Unit 13 · The Sewing Machine

Sit in front of a machine with it turned off and unplugged. Start at the top right. The spool pin is the post the thread spool sits on. Next to it is the bobbin winder, a small spindle that spins an empty bobbin to fill it with thread. On the right side is the hand wheel, a large wheel you turn toward yourself to raise or lower the needle by hand. Never turn it away from you; that can pull the thread out of the needle and tangle it.

Now follow the front of the machine down. Thread guides are small hooks or slots that keep the thread on its path. The tension discs are two metal plates that pinch the thread; a dial sets how hard they pinch. The take-up lever is a metal arm that rises and falls with every stitch. It pulls thread up to tighten each stitch. At the bottom is the needle, held by a needle clamp screw, and the presser foot, a small metal foot that holds the fabric flat against the bed.

Under the presser foot is the throat plate, a metal plate with a hole for the needle and lines marked for seam widths. Through slots in the plate come the feed dogs, rows of small metal teeth that move the fabric forward one stitch at a time. Below all of that, behind a small door, is the bobbin, a little spool of thread that supplies the bottom half of every stitch.

On the front or side are the controls: stitch selector, stitch length dial, stitch width dial and a reverse lever or button. On the floor is the foot pedal, which is the machine’s gas pedal. Press lightly and it sews slowly; press hard and it races. Touch each part and say its name out loud before you go on. On a practical test, the first question is usually a diagram with blank labels.

Look closely at a machine needle. It has a flat side on the shank at the top, a long groove down the front, a scarf (a scooped-out spot) on the back just above the eye, and a point. The flat side faces the back of the machine on most home machines, so the needle can only go in one way. The eye is near the point, not at the top like a hand needle, because the machine pushes the thread down through the fabric instead of pulling it.

Needles come in types by point shape. A universal needle has a slightly rounded point and handles most woven cottons and blends. A ballpoint needle has a rounder tip that slides between the loops of a knit fabric instead of piercing and cutting them; use it for T-shirt jersey and fleece. A stretch needle is for very stretchy fabric like swimwear. A denim or jeans needle has a strong, sharp point for thick layers. A microtex or sharp needle makes a fine straight hole in silky fabric.

Needles also come in sizes, written as two numbers such as 80/12 or 90/14. The first number is the European size and the second the American; both get bigger as the needle gets thicker. A 70/10 suits light cotton, an 80/12 is the everyday size for medium fabric, and a 100/16 handles denim. A needle that is too thin for the fabric bends and breaks; one that is too thick leaves visible holes.

Needles dull with use, and a dull needle skips stitches and punches instead of piercing. Many sewers change the needle at the start of every project or after about eight hours of sewing. To change it, turn the machine off, loosen the needle clamp screw, pull the old needle down and out, push the new one up as far as it will go with the flat side to the back, and tighten the screw. Drop the old needle into a lidded container, never a bare trash can.

Two machines side by side in a classroom can thread differently, take different bobbins and put the stitch length on a different dial. That is why the first tool for any machine is its manual. If the paper copy is lost, the model number is printed on a plate on the back or bottom of the machine, and the maker usually posts the manual online for free. Print the threading diagram and tape it to the table.

Open the manual and find four things before you sew. First, the threading diagram, drawn as numbered arrows from the spool to the needle. Second, the bobbin section: does the machine take a drop-in bobbin from the top, or a front-loading bobbin in a metal bobbin case? Third, the needle-threading direction: front to back on most machines, but some thread side to side. Fourth, the normal tension setting, often 4 on a dial that runs 0 to 9.

The manual also has a troubleshooting table near the back. It lists the problem in one column (thread breaks, fabric will not feed, skipped stitches) and the likely causes in the other. Almost every cause is one of four things: threading, needle, bobbin, or lint. Read that table once now, so that when the machine acts up, you know the list exists.

Class machines get shared, so the manual is also the record of what the machine can do. Note the stitches it offers, the widest zigzag it can make, and what presser feet came with it. A zipper foot or a buttonhole foot in the accessory box is useless if nobody knows it is there.

