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Mysterious damage.


btoth76

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Hello!

 

A month ago, I have noticed that the bridge pickup's tone knob developed a crack. Obviously, I did't wanted it to affect my tone, so I bought a new one. [rolleyes] As soon, as I removed it from the guitar, it split in two, in my hands.

 

WP_20160108_08_54_06_Pro_zpssfquyimg.jpg

 

After 5 years of use, and careful treatment it suddenly happens... :-k:-s

 

Best wishes... Bence

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Once I applied contact cleaner to the shafts of four push/pull pots. Right after that the pot knobs began making crackling noises and fell to pieces. I hadn't even come that far to push and pull several times in order to spread the cleaner. They obviously don't stand alcohol or the like.

 

One of my brand-new Gibsons came with golden top-hat knobs already having visible cracks. No problem for me since I anyway replaced them with speed knobs that I prefer.

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... Was the knob tight on the pin and overstressed perhaps?

 

Well, I guess it was. Nothing else I can think of.

 

Not a big deal after all. My only concern that new knob is labeled with different font size. I have to swap the inserts. The old one fell out from the broken knob, but on the new it is tight. I have to come up with something that does not damages the new one.

 

Best wishes... Bence

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At least, it is an easy replacement.

 

Unlike the one I have to perform on my Tele. The knob on the selector lever was loose from the beginning, so I applied some superglue on it. Of course, the switch got worn out. I bought a quality replacement part, but I can't get it off from the control plate. Cutting it off seems to be a dangerous thing to do. #-o

 

Cheers... Bence

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Guest Farnsbarns

Drill a small hole in the new one, from the back, the reflector will probably fall out but if not, easy to get out with the hole. Then put the old reflector in with superglue and cover the hole.

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Yes, sounds good.

 

Looking at the old one, the insert was held in place with a tiny amount of glue. First, I will try to rock it out with my thumb. Hopefully, it will separate from the glue.

 

If not, I will drill it out.

 

Thanks... Bence

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Having worked in the plastic injection molding industry I can tell you the end product can be brittle. It's a QC concern of course. Could have been improper drying of the raw product or the heat set too high on that particular machine or other things. QC dictates that products be tested of course. We developed a desktop tool for the QC department that looked a little like a slide hammer sitting upright, which had a weight that would drop onto some sample products to see if any shattered (as opposed to dimpled or even simply cracked lightly). Not rocket science, not the way WE handled it anyway, but it gave us a semi-consistent way of checking and therefore controlling.

 

My guess is this one was marginally brittle and just chose that day to die.

 

The plastics we used were polyurethane and came a wide range of hardness, and we chose what we felt was right for the job. Sole plates (that are molded inside your golf shoes) were very soft and pliable (54 on the durometer scale), football and soccer cleats a little harder (60) and golf spikes were quite hard (74). The golf spikes were more durable as a result of them being high on the D scale but also took us right up to where they could get brittle.

 

Sorry...coffee kicked in.

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These knobs are made of Poly(methyl methacrylate) (PMMA), also known as acrylic or acrylic glass as well as by the trade names Plexiglas, Acrylite, Lucite, and Perspex, besides a few others.

 

PMMA is sensitive to light, in particular ultraviolet, and also biodegradable under certain conditions. It tends to become brittle with time. Possible cracks in reflector knobs are likely to be hidden by the top inlay. Thus breaking apart may appear as some surprise, rather than with fully transparent ones where you might see it coming beforehand.

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