Butyrate Bobbins

[JGundry]

The sink varies from how the part was run batch to batch. Whenever the mold was reworked to change the core height the pieces of the mold that make the coil former would be redone. Measuring an original part is tricky because some things that might seem like poor tolerances in the finished piece are drafts built in to allow the part to eject from the mold.

There is room for interpretation when having these made. One example is the slug spacing on a PAF does not match the screw bobbin spacing. Matt and I kept this mismatch in spacing. But if you get the original parts to an experienced molder they can interpret just about every mark on the part accurately from a manufacturing standpoint and duplicate the process.

[Possum]

....

I've been fortunate to know the exact specs Gibson designed but can't say more than that.

There do seem to be two different sets of bobbin mold numbers, and all the Patents I've examined have identical core measurements, so yes there is room for interpretation but the master design was aimed at one tone.
I did a little research on dielectric ratings of CAB and ABS....
The dielectric of ABS plastic at 1 megahertz is from 2.8-3.8
CAB (butyrate) 1 megahertz = 2.5-6.2
You have to get up to radio frequencies for anything much different to show up. Having experimented with my "darkening" potting fluids at audio frequencies of course that range of difference is inaudible and keep in mind I am entirely soaking the interior of the coil, not just having someting butt against the core and top and bottom. Any differences you're hearing are due to design differences from these and what you were using before. And BTW I did find the ideal potting liquid, non-hardening, darkens coils, but was too hard to control how much saturation inside the coil so pretty much abandoned that idea and found better ways.

[clown_luthier]

wow
JGundry an Belwar, this bobbins look real nice

[JGundry]

The original PAF mold is a 4 cavity mold. When the coil former bit was remade they would have etched new cavity mold numbers. The suffix on the number indicates the cavity of the mold. The original parts are still at the molder but I'm pretty sure the font is a little different on one of the original parts. I will check that when I am at the molder today. The different font would probably indicate a different bobbin core height.

Any original specs. would have been adjusted with the Butyrate shrink factor applied by the place making the mold. They would also include any draft etc. needed for making the part. Things like the circle in the square pin were hand done and vary from cavity to cavity.

[cryptozoo]

Wow, those look great! Fantastic job, guys. I actually like the dimples / flow marks in the bobbins, all my original butyrate bobbins have those and it looks much more authentic to my eye. I suppose the discerning customer might prefer a 'perfect' bobbin, though...

[JGundry]

Matt and I both like the sink and the look of them. Personally that is what I want. I'm pretty sure customers will like it also. The flow marks are on some of the vintage bobbins but not all. I'm going to see if those can go away by tweaking temperature etc..

[Possum]

...

Yes the original specs include shrinkage, there are some features that weren't actually done, the original top flat spec was for radiused top and bottom of the lip, I think they didn't want to pay full price for their drawing spec and deleted certain things that weren't important vs. cost of the mold. I don't see parting lines in the tops of the originals though...

[JGundry]

I checked today and the shrink factor is .004" per 1" for Butyrate.

The mold for the top of the bobbin is 1 piece.

[clown_luthier]

I checked today and the shrink factor is .004" per 1" for Butyrate.

The mold for the top of the bobbin is 1 piece.

that's 0,1 mm right? 2,54%
i was thinking it is less, like 0,8%

[Possum]

.

I don't think there is only ONE formula for butyrate and probably the colorant might be involved. I remember someone saying there are CAB plastics that are real soft and some that are harder. There's probably going to be some slop no matter what you do, I've seen enough Gibson pole screws stripped from them forcing through stuff that didn't match up. I see a line in the middle of the slug bobbin going all the way across, thats not a parting line?

[clown_luthier]

There's probably going to be some slop no matter what you do, I've seen enough Gibson pole screws stripped from them forcing through stuff that didn't match up.

is this maybe possible because of baseplates holes? or becasue of keeper bar holes, i stripped some screws because smaller holes on keeper bars i made

[Possum]

....

Who knows, could be the keepers most likely. I make my own keepers and there is definitely a certain amount of slop I can get away with and some I can't. Pole screws don't always thread in perfectly straight when you drive them in either. Generally my buckers are very tightly fit together for best magnetic transfer...

[RedHouse]

wow
JGundry an Belwar, this bobbins look real nice

+1

Good work gents

When you get it all rolling, are you going to keep 'em locked-down in house, or offer 'em up for consumption?

[JGundry]

These are just for Belwar and I.

There are a bunch of things that come into play with the shrink. The size of the gate, temperature and even additives like talc effect the sink.

I'm not sure on this but I think Gibson had a machine that drove all 6 pole screws at once. I have seen some other old Gibson multi tool air driven machines at Heritage. I would think they might have taken the same approach for putting the pole screws in.

The shrink is .004" per 1". That is inches. So for screw spacing that is .008" of shrink more or less.

[bajaman]

"These are just for Belwar and I."
What a big teaser
I am sure there are many here who would like to try these bobbins too!
bajaman