Turn the machine off. Raise the presser foot with the lever behind it. This matters more than any other step: raising the foot opens the tension discs so the thread can slip between them. Turn the hand wheel toward you until the take-up lever is at its highest point, where you can see it through the slot. Now put the spool on the spool pin with the thread coming off in the direction the manual shows, and cap it with the spool holder if the machine has one.

Pull the thread to the left along the top of the machine and into the first thread guide. Bring it down the front channel, around the bottom, and back up. On the way down it passes between the tension discs; you may feel a tiny click as it seats. At the top of the channel it goes right to left through the eye of the take-up lever. If you miss the take-up lever, every stitch will be loose. Then bring it straight down through the lower thread guides to the needle.

Thread the needle from front to back on most machines, and pull about six inches of thread out behind the presser foot. Many machines have a built-in needle threader: a tiny hook that swings through the eye, catches the thread, and pulls it back through. Now lower the presser foot. Turn the hand wheel one full turn toward you, and the needle thread will catch the bobbin thread and pull a loop of it up through the throat plate.

Check your work with a tug test. With the presser foot up, the thread should pull freely. Lower the foot and pull again; there should be firm drag. If it pulls freely with the foot down, the thread is not between the discs. Pull it out and rethread. Threading takes thirty seconds when it becomes a habit, and it prevents most of the jams a beginner ever sees.

A bobbin is a small flat spool that holds the bottom thread. Use an empty bobbin made for your machine; bobbins look alike but differ by a millimeter, and the wrong one jams or rattles. Use the same thread as the top for ordinary seams. Put the spool on the spool pin, run the thread through the bobbin winder guide (often a small disc on top of the machine), and pass the end through the hole in the bobbin from the inside out.

Push the bobbin onto the bobbin winder spindle and click the spindle to the right, which disengages the needle so it will not move while you wind. On older machines you loosen the hand wheel’s inner knob instead. Hold the thread tail up, press the pedal slowly for a few turns so the thread catches, stop, and trim the tail close to the bobbin. Then press the pedal at a steady, medium speed and let the machine fill the bobbin. Most machines stop by themselves when it is full.

Watch the bobbin as it fills. The thread should lie in smooth, even layers. If it piles up on one side, the thread is not through the winder guide correctly; stop and fix it. Do not overfill; thread should not bulge past the rim. Cut the thread, click the spindle back to the left, and the needle is connected again. Turn the hand wheel a half turn to make sure.

Two common mistakes: winding on top of thread already on the bobbin, which makes uneven tension and a bird’s nest underneath, and winding at a jerky speed, which stretches some layers tighter than others. Keep a few extra bobbins wound in the colors you use most; running out mid-seam is a nuisance, not a disaster, but it always happens at the worst moment.

There are two systems. For a drop-in machine, slide off the clear cover in front of the needle. Hold the bobbin so the thread comes off in the direction the diagram on the cover shows, usually counterclockwise, like a letter P when you look at it. Drop it into the well, then pull the thread tail into the slot and along the guide path marked by arrows, which slides it under a small tension spring. Leave a few inches of tail and replace the cover.

For a front-loading machine, open the door below the needle and pull out the bobbin case by its little hinged latch. Hold the case in your left hand with the open side up and drop the bobbin in so the thread comes off in the direction the manual shows. Pull the thread into the slit on the side of the case and under the flat tension spring until it clicks out the end. Hold the latch open, push the case onto the center pin until it clicks, and let go of the latch.

Now bring the bobbin thread up. Hold the top thread loosely in your left hand. Turn the hand wheel one full turn toward you. The needle goes down, catches the bobbin thread and lifts a loop of it. Tug the top thread and the loop comes through the hole in the throat plate. Pull both tails out and lay them back under the presser foot, toward the rear. Starting a seam with the tails held behind the foot stops the first stitch from pulling down into the plate.

If the bobbin is put in backward, the thread unwinds the wrong way against its spring and the bottom stitches come out loose or the thread breaks. If the thread never went under the bobbin tension spring, there is no bottom tension at all, and loops of top thread show on the underside. Both look like tension problems. Both are really bobbin problems, and both take twenty seconds to fix.

