Plastics

[FunkyKikuchiyo]

Hey all,

I feel like I should know this already, but what type of plastic is it that is typically used for injection molded bobbins? I'm not talking vintage correct, just what is generally used. Is it the same material as the generic pickup covers that you see all over the place? PET? Polyethylene? I'd love to know for reference so I can look up data sheets on the materials.

Thanks

[belwar]

gernally it is ABS. More and more and using Cellulose Acetate Butyurate (CAB) for its sentimental PAF value. Others still have done fancier plastics yet - usually with the point of getting a thinner more rigid bobbin.

I've been working on a replica Dearmond 1100 and for the bobbin i'll probably use the same material that Graphtech TUSQ is made from.. Extremely rigid even when thin, but not brittle. It's a glass filled plastic (Maybe it's nylon like the new Duncan zyphers?).

[David King]

Bel,
I talked to Dave Dunwoody about the tusq years back, I think its a uniform blend, probably more like PEET with some teflon micro spheres thrown in. It could also have a ceramic component as well. I use a lot of it and I've learned to cut it on a diamond wet-saw.

[belwar]

David i know who supplies them if you need it bulk. Found it totally by accident.

[FunkyKikuchiyo]

belwar - thanks! That helped me like you wouldn't believe. I'd been chasing my tail a lot, but did learn an awful lot about plastics in the process. I like FR4 when I can use it, but sometimes I have to use existing parts, and there is no such thing as injection moulded FR4 last time I checked. Have you considered lexan for your project? It seems like it could be useful, though I don't know for sure. I've had trouble finding sizes conducive to pickup work, but I'm still looking, too.

Are there multiple formulations of TUSQ? What I'm thinking of as TUSQ could be cut with a steak knife, never mind diamond wet saw. There must be some confusion on my part with trade names. What is the stuff that companies like Taylor and Ibanez use stock in their instruments?

[belwar]

Many people do use some Lexan. Jason Lollar makes his sucessful P-90's using a forbon top and bottom flange glued to an Acrylic Core.

The key to working with Acrylic is that you have to buy "Casted Acrylic" and not "Extruded Acrylic". The casted material can be machined and cut also like wood (It can also be easily lasered). Extruded Acrylic just melts and burns.

My own personal tests taught me that I couldnt use acrylic for flanges unless it was at least 0.09" thick. My best test was from 1/2" cast where I used a keyhole router to produce the bobbin core.

[David King]

Belwar,
Is the tusq material granular pellets ready to be injection molded or is it available in extruded shapes and sheets? I'd be interested in the latter for sure.
Thanks

[peskywinnets]

The key to working with Acrylic is that you have to buy "Casted Acrylic" and not "Extruded Acrylic". The casted material can be machined and cut also like wood (It can also be easily lasered). Extruded Acrylic just melts and burns.

+1 to that (I found this out the hard way ....tip for fellow Brits if sourcing Plexiglass, avoid any of their products with XT in the name ....go for Plexiglass that has GS written on it)

I've a homemade CNC machine & I cut acrylic a fair bit - it's nice stuff to work with. That said, it's difficult to get nice thin edge on the bobbin with though - it goes transparent once you mill it down to below 1mm thickness....and it's failr weak at below 1.2mm

Alas, I've not located anyone that sells coloured cast acrylic in thickness less than 3mm.

[FunkyKikuchiyo]

+1 to that (I found this out the hard way ....tip for fellow Brits if sourcing Plexiglass, avoid any of their products with XT in the name ....go for Plexiglass that has GS written on it)

I've a homemade CNC machine & I cut acrylic a fair bit - it's nice stuff to work with. That said, it's difficult to get nice thin edge on the bobbin with though - it goes transparent once you mill it down to below 1mm thickness....and it's failr weak at below 1.2mm

Alas, I've not located anyone that sells coloured cast acrylic in thickness less than 3mm.

Thanks for that - I've been looking for something to basically use as a colored veneer .020" would be ideal - I used FR4 (and love it) but it is really, really ugly and I don't expect anyone to readily embrace it. Plus, I've even been hearing a lot of people see DiMarzios or other pickups with the FR4 bottoms and say "why are they using circuit board? Is it because they are too cheap?"... accuracy of that sentiment aside, it definitely is telling of what it looks like to consumers. I originally was thinking acoustic pickguard stock (tortoise pickups anyone?) but the thicknesses are all over the map and I really don't want to make tall pole pieces to compensate for extra thick stock.

Some folks I know that do lots of CNC stuff absolutely love both lexan and acrylic. Supposedly one is prone to gumming up in bits (acrylic I think) but all in all they come out beautifully.

[WolfeMacleod]

gernally it is ABS. .

It's not ABS....

[David King]

Acetal is a rewarding plastic to machine, unfortunately the price for sheet stock isn't so pretty. It isn't around in clear either. For pretty and thin and stiff I think you might do well to check out the aforementioned .032 formica. The "normal" formica is more like .050" (1.25mm) and very stiff and it comes in a million colors and patterns, often free for the taking as left-overs, cutoffs and samples.

[peskywinnets]

Acetal is a rewarding plastic to machine, unfortunately the price for sheet stock isn't so pretty. It isn't around in clear either. For pretty and thin and stiff I think you might do well to check out the aforementioned .032 formica. The "normal" formica is more like .050" (1.25mm) and very stiff and it comes in a million colors and patterns, often free for the taking as left-overs, cutoffs and samples.

That's a good lead...so you reckon 1.25mm Formica will be strong enough at the bobbin edge perimeter to stop the wire splaying the sides out? This issue remains my biggest headache when making my own bobbins - ie presenting a nicely finished 'upper bobbin' surface (the side that's visible when on the guitar), that's also strong enough to keep the wire in without at deformation at the bobbin perimeter (where the wire wants to push the bobbin edge out)

[peskywinnets]

Ok, 5 samples of Formica on their way to me .....no mention of their thickness on the samples site, I suspect it's likely to be nearer 0.8mm.

I like the idea of easy wipe Formia pickups - I can put beer & pizza on them.

[David Schwab]

Alas, I've not located anyone that sells coloured cast acrylic in thickness less than 3mm.

Paint the back of the clear acrylic.

[peskywinnets]

Paint the back of the clear acrylic.

But then it would look homemade - which of course it will be, but I actually want the finished item to look like it was made by the same team who churn out Iphones!

I've since ordered "Ipod type manafacturing for the hectic kitchen"