Plastic key repair - Page 1
Forum section: electronics / repair

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 14, 2020, 06:35:25 pm
content: I have a broken key from a digital piano that is no longer available as a spare.Anyone have any recommendations on which products are good, or useless, for repairing such a thing?I assume it needs to be white, easily polished, and waterproof.And it needs to feel good, as in playable, these keys have a gloss finish.My googling attempts found this that looks like it might do the job, but then I'm just guessing/hoping.https://www.amazon.co.uk/gp/product/B07GDMY3XG/ref=ox_sc_act_title_1?smid=ADNSKZTQ0HA6Y&psc=1Photo here of a key with a big hole in it:

author: andy3055
author_rank: Super Contributor
timestamp: October 14, 2020, 07:23:44 pm
content: There seems a lot of different products on that link. Check the info on the product you want to use. Apart from being white, you may want to look for something that can be filed to shape and polished so that it does not look ghastly, being a piano key.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 14, 2020, 07:39:50 pm
content: The amazon link works for me, maybe its country specific.Here is the manufacturers link instead.https://www.ed-supplies.co.uk/product-page/upvc-hard-plastic-epoxy-repair-putty-kit

author: wraper
author_rank: Unknown
timestamp: October 14, 2020, 07:44:53 pm
content: IMHO glue cracked pieces together with cyanoacrylate based glue (superglue). Put something under the hole coated with release agent then fill that hole with liquid epoxy. When hardened remove the backing.

author: HobGoblyn
author_rank: Unknown
timestamp: October 14, 2020, 11:29:50 pm
content: I don’t know how good they are, but just found these on Amazonhttps://www.amazon.co.uk/Demiawaking-52Pcs-Plastic-Keytops-Replacement/dp/B079GX88TNhttps://www.amazon.co.uk/dp/B07HBP359F/ref=dp_prsubs_2What make/model is the key from? You often find people selling individual used keys from old keyboards etc on eBay

author: Peacefrog
author_rank: Contributor
timestamp: October 15, 2020, 01:32:05 am
content: Tryhttps://syntaur.com- you may be able to look for the model directly.

author: DaJMasta
author_rank: Super Contributor
timestamp: October 15, 2020, 04:10:52 am
content: Aside from a donor unit, probably some generic patching epoxy/regluing existing pieces will probably give you the best treatment. Basically, you don't want to use too much extra material because additional weight on the key will effect the feel of it while playing. It also doesn't generally need to be that durable (current damage I can't imagine is common....), so the most important thing is getting something back in there and then making sure it is sanded and buffed smooth to match the height and feel of the surrounding bits - it will absolutely be noticeable to a player if there is inconsistent texture on the surface of the key, so my advice would be to match the finish as closely as possible and to use sort of whatever works for the actual patch.You may be able to find keytop stock for regular pianos - it's generally wooden levers with plastic fake ivory on top or similar - but because the thickness of that is molded into the key you have, to use it and maintain height with other keys, you'd probably need to cut/sand off most of the key top that you have, and then glue the replacement top to the remaining plastic frame.If you can determine the plastic, it's also worth mentioning that a plastic cement will probably give you best results if one can be found.

author: pickle9000
author_rank: Super Contributor
timestamp: October 15, 2020, 04:53:34 am
content: milliput

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 15, 2020, 07:43:52 am
content: Quote from: HobGoblyn on October 14, 2020, 11:29:50 pmI have since found a used key on Ebay which I have ordered, but would like to see how feasible it is to repair a key when one is not available, as I deal with quite a lot of vintage keyboards and one day I will need to do this properly.I'll give Milliput a try unless anyone can recommend a better product.Thanks to all.

author: pbarton
author_rank: Frequent Contributor
timestamp: October 15, 2020, 10:46:07 am
content: Sugru

author: Jeroen3
author_rank: Super Contributor
timestamp: October 15, 2020, 12:10:24 pm
content: You can probably use acetone smoothened 3D printed ABS key.If you can get the weight correct.

author: tooki
author_rank: Super Contributor
timestamp: October 16, 2020, 12:00:00 am
content: Quote from: pbarton on October 15, 2020, 10:46:07 amHeck no. Sugru creates a soft, rubbery material, neither of which is what you’d want here.

author: Cerebus
author_rank: Super Contributor
timestamp: October 16, 2020, 01:04:36 am
content: Quote from: tooki on October 16, 2020, 12:00:00 amDepends. If you want a sex-toy feel keyboard, yes. HaveThrobbing Gristlereformed?