A home sewing machine makes a lockstitch. It is nothing like hand sewing, where one thread goes in and out. Here two threads never actually pass through each other’s spools; they twist around each other once per stitch and lock in the middle of the fabric. Turn the hand wheel slowly toward you with the bobbin cover off and you can watch the whole thing happen.

Step one: the needle pushes the top thread down through the fabric and through the hole in the throat plate. Step two: the needle starts back up. Because the thread drags a little against the fabric, a small loop of top thread bulges out on the scarf side of the needle. Step three: the hook, a curved metal point spinning around the bobbin, catches that loop and carries it all the way around the bobbin case, so the loop now wraps around the bobbin thread.

Step four: the take-up lever rises fast and yanks the slack out of the top thread. That pulls the twist of the two threads up into the layers of fabric. At the same time the feed dogs push the fabric forward one stitch length. Step five: the needle comes down again and the cycle repeats. A machine at full speed can do this several hundred times a minute, and each stitch is locked by the one before it.

This is why the scarf on the needle matters and why the needle must be in the right way around: the hook has to pass right behind the eye to catch the loop. It is also why a bent or dull needle skips stitches. If the loop forms in the wrong place, the hook misses it, and no stitch forms for that beat. Understanding the cycle turns most machine problems from mysteries into checklists.

The stitch length dial controls the feed dogs. A higher number moves the fabric farther between needle strikes, so each stitch is longer. Most machines mark length in millimeters, from 0 to 4 or 5. Some older machines use stitches per inch instead, where a bigger number means shorter stitches. For ordinary seams in medium fabric, set 2.5 mm, which is about 10 to 12 stitches per inch. Set the dial before you sew; changing it mid-seam leaves a visible step in the stitching.

Use a long stitch, 4 to 5 mm, for basting: a temporary seam you will pull out later, or gathering, where you pull the bobbin thread to draw the fabric up into small folds. Long stitches are easy to remove. Use a shorter stitch, about 2 mm, for lightweight fabric and curves, where short stitches follow the shape better. Very short stitches, under 1 mm, are hard to rip out and can chew the fabric.

The stitch width dial controls how far the needle swings from side to side. On a straight stitch the width is zero and the needle goes straight up and down. Turn the width up and the machine sews a zigzag. A width of about 3 mm with a length of 2 mm gives a medium zigzag good for finishing a raw edge. A wide, very short zigzag becomes a satin stitch, the dense band used on appliqué and buttonholes.

Test every setting on a scrap of the same fabric first, doubled the way the seam will be. The scrap shows you whether the stitches lie flat, whether the fabric puckers, and whether the length looks right. Write the setting that worked on a sticky note and keep it with the project. A machine that is set right for one fabric is rarely right for the next.

Tension is how hard each thread is held back as it feeds. The top thread’s tension comes from the discs and the dial; the bobbin thread’s comes from the small spring on the case or well. When the two match, the twist where the threads lock sits in the middle of the fabric layers, and the seam looks the same on both sides. To learn to read tension, sew a test line with a different color in the bobbin than on top.

Look at the underside. If you see loops or straight runs of the top color lying on the bottom, the top thread is too loose: it is being pulled all the way through to the underside. Turn the top tension dial to a higher number, one step at a time, and test again. If instead the bobbin color shows in dots along the top of the seam, the top thread is too tight: it is dragging the bobbin thread up. Turn the dial to a lower number.

Before you touch the dial, though, check the path. In most classrooms, nine out of ten "tension problems" are a top thread that missed the discs or the take-up lever, a bobbin inserted backward, or a bobbin thread that never went under its spring. Rethread top and bobbin with the presser foot up and test again. Only if a correctly threaded machine still stitches unevenly do you change the dial. Adjusting the bobbin spring is a last resort and is usually a teacher’s job.

Some fabrics need a small change: thick layers may want slightly higher top tension, and very fine fabric slightly lower. Write down the dial number that gives a balanced stitch for each fabric, and always put the dial back to its normal setting, usually about 4, before you leave the machine for the next person.

