Author Topic: Modifications to 302 Bases to Prevent Thermoplastic Shells from Cracking  (Read 15198 times)

Online Dan/Panther

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My thoughts about that, if you pay $500.00 for a phone and then drop it, you deserve to have it cracked.
D/P
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I didn't mean that post to sound so cold blooded.
What I meant to convey as a message, was more along the lines of "Gheez people be careful with these rare vintage items, they aren't making them anymore."

D/P

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Offline Bingles

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Oh great.. now I'm afraid of my thermoplastic 302 splitting apart. hahaha!

Online Dan/Panther

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Oh great.. now I'm afraid of my thermoplastic 302 splitting apart. hahaha!

No Joke, they will shrink. and crack, under certain conditions, which I've not been told exactly what these conditions are. My guess extreme heat and low humidity.
D/P

The More People I meet, The More I Love, and MISS My Dog.  Dan Robinson

Offline HowardPgh

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Re: Modifications to 302 Bases to Prevent Thermoplastic Shells from Cracking
« Reply #48 on: September 19, 2012, 10:24:45 AM »
Can the corners of a tight case be heated and stretched out a bit?
Howard
Howard

Offline LarryInMichigan

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Re: Modifications to 302 Bases to Prevent Thermoplastic Shells from Cracking
« Reply #49 on: September 19, 2012, 10:33:44 AM »
My advice is to leave the plastic alone if at all possible.  I recently bought an ivory plastic 302 which was very tight around the base, so I carefully removed the shell and then gently banged the edges of the base with a small hammer to bend the metal inward slightly.  The shell fit comfortably over the base after that.

Larry

Offline George Knighton

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Re: Modifications to 302 Bases to Prevent Thermoplastic Shells from Cracking
« Reply #50 on: November 25, 2012, 09:59:40 AM »
Thank you very much for the information in this thread.  I'll be putting some of this advice to use very soon, probably by next weekend!
Annoying new poster.

Offline HowardPgh

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I ground  the base corners almost to the divot where the foot screw goes. Cover fits fine now and an invisible fix when the feet are put back on and the cover replaced.-Howard
Howard

Offline Bill

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Howard -

Like you, I ground back the corners of a 302 baseplate. I may not do that again. Do you notice how efficiently the magnets in the ringer collect the metal shavings?

On another 302, I banged back the edges and corners of the baseplate a bit, as suggested by LarryInMichigan. Worked just as well, and no mess to clean up.

Bill

Offline HowardPgh

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Bill,
I tried the banging in the corners but I couldn't get the clearance needed.
The 302 that I did had an aluminum baseplate.
The cure for for the shavings/filings problem is to remove the ringer and put it far away from your grinding area. (That goes for the receiver element too!)
The job is easier if you take all the removable components off of the baseplate.
Howard
Howard

unbeldi

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« Last Edit: September 02, 2017, 03:45:45 PM by unbeldi »

Offline AE_Collector

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So, keep heat and direct sun light away from Tenite phones (or other soft thermo plastics)

You don't have to tell PaulF that! He is still wondering how he is going to restore that clear AE 34 set!

Terry

unbeldi

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« Last Edit: September 02, 2017, 03:45:24 PM by unbeldi »

southernphoneman

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i have found that on my 302 when i have to take the housing(i have the bakeliteplastic 1949 version) off i put the phone on a bench or table, by this time i have unscrewed the bottom,i turn it around so i see the power cord hole and carefully take a screwdriver being careful not to touch any of the interior guts, with tip of the screw driver down and put the screwdriver on the outside upper part of the hole and very gently lift ,do not force it,but lift very gradually it will eventually come off. make sure to leave the phone on the table or bench. do not pick up and do it in mid air or even put it in your lap, because you can drop it and then it is ALL OVER.

southernphoneman

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also, the plastic shells of the 302s do shrink over time . especially if they have been in storage for years. what happens is the plastic shrinks around the base making it extremely hard to remove without breaking it.

unbeldi

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(i have the bakeliteplastic 1949 version)

I know you read in many places that it's Bakelite. But it is really a cellulose acetate derivative, quite different and made from wood chips. Eastman Kodak patented it under the trade name Tenite. I believe that they used the 'lightest' variety of Tenite, which they called Tenite Acetate. Having only a short carbon chain, it breaks down more easily than the other varieties, hence the shrinkage. This becomes very pronounced at higher temperatures. Over the span of decades the material will shrink and envelope the metal developing internal stress, but it may not even break while on the metal. But when it is removed from the metal the stress is suddenly relieved causing excessive internal strains and the housing cracks.

For the 500 series, WE initially switched to a different kind of Tenite, I believe it is the Tenite Butyrate. A WE conference paper and presentation about the design of the 500 called it "Tenite 2", but this must be some internal nick name, because there is no Tenite 2 that came from Kodak.

The characteristic smell of this plastic is what gives away its identity.  It has a foul odor which comes from the breakdown of the plastic into butyric acid or butanoic acid, by the more modern name. It is the same smell of rancid butter, from which it got its original name. Tenite Butyrate appears more stable over decades at normal temperatures, but it does also shrink at higher temperatures, like most plastics.  In the late 50s Western Electric abandoned it and switched to what I think is an ABS-based polymer (acrylonitrile butadiene styrene) which is also a thermoplastic but has better mechanical properties, especially higher impact resistance, and is very glossy compared to the cellulosics, which are very soft.

« Last Edit: November 01, 2014, 07:48:35 AM by unbeldi »