Okay guys, this post has turned into a pretty long and reasonably epic one and that's because there's not actually a lot of information out there on doing Full Bust Adjustments on fitted knit patterns. There are lots of tutorials for FBA's on wovens, but not knits - which I suppose comes down to the fact that knits are much more forgiving.
That being said, I completely understand that for some of you, an FBA may be needed, even on a stretchy knit like Bronte.
I would always do a muslin to check if you can get away without doing one first though, and one thing you may want to consider trying first is cheating the extra room you need in the front by grading up a size or two in the bust on the front pattern piece only, and then adding length at the 'Lengthen/shorten' line on both pattern pieces.
If you don't think that this is going to work for you though, then please read on...
Doing an FBA (Full Bust Adjustment)
The goal of an FBA is to add width and length to the front pattern piece to accommodate a bust that is larger than a B or C cup (most often a B cup in commercial patterns), without messing with the neckline. To do this, you generally slash and spread your pattern. (Note - you will end up creating a bust dart with a standard FBA, but don't worry, we'll talk about that in a moment).
For this reason, I wouldn't add in the normal amount you would on a woven. Perhaps try adding half your normal amount to Bronte first, and then see if you need more. For example, if you have a 1 inch difference, try adding in 1/2 an inch first.
One other thing you'll need to consider is where your apex actually sits on the pattern. Due to the fact that Bronte is a knit with negative ease, you can't necessarily hold the pattern up to you to find it (as you would on a woven). I honestly don't really have any scientific way of finding this either. All I can suggest is that you try on some other similar tops, locate your apex on them, and then transfer this to your Bronte pattern piece. Alternatively, make up a muslin without the FBA and locate it once you've got it on, then do an FBA on the pattern piece. I can't think of an easier way, but if you have one, do let us know!
What to do with that dart you've now created...Now that you've done your standard FBA, you're going to be left with a side bust dart, and that's because you've added length to the side seam of the front and not to the back. That dart takes care of the extra length you've added so that your front and back pattern pieces will match along the side seam.
Below is my 'faux' FBA on my mini Bronte pattern piece - I've just guessed where the apex may be and then have slashed and spread my pattern piece to create the imaginary extra room needed and therefore the side dart...
Do you see that pesky dart we created on the side seam underneath the arm pit?
Bronte (and most knit t-shirts) are dart-less, so how do you deal with this extra side length in a knit t-shirt? Below are three options, but there are probably more, so do let us know if you have one.
1 - Ease the dart into the side seamIf you don't want to sew in a side seam dart, then you could think about rounding out the dart and then easing the excess into your side seam.
I would approach this in much the same way I would when easing a sleeve cap into a set-in sleeve. Put some basting stitches into the seam allowance, gather them lightly into a 'cup' and sew up the side seam.
If you have a length-wise stretch in your fabric, you could also think about stretching your back piece down a little to help accommodate any excess side ease from the front. Be careful when doing this though as you don't want to stretch your fabric so much that you end up with wrinkles and ripples in the final garment.
2 - Dart Manipulation1. Once you've performed your FBA, you'll be left with a pattern piece that looks something like the below. You'll have a 'dart' at the side bust that you might want to rotate that dart out, so...
Does this picture look like half a Transformer to anyone else?
2. Transfer the straight line of your bottom left pattern piece (the red dashed line below) onto the paper below your pattern, you'll use this as a guide in the next few steps.
3. At the pivot point circled below, bring your bottom left bodice section back up and tape in place.
Below is what that'll look like, with the grey dashed line indicating the line you drew in step 2.
Using your pivot point, bring your bottom left section back up and align it with your original, dashed line.
5. True up your bottom hem.
And you're done!! The honey coloured outline below is the original piece - you can see that you've kept the additional length and width that came from doing the FBA, but you've eliminated the dart at the same time.
So that, Ladies, is how it's done. Let me know if you have any questions or have any success with this method! I'd love to hear about it.
3 - Sew the dart inFor some people, sewing the dart into the t-shirt might just be the best option, particularly if you have a large cup size. This might seem like a strange thing to have in a knit t-shirt, but it's only strange because it's uncommon, and uncommon doesn't mean it's a bad thing. It will mean you will have a beautifully fitting top, and if you have a busy print, you probably won't even notice that little dart line.
Two issues you may come across with sewing a dart in however are - if you have a lightweight knit, the dart may move around underneath, and with a heavier knit, you may see the outline from the right side. To combat both of these issues, you could cut the dart out close to the seam once it's been sewn in.
Do you have any tricks for doing an FBA with knits?