Hi Lloyd,
While I can't speak from direct experience that this is true in the board
manufacturing industry, it certainly is true in the metal machining
industry. We manufacture photoplotters to very tight tolerances using
highly accurate CNC machine tools. Any time a radius is required, we insure
that the radius of the cutting tool is less than the radius being cut.
Otherwise, you risk the result of "chatter" . One of the rules that we try
to follow is to insure that the cutting tool is always in motion along the
path being cut. For example, if you cut a right angle with the radius of
the cut equal to the tool radius, then one axis of the CNC machine must come
to a complete stop, while the other axis of the machine tool starts from a
standstill and accelerates along its axis. This causes the tool to stop for
a very brief period of time. However, the tool is still spinning very
quickly in the spindle. This causes the aforementioned "chatter". By
keeping the radius of the cut larger than the radius of the tool, you can
insure that neither axis comes to a complete stop and tool chatter is
avoided. Ideally, we program contouring paths to have a constant tool path
velocity.
Max P. Henzi, CEO
Lavenir Technology
2440 Estand Way
Pleasant Hill, CA 94523
voice: (925) 680-7400 fax: (925) 686-5131
email: [EMAIL PROTECTED]
Web: www.lavenir.com
-----Original Message-----
From: Lloyd N. Johnson [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, February 13, 2001 5:16 PM
To: Multiple recipients of list proteledausers
Subject: Re: [PROTEL EDA USERS]: Rectangle holes
Message text written by Hamid
>It is a bad idea to use an inside radius same as your router bit radius.
This
requires the router to come to a complete stop and then start moving at 90
degrees. There will invariably be some chatter and the router will cut
into the
sides. It is better to make a minimum radius larger than the router radius
so
the cut is programmed as an arc which will give a lot better results.<<
I don't want to sound too critical here, but this sounds like mythology to
me. Are you saying a router cannot stop and change directions without
creating some kind of problem? I have been working with board vendors for
20 years and no vendor ever told me anything remotely resembling this.
Do you have a reference for this? Is this from your personal experience?
Can you tell us who told you this?
Lloyd Johnson
DSS San Marcos
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