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 16, 2020, 01:09:58 am
content: Quote from: wraper on October 14, 2020, 07:44:53 pmCyanoacrylates are rubbish for use on plastics.The material is most likely ABS. Make a trip to a modeling store and purchase any of the water like liquid styrene plastic model welding solvents* which will do an excellent job of reassembly. Shave chips of a similar color and texture plastic and fill the void with chips and solvent welding liquid. Carve/sand as required.In model shops, you can usually purchase bulk white styrene extruded shapes used typically for scale model railroading. I would expect you could fashion a new key out of strip styrene if you’re handy. The material is very easy to work with.* - the welding solvent is a blend of MEK, acetone, and/or trichloroethylene, etc depending upon your locale.https://www.amazon.co.uk/Humbrol-AE2720-Poly-Cement-Clear/dp/B07TF9PQB7/ref=pd_sbs_229_1/262-1208501-4475761https://www.amazon.co.uk/s?k=evergreen+scale+models&i=toys&crid=EXN7HEKSR8NB&sprefix=Evergree%2Ctoys%2C283&ref=nb_sb_ss_i_3_8

author: amyk
author_rank: Super Contributor
timestamp: October 16, 2020, 03:17:36 am
content: What does any text on the part say? It might tell you what the exact plastic is.

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 16, 2020, 04:33:09 am
content: Yes, if it was produced in the last ten years, give or take, it should be labeled for recycling purposes.Most likely ABS or just styrene, depends on how much the item cost. It might be nylon but I doubt it based on the cracks. If it softens with mek or acetone, it’s styrenic something or the other. If not, likely nylon. If it was pricey, it could be a filled nylon.

author: drvtech
author_rank: Regular Contributor
timestamp: October 16, 2020, 02:58:18 pm
content: When you've repaired a key you might want to put it in the top or bottom octave where it will be slightly less visible and will get less use.

author: Cerebus
author_rank: Super Contributor
timestamp: October 16, 2020, 03:31:54 pm
content: A wise idea.However, and obviously I don't if it applies to this keyboard, some of these keyboards can be surprisingly non-uniform. It doesn't necessary go that the key from, say, G in one octave will fit in the position of G in another octave. Sounds crazy right, but I've seen it.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 16, 2020, 06:27:17 pm
content: Quote from: amyk on October 16, 2020, 03:17:36 amNo markings on the part other than the key i.d. unfortunately.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 16, 2020, 09:20:24 pm
content: Quote from: WattsThat on October 16, 2020, 01:09:58 amYes, I remember this kind of welding process when I used to assemble "Airfix" kits of model aircraft.I can't honestly remember ever having any kind of satisfactory result using Superglue, apart from gluing my fingers together.Maybe I'm doing it wrong.Araldite is way more reliable IMHO.

author: MarkF
author_rank: Super Contributor
timestamp: October 17, 2020, 08:49:21 am
content: I would create a 3D model of the key and print it on glass.If printed with the key top on the bottom (touching the glass), it will be very smooth already.Then all you need to do is polish it.It will be hard to match the other keys in color and gloss.But, the key itself would be uniform in color and feel.I'm new to 3D printing and have only printed in PLA.But, you can get some really nice finishes.Don't have a 3D printer?Here's you chance.You will be amazed all the uses you will find for one.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 17, 2020, 04:18:07 pm
content: I have recently been thinking about a 3D printer, for things like making unavailable knobs for old gear.I've been put off so far at the notion (inside my own head) that small parts like these would be difficult to print finely, and would need a lot of extra work to get them looking or feeling nice, if at all.Possibly some undeserved predudice there.To get good results on a small knob, for example, what entry level of machine are we actually talking?

