TOC: grading allowances altering seam allowances and pre-grading kinds of seams plain seam french seam mock french seam flat fell seam mock flat fell seam pieced flat fell standing fell seam lapped seam slot seam butt seam overcast seam taped seam faggot seam windowpane seam
An easy way to make sure no two allowances in a seam are the same width: First put all the allowances together, and trim to the width wanted for the widest allowance. Most of the time, you will only trim off long ravels. If you don't have a reason to do otherwise, put the widest allowance next to the right side, so that it can conceal the others.
Then separate the widest allowance from the bundle and trim a narrow strip off the remaining allowances. Repeat until all allowances are trimmed. This allows you to eyeball the widths; even if the allowances aren't perfectly uniform in width from one end to the other, each will be narrower than the one above at every point. The method is particularly useful when there are so many allowances that the difference between adjacent allowances is barely discernible.
When trimming allowances, you should, if at all possible, preserve any torn edges, because torn edges are thinner than cut edges.
It is often necessary to snip or notch seam allowances on sharp curves to allow them to lie flat.
You snip when the cut edge is shorter than the seam line. Make sure that the snips in one seam allowance *don't* line up with the snips in the other seam allowance, and don't make the snips any deeper than they need to be.
If your scissors don't cut as cleanly at the tips as you would like, or if there is danger of cutting too far, make your snips by sticking a sharp-pointed scissor into the allowance where you want the snip to end, and cut to the edge. A *sharp* seam ripper can also do the job.
You notch when the cut edge is longer than the seam line. Fold one allowance down out of the way; fold the fabric where the notch is wanted, and cut from the folded edge to the cut edge. This is faster than making two snips, it is more symmetrical, it give more-accurate control over the location of the notch, it makes it easier to avoid cutting too far, and it prevents you from leaving a tearing-snip at the bottom of the notch.
Position the notches in the second seam allowance by folding each tab on the folded-out-of-the-way seam allowance in half, so that the notches on this side are halfway between the notches on the other side.
When the allowances are sewn together and you can't separate them to cut each to a different width, hold the scissors parallel to the fabric so that you make a fuzzy, sloping cut.
One place where 5/8" is better is in the making of permanent-press shirts. You can make a french seam suitable for the heavy fabric of a no-iron shirt — heavy fabrics are more permanent-press than sheer fabrics of the same kind — by sewing a quarter-inch seam on the right side, then sewing a three-eighth inch seam on the inside. Even the sleeves can be set in with french seams; indeed it gives you two chances at the easing; if the first seam is even close to smooth, the second is dead easy. (Sleeves in shirts should be set in before the side seams are sewn. Most work clothing has the shirt-type sleeve, because it allows greater freedom of movement than the dress-type sleeve.)
Five-eighth seams are also useful in flat felling, since a quarter inch is, for the experienced seamster, easy to eyeball. Trim the under allowance to a quarter inch, turn the upper allowance to cover the raw edge of the under allowance, turn the seam to the side, topstitch.
Be sure to mark seam lines on patterns that *don't* have half-inch allowances. Allowances are likely to be wider on very heavy fabrics, narrower on fine fabrics, knits, and sharp curves.
Even in fine sewing, you can seldom use an allowance of less than one-eighth inch, but selvages can be whipped together with no allowance at all, and leather and felt are usually butt-seamed.
Sometimes you can sew seams already graded. When piecing denim scraps together with mock-fell seams, for example, I may cut strips to an exact length and whatever width is possible. Then I'll pin the edges together with one edge a quarter inch beyond the other, sew a half-inch seam, press the seam to one side with the quarter-inch allowance underneath, and top stitch.
Flat-fell seams can be made in a similar manner when both edges are straight, but require a half inch of offset instead of a quarter inch. Stitch a quarter inch from the edge of the narrower allowance, using your presser foot as a guide. Then press the wider allowance to meet the raw edge of the narrower allowance.
If the seam is curved, press the turn-under over a template, then sew with the raw edges touching.
When making garments, it's usually easier to match the edges and then trim one, but even when exact seams are required, it is possible to pre-grade edges that don't curve too much. The key is add to one allowance what you subtract from the other, so that you end up with the same total.
If you are attaching a waist with a half-inch allowance to a band with two half-inch allowances, pin with the waist edge one-eighth inch below the band edge, sew a five-eighth inch seam. This leaves you with the original half inch allowance on the waist and five eighths on the band. Make up for the stolen eighth-inch by turning under only three eighths on the other edge of the band.
