What will epoxy NOT stick to?
Paul Hovnanian P.E.
inserts into some (high value) wood. Specifically, these are cylindrical
inserts with wood screw threads on the outside and 10-20 machine threads
on the inside. The wood threads have loosened and I'm going to try to
fill the voids with epoxy. However, the inside (machine screw) threads
must remain epoxy free so that screws may be installed/removed
repeatedly.
If I just coat the outside of these inserts and install them, the
central machine threads will (undoubtedly) fill with the excess squeezed
out. Even if I insert a machine screw (dry), the epoxy could be squeezed
into the inside threads. So, I figure the way to go is to coat that
screw with some sort of grease that the epoxy will not adhere to. Once
the epoxy is cured, I can clean the grease off the inside threads with
solvent.
What's the best grease (or other coating) to use? It should be viscous
enough that it doesn't migrate to the outside of the insert and
interfere with the desired bond.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
In theory, practice and theory are the same, but in practice they
are different -- Larry McVoy
Phil Allison
"Paul Hovnanian P.E."
>
>I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
** Assuming the wood is a " hardwood" you may be better off using fast
setting "super glue" than epoxy - particularly the quick setting type that
tends to go soft over time.
If there is even the smallest gap around the threaded insert - super glue
will wick down it and be absorbed into the wood locking the insert tight.
Otherwise, unwind the insert a couple of turns, apply a film of super glue
to the outside and quickly screw it back.
One precaution, make sure the insert is quite clean on the outside before
you do any gluing, a wire brush is the go.
..... Phil
Damon Hill
@hovnanian.com:
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
Paraffin (candle wax) ought to work, be easily removed, and it'll lubricate
the threads. There's a coating material used for gold-plated edge
connectors to prevent a solder bath from adhereing that's probably a
silicone rubber that'll probably release (but not guaranteed to so).
--Damon
DaveM
news:498E46B6...@hovnanian.com...
I've used a product called "Mr. Grip Stripped Screw Repair Kit" to repair screw
holes in wood. It's primarily used with tapered wood screws, but I don't see
why it wouldn't work with an insert. Here's a listing for it.
http://www.amazon.com/gp/product/B00176J1VA?ie=UTF8&tag=wwwhomeadditi-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=B00176J1VA
An alternative to normal epoxy might be the kneadable epoxy putty. It shouldn't
run into the threads, and should hold just as well as regular epoxy.
Should be able to get either or both at Home Depot or Lowes.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.
Jim Yanik
news:Xns9BABBF620F0F2...@127.0.0.1:
also,if the wood is a tropical exotic,you may want to clean it with acetone
to remove oils.I've seen it recommended in Wood Magazine for some exotics.
--
Jim Yanik
jyanik
at
kua.net
Eeyore
"Paul Hovnanian P.E." wrote:
> I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
You lost me right there !
Graha
Martin Riddle
"Paul Hovnanian P.E." <pa...@hovnanian.com> wrote in message
news:498E46B6...@hovnanian.com...
> I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are
> cylindrical
> inserts with wood screw threads on the outside and 10-20 machine
> threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess
> squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be
> squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
>
>
Epoxy should be fine. It will wick into the grain of the wood and
provide a stong bond.
Look for the thicker Epoxies, they have a filler in them that will fill
the larger voids.
As for the machine threads wax would be good, or mold release.
Cheers
Rich Webb
wrote:
I'd second the epoxy putty, or even Bondo, for normal repairs but the
"high value" makes me skeptical whether any epoxy is a good idea. Had
not seen the Mr Grip gizmos before and they're probably the best idea to
at least *try* before gunking up a valuable piece.
>
>Should be able to get either or both at Home Depot or Lowes.
--
Rich Webb Norfolk, VA
bw
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
>
Vaseline
Paul Hovnanian P.E.
http://www.woodworkingparts.com/parts/brass_inserts.html
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Relax, its only ones and zeros!