A sewing machine needle moves faster than you can pull away. That sets the first rule: keep your fingers at least an inch behind the presser foot, and guide the fabric from the sides, not the front. Never push fabric into the needle from in front of the foot. Let the feed dogs do the pulling; your hands only steer. Tie back long hair, remove dangling bracelets, and keep sleeves off the wheel.

Pins are the second hazard. Pin across the seam line, not along it, so the pin heads stick out to the right and are easy to grab. Pull each pin out just before the presser foot reaches it. Sewing over a pin can snap the needle, and a needle fragment flies at eye level. If the needle does break, turn the machine off, find every piece, and drop them in the sharps container.

Turn the machine off, or at least take your foot off the pedal, whenever your hands go near the needle: threading, changing the needle, changing the foot, clearing a jam. Never leave a foot resting on the pedal while you talk. Unplug the machine before you open it to clean. Keep the cord where nobody trips over it, and keep drinks off the sewing table, because a spill in a machine is a repair bill.

Work at a steady, moderate speed. Beginners who floor the pedal lose control of the seam and their hands drift toward the needle. If something goes wrong, stop; take your foot off the pedal before you lift your hands to investigate. Sewing is a calm skill. The machine only bites people who rush it.

Every stitch shaves a little fluff off the thread and the fabric, and it collects under the throat plate around the feed dogs and the bobbin. Enough lint there stops the bobbin thread from feeding smoothly and can make a well-threaded machine skip or jam. Cleaning is simple. Unplug the machine. Remove the needle and the presser foot, take out the bobbin, and unscrew or unclip the throat plate.

Use the small stiff brush that came with the machine to sweep lint out of the feed dogs and the bobbin area. Tweezers reach the stubborn bits. Do not blow into the machine; breath is damp and pushes lint deeper. Canned air pushes lint into the works too, so most manuals say brush, do not blow. Wipe the plate and the bobbin case with a dry cloth, put everything back, and turn the hand wheel a full turn by hand to make sure nothing binds.

Some machines need oil; many newer ones do not, so check the manual. If yours does, use only sewing machine oil, never household oil or cooking oil, which gum up. Put one drop on the spots the manual marks, usually in the hook race where the hook spins, then sew a few lines on a scrap to carry off any extra so it does not stain your project.

Cover the machine when it is not in use so dust does not settle into it. Change the needle regularly. Once a year or so, a sewing machine shop can service it fully. A well-cared-for machine from fifty years ago still sews a perfect seam; the ones that die are the ones nobody ever cleaned.

A seam is two pieces of fabric stitched together, and the seam allowance is the fabric between that line of stitching and the cut edge. Most commercial patterns for garments and home projects use a 5/8-inch seam allowance, which is about 1.5 cm. Quilting uses 1/4 inch. The pattern tells you which, and every seam in the project uses the same one, or the pieces will not fit together at the end.

Look at the throat plate. To the right of the needle hole are engraved lines, usually marked 3/8, 4/8 (1/2), 5/8 and 6/8. Those numbers are the distance from the needle. Put the raw edge of your fabric on the 5/8 line and your stitching lands exactly 5/8 inch in. If your plate is unmarked, measure 5/8 inch from the needle with a ruler and lay a strip of masking tape there as your guide.

Here is the habit that makes straight seams: watch the edge of the fabric against the guide line, not the needle. Beginners stare at the needle and the seam wanders. Keep your eyes an inch or two ahead of the foot, on the line, and steer the fabric with light fingertips so the edge rides along it. Let the feed dogs move the fabric. If you push or pull, the stitches stretch or bunch.

Check a finished seam with a seam gauge or ruler: measure from the stitching to the edge at three places. If it reads 5/8 at every point, the pieces will match the pattern. If it drifts from 1/2 to 3/4, the seam is uneven and the next piece will not line up. Practice on lined paper with no thread until the line stays straight, then on scraps.

Sit down with the machine threaded, both thread tails pulled back behind the presser foot, and the needle in its highest position. Place the fabric under the foot so the raw edge is on the 5/8 line and the needle is about 1/4 inch in from the starting edge, on the fabric, not hanging off it. Lower the presser foot. Hold the two tails lightly with your left hand behind the foot for the first few stitches so they cannot get sucked down into the plate.

