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Old 16th Jan 2018, 9:33 am   #1
John G8MWF
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Default Milliput epoxy resin putty

One of my DAC90As, Ivory Case, has a broken bezel mount on the inside of the case - see enclosed picture.

Part of the screw thread is still intact and my plan in to insert the screw and mould Epoxy Putty over it, and once the putty is going off remove the screw and then allow it to fully set hopefully leaving a nice new thread in place.

The only trouble is that I haven't worked with Epoxy Putty before and getting things wrong on a Ivory case is not a mistake that I would like to make!

Does anyone have previous experience in making this kind of repair using Epoxy Putty ?

Cheers - John
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Old 16th Jan 2018, 10:04 am   #2
Boater Sam
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Default Re: Milliput epoxy resin putty

Epoxy putty, plastic metal etc. will do the job. You can either tap a new thread when its cured or use a good silicone release agent on the thread before casting. Don't try removing the screw before the putty has set, you will fail!
Adhesion to the plastic case (its not bakelite) will be enhanced if the surface is roughened and cleaned with acetone first. IPA may work, meths leaves a deposit, detergent likewise.
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Old 16th Jan 2018, 10:35 am   #3
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Default Re: Milliput epoxy resin putty

Hello again Sam, my intention is to smear a light coating of silicone grease on the screw first.
I think that I will make a ball of putty with a screw placed in it to get an idea of what to expect in terms of drying times and how well the screw releases - I don't want to find out the hard way by using the case as a test area!
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Old 16th Jan 2018, 10:39 am   #4
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Default Re: Milliput epoxy resin putty

A good idea!
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Old 16th Jan 2018, 1:04 pm   #5
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Default Re: Milliput epoxy resin putty

Yes, experiment first. They even suggest that you do that in the instructions.

My tip would be to make sure the Milliput is at room temeperature (i.e. not too cold) when you use it, and that mixing/kneading seems to be a lot easier and less messy if you use a pair of disposable gloves.
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Old 16th Jan 2018, 3:38 pm   #6
John G8MWF
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Default Re: Milliput epoxy resin putty

OK thank you all for your advice.

The White version of Milliput Putty should be with me by Friday and I will experiment with it first.
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Old 16th Jan 2018, 4:06 pm   #7
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Default Re: Milliput epoxy resin putty

I have sometimes provided reinforcement for this sort of repair by drilling a hole in the remaining plastic just big enough to take a metal pin and Aralditing the pin in place before applying filler. I use brass panel pins or stainless steel wire according to the size of the repair and space available. Milliput is excellent stuff.
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Old 16th Jan 2018, 4:20 pm   #8
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Default Re: Milliput epoxy resin putty

I do the same when using Araldite-type Epoxy to repair things like control-knobs: my most-recent repair like this was on the Bakelite base to a 1930s knurled-screw-down-terminals type terminal block which had cracked into three pieces, one of which had been lost. Dremel to machine shallow grooves into the back of the remaining bits, panel-pins araldited in, then Milliput used to make up the replacement for the missing piece.

One tip: don't rush it - though Epoxy may seemingly 'harden' in a few hours they become progressively harder over subsequent days. Avoid the temptation to handle your Milliputted repair too soon - let it 'cure' properly [warmth helps] so it gets its full strength.
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Old 16th Jan 2018, 4:46 pm   #9
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Default Re: Milliput epoxy resin putty

I am not sure if pins are possible in this case as there are no other parts.
The area to be repaired/replaced is also very small and the whole screw is less than1/2" long.

True I could tap out the hole, which is tight in the space available, use a longer screw AND use putty but I am hoping the first option will do the job.

Hopefully I will have created a 'new' thread by leaving the screw in place while the mould sets and it will adhere to the broken surface with enough strength to hold in place.

I have enclosed 2 pictures for comparison, one of the good pillar and the other of the broken one.
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Old 16th Jan 2018, 4:51 pm   #10
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Default Re: Milliput epoxy resin putty

I'd abrade the case round the broken bit. for some distance down the 'ridge' as well. Can you drill a hole at 90 degrees to the direction of the screw, some way down the 'ridge', then put a pin in this, sticking out, then mould Milliput round the whole thing?

That way the pin will at least be taking some of the tension from the screw, rather than depending solely on the adhesive grip of Milliput to the old plastic?
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Old 16th Jan 2018, 4:58 pm   #11
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Default Re: Milliput epoxy resin putty

Yes that is possible. Would something like a resistor wire be good enough as a pin - the joint will be under a little tension when re-assembled?
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Old 16th Jan 2018, 5:29 pm   #12
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Default Re: Milliput epoxy resin putty

I think a resistor 'offcut' would be too flexible and would just bend if subjected to any sort of shear-load. You need a hard wire not something bendy.
A panel-pin would be ideal; if not available you could cut down a thick needle!

[Take *great* care if trying to cut a needle or any other seriously-hard wire using pliers or side-cutters: when they suddenly cut through the two cut-pieces fly off at phenomenal speed and could easily blind you or cause injury to anyone they hit]
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Old 16th Jan 2018, 5:35 pm   #13
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Default Re: Milliput epoxy resin putty

Quote:
Originally Posted by G6Tanuki View Post
[Take *great* care if trying to cut a needle or any other seriously-hard wire using pliers or side-cutters: when they suddenly cut through the two cut-pieces fly off at phenomenal speed and could easily blind you or cause injury to anyone they hit]
Stick a bit of masking tape either side and cut through that.
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Old 16th Jan 2018, 6:07 pm   #14
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Default Re: Milliput epoxy resin putty

The stainless steel wire I use is dental wire in a range of diameters down to 0.2mm that I got from the late lamented "Proops" many years ago. To relieve the mended area of strain, you could drill a clearance hole though the mended area and drill and tap a hole in the remains of the original pillar, using an extra-long screw. This would ensure that the mended area was always in compression.
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Old 17th Jan 2018, 8:51 am   #15
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Default Re: Milliput epoxy resin putty

Paper clip? Extra pinning is a good idea, like soldering, a good mechanical joint first then goo. You should be able to sink a hot wire pin into the existing plastic, it is a sort or thermoplastic.
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Old 18th Jan 2018, 11:10 am   #16
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Default Re: Milliput epoxy resin putty

Paper clips are a bit soft. Safety pin steel is a lot harder. (Try picking a cheap padlock or a frame tumbler type lock with a paperclip, then a safety pin!)
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Old 18th Jan 2018, 11:16 am   #17
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Default Re: Milliput epoxy resin putty

Sounds like a misspent youth to me!

Just waiting for the stuff to arrive and I will be experimenting with different options.

Cheers

John
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Old 18th Jan 2018, 8:56 pm   #18
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Default Re: Milliput epoxy resin putty

could you mould-in a threaded insert, like the ones they use in ABS project boxes, with a screw just screwed so far in? Or maybe even a threaded pcb pillar, or rivnut?
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Old 19th Jan 2018, 12:26 am   #19
John G8MWF
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Default Re: Milliput epoxy resin putty

I must admit I hadn't considered that!
Not sure if there is enough room/plastic for it to work but I will certainly have a look.
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Old 19th Jan 2018, 10:24 am   #20
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Default Re: Milliput epoxy resin putty

As noted in the instructions, Milliput is most easily moulded with wet hands (gloves if you like, but it rinses off easily). Seems a bit counter-intuitive to me, but true nonetheless!
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