Repairing plastic hinges

Hi

Does anyone have any good tips for repairing plastic hinges? I mean the type that are moulded into the box and flex as you open and close the box. My Mitutoyo dial caliper box is starting to show definite signs of failure and I'd like to catch it before they part company completely.

As an aside, I'm also going to replace the foam inserts which have completely disintegrated - any tips for what to replace those with?

Many thanks,

Rob

Look up "Shadow foam" for the latter, no connection etc.

For the former, I don't know but you might try a glue gun, or carefully applied strips of gaffer tape, having thoroughly cleaned the hinge surface first of course.

Foam inserts are best replaced with Plastazote

[ trade name … ‘clones’ appear to be available ]

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To the best of my knowledge there is no way of repairing a failed Polypropylene hinge … just use tape or add a proper mechanical hinge.

MichaelG.

I've used the green polyester felt from Hobbycraft to line an old steel micrometer case. It's very thin, but cushions the old micrometer. I glued it using contact adhesive.

Bill

You used to be able to get plastic hinges for model aircraft control surfaces maybe they still use them.

Perfect opportunity to make yourself a nice wooden box. Oak or walnut, brass hinges and a custom cutout for it to sit in lined with felt. 😎

Edited By Hollowpoint on 03/04/2023 13:49:11

A decent duck tape does those funny ones, cut to shape

I thought oak caused steel to rust?

I made this insert to fit into one of my draws, it would be so easy to add hinges and a lid. This was made from mahogany and then lined. You can buy sticky backed felt to line it with to protect the instrument.

It was marked out and then a router used to take out material for the micrometer to fit

Do NOT use oak. The tannin will stain the caliper

Roy

I noticed Duncan typed faster than me

Dave Halford is correct about the hinges, there are many types, proper miniature hinges, moulded plastic ones and strips of Mylar film about 20mm wide. Mrs Google will find your nearest stockist,

I think it’s the oxalic acid in oak that induces corrosion.

regards Martin

Some plywoods do to.

Edited By Martin Kyte on 03/04/2023 20:34:31

There is no cure for fatigue. Once the failure has started, there is very little chance of repair - except renewal, which is not repair sensu stricto ( or should it be senso strictu?). The problem is that fatigue works by extending a crack - and the crack is the source of further failure. It may be possible, in some cases, to remove the crack completely including the material on both sides, and filling the space with new material which is integrated (not just glued or stuck) into the original. Perhaps possible with a steel component restored by welding, but even then there are likely to be future problems with the weld not being the same as the original metal, or the heat of the weld affecting the condition of the surroundings in various ways.

A cloth hinge, if you can manage it, is likely to last at least as long as the original plastic. But the glue might not.

Cheers, Tim

Thanks chaps, all useful info as usual. I think I've found an equivalent type of foam and some wing hinges on Amazon. Might just try some Gorilla tape in the interim and see how that goes on the hinges.

The wooden box idea will go on the "to do" list, though!

Thanks again.

Rob

Plastazote looks good, but you will need special tools to cut it cleanly and uniformly at varying depths. Shadowfoam is designed for the person without such tooling, yet still provide a professional looking result. It is made from many layers of material that are bonded together but cleanly separate at the depth you require, once you have cut the outline of the item into the foam.

If you have any old and unused 3.5 inch floppy discs you can open them up to use the disc material as a hinge, work a treat.

Emgee

I made a collet box for ER16 collets by CNC machining in a block of MDF, with a matching block that sits on top to "close" it. To reinforce the material and proof it I soaked it in several coats of Ronseal wet rot treatment - this is a penetrating "lacquer" that soaks into the material and dries and hardens. Not sign of any corrosion after 10 years. May work on other woods too.

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For what it’s worth … Plastazote cuts very cleanly with a knife, or with a sharp-edged tube

[but yes, to make a flat-bottomed recess, you would need to glue layers together]

The reason I particularly recommend it though, is its widespread use in modern military packaging …From personal experience testing such stuff; I think it is probably the available material that is least-likely to degrade with age or climatic cycling.

MichaelG.

i have the same problem. one day i will make a new box. from pallet wood

You're the one staring at the actual article of course, Rob, but it might not be as bad as you think. I have a daily pill reminder with 7 compartments that I've used continually since 1986. I expect many here have too. I remember wondering at the time how long the 'living hinges' (what the artsy designers called them at the time) could last. But none of the seven has failed in all that time though they've "showed signs of fatigue" for years.