system called DUCT. This is the UK 
market leader for the tool and mould making industries, and has specific 
features for finding parting lines round objects with complex geometry (see 
earlier definition of complex).
Once the part line has been generated the shut-out faces of the mould can be 
surfaced quickly and simply, to ensure correct registration (see I'm 
learning!). The part can then be NC machined or FFFF'd, whichever takes your 
fancy. The problem is that CAD time is still fairly expensive for the 
sub-contractor, compared to the time on an NC machine, and it is only by 
turning big bits of metal into smaller ones that toolmakers make money. 

Another consideration is that most subcontractors these days are sent data 
via IGES, and busting one of those mothers open and finding out what is 
**really** going on can take a while. If a prototype part is wanted the 
destructive FFFF route can be really attractive, and has the added benefit 
that the mouldmaker ends up with a physical part which he can look at. Tool 
design is a task which requires a great degree of skill if sensible, 
efficient tools are to be produced. Any lunatic with a CAD system could 
design a tool, but without an intimate knowledge of what actually goes on it 
would be worse than useless. And that, of course, is the danger - just 
because it's been done in CAD doesn't mean it's right. 

Lets also make it clear that we are, in all these cases, talking about 
**prototype** parts only, and usually one-off at that. Because it's a 
prototype, the chances are it will be modified, meaning that most (if not 
all) work done on the tool design will be scrapped, or need drastic 
modification later. If many parts are needed, then the extra time and effort 
**has** to be expended to find a non-destructive method.

'Sticky String' yes, that sums it up. I like it! 

I have spoken by 'phone to Prof. Tom Childs from Leeds University. He is 
heavily involved in CARP, and was most interested to hear about the mail 
group. You should hear a 'ping' from him
sometime soon! Leeds University kind of hold the 'intellectual copyright' on 
the benchmark, so I'm waiting for official clearance from him before going 
any further with sending the thing out.

And finally!! Thanks again for your messages. It makes a change to 'talk' to 
someone who seems to look on things from roughly the same perspective as myself.