Sew three or four stitches forward. Then press and hold the reverse lever or button and sew three or four stitches back over them. Release it and sew forward again, on top of the same line, and continue down the seam. That is a backstitch: a small knot of stitching over itself that locks the seam start. Without it, the thread ends are loose and the first inch of the seam can unravel the first time it is tugged.

At the end of the seam, sew to within a few stitches of the edge, then backstitch three or four again and stop. Turn the hand wheel toward you until the needle and the take-up lever are at their highest point; if you stop with the lever low, the thread pulls out of the needle when you move the fabric. Raise the presser foot, slide the fabric out to the back and left, and cut the threads, leaving tails of a couple of inches on the machine for the next seam.

Two mistakes to avoid: starting with the needle off the edge of the fabric, which lets the machine chew the thread into a nest under the plate, and forgetting the backstitch at the end, which is where a bag or a hem always starts to open. If you are basting a seam that will be pulled out later, skip the backstitch on purpose so it removes easily.

A square corner on a bag or a pillow is sewn with a pivot, not by steering around the bend while the machine runs. Sew along the first side with the edge on the 5/8 line. As you approach the corner, slow down. You need to stop exactly 5/8 inch from the end of the fabric, where the two seam lines cross. Many sewers draw a small pencil dot at that point on the wrong side before they begin.

Stop with the needle down in the fabric at the dot. If the needle stopped up, turn the hand wheel toward you until it goes down. Now the needle is holding the fabric like a pin, so it cannot slip. Lift the presser foot. Turn the fabric a quarter turn so the next raw edge lines up on the 5/8 line. Lower the foot. Sew on. The corner is exactly square and the two seam lines meet at one point.

For a very sharp point, such as the tip of a collar, take one stitch across the corner instead of a hard pivot: pivot, sew one stitch, pivot again. That one diagonal stitch gives the seam allowance room to turn without bunching at the tip. Then, before turning the piece right side out, trim the corner: cut the seam allowance off diagonally, close to but not through the stitching, so the corner turns crisp instead of lumpy.

Common mistakes: lifting the foot with the needle up, which lets the fabric slip so the seam lines miss each other; pivoting too early or too late, which makes a corner that is not square; and forgetting to lower the foot again, which sews with no pressure and produces loose, wandering stitches. A pin can hold the corner while you learn, but the needle-down habit is the one to build.

Cut a strip of woven cotton and rub the edge between your fingers. Threads pull loose. Every wash pulls more, and an unfinished seam allowance inside a bag or a garment slowly frays until the seam itself lets go. A seam finish is anything that stops the raw edge from fraying. The right one depends on the fabric, the machine you have and how much wear the piece will get.

The finish every machine can do is the zigzag. Set a medium zigzag, about 3 mm wide and 2 mm long, and sew along each seam allowance edge so the needle swings just over the raw edge on the right-hand side. The thread wraps the edge and holds the loose fibers. Do this before sewing the seam, on each piece separately, or after, on each side of the seam allowance. A tighter overcast stitch, if the machine has one, works the same way.

Pinking is the fastest finish. Pinking shears cut a zigzag edge, and the short diagonal cuts fray far less than a straight edge. It suits firm cottons that will not get heavy wear, and it is not enough for loosely woven fabric. A serger, also called an overlock machine, trims the edge and wraps it in three or four threads in one pass; it is the finish inside most store-bought clothes. A clean finish turns the edge under 1/4 inch and stitches it down, which is neat on light fabric.

Whatever you choose, do it before pressing and before the piece is assembled where you cannot reach the edges. For a drawstring bag, zigzag all four raw edges of both rectangles before you sew anything, and the inside of the bag will look as tidy as the outside. Skip the finish on a felt or fleece project; those fabrics do not fray.