Another way (for lightweight fabric): cut the band four times the desired final width. Sew the waist on as above, then turn the free edge down to meet the wider seam allowance, making a band half the original width, i.e. twice the desired final width. When the band is folded in half, the free edge inside will creep toward the edge of the waist allowance, blurring the transition from five layers to four.
If a light band is to be attached to a heavy fabric, it may be desirable to make the seam allowance on the heavy fabric almost as wide as the finished width of the band, so that the band is padded evenly.
A pre-graded method for pleating fabric onto a lined yoke, suitable when other seams in the piece are to be flat fell:
On the right side of the yoke piece, mark a line one quarter inch from the cut edge, then form the pleats so that their raw edges fall along this line. Sew a five-eighths-inch seam. This makes one allowance five eighths and the other three eighths, which adds up to two halves. The piece will be the planned length, but the seam will be an eighth of an inch high.
Fold the half-inch seam allowance on the lining under, then turn to the right side and stitch near the fold, as if making a flat-fell seam. The fold of the lining will extend an eighth inch beyond the stitching, with a comfortable three-eighths of allowance inside the stitching.
In practice, it doesn't work out this neatly — cloth stretches and whatnot. Working on the wrong side, tuck the raw edge of the lining under, so that the fold just conceals the stitching, and try to make it extend beyond the stitching by the same amount all across. Smooth out wrinkles as you go, and use lots of pins in lieu of pressing the crease. (Many fabrics will stay put long enough to get pins in when squeezed with the fingers; others require the help of an awl to hold inner layers in place.: It helps to work in sections which you repeatedly divide in half until all of the allowance is secured. That is, pin the middle and the ends, then pin in between. Put the pins in at right angles to the proposed stitching, so that you can put pins in the other side before you remove them.
When the lining is firmly in place, turn to the right side and re-pin, putting the pins in the proposed stitching line so that they will point toward the sewing-machine needle as they approach it. (If you are sewing by hand, turn the heads of the pins toward your hands, or baste from the wrong side instead of pinning from the right side.) Remove each wrong-side pin when it gets in your way — and make sure that you get all of them out before you begin to sew. Inspect the wrong side to be sure the pins are a comfortable and uniform distance from the fold.
If you are sewing without topstitching, by rolling up the shirt back or whatever, and putting it inside the inside-out yoke, it's usually better to make all the allowances the same width, or at least to make the yoke and its lining match. (This style of yoke is discussed under "shirts", since that is where it's most often found.)
In fine sewing, the first seam is trimmed very narrow, so that the finished seam can be very narrow. In this case, press the seam open without first trimming the ravellings, then press it flat again and trim it, then press it first to one side and then to the other side, which will leave it standing upright on the fabric. Then fold the raw edges inside and sew the second time.
If you overlook a ravelling and find it sticking out on the right side, grasp it with tweezers and put a slight tension on it, so that more of it is sticking out than will stick out after you let go. If it happens to be a loose thread that was just floating by, it will come out when you do this. If it is anchored at the other end, trim it close to the fabric with fine scissors. It will snap back inside the seam when the tension is released.
This is useful mainly for bridging the gap between two french seams: for example, at the corners of a side-seam pocket.
Mock french seams sometimes come in handy when mending.
If you should, for some reason, need to make a long mock-french seam, first press the seam open, then turn the edges of the allowances toward the stitching, then press to the final position.
Another plan is to turn the edges in first, match the folds, stitch near the folds, stitch again on the stitching line. It is probably a good idea to press over a template to make the folds accurate.
In hand sewing, the hemming is usually blind, that is, not intended to show on the right side. Since flat-felled seams are supposed to be durable, the hemming thread is also concealed as much as possible on the wrong side.
In machine sewing, the hem is always secured by topstitching — often two rows, the first near the first line of stitching, and the second near the fold of the upper seam allowance. Since it is secured by three rows of stitching, it is rare for a twice-topstitched flat-fell seam to fail before the adjacent fabric has worn through, so this is a popular seam for heavy-duty clothing.
When topstitching contrasts with the fabric, it is traditional to make it show even more by using a thick thread.
To make a flat-felled seam, sew with the right sides together as when making a plain seam. Trim the underneath allowance to a quarter inch, and turn under the upper allowance a quarter inch, making a seam which would be symmetrical if the initial stitching were to disappear.
Since it's easier to press a seam to one side if it has been previously pressed open, press the seam open, trim, press to original position, press the turn-under, press open again (re-flattening the turn-under), press to the side.
