13 Feb
2014
13 Feb
'14
2:39 p.m.
On 02/13/2014 12:22 PM, Tony Duell wrote:
I am nto very happy about threading scres into
palstic. The less said
about self-tapping screws the better (one of my mad friends calls them
'self stripping screws' for good reason), and I doubt most machine screw
threads would hold that will in this plastic. Putting the bolt right
torugh and htne fitting a nut seems ot be the stringest way.
To be fair, there are special screws for thermoplastics. They've got
deeper threads and generally a 30 degree or so flank angle. The trick
when forming bosses for them is to slightly relieve the top of the screw
hole to allow space for the burr that always develops. A
properly-installed screw should last for decades.
The alternative is to incorporate a brass threaded insert into the boss,
which I'm not wild about.
FWIW
--Chuck