Robert Baer
> I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
>
Teflon-loaded silicon grease?
Liquid graphite?
Jasen Betts
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
wrap teflon pipe tape on the machine screw threads first.
(if you haven't got any use wax or grease)
Greegor
epoxy paper or cloth over bottom end of each and allow
to set before mounting the inserts?
smaller hole drilled in center to form a well?
(so excess doesn't back up into threads)
MooseFET
> I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
naturally slippery and smooth so even it a bit of epoxy does touch it,
you will be able to get it out.
Michael
I've used those threaded inserts for many years. The 1/4"-20 are favorites. Every insert, no mattr
its size, was a bugger to install but not even one of them has come loose. Maybe your pilot hole
was too large? Or your wood is soft/crumbly? (I work with hard maple mostly, some walnut and
cherry.) Well, anyway....
If I were doing the repair job you describe, I would stuff the insert with beeswax and heat until
melted, topping off as needed. I'd use beeswax instead of candle wax because it is soft. (I happen
to have blocks of beeswax, left over from my misspent youth when I used it to wax heavy thread for
stitching leather.)
By the way, coating whatever-fastener with varnish before inserting into wood is an old woodworker's
trick.
qrk
<pa...@hovnanian.com> wrote:
>I have a small project which involves expoxying some brass threaded
>inserts into some (high value) wood. Specifically, these are cylindrical
>inserts with wood screw threads on the outside and 10-20 machine threads
>on the inside. The wood threads have loosened and I'm going to try to
>fill the voids with epoxy. However, the inside (machine screw) threads
>must remain epoxy free so that screws may be installed/removed
>repeatedly.
>
>If I just coat the outside of these inserts and install them, the
>central machine threads will (undoubtedly) fill with the excess squeezed
>out. Even if I insert a machine screw (dry), the epoxy could be squeezed
>into the inside threads. So, I figure the way to go is to coat that
>screw with some sort of grease that the epoxy will not adhere to. Once
>the epoxy is cured, I can clean the grease off the inside threads with
>solvent.
>
>What's the best grease (or other coating) to use? It should be viscous
>enough that it doesn't migrate to the outside of the insert and
>interfere with the desired bond.
If you get epoxy on the machine threads, chase the threads with a
bottom-tap to clear out the epoxy.
MooseFET
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
The teflon tape used in plumbing can also be used to prevent epoxy
from sticking to a screw.
>
> --
> Paul Hovnanian mailto:P...@Hovnanian.com
Paul Hovnanian P.E.
>
> On Sat, 07 Feb 2009 18:43:02 -0800, "Paul Hovnanian P.E."
> <pa...@hovnanian.com> wrote:
>
> >inserts into some (high value) wood. Specifically, these are cylindrical
> >inserts with wood screw threads on the outside and 10-20 machine threads
> >on the inside. The wood threads have loosened and I'm going to try to
> >fill the voids with epoxy. However, the inside (machine screw) threads
> >must remain epoxy free so that screws may be installed/removed
> >repeatedly.
> >
> >If I just coat the outside of these inserts and install them, the
> >central machine threads will (undoubtedly) fill with the excess squeezed
> >out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> >into the inside threads. So, I figure the way to go is to coat that
> >screw with some sort of grease that the epoxy will not adhere to. Once
> >the epoxy is cured, I can clean the grease off the inside threads with
> >solvent.
> >
> >What's the best grease (or other coating) to use? It should be viscous
> >enough that it doesn't migrate to the outside of the insert and
> >interfere with the desired bond.
>
>
> That way there is no build up.
>
> You should consider, however, drilling out the threads that are loose,
> and installing an insert.
The wood threads are loose. I guess I could find a larger insert, but
this happens to be in the end of a 1" diameter dowel, so there's not
much material left to play with.
