I have a 1/2" x 20 UNF bayonet style electrical connector threaded into PVC.
The PVC is the standard gray material bought as a round bar off the shelf.
Mechanical constraints prevent using a locking nut or radial set screw
Does anyone have any suggestions as to what chemical means might be
useful to lock or bond the (probably stainless) metal connector to the
PVC to prevent unscrewing?
On Mon, 11 May 2015 06:34:04 -0700 (PDT), " email@example.com"
Boat/Marine supply stores have tons of sealants that bond to multiple
materials including PVC and stainless. You might consider Dow Corning
795 - I have used it to bond plexiglass windows to stainless hatches.
It probably would work with PVC but check the materials sheet.
Part of the question here is whether you want to *permanently* lock
those threads, or if you want to be able to disassemble the joints in
the future. The commercial thread-lockers, including both Loctite
acrylics and the commerical epoxy beads used in production, are
calibrated to keep a tight joint and to tolerate a lot of vibration,
but also to have a low breakaway shear strength that allows the joint
to be unscrewed when necessary. Loctite, for example, comes in
different degrees of breakaway shear strength for different jobs.
If you don't care about future disassembly, ordinary household
two-part epoxy should do the job. The amine hardener is pretty active,
however; I've never checked to see which plastics are safe with it,
but it should be easy to Google. Unlike the epoxy beads made
specifically for thread-locking, household epoxies are not made for
specific breakaway shear strength.
If you do want to be able to disassemble, I'd go for one of the gooey
pipe-thread sealants. I've used a liquid Teflon-containing sealant for
decades, and it both locks joints tightly and allows joints to be
unscrewed. I have them all over my house, in plumbing and (hot water)
heating, and they work perfectly. I have some of them on metal-to-PVC
threaded joints and I've never noticed any deterioration of the PVC.
You application doesn't sound particularly demanding. It should be
easy to find some sealant that has decent joint strength without
permanently binding the joint, and without destroying your PVC. Read
the labels on the tubes in some hardware-store plumbing departments.
They'll probably answer the PVC question.
The epoxy is another route worth looking at. We already use an epoxy
with the same PVC ans it bonds quite well. It will actually break away
some of the PVC if you try to chip it off too fast. The main worry is
the connector is a bayonet style and we have concerned end users may
over tighten or not push inward when undoing them and force the
connector to unscrew rather than disconnect.
Hmm ... from the description, snipped a few posts upthread, the
connector sounds like a BNC. And it is common for those to have a
D-shaped threaded stem, so it will be non-rotating in a punched hole in
sheet metal. If so, then the solvent (not really an adhesive, I think)
would soften the hole and allow it to deform partially into the flat of
the 'D', so that would likely work.
As for the material of the connector -- assuming it is a real
BNC, it is likely a copper alloy, plated with either nickel for the low
grade ones, or with silver for the really high quality ones.
BTW The BNC is also supplied with a square flange with four corner
holes for screws, so you could drill and tap the holes for those
in the PVC if that would work better for you.
Hey Don, it's a large bayonet style connector. It has half a dozen
conductors but uses a bayonet fitting about 2x the diameter of a BNC to
lock & seal. Judging by the price and the look of the thing I'm pretty
sure its a custom made connector housing.
Oh -- multi-pin. Glass (light green) seal holding the pins, or
dark brouwn soft rubber?
Three bayonet ears instead of two?
If so -- it sounds like one of the MS series connectors, which
come both with solder cups (and a rubber strainer which is held in place
by screwing onto the back of the connector body -- usually with a metal
ring inside the shell), and with crimp-on pins, which are inserted from
the back of the connector into the soft rubber pin separator/supporter.
If glass seal, and bare metal finish, it is for soldering onto
the housing of hermetically sealed things like aircraft instruments.
But the thread at the back sounds like the ones made for as
screw-on back shell -- with or without a cable clamp, depending. If so,
that *should* have the rubber strainer through which each wire passes,
and which is then squeezed down by the back shell and ring, to make a
They used to be refrred to as "Bendix" connectors, but the line
is now produced by Canon -- and some by Deutch and other companies. All
at painful prices. :-)
If 6 pins, it should have moulded into the rubber separator some
number endig nin "-6" -- the number being the diameter of the mounting
hole in 16th of an inch IIRC. Maybe 32nds of an inch. I would have to
dig back into the catalog to be sure. The whole shell should have a
number staring with MS-??? which defines the style and shell size.
No its not the Amphenol MS series. It's a 2 pin bayonet with a 1/2NF
threaded back end. The internal connector parts look like the small Lemo
stuff. It comes with flying leads potted in to the back end.
Take the connector out. Mill a slot up one side to half of the depth per
width (1/8" wide slot Mill 1/16" deep). Install the connector and use a
drill bit to "transfer" the slot to the PVC and finish the hole to size.
(1/16" in the connector 1/16" in the ABS). Now take a chunk of PVC
welding rod or ??? that is 1/8" and apply some PVC glue and insert it
into the hole. Once it cures the connector won't move.
Basically a linear locking spline. Same idea as used on key lock thread
inserts. However instead of using the steel pins those use you have PVC.
That way if you ever did need to remove it you could heat the connector
and turn it to shear the PVC spline.
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