To hear the laminations of their women

[jonson]

Sorry Joe I missed that post but yes I will ask the man lots of questions he's over next tuesday. Will also ask unless someone on here knows what glue is used for what David is talking about on transformers. I've tried that both with clamps and in my presses but they are set at mo for 6000lb per sq in. all to no avail. With just glue the laminations short out allthough probably not if I was to coat and let dry and then glue them together. Will have to find answers cus this stuff could be pressed in big sheets and then cut to size afterwards. Yes Joe but i'm allready logged in so how many more times do they want me to do that?

[Joe Gwinn]

Sorry Joe I missed that post but yes I will ask the man lots of questions he's over next tuesday. Will also ask unless someone on here knows what glue is used for what David is talking about on transformers. I've tried that both with clamps and in my presses but they are set at mo for 6000lb per sq in. all to no avail. With just glue the laminations short out although probably not if I was to coat and let dry and then glue them together. Will have to find answers cuz this stuff could be pressed in big sheets and then cut to size afterwards.

At 6000 psi, they will short unless there is a real insulation layer. As an alternative to paper, how about thin mylar?

Transformer laminations are precoated and dried before assembly.

Yes Joe but i'm already logged in so how many more times do they want me to do that?

Huh?

[Dave Kerr]

They want you to register.

OK. What's the shortest distance to air, about 1"? How do you cut the laminated stack?

Well, cheapskate that I am, I tried using 30 minute golf shafting expoxy instead of Steve's high priced spread. Tin snipped the shimstock, sanded, soaked in TSP, rinsed, roughed up with 150 grit sandpaper, wiped down with acetone, air dried, doused the paper well with the epoxy, gave the steel a good schmear, set them in a jig and clamped firmly.

After setting overnight, I popped them out - they seemed well bonded, I couldn't pry a utility knife between the layers. The layers had shifted a slight amount, so I thought I'd even them up a bit using a grinder. Big mistake, the heat caused them to delaminate. I had thought that epoxy was pretty heat resistant. All I can think is that the coefficients of expansion between the steel and paper differ enough to cause the failure.

[Joe Gwinn]

Well, cheapskate that I am, I tried using 30 minute golf shafting epoxy instead of Steve's high priced spread. Tin snipped the shimstock, sanded, soaked in TSP, rinsed, roughed up with 150 grit sandpaper, wiped down with acetone, air dried, doused the paper well with the epoxy, gave the steel a good schmear, set them in a jig and clamped firmly.

After setting overnight, I popped them out - they seemed well bonded, I couldn't pry a utility knife between the layers. The layers had shifted a slight amount, so I thought I'd even them up a bit using a grinder. Big mistake, the heat caused them to delaminate. I had thought that epoxy was pretty heat resistant. All I can think is that the coefficients of expansion between the steel and paper differ enough to cause the failure.

Temperature coefficient isn't the issue. What probably happened was that the grinding heated the steel up to 300 F, at which point the epoxy let go. This can happen even if the outer laminations are not too hot to hold, as the inner laminations are pretty well insulated from the outside by the paper layers.

The 8-hour epoxy yields a far harder bond, so thermal delamination is less likely. If you are curing overnight, there is no reason to use faster epoxy. Curing in an oven yields an even stronger bond.

Wet grinding with a slow wheel (as for sharpening a knife) would eliminate delamination.

If the steel isn't too hard, a file would also work.

How many steel layers were there? What is the thickness of each steel lamination and of each paper layer?

[Dave Kerr]

6 layers of .015" steel, Kraft paper (from a grocery bag) between. I used the 30 minute epoxy because it's what I had on hand. I'll give them another shot, will hand file them if needed this time, but be a bit more precise in shearing the shim stock and setting up the clamping jig to reduce the amount to be filed down.

[jonson]

Joe's right I dont think there are too many glues to withstand the temperature of grinding. The highest I ever found was Araldite 2004 but that only went to about 200 degrees before breakdown. Spoke to my glue bofffin this week and posed the question of saturating the paper and he replied that the best method was thin the glue (both parts seperately) with acetone. Will not break down the glue structure and should soak well into the paper and evaparate fast. Just advised to leave a slightly longer set time. Given a pair of tubes of Acrylic to another member and hopefully he will come back as to his findings on it's uses.

[Dave Kerr]

Maybe I should have just gone ahead and bought

this stuff - I'd think 1/5 liter would go a long way. You'd think an amateur pushing 50 years old would have learned by now to listen to a pro when he speaks up.

