P90 Winding Frustration - Bobbin Flare

[belwar]

Well I've just started winding P-90's and i'm already getting frustrated. I've wound about 20 now trying to find a happy medium of tension. So far I either have flared bobbin ends, or a loose center. There doesnt apear to be a happy mediumI'm putting on about 10000 winds of 42. The bobbin is acrylic. Im wondering if the acrylic is softer. My felt tensioner is very close to my wire guide - Perhaps 1" away, but my wire guide-way is almost 5" long.

Is it normal to have some flare in the bobbin because of the large size of the coil?

Right now the base is made from 3/32" acrylic and the top is 1/16th, I'm thinking of making the top from 3/32 as well. Thoughts? Comments? Too much tension still?

PS: The bobbin looks ugly right now because I didnt have the right thickness plexi so I have to level the pieces down. The haze is cutter marks.

PPS: I sure love working with a clear bobbin as I can really see what im doing.

Belwar

[jonson]

plexi

Going by my own experience with this wonderful (at times) material. We call
it perspex in the uk. Youv'e thinned it down and broken the surface tension so a piece of thinned 3/32 or 1/8 to 1/16 is a fair bit more pliable than a piece of 1/16 nominal. Cell Cast plexi (acrylic) is stiffer than extruded sheet so check what you have. I normaly wind between faceplate and tailplate but try just doubleside tapeing a thicker piece of plexi or even a piece of ply or mdf to the top face during the wind and then remove it after. It may help along with getting the right tension as too tight will bend it as well.

[belwar]

I didnt really consider that was I was weakening the surface tension of the plexiglass by shaving it down.. Thats a really good thought! I bet you that is my problem. I know with phenolic when you "open" one side the stuff warps and arches immediately within seconds. I didnt stop to consider that this might occur with plexi too, and I might be weakening it. The plexi I am using IS cast acrylic, as it is the only type that actually is machinable. I have two sheets of plexi on order now .. 1/16th and 0.1". I'll wait till they get here and thry that before I make the top plate thicker.

Thanks for the advice!

Anyone else with other thoughts?

[jonson]

machining

Love your cnc work. I machine both cast and extruded but use White Spirit/Turpentine substitute as a cutting fluid and both polish as well but admit the cell cast material is easier to work.

[belwar]

Thanks! It was actually the first project I ever got to use rigid taping on. Having the CNC tap the bobbin holes helps a ton. Everything shown was machined totally dry - No cutting fluid or lube. The key was a #5-40 Spiral Flute Tap so that the chip come UP the hole, not down like a standard tap.

I think the bobbins will *look* alot better when I dont have to level them to thickness. The plastics place by my house sells remenants but they never have any 0.1 or 3/32 :< I had to order a whole sheet of 4x6.

[RedHouse]

Just make some backing plates out of .090 aluminum, that will prevent the warping.

If you still have problems when using backing plates, then after you wind a pickup, let it sit for 15 minutes before you remove it from the bobbin flange, it will take a "set" and usually won't warp the bobbin then.

Like this:

[David Schwab]

Is it normal to have some flare in the bobbin because of the large size of the coil?

Do you mean flair on the wire, or the bobbin?

Your coil looks fine.

[Dude]

My First Post Ever

I just joined this forum to join in on the conversations. My first post was going to be a question asking for thoughts on hand made plexi P-90 bobbins; you beat me to it. My questions were answered. I have a new question: what kind of glue did you use or recomend?? I tried epoxy first but when the wind blew, it fell apart. So I switched to cyano. I'm not looking to offend anyone on my first post, but it looks as if your top is separating from your core on the bass side (or treble).

I'm afraid to push "submit reply." It's my first post.

[jonson]

adhesive

Not sure what Belwar is using but it don't look messy. I went through trying everything to get a good bond and ended up with Cryano but managed to go a step further. Talk to your sheet supplier or a plexi signmaker and get some of the glue they use. Its based on chloroform and will track through a join or just bond acrylic together but leaves no telltale so polished surfaces remain just that. I dont know what it's called as my guys just stuck some in a bottle for me but I will ask and get an answer.

[jonson]

glue

what I use is tensol 70 I'm told but cannot find it Stateside but have you tried this.
http://www.tapplastics.com/shop/product.php?pid=131

[SK66]

The bobbin flare is primarily due to tension. I find that at the outer winds of a P-90 I have to reduce the tension slightly. I think this is because there is less "whipping" of the wire as it goes around a larger/rounder coil shape and results in an increase of tension in the winding itself. Also, it is further from the anchor point of the bobbin plate and therefore has more leverage to cause bobbin flare. And I agree, it looks like that leverage has debonded the bobbin plate at the left end.
One thing to consider if the material you're using has a defined warp direction, put it so that it's warp tendency will counter flare tendency. (i.e. flip the material over)

[belwar]

I just joined this forum to join in on the conversations. My first post was going to be a question asking for thoughts on hand made plexi P-90 bobbins; you beat me to it. My questions were answered. I have a new question: what kind of glue did you use or recomend?? I tried epoxy first but when the wind blew, it fell apart. So I switched to cyano. I'm not looking to offend anyone on my first post, but it looks as if your top is separating from your core on the bass side (or treble).

I'm afraid to push "submit reply." It's my first post.

Welcome Dude! (Big Lebowski reference?)

I'm currently using the glue he listed.. ( http://www.tapplastics.com/shop/product.php?pid=131 ) and it works very good. I had a bit of a learning curve with it. The bobbins you are looking at are the first ones I created and at the bottom of that learning curve. I figured out that I have to use more glue and clamp the bobbin briefly. The Glue is thinner than water and evaporates quickly. Plus the other problem is that I have too much tension on the coil so i'm flexing the ends of the bobbin to its breaking point. I'm getting new plastic today so I'll take some pictures of the new ones when they are done.

[belwar]

The bobbin flare is primarily due to tension. I find that at the outer winds of a P-90 I have to reduce the tension slightly. I think this is because there is less "whipping" of the wire as it goes around a larger/rounder coil shape and results in an increase of tension in the winding itself. Also, it is further from the anchor point of the bobbin plate and therefore has more leverage to cause bobbin flare. And I agree, it looks like that leverage has debonded the bobbin plate at the left end.
One thing to consider if the material you're using has a defined warp direction, put it so that it's warp tendency will counter flare tendency. (i.e. flip the material over)

Mixing tension .. Hmm I had considered it but I think its time to try it. I think I could go pretty high tension for the first 3 thousand winds and then back it off for the next 5, and then wind loose for the next 2. As far as the plastic goes I agree and wont be thicknessing the next batch of plastic so it wont be a problem. Thanks for the tip!

[Dude]

Thank you all very much. I'm sure I can pick that adhesive up at my local plexi supplier.

It's not a Lebowski reference, I've just always been called Dude. I'm part of the Beavis and Butthead generation.