Flat-felled seams are also used in fine sewing; in this case the under allowance is trimmed very narrow, and the final seam may be only a quarter inch wide, or even less.
Pin right sides together with the raw edges touching. Stitch the width of the original seam allowance from the fold. This automatically adds to one allowance what was deducted from the other.
It may or may not be desirable to add to one allowance and deduct from the other before cutting, in order to keep the first row of stitching on the seam line. Most of the time, having the seam line halfway between the two rows of stitching is acceptable.
Press the allowances to one side, covering the raw edges. Stitch again three-quarters of the original allowance from the first row of stitching. If all goes well, this row of stitching will run right down the middle of the first turn-under, with no risk of falling off the fold or failing to secure the raw edge.
You may, of course, run two or more lines of topstitching, working all of them from the right side.
Another way: first top-stitch on the right side, guiding on the fold you can see, then top-stitch from the wrong side, guiding on the fold you can see.
Sometimes it's easier and neater not to press the allowances to one side, but rather flatten them against the bed of the sewing machine just before they go under the needle. This produces a softer sewn-in fold on the right side.
David Coffin recommends this seam for attaching sleeves to shirts, using 7/8" on the sleeve cap and 3/8" on the shirt body. 3/8" is folded under on the sleeve cap, and the raw edges overlap by a quarter inch. (This uses up the 5/8" allowances on commercial patterns, and allows more margin for error in the last row of stitching.)
When you press a fold along a curved edge, it is helpful to use a template. Cut a piece of heavy paper or thin cardboard by your cutting pattern, then trim off the amount you intend to turn.
Perhaps the easiest way to make a template is to mark the folding line on the pattern, then copy it onto the cardboard with tracing paper or typist's carbon. It helps to draw a line on the template to show where the raw edge should fall when the fold is pressed. This is easiest to do before cutting the template, particularly when you are folding under exactly half the seam allowance — you can use the original stitching line for the raw-edge-here line.
Copy all data from the pattern piece to the template, and add the width of the trimmed-off strip, the date, and the fabric or other ID for each garment it is used to make.
If you don't wish to use a template, draw a line on the fabric where the raw edge should fall, then fold and pin key points, putting the pins in at right angles to the line to avoid constraining the fold. Add more pins until the spaces between them are short enough that you can fold the edge without wrinkles, ripples, or wandering width. Then baste the fold into place by hand or, if you want a machine-stitched gathering thread, put pins in nose-to-tail, then stitch by machine.
When hand-basting, you can often eyeball the turn-under as you stitch. Sometimes hand basting can take less time than pressing, particularly on a sharp curve — hand-basting as you fold makes it much easier to ease out the little darts that try to form.
Sometimes a flat-felled seam is made on the right side of the fabric. In this case, it is top-stitched only once, but it appears to have been top-stitched twice, because the original line of stitching shows on the surface.
A special edge-stitching foot with a guide for stitching along a folded edge is convenient for top-stitching flat-felled seams. It maybe be called a "hemming foot" if it can be adjusted to stitch near, rather than on, the folded edge. All feet that I've seen have the guide on the right, because the blind-hemming stitch on a machine zigs to the left. This is very annoying when one wishes to top-stitch a hem, but works very well for flat-felling seams.
Sometimes one can use the same adjustment of the edge-stitching foot for parallel rows of top stitching by changing the needle position. This trick also serves when you are guiding the edge of a zig-zag foot along a seam or other guideline. The trick won't work with a straight-stitch foot, but will work with my two-sided zipper foot, which happens to be exactly as wide as the shift of the needle.
A hearsay flat-felled seam: If you want your seam as thick and lumpy as those on ready-to-wear jeans, here is an easy way to do it: pin the fabric wrong sides together, with one raw edge a little more than a quarter inch from the other. Fold the wider edge over the narrower edge, then stitch a quarter inch from the fold. The stitching should run near the raw edge, but far enough from it to secure this first fold when you fold the seam to one side, enclosing the visible raw edge the same way that you enclosed the other raw edge. Top stitch near the fold, a little less than a quarter inch from the first row of stitching. On the right side of the fabric, this seam appears to have been topstitched twice.
My source claimed that these measurements precisely use up a 5/8" seam allowance, but does not say how big "a little" is.
Note that both rows of stitching show on the right side, but only one shows on the wrong side. Note also that the bobbin thread of the first row shows, and the needle thread of the second row shows, so it is particularly important to balance the tensions.
