Ecore Air Gap Creation

"Jim Flanagan"

** Send it to a workshop that has the special grinding gear required. ** Unless you want the core to break in half - yes.

..... Phil

You can add shims to all three legs, of half the thickness of the air gap that you wanted in the center leg. The field won't be quite as contained.

Best regards, Spehro Pefhany

--
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As others said, you can distribute the gap over the inner and out legs. As this halves the gap in the center leg, eddy current loss may reduce.

If, for some reason, you only want the gap in the center leg, you can use a small silicon carbide sharpening stone that fits in between the outer legs. Some water with very little soap and patience will give you the gap. I used this method to make some gapped cores for leakage transformer experiments.

Best regards,

Wim PA3DJS

remove abc before using PM

The ground gaps have to be carefully ground flat and true without chips or other faults. It could be done by hand but why bother? For production, cores are machine ground with diamond tools. For one core, add shims. It's the easiest and is changeable to alter your design if required. It gives you the greatest flexibility.

A gap on all three legs has to be half the distance of a center leg only gap. Paper or paper tape is the simplest material to use for gapping. Masking tape works well because it sticks to the core making assembly easy. Because paper or tape is thin, several mils, gaps of any dimension can easily be piled up with multiple layers and of course they can be easily changed. Use a caliper or micrometer to measure the gap pile. Do not assume that the actual dimension is necessarily the sum of the layers. Air and glue can alter the dimensions slightly.

If the design is going into production, you can have cores gaped by grinding to any spec. by the manufacturer. For small quantity experiment and bread boarding, use shims.

You'd need to find a shop with a surface grinder with a magnetic workholder.

How much gap do you want? if it's only a few mils, paper might work. Some old-fashioned TV flyback transformers were made with "gapping papers", about .003" thick on both limbs.

You must shim all three legs, or the core will break when it's clamped up.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Here's a toy version of a glass grinder.

Units that run wet keep down the dust.

RL

My wife has one of those! It has been in the closet for years and I had forgotten about it.. Guess I could give it a try, but I will try the shim method first.. Thanks for tickling the memory.. Jim