In this article I will look at some of the theory behind underwires in bras and answer the question "Why do I have fisherman's scales in my bra pattern drafting kit?" 

There is nothing to make in this article unless you fancy having a go at making your own metal underwires (be prepared later in the article to do some hot metal bending) but think of this article as a precursor to the next article where we will try to recreate two unusual strapless wired bras from the 1940/50's and we will have to make our own wires for the bras (some more hot metal bending).

So, welcome to "Engineering Craft Studies 101" (125 credits) :)

 

 

Bras as Fulcrums and Levers

An underwired bra should "cantilever" the weight of the breasts to support them, but how is this "cantilever" action achieved?

First we must look at how we can use a lever and fulcrum to lift a load and compare the system to an underwired bra. In this lever system the load to be lifted is placed at one end of a lever and a fulcrum (a pivot point for the lever) is put under the lever.  When we press down on the end of the lever, the lever pivots on the fulcrum and the other end of the lever lifts the load up.

 

Now if we compare the lever system to the underwired bra we should see that the cup, cradle / underband and wing of the bra together form the lever. The underwire is the fulcrum (the pivot point) and of course the breast is the load to be lifted, sitting in the cup at the end of the bra lever. The elastic tension (pull) of the bra wing holds the underwire (fulcrum) into the breast root and the elastic tension also holds the whole cup/cradle/wing lever down in position against the weight of the breast pushing down at the other end of the lever. "And the bra straps?" I hear you ask? They stop the load from falling off the end of the lever.
No seriously, the straps should only be carrying about 20% of the breast weight: 80% of the breast weight should be held up by the cup/cradle/wing lever. Of course if you have no straps and the underwired part of the cup is not deep enough, then the breast would "spill" out of the cup (fall off the end of the lever). That is why strapless bra underwires should be deeper than strapped "daywear" underwires.
If you do not have enough wing / cradle tension holding the underwire fulcrum into the breast root and tension holding the bra "lever" in the right place you can end up with the breasts not being lifted up, the underwires tilting forward and too much breast weight being carried by the bra straps. Underwires pressing on breast tissue = pain and red marks on the shoulders = more pain. This can happen if your bra has lost its elastic tension or pull due to its age (Powernet does not last for ever), or if you have been fitted for the wrong back / band size. If it's a fitting problem, go down a band size but up a cup size - instead of 34"B, try a 32"C bra, which has a smaller back (correct tension) but the same cup volume. (Remember "Cup cross grading" from my first bra article.) If it's a case of "perished Powernet", MAKE A NEW BRA!!

 

Elastic Tension

But how much elastic tension do we need? Enter the fish weighing scales. Remember, when we draft a bra pattern we start with the underwire and "spring" open the underwire by 1.5cm to give us the curve of the cup to cradle seam that will fit the breast root. We can measure the tension we need from the other bra parts to do this. Simply hold down the centre front end of the underwire and then pull open the wire with the scales to 1.5cm or your breast root trace. This pull weight will give you a good idea of how much elastic pull your intended bra wing design should have.

Then by adjusting the length of a "test" bra wing we can obtain the correct elastic tension for the intended underwires. When designing the bra wing to apply the right amount of underwire spring we must take into account any plush elastics sewn to the hems of the wing and not just test the pull of the Powernet / main wing fabric.

 

One check you should also carry out on a new bra is to lay the bra flat out on a flat surface and take measurements across the unsprung underwires. Then stretch the bra out to its intended band size and check that the underwires have sprung out by the correct amount.

The Bra in the picture under test is intended to fit a UK size 34"B bust, so it will be stretched out to a band size of 75cm (29 ½ "). Un-stretched, the bra measured 62cm from hooks to eyes and across the underwire measured 12cm.

When stretched out to its intended band size of 75cm the underwire measured 12.75cm.

Is this bra OK?

 

You can also use the weighing scales to test the elastic pull / tension of one of your favourite bras and compare the measurements to the bra you are designing / making to get a good personal fit. As well as checking the underband / wing tension, you can check the elasticity of the straps on both bras.

 

Underwire Grading

As with a bra pattern grading to obtain different sizes, so the underwires that go in the different size bras are also graded. The length of the wire from one tip around the curve to the other tip changes by a set amount for each size step and to make things even more complicated there are different grading steps for different types of bras / countries!

(I never said this bra-designing lark was easy )

• 21mm step. UK retail store standard for core sizes
• 19mm step. American standard for fashion bras
• 16mm step. Specialist plus fit bras and swimwear.
• 12mm step. Moulded bras and bikini styles

The underwire-grading step to go with the bra drafting in these articles is the UK 21mm step, i.e. for each cup size (1 to 16) the length of the underwire increases by 2.1cm, so a size 4 cup (approximately UK34B) the "daywear" MS20 underwire length is 195mm, graded for a size 5 cup (UK34C) the underwire length would be 195 + 21= 216mm.

For reference, a UK34"B (size 4) Daywear MS20 underwire is around 195mm in length, a UK34"B (size 4) Strapless MS08 underwire is around 206mm in length and a UK34"B (size 4) Plunge style MS09 underwire is around 173mm in length. All can be graded up or down in 21mm steps for the different cup sizes.

Now you know how to work out the length of underwire you need for your particular size of cup, you can then test the wire to design the rest of the bra.

