On 05/08/2010 21:07, Spehro Pefhany wrote:
> At 02:46 PM 05/08/2010, you wrote:
>> 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?
> You should simply refer to the data sheet err.. table:
>
> http://littlemachineshop.com/Reference/TapDrillSizes.pdf
>
> Chris conveniently includes the closest US sizes.
3.0mm drill hole might damage the thread slightly. Or be very tight. How=20
do you accurately place the hole?
3.2mm if it's precision and you are good.
3.5mm hole for reasonable precision and clearance
If you are rubbish at metal work and there are 4 holes to match an=20
existing thing, consider washers and 4mm :)
2.5mm will work for thin sheet and trilobal self tapping screws.

--=20
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