The problem was that these inserts were (are) used as a part of a
coupling system to connect a series of dowel sections together end to
end. Occasional disassembly, if the machine threads have become over
tightened, results in the wood threads backing out instead. Once this
happens a few times, the wood threads become loose and unscrew more and
more often, exacerbating the problem.
> You get the right sizing, and do not have to
> jump through these hoops. Heli-coil?
Heli-coil in wood?
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Incorrigible punster -- Do not incorrige.
Paul Hovnanian P.E.
Right, That'll work as long as the central threads don't actually fill
up. I suppose I could drill out the epoxy, but I'd risk buggering up the
brass threads.
If a greased screw can keep most of the epoxy out of the center, then a
tap can clean the rest.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
If life was fair, Elvis would be alive and all the impersonators
would be dead. -- Johnny Carson
Phil Allison
"Archimedes' Lever"
"Phil Allison"
>>, a wire brush is the go.
>
>
> Yes, there are nice, tiny wire brushes out there specifically meant for
> fine thread cleaning. NOT!
** A brass wood screw does not have a very fine thread.
Sheesh, dude. Think about the application!
..... Phil
John Ferrell
<pa...@hovnanian.com> wrote:
>I have a small project which involves expoxying some brass threaded
>inserts into some (high value) wood. Specifically, these are cylindrical
>inserts with wood screw threads on the outside and 10-20 machine threads
>on the inside. The wood threads have loosened and I'm going to try to
>fill the voids with epoxy. However, the inside (machine screw) threads
>must remain epoxy free so that screws may be installed/removed
>repeatedly.
>
>If I just coat the outside of these inserts and install them, the
>central machine threads will (undoubtedly) fill with the excess squeezed
>out. Even if I insert a machine screw (dry), the epoxy could be squeezed
>into the inside threads. So, I figure the way to go is to coat that
>screw with some sort of grease that the epoxy will not adhere to. Once
>the epoxy is cured, I can clean the grease off the inside threads with
>solvent.
>
>What's the best grease (or other coating) to use? It should be viscous
>enough that it doesn't migrate to the outside of the insert and
>interfere with the desired bond.
You have a lot of interesting answers! I run into this thing with RC
airplanes. Usually mine involves T-Nuts instead of inserts. To keep
the goo off of the threads I tape the ends closed.
HOWEVER, if you are dealing with a blind hole the hydraulic forces
will overpower any seal you might try. You could cut some relief slots
in the side walls to relieve the hydraulic pressure but it would be
iffy. Glueing a wood plug (better than a dowel!) in the hole which
has been cleaned up to provide a snug fit and redrilling is probably a
better solution. If you have access to a metal lathe you could also
make an oversize insert like the commercial one. This is the route I
would prefer on a gun stock.
John Ferrell W8CCW
Rich Grise
> I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
The most professional-looking repair would be to backfill the hole
with something like "plastic wood", and re-drill/re-thread it. Or, you
could tap the existing hole one size bigger and use a Helicoil.
Otherwise, I'd try Vaseline on the screw.
Good Luck!
Rich
JosephKK
<pa...@hovnanian.com> wrote:
It finally clicked in, there was a discussion here recently about
trying to use adhesives of any kind on polyethylene, and pretty much
nothing worked. Will that do?
Eeyore
"Paul Hovnanian P.E." wrote:
> Eeyore wrote:
> > "Paul Hovnanian P.E." wrote:
> >
> > > I have a small project which involves expoxying some brass threaded
> > > inserts into some (high value) wood. Specifically, these are cylindrical
> > > inserts with wood screw threads on the outside and 10-20 machine threads
> >
> > You lost me right there !
>
> http://www.woodworkingparts.com/parts/brass_inserts.html
I know what an insert is.
10-20 is a vision specification. ;~)
PLEASE metricate !
Graham
Eeyore
Archimedes' Lever wrote:
> Eeyore <rabbitsfriend...@hotmail.com> wrote:
> >"Paul Hovnanian P.E." wrote:
> >
> >> I have a small project which involves expoxying some brass threaded
> >> inserts into some (high value) wood. Specifically, these are cylindrical
> >> inserts with wood screw threads on the outside and 10-20 machine threads
> >
> >You lost me right there !
