What glue to join plastic and wood ?

[MathWizard]

All the feet have broken off one of my old benchtop DMM's, so I was just going to glue on some little blocks of wood, or 2 big long ones. I have carpenter's glue, maybe some superglue (if it's still usable), silicone chalking and something similar that is more a glue than just a sealer.

Would the carpenter's glue be good enough ?

[xrunner]

Would the carpenter's glue be good enough ?

No. Use epoxy.

[jpanhalt]

I think you need something that can fill small gaps.  Super glues do not do that well and may cause delayed cracking of the plastic case.

That application might be great for moisture-reactive polyurethane adhesives, like Gorilla glue, or two-part polyurethanes.   Silicone adhesive/sealant and Pliobond (old formula) might be considered.   I use epoxy regularly to attach wood to fiberglass and plastic. 

For permanent attachment, I would probably go with polyurethane or epoxy.

[xrunner]

All the feet have broken off one of my old benchtop DMM's, ...

How were the feet attached in the first place? You mean they were part of the plastic of the case? You can also use double-sided foam tape by the way.

[MathWizard]

Yeah I don't have epoxy, and didn't really want to buy anything. The bottom of the case is smooth plastic, so I'd sand it rough too I guess. Actually 1 tube of the chalking is meant for gluing down plastic tub surrounds, so that should work ok, it's a bit like tar, so maybe it won't dry and crack like superglue.

The feet were moulded standoff's built into the case, with rubber pads, I think 3 of 4 feet were missing when I got it.

[themadhippy]

sprinkle a layer of baking soda on the wood,apply super glue to the plastic(after checking superglue is ok  with the plastic),and push the  parts together.

[jpanhalt]

As I suggested earlier, super glue ("CA") or its fumes can destroy some "plastics" over time.  Two personal instances for example: 

1) I had two WWII IDFF models made of hard rubber brought home by my father (a B17 and B29).  They were stored in a case with CA.  After a few years, the B29 fell apart.  The B17 was severely damaged.  It is now stored in open air with no further damage.
2) Modelers, specifically those building large scale sailplanes, used CA to attach long plastic tubing (probably an acrylic) to the fuselage for pushrod guides.  A few crashed when that tubing broke into many pieces, and the model became uncontrollable losing both elevator and rudder control.  I tested a sample of the suspect tubing with CA, and within days, it cracked apart.

I would not use CA on any plastic unless I knew more about the plastic and whether it was CA-safe.  The damage can take a long time to appear.

EDIT: I have also used double-sided masking tape (McMaster-Carr) to attach wooden blocks to my bench or each other.  It works and the masking tape can fill a void, but the bond is not permanent and is not very strong in shear (e.g., twisting).  It's a bit better in peel.

[Jwillis]

I wouldn't use any glue. Open up the units case. Cut away the broken plastic so there is a smooth surface. Drill some small holes through the plastic into the wood blocks and screw the wood blocks to the plastic case. I hate glue. Makes to much of  a mess.

[5U4GB]

It depends on what type of plastic it is.  Some plastics, like the very widely-used polyethylene (PE) and polypropylene (PP) are essentially ungluable, they exhibit low surface energy which means virtually nothing will stick to them, which is also why they're so widely used, something that nothing will stick to is easy to clean.  PE and PP have only slightly higher surface energy than Teflon and are also only slightly easier to glue, they laugh at cyanoacrylate and epoxy adhesives.  This is why @Jwillis' suggestion is quite sensible.

If you really need to glue PE or PP, one of the few single-component glues that'll do it is Konishi-bond styrene-butadiene cement (apparently that's the magic ingredient, although usually they use silylated resins), you may be able to find it in Japanese-import stores.

[Ian.M]

Its worth looking inside the case to see if there's any markings that indicate the plastic.  If you are lucky there will be a moulded in code for the plastic used.

Many plastic instrument cases are ABS.  You can solvent bond ABS to ABS with pipe cement or with a slurry of ABS dissolved in acetone.  Other glues are also likely to work if both surfaces are roughened.  Ideally, 3D print replacement parts in ABS and solvent bond them in place.

Gluing it to wood is more problematic due to the different coefficients of thermal expansion and woods lack of dimensional stability with respect to changing humidity.  If you make the feet out of plywood, and glue its surface, not its edge, epoxy would probably do the job, but for solid wood, not epoxy encapsulated, you'd probably need a relatively thick layer of polyurethane adhesive/caulk, or other rubbery adhesive, so the joint can flex in sheer as the wood grows/shrinks relative to the plastic.

[Jason Henry]

Carpenter's glue should work well for reattaching the feet on your benchtop DMM. It provides a strong bond for wood and should be a suitable choice for this repair.

[jpanhalt]

PE and PP have only slightly higher surface energy than Teflon and are also only slightly easier to glue...

It all depends on doing the proper surface prep.  I have very little experience with PE and PP but have read that plasma etching with a soft flame will work for bonding with epoxy.  There are also epoxies designed for those plastics.  Some are listed by McMaster-Carr.

I have much more experience with Teflon and used it frequently as a guide guide tube for push rods in models.  Special preps are available which basically are a solution of sodium in an appropriate solvent (e.g., naphthalene in a non-protic diluent).*  When applied to Teflon, the surface is lightly etched and usually turns a very light tan.  Obviously, they are sensitive to moisture.  Once treated in that manner, epoxy binds fine.  I have never had a failure, and it is quite difficult to pull the Teflon out.

Except for plasma etching, those methods are not very practical for one-offs or most homes, but they do exist.

