What glue to join plastic and wood ? - Page 1
Forum section: electronics / repair

author: MathWizard
author_rank: Super Contributor
timestamp: March 11, 2024, 12:08:10 pm
content: 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 ?

author: xrunner
author_rank: Super Contributor
timestamp: March 11, 2024, 12:12:23 pm
content: Quote from: MathWizard on March 11, 2024, 12:08:10 pmNo. Use epoxy.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 11, 2024, 12:21:08 pm
content: 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.Forpermanentattachment, I would probably go with polyurethane or epoxy.

author: xrunner
author_rank: Super Contributor
timestamp: March 11, 2024, 12:27:50 pm
content: Quote from: MathWizard on March 11, 2024, 12:08:10 pmHow 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.

author: MathWizard
author_rank: Super Contributor
timestamp: March 11, 2024, 01:22:57 pm
content: 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.

author: themadhippy
author_rank: Super Contributor
timestamp: March 11, 2024, 01:32:03 pm
content: 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.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 11, 2024, 02:11:43 pm
content: 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.

author: Jwillis
author_rank: Super Contributor
timestamp: March 11, 2024, 03:47:09 pm
content: 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.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 12, 2024, 07:13:51 am
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: March 12, 2024, 08:28:03 am
content: 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.

author: Jason Henry
author_rank: Contributor
timestamp: March 12, 2024, 08:50:50 am
content: 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.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 12, 2024, 10:08:20 am
content: Quote from: 5U4GB on March 12, 2024, 07:13:51 amIt 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.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 12, 2024, 10:30:40 am
content: 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.

author: Haenk
author_rank: Super Contributor
timestamp: March 12, 2024, 12:58:19 pm
content: Quote from: Jason Henry on March 12, 2024, 08:50:50 amNonsense, 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.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 12, 2024, 02:03:41 pm
content: sillicone adhesive ? dont tell me you dont have something similar ?

author: GLouie
author_rank: Regular Contributor
timestamp: March 12, 2024, 05:41:17 pm
content: 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.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 12, 2024, 10:12:19 pm
content: 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.

author: aeg
author_rank: Regular Contributor
timestamp: March 12, 2024, 11:45:56 pm
content: Since the original feet are gone and you're not trying to keep it original, how about just sticking on some Bumpons?

author: vk6zgo
author_rank: Super Contributor
timestamp: March 13, 2024, 12:59:44 am
content: Quote from: 5U4GB on March 12, 2024, 07:13:51 amInterestingly, 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.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 13, 2024, 01:50:42 am
content: Quote from: Haenk on March 12, 2024, 12:58:19 pmNot 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.

author: Bud
author_rank: Super Contributor
timestamp: March 13, 2024, 02:30:13 am
content: A twin Epoxy tube is a couple bucks at Dollarama, why not.I do not use superglue for anything, it is garbage.

author: xrunner
author_rank: Super Contributor
timestamp: March 13, 2024, 10:58:14 am
content: Quote from: Jason Henry on March 12, 2024, 08:50:50 amThis 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.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 13, 2024, 02:02:11 pm
content: 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.

author: tooki
author_rank: Super Contributor
timestamp: March 13, 2024, 10:39:55 pm
content: Quote from: MathWizard on March 11, 2024, 12:08:10 pmWood 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…

author: MathWizard
author_rank: Super Contributor
timestamp: March 14, 2024, 03:51:31 am
content: 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

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2024, 08:21:06 am
content: What exactly is missing? The rubber feet on those are just standard 3M Bumpon. I’ve done that exact replacement on my Keithley 197’s. They’re self-adhesive, just use Goo-Gone to remove the old adhesive first.If the cord wrappers have broken off (the things the feet are glued to), I’d just stick big fat Bumpons to the case.If you’re just missing the tilting bale, you can probably find a replacement on eBay, otherwise there are generic ones made that just screw to the bottom of the case.Wood glue to plastic will not work: it won’t adhere to plastic. There is no point in trying, and you’ll just make a mess you have to clean up.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 14, 2024, 11:57:16 am
content: Quote from: MathWizard on March 14, 2024, 03:51:31 amUh, that's the exact thing that several people have indicated won't work. Short of, say, spit, it's probably the least useful glue you can use with ABS/PE/PP/whatever the multimeter is made of.Of the commonly-available glues something like Uhu might do it, but even then I wouldn't bet on it holding PE or PP. In fact go to your local hardware store and look at every glue they stock, pretty much all if not actually all of them will say "not for PE or PP", if that's what the multimeter case is made of. For example looking at the Uhu site it says:QuoteSo in effect "glues absolutely everything you can think of, unless it's PE or PP".

author: Haenk
author_rank: Super Contributor
timestamp: March 14, 2024, 01:35:01 pm
content: But really, which manufacturer of professional equipment would use PE/PP for a case? It has to be ABS. (PE/PP would have a "waxy" touch to it, but I'm 100% sure, it's not...)

