On Thu, 05 Aug 2010 16:44:21 -0300, you wrote:

> Em 5/8/2010 15:46, V G escreveu:
>> Hi all,
>>
>> I'm going to be using hex standoffs to stack PCBs on top of each
>> other. These hex standoffs use M3 screws which I have found to use
>> screws 3 mm in diameter. For drilling holes appropriate for these
>> screws, I have chosen to use tungsten carbide drill bits. Should I
>> select a drill bit exactly 3 mm in diameter (such as this one:
>> http://cgi.ebay.ca/Tungsten-Carbide-Multipurpose-Drill-Bit-3mm-/16043985=
3750?cmd=3DViewItem&pt=3DUK_Home_Garden_PowerTools_SM&hash=3Ditem255af5e2b6=
#ht_673wt_913)
>> or should I select something slightly larger? The question is: will
>> the screw slide through if I use a drill bit exactly 3 mm in diameter?
>
>A 3mm diameter drill should be OK. 3mm is the diameter of the stock that
>is used to make the screw.
>
>If you want to tap a hole for the screw, use a 2.5mm drill bit.
>
>Isaac
>
>__________________________________________________
>Fale com seus amigos  de gra=E7a com o novo Yahoo! Messenger=20
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You need to think not only about the hole size but any tolerances on the po=
sition of the holes. A
3mm screw in a 3mm hole allows no room for errors. If you are just stacking=
 PCBs on other PCBs then
the holes should all be accurate, although it won't hurt to up the hole siz=
e to maybe 3,2mm - you'll
probably find this will make assembly easier, as with a very close hole siz=
e, the screw will be
quite fiddly to get in the hole, as it will need to be exactly straight bef=
ore it will go in - a
larger hole will make life easier.=20

Wher you have something like threaded pillars in a case, you want whichever=
 end gets screwed in
first (typically the end in  the case) to be fairly close in size, e.g. 3.2=
,  to get the posiiton as
accurate as possible, and slightly larger holes in the PCB to cope with any=
 tolerance errors in the
case hole positions.=20

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