*Years ago, I got that brew from McMaster-Carr, but can't find it there now.  In the lab, we just used liquid ammonia and dissolved either potassium, sodium, or their amalgam in it.  It glows dimly in a dark room.  The naphthalene-based material is more stable.

[5U4GB]

Yeah, I didn't mention any of those because, as you say, they're somewhat impractical.  You can also get chemical "activators" like polyolefin primer but they tend to be pretty nasty, and any of them would be a lot of effort and cost just to re-fit the legs on a DMM.  The Konishi-bond adhesive I mentioned is one or two dollars a tube and you can use it just like any random glue so possibly the least-effort/cost solution, I think it's Konishi Bond GP Clear and used to be sold in Daiso stores.

Another one that might work that I haven't tried is B7000 adhesive a.k.a. cellphone repair glue, you can get that for a few dollars as well from your favourite crapvendor and that claims to do PE, PP, and ABS.  The possible downside is that there's dozens if not hundreds of sellers/producers of this stuff and no way to tell what's in the particular "B7000" that you're getting.  I tested the Konishi-bond by gluing some otherwise ungluable plastic bottle caps together, you could do the same with some B7000 to check it's the real thing.

[Haenk]

Carpenter's glue should work well for reattaching the feet on your benchtop DMM. It provides a strong bond for wood and should be a suitable choice for this repair.

Nonsense, that glue will peel of off any smooth plastics.
If it's old (60s or newer), it very likely is ABS. However UV makes ABS very brittle over time, depending on which and how much UV blocking chemicals have been used. So more damage is to be expected.
Epoxy would be the best choice for glue, I guess. Maybe ask around, if someone has some expoxy to spare.

[coromonadalix]

sillicone adhesive ?  dont tell me you dont have something similar ?

[GLouie]

I'd use RTV silicone adhesive. But this is why I keep some stock of 3M Bumpons, little self adhesive feet. In fact many manufacturers seem to just use these, peel and stick.

[Zenith]

I'd go for the Jwillis solution of drilling holes and attaching the wood with nuts and bolts. I've had some disappointments with glues. It needs to be the right glue for the materials being bonded. In my experience, superglue, which may not be the right thing for this job anyway, is only any good if it's freshly opened. If you have doubts as to whether it's usable, it probably isn't.

[aeg]

Since the original feet are gone and you're not trying to keep it original, how about just sticking on some Bumpons?

[vk6zgo]

It depends on what type of plastic it is.  Some plastics, like the very widely-used polyethylene (PE) and polypropylene (PP) are essentially ungluable, they exhibit low surface energy which means virtually nothing will stick to them, which is also why they're so widely used, something that nothing will stick to is easy to clean.  PE and PP have only slightly higher surface energy than Teflon and are also only slightly easier to glue, they laugh at cyanoacrylate and epoxy adhesives.  This is why @Jwillis' suggestion is quite sensible.

If you really need to glue PE or PP, one of the few single-component glues that'll do it is Konishi-bond styrene-butadiene cement (apparently that's the magic ingredient, although usually they use silylated resins), you may be able to find it in Japanese-import stores.

Interestingly, pieces of sheet Teflon will stick to passivated steel quite well using cyanoacrylate.
Both materials have very smooth surfaces, so there are minimal gaps.
They could almost adhere together without any adhesive due to Van Der Waals forces.

[5U4GB]

Nonsense, that glue will peel of off any smooth plastics.

Not only will it peel off, it won't even dry/cure.  To see this in practice, get two pieces of clear plastic, put a dollop of PVA glue between then, and squeeze them together as you'd do for anything else you're gluing.  Leave it for a week.  It'll still be mostly liquid/uncured after that time.

[Bud]

A twin Epoxy tube is a couple bucks at Dollarama, why not.
I do not use superglue for anything, it is garbage.

[xrunner]

Carpenter's glue should work well for reattaching the feet on your benchtop DMM. It provides a strong bond for wood and should be a suitable choice for this repair.

This user was banned. It looks like from the post history it was all made up of ChatGPT answers. And from this answer, I don't want ChatGPT giving me advice on glues. 

[5U4GB]

Since we're throwing out ideas, here's another one that costs almost zero: If the OP has a hot-air rework station then he could plastic-weld the feet on, all you need is a stick of the same plastic as the multimeter, set the hot-air gun to the plastic melting temperature which you can look up online, then heat the join area and push the plastic stick into it.  It's pretty simple to do, there's bound to be a pile of Youtube videos showing it being done.

[tooki]

All the feet have broken off one of my old benchtop DMM's, so I was just going to glue on some little blocks of wood, or 2 big long ones. I have carpenter's glue, maybe some superglue (if it's still usable), silicone chalking and something similar that is more a glue than just a sealer.

Would the carpenter's glue be good enough ?

Wood glue won’t work, as others have said. Superglue is inadvisable for numerous reasons. One nobody has mentioned yet is that it is usually completely brittle when cured, so if the enclosure flexes at all during use, the glue may fracture.

Instead of ghetto-rigging wood blocks, why not use stick-on rubber feet (Bumpons) like aeg already said? Or screw-on or press-fit rubber feet? Or screw-on plastic feet (or even folding legs) if applicable? There seem to be a plethora of superior solutions…

[MathWizard]

I haven't touched it yet, it's an old Keithley177, it's no big deal either way, I guess I've hardly ever glued to plastic.

I'll test some wood and glue inside it, but yeah I should cut off the old feet too. Electrically it's doing great, for a 4.5 digit meter, that hasn't been calibrated for years or decades, it pretty much agrees with my SDM3065X 6.5 DMM