>
> If you do not know what an insert is, you are not going to be familiar
> with their construction, and should certainly not be in a discussion
> about something you know nothing about.
>
> Wait... that happens with you all the time!]
There is no such thread as 10-20 in 95% of the civilised (and even uncivilised)
world.
Graham
qrk
When you live in a country where it's difficult to find metric, you go
with what's common, thus imperial threads. Sometimes, it just makes
sense to use imperial since the metric equivalent is hard to get, like
M3.5 screws (6-32 equiv). Titanium metric hardware over in 'Merica is
really expensive compared with imperial. Ended up sourcing the
material in Singapore.
Parts of the UK still use the stone as a weight measurement.
I had a laugh when I was talking to some Swedes about their
construction industry back in the mid 90s. I asked what measurement
system they used for timber, which they replied, "the tum" (Thumb).
The look on their faces was precious when they realized the tum was an
inch.
---
Mark
Rich Grise
> "Paul Hovnanian P.E." wrote:
>> Eeyore wrote:
>> > "Paul Hovnanian P.E." wrote:
>> >
>> > > I have a small project which involves expoxying some brass threaded
>> > > inserts into some (high value) wood. Specifically, these are cylindrical
>> > > inserts with wood screw threads on the outside and 10-20 machine threads
>> >
>> > You lost me right there !
>>
>> http://www.woodworkingparts.com/parts/brass_inserts.html
>
> I know what an insert is.
>
> 10-20 is a vision specification. ;~)
>
Maybe he was guesstimating the NUMBER OF TURNS, as ten to twenty.
Have you ever looked down the throat of an insert and counted turns?
> PLEASE metricate !
Doesn't that make hair grow on the palms of your hands? ;-)
Thanks!
Rich
Chris Jones
> I have a small project which involves expoxying some brass threaded
> inserts into some (high value) wood. Specifically, these are cylindrical
> inserts with wood screw threads on the outside and 10-20 machine threads
> on the inside. The wood threads have loosened and I'm going to try to
> fill the voids with epoxy. However, the inside (machine screw) threads
> must remain epoxy free so that screws may be installed/removed
> repeatedly.
>
> If I just coat the outside of these inserts and install them, the
> central machine threads will (undoubtedly) fill with the excess squeezed
> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> into the inside threads. So, I figure the way to go is to coat that
> screw with some sort of grease that the epoxy will not adhere to. Once
> the epoxy is cured, I can clean the grease off the inside threads with
> solvent.
>
> What's the best grease (or other coating) to use? It should be viscous
> enough that it doesn't migrate to the outside of the insert and
> interfere with the desired bond.
>
As long as you don't leave a screw in the hole of the insert, it probably
doesn't matter too much, you can very quickly clean out the thread with a
tap, as the epoxy is softer than the brass, especially if it is warm.
Chris
JosephKK
There are damn few cases where US customary threads dimensions have
any interchangeable metric equivalent. The nearest metric size is 2.5
mm 1.25 thread. Not interchangeable.
JosephKK
<rabbitsfriend...@hotmail.com> wrote:
It is just so damn weird to "hear" a Brit not know English thread
standards.
JosephKK
Oh my! Was there any "full cascade" faces?
John Fields
>On 2009-02-08, Paul Hovnanian P.E. <pa...@hovnanian.com> wrote:
>
>> If I just coat the outside of these inserts and install them, the
>> central machine threads will (undoubtedly) fill with the excess squeezed
>> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
>> into the inside threads. So, I figure the way to go is to coat that
>> screw with some sort of grease that the epoxy will not adhere to. Once
>> the epoxy is cured, I can clean the grease off the inside threads with
>> solvent.
>
>wrap teflon pipe tape on the machine screw threads first.