Sewers say "press," not "iron," and they mean it. Ironing slides the iron back and forth over finished cloth to remove wrinkles. Pressing lifts the iron, sets it down on one spot for a few seconds, lifts it again and moves to the next spot. Sliding stretches a freshly sewn seam and pushes it off grain. Pressing flattens it exactly where it lies. Set up the iron at the temperature for your fiber: high for cotton and linen, medium for wool, low for polyester and nylon. When in doubt, test on a scrap.

First, set the stitches: lay the seam flat, still closed, and press right along the stitching line. This sinks the thread into the fabric and evens the tension. Second, open the seam. Lay the piece wrong side up and use your fingers to spread the two seam allowances apart, one to each side. Press down the center of the open seam with the point of the iron, moving along in short lifts. Third, turn the piece over and press lightly from the right side, with a press cloth between the iron and the fabric if it is dark or shiny.

Steam helps set cotton and linen; a burst from the iron or a damp press cloth makes the seam lie flatter. Skip steam on fabrics the care label says to keep dry. For a seam that is pressed to one side instead of open, such as a quilt seam, press both allowances toward the darker fabric so they do not show through.

The rule is: press every seam before you sew across it. A side seam gets pressed open before the casing goes on. A seam that is crossed while still folded leaves a lump that no amount of pressing fixes later. Keep the iron on its heel when your hands are off it, keep the cord away from the machine, and never leave a hot iron face down on the board.

Before you cut, decide on the finished size and work backward. Suppose you want a bag about 8¾ inches wide and 11 inches tall, big enough for gym shoes. Each side seam takes 5/8 inch, so add 1¼ inches to the width: cut 10 inches wide. The top casing takes a ½-inch fold plus a 1¼-inch fold, and the bottom seam takes 5/8 inch, so add about 2½ inches to the height: cut 13 inches tall. Two rectangles, 10 by 13 inches each. Write the numbers on your plan.

Wash and dry the fabric first if the bag will be washed, so it shrinks before you sew, not after. Press it. Find the grain: the lengthwise threads run parallel to the finished edge, called the selvage. Lay the rectangles so the 13-inch side runs along the grain; a bag cut off grain twists after washing. Measure with a clear ruler or tape, mark the cutting lines with chalk or a washable marker on the wrong side, and check every measurement twice.

Cut with sharp fabric shears, taking long strokes and keeping the lower blade flat on the table. Do not lift the fabric into the air as you cut, or the line wanders. If you have a rotary cutter and mat, use a ruler as a guide and keep fingers well back from the blade. Zigzag all four edges of both pieces now, while they are flat.

Last, gather the notions: matching thread, two cords or lengths of ribbon about 30 inches each, a large safety pin for threading the cord, and pins. Make a short step list with the seam allowance written at the top. Cutting is the one step you cannot undo, so the plan gets checked before the shears come out.

Lay one rectangle on the table right side up. Lay the second on top, right side down, so the two right sides face each other; that is how nearly every seam in sewing is made, so the seam allowance ends up inside when you turn the piece. Line up all the edges. Pin across the seam line along both long sides and the bottom, with pin heads sticking out to the right, about every three inches.

Mark the cord opening. On each side seam, measure down from the top edge and make a chalk mark at 1¾ inches; the casing will fold at ½ inch and again at 1¼, so the opening has to sit below that fold. You will sew the side seam from the bottom up to that mark and stop, leaving the top 1¾ inches of each side unsewn. That gap is where the cord will come out of the casing.

Start at the top of one side at the 1¾-inch mark, needle on the fabric, edge on the 5/8 line. Backstitch, sew down the side, pull pins as you reach them. At the bottom corner, stop with the needle down 5/8 inch from the edge, lift the foot, pivot, lower the foot, sew across the bottom. Pivot again at the second corner and sew up the other side to its 1¾-inch mark. Backstitch and stop. Trim both bottom corners diagonally.

Press the seams flat to set them, then press each side seam open from the wrong side, including the unsewn 1¾ inches at the top, which you fold under along the 5/8 line and press. Those little pressed-under flaps make a neat edge around the cord opening. Stitch around each opening close to the fold so the flaps stay put. Now the bag is a pocket with a raw top edge, ready for the casing.

