handmaking bobbins

[paulgarstki]

Sorry, everyone -- I posted this in the wrong forum and trying to figure out how to move/delete it! --Paul

Having noticed in a Seth Lover interview that some prototype bobbins were handmade, I'm wondering if anyone has a general approach for handmaking bobbins that are not magnet-based. (In other words, I know how to make Fender-style bobbins; I'm asking about bobbins that take screws or slugs).

I'm especially interested in workable materials. I've had a little success with wooden drilled cores and fiber tops and bottoms -- but that seems a little crude and I keep feeling I'm missing some basic technique.

SL on making the "Alnico" pickup:

SWD: How was the bobbin made? Was it cut out with a routing template.
Seth Lover: No...this is a handmade coil form made from a rectangular piece of celluloid and we glued the ends on, drilled the holes out and filed it out to shape to fit the rectangular magnets and this was one of the first hand made ones made ( from Seth Lover interview 1978 vintage gibson PAF humbucking humbucker pickups guitars )

I don't think celluloid is commonly available in small quantities anymore...

So: drop some suggestions here. Pointers to outside resources okay, but I think I've seen most of the DIY hobby approaches. I'm interested in approaches that I could use for clients who want custom-sized bobbins, without embarrassing myself.

[Mystic]

I'd use delrin and a router.

[Magnut]

I was watching public television, a show called "makers" I think. Cool program...

Someone was using this stuff called Shape Lock to create some interesting things. I realize this may not be perfect for what your wanting to do, but who knows what a little imagination can do.

It's a moldable plastic. I was thinking of creating some custom pickup covers out of it. It would be neat to try out some ideas. There is a "free" offer for a trial size but you do need to pay shipping. Might be worth playing with.

[belwar]

There's all kinds of different materials that you can use. Delrin, Phenolic, cast (not extruded) acrylic. "celuloid" can mean alot of things. tons of guitar makers - including myself - use celluloid today in the form of Ivoroid.

Dont even both with it. As a material it downright sucks. Its amazingly flammible, prone to shrinkage at the slightly touch of heat, and is not very rigid.

I'd do it with delrin and try to cut the bobbin from a single piece. In fact i've done this several times and am currently making some prototypes of the PAF replica bobbins senior gundy and I are working on. I say make it from one piece because you can glue the stuff well. You could make a rough bobbin on a table saw if you had mad skills.

If you wanted to go REALLY high tech, you could always have someone rapid prototype something for you. :> I've always wanted to have that done. I had some quote for it from $40-$200 per set of bobbins.

[David King]

liquid approach

I'd also suggest checking out a casting supply place and making a silicon rubber RTV mold of an existing bobbin and than casting your parts out of polyurethane 2 part which can be colored to match just about any plastic, take 20 minutes to set up hard and you can make multiple molds and actually produce a bunch of high quality parts in not much time.

[David Schwab]

If you wanted to go REALLY high tech, you could always have someone rapid prototype something for you. :> I've always wanted to have that done. I had some quote for it from $40-$200 per set of bobbins.

I did a set of pickups that way once, but I have a friend who has a SLA machine at his job.

It was just flatwork, supported by the blade. Now I have the same thing laser cut.

We did a cover too, but the surface finish wasn't that great.

[mickmutante]

I did those for a 7 string guitar... I made top of Incienso wood and back with Granadillo wood... then I put the screws.. and cover them with some tape...

[paulgarstki]

Thanks, everyone -- some very good suggestions here. I'm encouraged to dive in.

David King, funny you should mention casting. A different thread here about epoxy potting humbuckers led me to jgreer.com - Epoxy Resin, Urethane Foam, Silicone Mold Making Rubber, Carbon Fiber, and I ordered some silicone mold rubber and casting resin to try the casting approach.

Regarding delrin, I'm curious about the one-piece approach. I could imagine coming in from the sides on a routing table with a spiral-cut bit, but I think I'd make some kind of jig to hold the delrin securely. (No CNC machine, alas...)

belwar: I've done some (non-pickup) things via e-machineshop.com. They do plastic now as well as metal -- kind of $$ for a one-off, but not bad if you need a whole bunch. The nice thing is that it's super-accurate. Also, you can run an instant quote at any point in the CAD process. Haven't yet played around with plastic as a material.

mickmutante: Those are beautiful! Did you tape the screws before winding?