---
Good trick... they're _internal_ threads.
JF
Jim Yanik
news:23h6p4p1m092nduli...@4ax.com:
the -machine screw- he plans to thread into his brass insert does not have
internal threads,the insert does.
--
Jim Yanik
jyanik
at
kua.net
RFI-EMI-GUY
I have seen a tube of Teflon pipe dope that could be used to displace
epoxy in an internal thread scenario.
--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©
"Use only Genuine Interocitor Parts" Tom Servo ;-P
MooseFET
No, you can't use metric threads in brass. It will rip out. :)
MooseFET
> On 8 Feb 2009 11:23:55 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:
>
>
> >> If I just coat the outside of these inserts and install them, the
> >> central machine threads will (undoubtedly) fill with the excess squeezed
> >> out. Even if I insert a machine screw (dry), the epoxy could be squeezed
> >> into the inside threads. So, I figure the way to go is to coat that
> >> screw with some sort of grease that the epoxy will not adhere to. Once
> >> the epoxy is cured, I can clean the grease off the inside threads with
> >> solvent.
>
> >wrap teflon pipe tape on the machine screw threads first.
>
> ---
> Good trick... they're _internal_ threads.
Not really, You use a long version of the machine screw you intend to
use and wrap the tape on it. You then thread that into the insert.
You then epoxy the combination into the wood. When the epoxy is hard,
you thread the machine screw out and then pull the tape out. It is a
trick that I have used.
>
> JF
John Fields
---
Yup, and I'm pretty sure those were the insert machine screw threads he
was referring to.
JF
Jim Yanik
but NOT the threads he was planning on wrapping tape *around*.....Sheesh!
John Fields
---
Yup, looks like I misread it. :-(
JF
Jasen Betts
a machine screw with internal threads?
I meant wrap the screw and screw it into the insert before gluing the insert in,
Jasen Betts
>>
>> On Sat, 07 Feb 2009 18:43:02 -0800, "Paul Hovnanian P.E."
>> <pa...@hovnanian.com> wrote:
>>
>> >I have a small project which involves expoxying some brass threaded
>> >inserts into some (high value) wood. Specifically, these are cylindrical
>> >inserts with wood screw threads on the outside and 10-20 machine threads
>> >fill the voids with epoxy. However, the inside (machine screw) threads
>> >must remain epoxy free so that screws may be installed/removed
>> >repeatedly.
>> >
>> >central machine threads will (undoubtedly) fill with the excess squeezed
>> >out. Even if I insert a machine screw (dry), the epoxy could be squeezed
>> >into the inside threads. So, I figure the way to go is to coat that
>> >screw with some sort of grease that the epoxy will not adhere to. Once
>> >the epoxy is cured, I can clean the grease off the inside threads with
>> >solvent.
>> >
>> >enough that it doesn't migrate to the outside of the insert and
>> >interfere with the desired bond.
>>
>>
>> That way there is no build up.
>>
>> You should consider, however, drilling out the threads that are loose,
>> and installing an insert.
>
> The wood threads are loose. I guess I could find a larger insert, but
> this happens to be in the end of a 1" diameter dowel, so there's not
> much material left to play with.
>
> The problem was that these inserts were (are) used as a part of a
> coupling system to connect a series of dowel sections together end to
> end. Occasional disassembly, if the machine threads have become over
> tightened, results in the wood threads backing out instead. Once this
> happens a few times, the wood threads become loose and unscrew more and
> more often, exacerbating the problem.
it seems like the wrong part.
you gan get wood screws with a machine thread at the head end.
put a thread joiner on one of them, drill a recess (for the joiner)
and pilot hole (for the screw) into the dowel and screw it in.
(use a lock nut - standard metalworking practice)
having the thread away from the end of the dowel will greatly increase
the strength,
using varnish or polyurethane wood glue to lubricate the screw seems
like a good idea too,
PS. it's not a pool cue is it?