This seam is four layers thick from edge to edge. The Coffin seam is three layers thick all the way across, if you do it my way rather than Coffin's. (The afterthought seam I described first is four layers thick in the middle and three layers thick at the folds.)
I have never made a seam in this manner — hence my label of "hearsay". (These seams must have proper names — and the names certainly aren't "afterthought", "Coffin", and "hearsay".: (I've settled on "pre-graded flat-fell seam" for the Coffin seam. It's accurate, and sufficiently obvious that it shouldn't matter that I'm the only person in the world using this term. There may be bits here and there that I wrote before making this decision and haven't edited since.)
In many places where fine sewing or ready-to-wear would use a flat-fell seam, rough sewing presses both allowances to the same side, then runs two or three rows of top-stitching on the right side. This isn't done to save the time spent hemming the seam allowance, but to save lumpiness. Though it leaves fringe showing on the inside, and sometimes needs ravelings trimmed off after the first washing, the mock flat-fell seam is more durable than the flat-fell seam when the fabric is heavy.
Always use at least three rows of top stitching when the fabric is inclined to ravel. Or you may zig-zag or overlock the raw edge before topstitching. This thickens the edge, but usually doesn't thicken it as much as turning it under. Overcast only the upper allowance, and trim a little off the lower allowance to make sure it stays out of sight.
Seams in wool flannel can be given a beautiful finish by putting a china-silk hong kong binding (see "edge finishes") on the upper allowance.
Adapted from my 2014 sewing diary:
I've figured out how to piece the black pedal pushers into long pants.
I shall cut a cross-grain strip of red linen one inch wide, fold a quarter inch of one end to the wrong side, pin it to the leg right sides together with the leg sticking out an eighth of an inch, and stitch the width of the toe from the raw edge of the red linen. Then I'll cut off the excess strip, hand-sew the ends together, and press as for a mock-fell seam, with the red linen creased, the black leg flat, and all raw edges behind the red linen. (Or I might press it as it lies and make the crease with my fingers and the presser foot.)
Then I'll press a quarter inch to the right side of the leg extension (and a quarter inch to the wrong side at the other end, in preparation for the hem) and begin as if to make a pre-graded flat fell seam, but I'll press that first round of stitching as it lies, then turn up the seam allowance to cover the stitching of the first seam. I'll probably hand-baste the fold to the single layer as close to the stitching as I can, so that I can see what I'm doing while I top-stitch along the mock-fell seam from the right side to secure the free edge of the seam allowance. This should make a small tuck at the bottom of the red stripe. I'll press that tuck flat and edge-stitch it to give the impression of a stripe appliquéd to the pants.
It will be nicely finished on both sides, and not a lot thicker than it would be if I really had appliquéd a stripe to whole cloth.
You can make a seam and hide the raw edges in one operation just by putting the two pieces right sides together and running them through your narrow-hemming foot. It looks like a french seam, but is somewhat thicker.
This version of standing fell is used almost exclusively in the cheaper brands of ready-to-wear, but a hand-sewn version is used in fine sewing. (See a book on fine sewing for instructions.)
One way to make a lapped seam is to turn the seam allowance on one piece to the wrong side, pin it to the other piece with the fold lying along the seam line, and top stitch. If a line of top stitching is close to the fold, the lapped seam looks like a mock-fell seam. Stitching farther from the fold makes the seam look like a tuck.
Another way to make a lapped seam is to turn half the seam allowance on one piece to the front, turn half the allowance on the other piece to the back, overlap the pieces with the raw edges touching, and stitch near both folded edges. This looks like a flat-fell seam.
The edges of the fabric can be finished in other ways, such as overlocking, binding, or the Hong Kong finish, and some fabrics don't require any finishing.
Lapped seams are good for very heavy fabric such as blanketing. To piece a blanket, I draw a chalk line half an inch from the edge of one piece, and match the edge of the other piece to this line. I zig-zag stitch down the middle of the overlap, guiding on the edge of the upper piece. I use a 4 mm stitch, since the fabrics are very thick, and some of the stitches may have to come out.
Then I examine the other side of the fabric to make sure the fabrics didn't slip; if the stitching wanders close to or too far from the other edge, I pick those stitches out and do them over.
Finally, I set the zig-zag as wide as possible — usually still as long as possible, since the fabrics are very thick — and stitch over each of the edges to blend them into the background. Zig-zag stitches are surprisingly inconspicuous on blanketing.
These instructions assume that the fabric has little inclination to ravel; if it frays easily, it would be well to stitch near the edge as well as over the edge. The extra line of stitching can be done before joining, if you don't want it to show on both sides of the seam.