[mickmutante]

paulgarstki: Yes, I tape the screws first.. to protect the wire...
I'm glad you like the pickups..
I hope they sound good as they look..! hahahhaa...

[David King]

Delrin (acetal) is expensive. I'd try ABS or the cast acrylic first.
You could make the whole bobbin on a table saw with a dado stack, no need for a router here except to radius the ends. You can do the radiusing on a sander with a pattern follower.

[paulgarstki]

Hmnn... Okay, it happens I do have a nice quality dado stack.

So... my dado width is the height of the coil, and the dado height is ((bobbin width) - (core width)) / 2. The plastic block is the size of the outside dimensions of the bobbin. Then I set the fence so the dado is centered on the edge of the plastic and make 4 passes, one for each side and end of the bobbin.

Zip, zip, zip zip. Round the edges, drill the holes. Bobbin is done (except the core has sharp corners, so I stick a skinny file in and round them off.)

Is that pretty much what you are suggesting?

I agree that delrin (yes, acetal) is $$. I've had trouble with ABS melting when I try to machine it, but maybe I've tried the wrong variety or something.

--Paul

[Bruce Johnson]

Paul;

I hope that you have enough experience with tablesaws to know that it would be very dangerous to try to push a small plastic block across a spinning dado blade, just holding it by hand! One slip and it could spit the block back in your face and dado your fingertips. I mention this so no one reading this hurts themselves.

I would drill the magnet holes in the block first, and make up a simple wooden jig that holds the block securely. Use screws or pins through the two end holes to fasten the block to the jig. The jig slides on the tabletop and against the fence. Besides safety, a jig like this will give you more repeatable results.

Re: plastics melting while cutting: Most plastics will melt to some degree while being sawn, drilled or machined. Delrin is one of the cleaner and easiest to machine plastics that you'll find. That's why it's popular, although it isn't cheap. In general for cutting plastics, you want the tools to be razor sharp and have lots of clearance for getting the chips out of the way. If the chips pack up in the cutter teeth, they all melt together into blobs of goo. Then the part jams, spins, cracks, and/or gets thrown at you.

[Joe Gwinn]

Paul;

I hope that you have enough experience with tablesaws to know that it would be very dangerous to try to push a small plastic block across a spinning dado blade, just holding it by hand! One slip and it could spit the block back in your face and dado your fingertips. I mention this so no one reading this hurts themselves.

I would drill the magnet holes in the block first, and make up a simple wooden jig that holds the block securely. Use screws or pins through the two end holes to fasten the block to the jig. The jig slides on the tabletop and against the fence. Besides safety, a jig like this will give you more repeatable results.

Re: plastics melting while cutting: Most plastics will melt to some degree while being sawn, drilled or machined. Delrin is one of the cleaner and easiest to machine plastics that you'll find. That's why it's popular, although it isn't cheap. In general for cutting plastics, you want the tools to be razor sharp and have lots of clearance for getting the chips out of the way. If the chips pack up in the cutter teeth, they all melt together into blobs of goo. Then the part jams, spins, cracks, and/or gets thrown at you.

Bruce has it exactly right - make a jig.

A standard trick when machining plastic is to flood the work area with tapwater, which cools things down and prevents melting. Not that this will work with a table saw.

[paulgarstki]

Hi Bruce,

Absolutely -- I've been making furniture for years, so I use a jig for EVERYTHING. My fingers are never closer than 1-1/2 feet to the blade.

But I'm glad you mentioned it, because lots of people may read this and try it for themselves! Fingers are very important for pickup making, guitar playing, etc., etc.

Also true for routers, by the way. Lots of people seem to think router tables are safer than table saws -- not necessarily true.

[David Schwab]

Anything with a blade is dangerous! The safest saw is probably a band saw, and I've cut myself on one... as I was thinking how safe they are! I wasn't paying attention and moved my hand up past the blade guard...

That was the first and only time I've cut myself on a power tool. I plan on it being the last time too.

I had a Jet long bed jointer once ... that was like looking into the jaws of hell!