[jonson]

Try this Dave as this one iv'e used a lot.
http://www.permabond.com/en/en-acrylics.htm

[Dave Kerr]

Thanks, I'd searched for a source when you posted that link before and didn't turn up anyone. I've emailed customer assistance, though I've taken to using bricks-and-mortar stores as much as possible of late - the mrs has taken note of all the mail-order stuff coming in the door and has gently suggested that I remember that we're paying 2 college tuitions as well as a mortgage.

[jonson]

couple more.
http://www.glueguru.com/acrylic.htm

http://news.thomasnet.com/fullstory/26826

[David Schwab]

Here's info on laminated cores:

Cold Rolled Motor Lamination Sheet

They talk about eddy currents and such. Apparently "Cold Rolled Motor Lamination Sheet" is the stuff we would want for pickup cores.

Electrical currents that are generated within the core material by the magnetic field. These can be minimized, but not avoided in total. Since there is a current flowing in the core material (steel), heat is generated. Remember, it is an inherent characteristic of metals that current flow generates heat because of the resistance to current flow that is part of all steels. This source of electrical energy loss is called "eddy current loss".



Eddy current losses are lowered by increasing the resistance of the path through which the eddy current flows.

The resistance of the core is increased in two ways:
1. constructing the core from a number of thin sections (light-gauge sheets) or laminations*, and
2. alloying the steel with elements such as manganese, silicon, and aluminum; elements that increase the electrical resistance of steel.

*Thin sections of steel sheet restricts the current to very small paths assuming that the laminations are insulated from each other.

Someone has to sell such stuff already made...

[Joe Gwinn]

Here's info on laminated cores:

Cold Rolled Motor Lamination Sheet

They talk about eddy currents and such. Apparently "Cold Rolled Motor Lamination Sheet" is the stuff we would want for pickup cores.

Someone has to sell such stuff already made...

Yes. But it's easier to buy transformer laminations, which can be got in much the same kinds of silicon steel.

[Joe Gwinn]

6 layers of .015" steel, Kraft paper (from a grocery bag) between. I used the 30 minute epoxy because it's what I had on hand. I'll give them another shot, will hand file them if needed this time, but be a bit more precise in shearing the shim stock and setting up the clamping jig to reduce the amount to be filed down.

The grocery bag stock I have is 0.0065" thick, so the whole stack will be 6(0.015)+5(0.0065)= 0.1225, call it 1/8".

The variables available to be manipulated are total steel thickness and total number of laminations. Together these will determine the balance of effects.

I imagine thinner paper could be used. The voltage is slight. For example, if one has a 10,000-turn coil developing 4 volts peak-to-peak on attacks, that's 4/10000= 0.4 millivolts per turn. An eddy-current loop is one turn. Even cigarette paper would suffice to stop such a voltage, so the remaining issue is mechanical - the layer needs to be robust enough to withstand manufacturing, and thick enough so that the burrs from machining don't short the layers together.

It's OK to short the layers together in exactly one place, say for grounding, but two places will allow eddy currents to flow.

[David Schwab]

It's OK to short the layers together in exactly one place, say for grounding, but two places will allow eddy currents to flow.

I was wondering about that...

[R.G.]

Laminating steel shim stock (.015", grade somewhere between 1008 and 1012 - McMaster #9011K29) and fishpaper for a bass blade humbucker - any suggestions for best bonding results? Contact cement is the direction I'm leaning towards.

Something that came up in a motors project back in school was that you can also "laminate" a shape out of soft iron wire cemented/glued together into a form, then when the glue sets, saw the shape you want out of the completed lump.

I'm not sure you can get 0.015" iron wire, and I'm not sure of the shape you want, but it's a trick you might keep in your back pocket. We were trying to get a cylindrical "laminated" shape with holes down the axis of the cylinder. Radial laminations were clearly called for, but this was a zero dollar student project. One really smart guy suggested we wind iron wire around a wooden cylinder the size of the coils inside, then epoxy the iron wire. When the epoxy set, we drilled the center hole through the ends, tearing only a few wires loose, and then sawed the cylinder across a diameter. Result, two iron-wire "laminations" with lower eddy loss than radial laminations of the same thickness.

Commercial iron wire is usually mill-scale insulated, so all you have to do is get it unbelievably clean of the mill oil and other dirt. The scale is a high resistance path that's as good as many transformer laminations. Sizes may be a problem though.