Making Underwires

Do you still want  to have a go at making your own underwires?

As I have already mentioned, think of this article as a precursor to the next article where we will try to recreate two unusual strapless wired bras from the 1940/50's. For the two bras we will be making "Overwires" not underwires! But we will use the same wire bending techniques for the overwires as for underwires.

So now it's "Hot Metal Time".

For the under and over wires we can use Piano Wire, the springy high carbon steel wire I have talked about before in other articles (not the strings of the musical instrument!).

I will not lie to you, piano wire is tough stuff to cut and bend, so if your hands are not strong enough, enlist the help of a stronger friend to do the bending and cutting.

As to the thickness of wire to use, in the other articles I said that piano wire comes in "swg" (Standard wire gauge) thickness, but some suppliers in other countries may not follow swg sizing, so the table below may help you to obtain the correct thickness of wire for the under and over wires.

No. Of Standard Wire Gauge, swg	Imperial Standard Wire Gauge		Brown and Sharpe’s American Wire Gauge
	Inches	Millimetres	Inches	Millimetres
10	0.128	3.251	0.102	2.588
12	0.104	2.641	0.081	2.052
14	0.080	2.032	0.064	1.627
16	0.064	1.625	0.051	1.290
18	0.048	1.219	0.040	1.009

As piano wire is reasonably inexpensive, get several straight lengths of 12, 14 and 16swg wire so you can practice and experiment. Piano wire is also good for making light boning for long line bras and "Merry Widow" basques.  For cup sizes 1 to 8 try 14swg wire for underwires, and for cup sizes above 8 try using 12swg wire.

To get the right curve for your underwires, take a breast root trace. To do this see the second bra pattern drafting article.  Then on the paper put a mark 1.5cm in from the underarm side of the trace.
Using a Flexi or French curve, smoothly join the mark up with the breast root trace curve at the point below the "point of bust". This point should also become the "balance point" of your underwire. This new curve is the template for your DIY underwires.
Work out how long your underwires would be, then add 2cm to that. The 2cm is for 1cm folded over ends. Then cut the wire to length using electricians' large wire cutters.

 

Next we need to round of the cut ends of the wire using a grinding wheel. REMEMBER TO USE EYE PROTECTION WHEN USING ANY CUTTING OR GRINDING POWER TOOLS!

[Please be careful, and be very aware of safety - using these tools can be dangerous, and neither Harman Hay Publications nor our writers can be held responsible if you hurt yourself or others. See item 4 of our Terms of Service. We leave you, as adults, to be sensible about the way in which you conduct your projects using our writers' instructions. If you have any doubts or are not familiar with the tools, methods or activities involved here, we advise that you either do not attempt this project, or that you find someone who *is* familiar with them to help you. In any case, make sure someone else is in the room to help in case something goes wrong. - Cathy]

Grip the wire firmly in your hands and, resting the end of the wire on the "tool rest" in front of the wheel, gently feed the wire end up against the rotating wheel at an angle; slowly rotate the wire to round of the cut end. Only a very small amount of grinding is needed just to take any sharp edges off the ends of the wire.

 

Before you bend over the ends of the wire you must curve the length of wire into the correct curve for your underwire. This involves moving along the wire slowly and gently, bending the wire into the curve (no sudden changes in direction), stopping from time to time to check the curve against the template curve on your breast root trace.

Bending the Ends

When you have bent two underwires to the correct curve you are now ready to bend over the ends of the underwires to make them safe to wear. If you try to bend them right over (180°) the ends of the cold piano wire may crack and break off, so we must heat up the end of the wire and bend it over while still hot.

We must heat up the wire to a bright red colour and to do this we can use a plumbers gas blow lamp, a gas camping stove or you can even use your gas cooker. Plumbers' blowlamps with replaceable gas canisters can be obtained from good DIY stores. You will also need a pair of "snipe nosed" or "radio" pliers to bend the red-hot wire with.

[Please be careful, and be very aware of safety - using these tools can be dangerous, and neither Harman Hay Publications nor our writers can be held responsible if you hurt yourself or others. See item 4 of our Terms of Service. We leave you, as adults, to be sensible about the way in which you conduct your projects using our writers' instructions. If you have any doubts or are not familiar with the tools, methods or activities involved here, we advise that you either do not attempt this project, or that you find someone who *is* familiar with them to help you. In any case, make sure someone else is in the room to help in case something goes wrong. - Cathy]

Light the blowlamp and hold the end of the wire in the flame until it glows bright red. Now quickly bend 1cm over using the pliers, then put the end back in the flame to heat up again.

 

 

And then finish off  by flattening the bend with the pliers. Allow the first end to cool down,  then bend the other end.

 

Now, after cooling, using a dishwashing scouring pad and washing up liquid, clean and degrease both wires. You can now paint the underwires to stop them from rusting when you wash the bra. You can use spray-on enamel paint to coat the wires... unless you have access to an industrial "fluidised bed hot plastic coating bath" . (You can make one using a vacuum cleaner on blow, a wooden box with a shelf inside it, some thin foam----- NO more!!)

Next Time

Next time, the "Overwired" Strapless bra. Do they work? Or are they a "cantilever" bridge to far? 

We will make one and you will find out.

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