author: MarkF
author_rank: Super Contributor
timestamp: October 17, 2020, 05:38:31 pm
content: I bought a $300 USD Creality CR-10 Mini over a year ago.It has a 300mm x 220mm x 300mm build area. Which has been big enough for me.I did have to divide one or two prints into two pieces because they were too long.I've been out of the market for a printer for over a year.However, I see a lot of talk of Creality's CR-10 and Ender models.There are also the Prusa printers for more money.

author: helius
author_rank: Super Contributor
timestamp: October 17, 2020, 06:37:35 pm
content: Most of these keys are in fact made of acrylic plastic. They are commonly weighted with small weights glued in the bottom; one of the causes of failure is the glue decomposing and dripping out, resulting in loss of the weights. In the most common type of switch, the key has two pegs underneath that strike a rubber membrane. The pegs need to be exactly the right size and position to register a note.

author: MarkL
author_rank: Unknown
timestamp: October 17, 2020, 06:54:40 pm
content: I bought some of this stuff a few months ago and have used it a few times now with good results:https://www.plast-aid.com/It works well when it chemically bonds with the plastic such as ABS and PVC, but mechanical bonds work ok too. It dries very hard. You can fill the hole, and then sand and polish it smooth. It's a translucent white, but they also sell a color matching kit (including opaque white) so you might be able to get pretty close.https://www.plastex.net/is another that looks the same as the Plast-Aid. I'm sure there are others.

author: Cerebus
author_rank: Super Contributor
timestamp: October 17, 2020, 07:38:31 pm
content: I'd like to raise a note of caution surroundinganyof the processes involving solvents (so the above and the earlier suggestion of dissolving scraps in solvent).Were I repairing this, I'd want to clamp the key with the face firmly pressed to a smooth surface. Both to try and get a good surface finish, but also to get the repair surface co-planar with the rest of the key's existing surface. I'd probably clamp a couple of slats of something rigid over the top and press the sides of the key down to a flat surface (glass or metal treated with a release compound) to do that. That would put the sides in compression. I'd be concerned about them softening from solvent fumes while any solvent based infill dries. It would be quite easy to distort the sides under those circumstances.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 17, 2020, 08:04:51 pm
content: Why would you not use a putty instead?Pro's and cons's obviously, but I'd like to hear them.

author: helius
author_rank: Super Contributor
timestamp: October 17, 2020, 08:05:24 pm
content: That's true. Solvents can also cause stress cracking in surrounding material.

author: Cerebus
author_rank: Super Contributor
timestamp: October 17, 2020, 09:08:39 pm
content: Quote from: Audiorepair on October 17, 2020, 08:04:51 pmNo, I'm not saying that - just wanted to flag up the thoughts that had crossed my mind about one possible risk of a solvent based repair. Putty has a lot going for it, I'd be a bit concerned about getting good adhesion from past experience with using them.I'm not sure that I've got a good strategy to offer. Best I can say is that if I were to do it myself I might go for a mixed strategy - A lightweight repair to the surface with a thin layer of a like material, probably solvent based in the hopes of consolidating the remains - as little as I thought I could get away with to minimise exposure of the rest of the part to solvents, then a bit of reinforcing glassfibre tissue with some epoxy on the back of the lightweight repair for strength and durability. My biggest concern would be getting a good surface finish and to achieve that I think I'd start off by clamping the part to a suitable flat surface that the repair could be built up against, and keep it clamped until I'd laid up all the layers. My two cents for what they're worth.

author: MarkF
author_rank: Super Contributor
timestamp: October 18, 2020, 07:53:12 pm
content: Quote from: Audiorepair on October 17, 2020, 04:18:07 pmHere's a sample of some small parts I've printed.They are untouched direct from the printer.Printed with Hatchbox White PLA at 0.28mm layer height (What I consider 'draft mode').Particularly note the white puzzle piece.The touch, feel and look are almost identical to the piano keys.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 18, 2020, 08:04:04 pm
content: Well I'm quite tempted to get into 3d printer world now.Can you also get stock that turns out more squishy? More rubber like?

author: MarkF
author_rank: Super Contributor
timestamp: October 18, 2020, 08:15:44 pm
content: Quote from: Audiorepair on October 18, 2020, 08:04:04 pmIt's harder and I have not printed any.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 18, 2020, 08:28:51 pm
content: Blimey,this IS the future, isn't it. Took me a while.Thanks.