The slot seam can be thought of as two lapped seams. The seam allowances are turned under, then the two pieces are sewn to a ribbon or tape with the folds just touching. The stitching is set back from the folds a bit to leave a slot defined by two tucks.
Lace, braid, and other trimmings can be inserted the same way, with the folds farther apart to show the insertion. In an insertion seam, the stitching is usually close to the folds, rather than set back to form tucks. You may sew both pieces to the insertion with plain seams before or instead of top stitching.
The slot seam is usually used only in tailored garments, and insertions are usually used only in fine sewing, but variations of these two seams can be useful in rough sewing. For example, if you want to join a fabric so heavy that even a lapped seam is too lumpy, and the edge isn't suitable for an overcast seam, you can sew both edges to a thin, tough tape, then cover the raw edges with a line of zig-zag stitching or a narrower tape.
A seam in which the two edges meet without allowances. See "slot seam", "overcast seam", and "windowpane seam".
Mostly used to join selvages, as in the leaf carrier described in "household linens", more rarely to join folds. By butting the edges together, the overcast seam minimizes bulk and lumpiness. It was once used to join narrow widths to make sheets, and is still used to join pieces of leather when real chamois is used to line the saddle area of bicycle shorts.
You lay the edges one on top of the other, overcast them together, and then open out the seam by pressing it with your thumbnail. If the edges caught in the overcasting are narrow enough, they end up butted neatly together inside the spiral of thread.
When worked by hand, only one thread of the edge is caught, and the seam is joined securely without further stitching. A hand-overcast seam is the least-obtrusive seam possible.
Theoretically, one could overcast with a zig-zag machine in the same way, and make a seam thicker than the hand-overcast seam by only one thread. In practice, the most expert machine operator must frequently catch two or more threads, and a few stitches miss the fabric altogether. So the overcasting is regarded as permanent basting, and is cut as required to remove pleats and puckers. Once the seam is nice and flat, a second row of zig-zag stitching secures it.
Use a multiple zig-zag for the second stitching, if you have that option.
If you use a machine-overcast seam to make a chamois lining for bicycle shorts, use only size A reeled-silk thread — it's strong, but not too strong, stands up to all washing methods used on chamois, and does not irritate sensitive skin. Color does not matter, as sweat will remove the dye.
You can zig-zag over the stitching of a plain seam, to strengthen it and make it stay pressed open. If you have an embroidery machine, ornamental stitches can serve the same function.
Unfortunately, zig-zagging over a seam in a knit fabric is likely to weaken the fabric more than it strengthens the seam.
Trim the seam allowances, press them open, and appliqué a tape, ribbon, or braid over them. Seams are usually taped on the outside of the garment as an ornament. Tape may be used as a seam finish on the inside, but it is difficult to make the stitches that show on the outside neat.
Originally, "faggoting" was a stitch in which threads were gathered into bunches that resembled faggots of wood; now it means any sort of embroidery in which threads bridge a space between two pieces of fabric.
Faggot seams are mostly found in hand embroidery, but some are made by working machine embroidery between two edges basted to removable stabilizer. The edges of a faggot seam are often turned under, but they may be finished by any of the methods used for free edges.
When sewing machines were new, faggot seams were also made by putting a spacer between two pieces of cloth while making a plain seam. This style fell out of favor because it looks too much like a seam sewn with sloppy tension.
Faggot seams are not suitable for garments meant for hard wear, but they can be made somewhat more durable by backing them with a contrasting ribbon or fabric.
A variation, suitable only for decorative garments to be worn over other garments, is to baste finished edges to stabilizer touching, as if to make a butt seam, then tack them together with spots of embroidery, with slits between the spots.
I took both the name and the method from "Windowpane Patchwork", an article by Stephanie Corina Goddard in Threads #90, August-September 2000.
This seam works best on straight edges, as in patchwork. The finished effect looks like two bound edges slip-stitched together.
For sashing, cut lengthwise strips of a contrast fabric four times the width of the desired seam allowance. (It is possible, but not easy, to use bias tape to join curved edges.: Cut the pieces to be joined with no seam allowance.
Place two sashing strips right sides together and stitch exactly down the middle. Press this seam open on both sides.
Sew one of your pieces to one of the strips, with the wrong side of the piece against the right side of the strip. Press both allowances toward the sashing, then turn under the edge of the other half of the strip and topstitch it down to hide the first row of stitching.
Join another piece to the other side of the sashing in the same way.
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