How to fix a stripped coupler mounting hole?

[nickelplate759]

I had a  moment and drilled out a coupler mounting hole with a #56 clearance drill instead of a #62 tap drill, in a plastic floor.
It's in exactly the right place, of course...

Suggestions for fixing this?   In woodwork, I'd put a couple of wooden matchsticks in the hole with a little wood glue...

Styrene rod?   Tiny styrene tube (is there even such a thing)?   Styrene shavings and a little glue (like the wood matchsticks idea, but tinier)?

What have people tried that seems to work?

[Maletrain]

There are lots of ways to fill a hole, redrill and tap.  It depends on what material you have on hand.  I tend to have JB Weld, but that gets pretty hard and requires a good tap. 

Do you have a nut for the type of screw you are using?  Can you just widen the hole enough (and shallowly enough) to glue a nut in there?

[nickelplate759]

There are lots of ways to fill a hole, redrill and tap.  It depends on what material you have on hand.  I tend to have JB Weld, but that gets pretty hard and requires a good tap. 

Do you have a nut for the type of screw you are using?  Can you just widen the hole enough (and shallowly enough) to glue a nut in there?

The nut is an interesting idea, but I think the hole in this case is too close to the edge of the material to drill out the hole big enough for a nut.

[C855B]

I haven't had to do anything like this in decades, but today, a drop of UV-curable resin and a cheap UV flashlight would be my go-to. I would avoid epoxies because the plug will be harder than the surrounding material and the drill bit on the re-drill will want to wander.

Styrene rod like you suggest is also a possibility. Just take a piece of sprue, chuck it in a drill, and use a file to taper to a point. Just give the (solvent-based) plastic glue enough time for everything to harden.

[sizemore]

I'd second the option of UV resin or filler, below is the stuff I use:

https://www.amazon.com/dp/B0F9XLCLD7?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_4

It's actually a tad harder than the plastic but still workable with regular modeling tools. I tend to find styrene (everygreen/plastruct) to be softer than plastic used for shells, and I get bit drift on the odd occasion.

The S.

[GaryHinshaw]

I've had very good luck with styrene rod and solvent cement.  Make the fit as tight as possible: 1) select a rod size that is (just) larger than the existing hole, 2) ream the hole ever so slightly with a tapered bit until you can barely fit the rod, 3) apply a bit of solvent to the hole and rod and twist it into place, 4) let it set for a bit, then trim off the excess.  I have not had a failure yet.

[nkalanaga]

On a styrene floor, I do the same as Gary:  Styrene rod.  Evergreen makes a nice selection of sizes.

Depending on the car, I've used nuts the old-fashioned way - inside the car.  That works on boxcars and such, if one can get to the inside.  In particular, I've had MT floors where the cast-in holes were a little too big to tap for a 00-90 screw, so I drilled them to clear the screw, put the screw in, and put a nut on top.

[thomasjmdavis]

Yep... What Gary just said.... I've used styrene rod - or left over sprue material, and solvent glue for  the very issue described in the OP,  and also for filling truck mounting holes over the years with good success.

[jpwisc]

I’ve also used the same method Gary said. It works well on plastic floors.

[Maletrain]

When  gluing "something" into a clearance sized hole so as to be able to thread it, remember that those threads will cut completely through the fill material, or nearly so.  So, what you are really left with is pretty much just a spiral of the filler material attached to the wall of the clearance hole.

So, that attachment needs to be pretty strong.

Gary's method of using solvent to weld a rod works well the way Gary does it.  He is using force to twist the rod into the hole, which already has solvent in it.  That makes for a pretty good weld.  On the other hand, simply pushing the filler rod into the hole and then trying to wick-in the solvent is much less likely to be successful, especially if the solvent is one of those "less hazardous" formulations.

Using something dissimilar to the floor material, like cyanoacrylate ("Super Glue"), to attach the filler, or as the filler, might not be as successful. I have found that it is not so good at resisting shear forces between glued surfaces.  And the screw threads are dependent on shear force to hold.

[robert3985]

Yeah...I do what Gary does, and I use left-over plastic sprue too.  I've got a lathe, so that makes the operation a bit more precise, and even with my lathe, I'll just sand down the sprue using a small sanding block then a fine file when I'm getting close, which could easily be done with a drill motor, or drill press.

I've used Tenax 7R solvent glue for decades and when they went out of business, and after I'd used up my supply, I bought straight methylene chloride, also known as dichloromethane (DCM) at my local chemistry store and for workbench use I put some of it in eight of my old Tenax bottles, which for some reason I saved, which was a good thing because the big bottle I got from the chemistry store didn't seal well and it all evaporated after a year or so of storage.  Now I only have 8 small, full Tenax bottles...which is a pretty good supply, but I know where to go for more.

Another "plastic-welder" that works well (I've heard) is Tenax 7R "alternative" Styrene Tack It II, which is actively advertised as having the same qualities as Tenax 7R, except with "improvements" the main one being it's also able to weld Acrylic...buy it here: https://www.jmhobbysupply.com/styrene-tack-it-and-track-tack-it.php  Another DCM based solvent cement for Styrene is Plast-I-Weld from Flex-I-File, which also has a handy selection of bottle holders, and different applicators available here: https://flex-i-file.com/collections/the-touch-n-flow-applicators-adhesives

There's one more, which is touted as a Tenax 7R replacement, DELUXE MATERIALS Plastic Magic 10s, which may be available at your LHS, or, if not, you can get it at Amazon here: https://www.amazon.com/gp/product/B07D7WGGW6/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B07D7WGGW6&linkCode=as2&tag=mrhmag-20&linkId=a1d3e75428dd9edb8781a933dadd4438    However, it's not DCM-based, the active ingredient being 1,3-Dioxolane, which, from reading about its polystyrene solvent attributes, should work as well as DCM, except maybe not quite as quickly...BUT, it is less toxic and environmentally friendlier, always being labeled as "green" compared to DCM.  Hmm...maybe I'll try some just to increase my knowledge base.

I don't like, nor do I normally use MEK-based solvent welders, such as Tamiya and Plastruct solvents, although for some applications and types of plastic, MEK-based solvents work okay.  For polystyrene plastics, which most models are made from, I much prefer dichloromethane (DCM) based solvent "welders", which work much quicker, and, in my opinion, more effectively than MEK based solvents...with less "imprinting" on the surface of a molded part if you happen to get too much on the joint...which is easy to do.

Hope this helps.

Cheerio!
Bob Gilmore

[MetroRedLine]

I've done it many times by filling the hole with Squadron Putty or equivalent (I think I most recently used Tamiya Basic Putty).

[peteski]

I have also used the oversize plastic plug method described by others here.  I have several diameter of Evergreen styrene rods which come in handy for this (makes easier to select the correct drill size. I use whatever liquid cement I have on hand at the time.

I stay away from using putty as it is too crumbly for my taste. I generally dislike using putty for any modeling work - using it only when it is absolutely necessary.

[garethashenden]

When  gluing "something" into a clearance sized hole so as to be able to thread it, remember that those threads will cut completely through the fill material, or nearly so.  So, what you are really left with is pretty much just a spiral of the filler material attached to the wall of the clearance hole.

It may be worth enlarging the hole somewhat before filling it. Then you can have solid material to tap.

[Dwight in Toronto]

Yet another thumbs up for the styrene rod solution.  Easy peasy.