author: tooki
author_rank: Super Contributor
timestamp: March 15, 2024, 09:29:56 am
content: Quote from: 5U4GB on March 14, 2024, 11:57:16 amPolyethylene and polypropylene aren’t used for electronics enclosures, they’re too soft. They’re commonly used for milk jugs, bottles for solvents and cleaners, and various films and wraps. Not relevant here.Quote from: Haenk on March 14, 2024, 01:35:01 pmIndeed.I just checked my Keithley 197, which uses the same case, and unfortunately there are absolutely no markings indicating what resin it is. But it certainly looks and feels like ABS, and I don’t see any reason why they wouldn’t have used ABS for this type of product. It just stands to reason that it is. The only other plastic it plausibly could be is polycarbonate. I’m not willing to do any destructive testing to determine which it is.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 15, 2024, 10:57:20 am
content: Tests to identify ABS. I mentioned before the flame tests. The sooty, pungent smell is characteristic. Sooty alone is not. ABS sinks in water and floats in glycerin.https://www.wikihow.com/Identify-Abs-Plastichttps://www.ji-horng.com/plastic-material-identification-by-burn-test

author: tooki
author_rank: Super Contributor
timestamp: March 15, 2024, 01:08:24 pm
content: Quote from: jpanhalt on March 15, 2024, 10:57:20 amI’m not willing to damage my bench meter’s housing to perform destructive testing, and I assume OP isn’t, either.Quote from: jpanhalt on March 15, 2024, 10:57:20 amI love how 3 of the 4 “non damaging” tests they lost involve potentially damaging the sample…

author: Haenk
author_rank: Super Contributor
timestamp: March 15, 2024, 01:14:33 pm
content: Quote from: tooki on March 15, 2024, 09:29:56 amPC is very hygoscopic, that would not be a good choice for electrical measuring instruments, so: extremely unlikely.

author: themadhippy
author_rank: Super Contributor
timestamp: March 15, 2024, 02:20:33 pm
content: Another option,one of the many grab adhesives like "sticks like sh*t" that stuff sticks almost anything to anything.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 15, 2024, 03:18:59 pm
content: Quote from: Haenk on March 14, 2024, 01:35:01 pmFluke. That's a carrying case not the DMM case itself because no-one seems to specify what those are made of, but it indicates PP is used in some cases.

author: ddosegov
author_rank: Contributor
timestamp: March 15, 2024, 03:29:07 pm
content: First cover wood with thin coat of lacquer, paint or epoxy, let it dry for a few days, then use 3M 03609/03614/03615/03616.

author: tooki
author_rank: Super Contributor
timestamp: March 15, 2024, 03:42:23 pm
content: Quote from: 5U4GB on March 15, 2024, 03:18:59 pmWe are talking about the device enclosures themselves, notcarrying cases!

author: tooki
author_rank: Super Contributor
timestamp: March 15, 2024, 03:47:31 pm
content: Quote from: Haenk on March 15, 2024, 01:14:33 pmIt may be “very hygroscopic” from a molding (including 3D printing) point of view, but I don’t think it matters in terms of normal-voltage electrical performance. It’s a widely used material for electrical enclosures.Keithley knows how to design sensitive measurement circuits properly; I can’t see how the enclosure could have an influence.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 16, 2024, 04:35:04 am
content: Quote from: tooki on March 15, 2024, 03:42:23 pmUh, that's exactly what the message you're quoting says, "we don't have any data on DMMs but the closest thing that we have data for is made of something notoriously difficult to glue".

author: tooki
author_rank: Super Contributor
timestamp: March 16, 2024, 03:39:02 pm
content: Quote from: 5U4GB on March 16, 2024, 04:35:04 amBut it’s not a “close thing” at all. Carrying cases aren’t DMM housings.I wasn’t saying that what you said was untrue. I’m saying that it’snot relevant to the discussion in any way.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 18, 2024, 01:21:40 am
content: I have had a lot of success with "Selleys Allfix".I doubt it exists outside Oz, but the ingredients are fairly vaguely described on the container as:-30-60%Acetone10-30% Ethylene Acetate1-10% Butyl Acetate.I have used it to stick a large Bakelite Morse Key base back together after I dropped it, and at another extreme, to stick the plastic segments of the cover of a barrel type connector on the end of the charging lead for this laptop.The moulded cover of the connector is made of what looks & feels like the soft outer cover on my Fluke 77.One thing that seems essential is to clamp it during its setting period------ for the bakelite bit with an actual clamp & for the connector a combination of cable ties & a vyce.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 18, 2024, 09:18:10 am
content: Quote from: vk6zgo on March 18, 2024, 01:21:40 amThat looks pretty identical to the Uhu glue I mentioned, acetone + one or more acetates, which indicates that similar mixes would be available under different names in other countries that don't carry Selleys products.For people in countries that do carry Selleys, if you want it cheaper than the Selleys prices then buy it under the name Parfix, it's the same stuff but sold at a lower price point.