With the bag still wrong side out, fold the top raw edge down ½ inch toward the wrong side all the way around and press. Fold again 1¼ inches and press. The raw edge is now hidden inside the fold, and the pressed-under flaps at the cord openings sit inside the fold too. Pin the fold across, every couple of inches, with the heads out.

Turn the bag so you can sew around the inside of the top. Sew close to the lower folded edge, about 1/8 inch from it, all the way around, removing pins as you go. Backstitch where you start and where you meet your starting point. This stitching line closes the casing; the space between it and the top fold is the channel the cord runs through. Check that the two side openings are above the stitching and open into the channel.

Cut two cords about 30 inches long. Pin a large safety pin through one end of the first cord and push it into the left opening. Scrunch the fabric along the pin and pull it through, all the way around the bag and back out the same opening. Tie the two ends together. Do the second cord from the right opening the same way and tie it. Now pulling both knots in opposite directions closes the bag.

Turn the bag right side out, poke the corners square with a blunt tool such as a chopstick, and give it a final press. Then evaluate: measure the finished width and height against your plan, check that every seam is 5/8, look inside for raw edges, and test the drawstring ten times. Write down what you would change on the next one. A bag that closes, holds its shape and has no loose threads is a pass.

A seam with skipped stitches has long gaps where a stitch should be, then a few good stitches, then another gap. The hook is missing the loop on some strokes. Because the loop forms next to the needle, the needle is the first suspect. Turn the machine off. Take the needle out and roll it on the table; a bent one wobbles. Run a fingertip along the point; a dull or burred one catches. Either way, throw it in the sharps box and put in a fresh one.

Second suspect: the wrong needle for the fabric. A universal needle on a stretchy knit pushes the loops aside and skips; a ballpoint fixes it. A fine needle on thick denim flexes and skips; a 100/16 denim needle fixes it. Third: the needle is in wrong. It must be pushed all the way up into the clamp with the flat side to the back and the screw tightened firmly. A needle that sits 1/16 inch low puts the loop out of the hook’s reach.

Fourth: threading. Pull the top thread out and rethread with the presser foot up, making sure the thread goes through every guide and the take-up lever, and that the needle is threaded front to back. Fifth: thread and needle mismatch. Very thick thread in a small needle cannot form a clean loop. Use ordinary all-purpose thread for class projects and the needle size the fabric calls for.

Work down the list in order and test on a scrap after each step. Most of the time the first or second step ends it. If a fresh, correct needle, correctly inserted and threaded, still skips, the machine’s timing may be off, and that is a repair-shop job, not a classroom one. Tell the teacher and switch machines.

The classic beginner’s disaster is the thread nest: a wad of loops under the fabric and a machine that stops with a thunk. Surprisingly, a nest on the bottom is almost always a top-thread problem. Either the machine was threaded with the presser foot down, so the thread never seated in the tension discs, or the foot was left up while sewing, so there was no tension at all, or the tails were not held at the start and got pulled down. Cut the fabric free, clear every scrap of thread from the bobbin area, and rethread the top with the foot up.

If the machine sews a few inches and then binds, or the bobbin thread keeps breaking, look under the plate. Check that the bobbin is the right one, in the right way round, with its thread under the spring. Check for lint packed around the feed dogs and hook, and brush it out. Check that there is no thread wrapped around the hook. Turn the hand wheel by hand a full turn; if it turns freely, you are ready to try again on a scrap.

If the fabric will not move, the presser foot is probably up, the feed dogs may be lowered by the darning switch, or the stitch length may be at zero. If the seam puckers, drawing the fabric up into little ridges, the top tension is too tight, the needle is too big or dull for a fine fabric, or the stitch is too long for it; try a smaller needle and a shorter stitch, and lower the tension one step. Pulling the fabric through by hand also puckers and can bend the needle.

Make yourself a card for the machine: nest underneath, rethread top with foot up. Jam or breaking bobbin thread, check bobbin and lint. Fabric will not feed, foot, feed dogs, length. Pucker, tension, needle, length. Every fix begins with the machine off and the foot off the pedal, and every fix ends with a test on a scrap before you touch the project again.