Abd ul-Rahman,
        I agree with your general idea but suggest it is not practical with
a most designs. The text size would have to be so small as to make it
unreadable on anything but an E size print. How many companies even have E
size plotters left hanging around these days? If the text size were not so
small then you would have text overlapping text with equally illegible
numbering. Most fab shops that I have dealings with would only be able to
print B size docs and they don't typically supply CAD stations to
inspectors.
        As for the number of drills, David's answer suggests that he has
good reason for so many drills. Not common but in some rare cases I guess it
is a necessity. I usually top out at 8 - 10 on a demanding design and it
still makes me wince at the thought of so many sizes. The larger proportion
of my hole sizes aren't electrically driven but mechanical as in David's
design.

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com

Visit us at Booth 2G2-09 at CommunicAsia 2002 in Singapore June 18-21.



> -----Original Message-----
> From: Abd ulRahman Lomax [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, May 16, 2002 12:54 PM
> To: Protel EDA Forum
> Subject: Re: [PEDA] Too many hole sizes
> 
> 
> At 11:31 AM 5/16/2002 -0700, Brad Velander wrote:
> 
> >         The KB 1472 is so nice, they don't even suggest that letter
> >characters might solve the problem so you are left to 
> wonder. Is there a
> >limit of 16 sizes even with the letter symbols?
> 
> Actually, in my opinion, the best practice is to use the hole 
> size itself, 
> which is one of the options. It may need to be very small 
> text, but the 
> purpose of showing hole positions/sizes on a drill drawing is 
> mostly to 
> make hole size checking easy. Having the hole size in place is *much* 
> easier to check, because you don't need to refer to a table.
> 
> I doubt that there is a limit of 16, per se; I would not be 
> surprised, 
> however, to find a letter limit of 26. There is no limit when 
> the size 
> itself is used.
> 
> On the other hand, good PCB design practice is to reduce the 
> number of 
> different drill sizes used. It helps manufacturing by 
> reducing the number 
> of drill changes needed. Note that fabricators will typically 
> combine hole 
> sizes to a single drill where the holes are still likely to 
> remain within 
> specification (+/- 0.003 perhaps with small holes). 16 sizes 
> is quite a 
> few; though, certainly, there might be a design that demands 
> more than 16, 
> it would be unusual.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/leave.html
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Forum Guidelines Rules:
* http://www.techservinc.com/protelusers/forumrules.html
*
* Browse or Search previous postings:
* http://www.mail-archive.com/proteledaforum@techservinc.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Reply via email to