3 indents in patent number pickups

[guitarteck]

Does anyone havea clue as to why the 3 indents are seen on some t tops? i have a pair like this and they look melted with the indents and i have no clue if its manufacturing. any ideas?

[Possum]

they are simply sprues where the plastic was injected into the mold, the ones that sink are simply from cooling of the part....

[David Schwab]

It was never intended for you to see the bobbins since the pickups had covers, so they didn't really care what they looked like.

[guitarteck]

you know, I never even thought of that! thats why im a novice. i have a pair that has holes in the same place but totaly sucked in

[David King]

The plastic shrinks 1-2% as it cools so if the injector pressure was a little low the mold will pull in a little air before the mold ejects the part resulting in little sink holes or bubbles in the thickest area of the part.

[Bruce Johnson]

For your obscure technical knowledge file: The little circles that you see on the surface are caused by the ejector pins. The mold is made with a group of holes and sliding pins that are operated by a pneumatic cylinder. During the molding cycle, the tips of the pins are flush with the inside surface of the mold. When the plastic is cooled, the mold opens, and the cylinder pushes the pins, which ejects the part from the mold. The little circles are the result of the small amount of clearance needed between the pins and the holes that they slide in. The injection pressure causes a little ring of plastic to seep into that clearance. As the mold wears from thousands or millions of cycles, the pins get sloppy in the holes and the circles of plastic stick out more.

David's right, the depressions are caused by some misadjustment of the temperature/pressure/cooling cycle. If it's out of adjustment, some areas of the part will cool too quickly, causing the depressions. Injection molding is a fussy process.

[Jim Shine]

If you get some of the NOS clear ones floating around, every one that I have had so far has a little air bubble trapped underneath each of those depressions.

[SonnyW]

If you get some of the NOS clear ones floating around, every one that I have had so far has a little air bubble trapped underneath each of those depressions.

I have a few of those, the Gibson NOS Clear T-Top ones, that surfaced a few years ago. I would say about 1/3 of mine have the depressions and bubbles. I tried to take a photo using my laptop screen as a backlight. I noticed on mine, that the bigger depressions are in the wall of the core, not on the tops. Not that this info is is all that useful, it is just interesting.

[David Schwab]

I have a few of those, the Gibson NOS Clear T-Top ones, that surfaced a few years ago.

Vintage Gibson Parts Clear Pickup BOBBINS T Tops 8 Pcs | eBay

[Jim Shine]

Heads up to anyone interested in using those. They are very brittle. You can't put even a medium amount of tension on the wire without them cracking.