"Lloyd N. Johnson" wrote:

> 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?

It is not the routing machine, but the way the cutting tool cuts material.
When the router is moving in a straight line, the tool has constant cutting
forces,
and the line cut is straight, if the machine is operating within limits.  When
it gets
to a corner, the inside corner of the material may 'trap' the cutter for a
moment
and cause it to 'orbit' in the hole, leaving gouges and/or rough edges and wavy

patterns in the side of the hole.  This is most severe when the router is only
trimming a small amount from a previously cut edge, and is moving fairly fast.
This might be a finishing pass, where it takes just a few last thousandths off
to bring the hole to final size.  If doing a one-pass routing, where the cutter
is
cutting full depth and full width already, inside radii are not going to make
much
difference.

If it causes a problem, the board house would be much better prepared to know
when it will happen, and know what steps to take to prevent it in advance.
You probably don't even KNOW what size tool they will select to do the job,
anyway!  Generally, the board fabricator writes the CNC toolpath for the
router, not the board designer, and they know if their machine and tool
combinations are going to cause this.  If they expect a problem, they will
write
the toolpath with radii in the corners to prevent it.

I guess you could specify acceptable corner radii on the hole, which gives them

the go-ahead to do this when necessary.

Jon



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