A serger (or “overlock” machine) is not a replacement for a conventional sewing machine. A conventional sewing machine is kind of like a Swiss Army Knife; a serger is more like the butcher cleaver in your kitchen: very good for making quick work of some big things.
A serger performs 3 basic functions…
It lays down a line of stitching
It trims the excess seam-allowance
It wraps the raw edge of the fabric
…and it does this all very quickly, using between 2 and 5 threads simultaneously.
A serger is good for:
Binding the edges of a piece of material
Sewing straight or gently curving seams in stretchy material
Sewing straight or gently curving seams in material that frays easily
Sewing straight or gently curving seams in just about anything
Look at those two lists, and you should be able to puzzle out what sergers aren’t good for:
Sewing wildly curving seams
Sewing sharp corners
Sewing in the center of a piece of fabric
The trimming knife and the overlocking (wrapping) function both make extreme curves and corners tricky, and sewing away from an edge nearly impossible (although an experienced overlocker will tell you there are myriad ways to fold fabric create an “edge” to work with nearly anywhere, and you may find the application rather esoteric and less exciting than the person explaining it does).
I hate to say it, but I’ve got to describe things mostly in terms of voodoo.
Before the fabric reaches the needle, a knife trims the edge of the fabric.
One, two, or three needles carry the top (or needle) threads. They oscillate like the needles on a conventional machine.
One, two or three loopers carry and shift the lower threads to knit or crochet them together with the needle threads. It’s the best I can explain it. There are a lot of things going on below and around the edge of the fabric while this happens.
Not a very satisfying explanation, I know, but it’s the best I can give you.
A basic serger does a series of overlock stitches. These stitches are differentiated by the number of threads used. More advanced sergers can also do a mock-chain (or “safety”) stitch at the same time. Really advanced sergers can do variants on the mock-chain stitch.
Most folks are familiar with 3-thread and 4-thread overlock stitches. In this stitch, two threads are looped around the edge of the fabric (after the knife has trimmed it) while one or two needles and threads lay down a line of stitching that locks it all together. This is a stretchy stitch, and results in a pretty tight seam (though not usually as tight as a lockstitch from a conventional machine).
A 2-thread overlock stitch uses one needle thread and one lower thread to lay down a line of stitching and wrap the edge of the fabric. It’s not very useful as a seam, but does make an excellent edge finish. Many sergers can use this stitch to roll a hem edge on very lightweight fabric, resulting in a clean edge without adding too much bulk.
A mock-chain stitch uses 2 threads to create a stitching line that is not necessarily along a wrapped and trimmed edge. It’s nearly as tight as a standard lock-stitch, but will stretch a little and like a chain-stitch can unravel if the threads are cut. It’s not a replacement for the standard lock-stitch or other stretch-stitches a conventional machine can do. Most sergers that can do a chain-stitch will combine this stitch with a 2-thread or 3-thread overlock stitch at the same time.
A cover-stitch is a variant on the mock-chain stitch that uses 2 or 3 needles and threads to create parallel lines of stitching on the topside of your fabric, while the lower side is knit together into a kind of honeycomb pattern. Underwear and swimwear often features this sort of stitching at the hem.
Most sergers are described in terms of the number of threads they can use. Watch out, though, as some only indicate the maximum number, and that doesn’t always tell you enough about the serger’s capabilities. For example, there are several very different “4 thread” serger types.
Not all machines that can do chain-stitch can also do cover-stitch. Cover-stitch can be found on some fancier 2/3/4 and 2/3/4/5 models.
In addition to the stitches, there are several additional options available on many sergers. I’ve already mentioned the rolled-hem option, and some sergers offer a free-arm that you’re already familiar with.
Differential feed is an option on many sergers. It operates the feed dogs before and behind the needle at different speeds. This can either stretch or bunch up the fabric under the needle. This is obviously an advantage when working with stretch fabrics, but can also help when working with satins or other slippery fabrics.
A good 2/3/4 thread serger with differential feed will meet most of your overlocking needs (including many I haven’t even mentioned here).
Unless you’re producing lots of garments professionally, a 2/3/4/5 thread machine is probably overkill. You can get the same kind of results by taking one pass through the conventional machine and another through the serger.
Cover-stitch is valuable if you’re making lots of swimwear, lingerie or other form-fitting spandex clothing.
Air-threading is a new feature that Babylock introduced in the late 90s. It sounds like a gimmick, but it's really nice. Since that patent expired, other manufacturers have started selling air-threading machines.
Once you know what features you want, it’s time to figure out what brand to get.
All sergers you’re going to find are made in the Asia/Pacific region. That “German” Pfaff or “Swiss” Elna says “made in Japan” on it somewhere. The Bernina you’re looking at is made in the same factory as the Juki sitting next to it. If you spend the time to research where the name-brand sergers are being made and by whom, you may find the same machine cheaper with a different name on it.
Don’t bother getting a new machine without differential feed. You’ll regret it later.
Go shopping. Try out machines.
Bring your own fabric. Those little strips of pink cotton with so much sizing they’re like cardboard they give you in the store are useless.
Try threading the machine from scratch. People will tell you that you’ll never thread the machine from scratch; you’ll always “tie-on” but don’t believe them. Pay particular attention to the threading order. It makes a difference.
Try converting to 2-thread overlock stitch.
Try converting to rolled-hem.
Try changing needles (this is the killer).
All sergers have a fixed cutting blade set into the work surface. Different companies may put the moving blade on an arm above the work surface, or have a hook-shaped blade positioned below. Make sure you can disengage the blade. Upper blades are often easier to disengage; lower blades are often easier to see around. Check to see if the blade gets in the way when you’re changing the machine around (or when it’s disengaged).
Try all the stitches you might want to use. If you’re going to be making tights or bicycle shorts, try the cover-stitch.
Consider used machines. You can often find a good 2/3/4 machine used (usually without differential feed) for a fraction of the price of a new machine. Often the price difference is worth giving up differential feed (unless you’re working with satin and spandex).
Unless you've got a lot of serger experience, avoid industrial machines. They're big. They're bulky. They're difficult to thread. They're not really designed to change stitches often. The speed controller is very different from a home machine. On the upside, they're very fast and very consistent.
Juki: This is the same "Juki" that makes industrial sewing machines and sergers. There's a lot in common between Juki home machines and Juki industrial machines, particularly the older Juki home machines. They're also the original manufacturer of sergers for Babylock Global and until Babylock Global's first patents expired, the only manufacturer of home sergers from many brands under Babylock's license. Juki now makes machines with air-threading.
They're sturdy, reliable workhorses. It's difficult finding Juki in sewing machine shops, but they are available from online retailers, and I highly recommend them to people who have experience with sergers and don't need start-up classes. I own a Juki MO-735 combo 2/3/4/5-thread serger with 3-needle coverstitch.
Juki is, hands down, the most machine you can get for your money.
Babylock: Babylock is a complicated brand. Babylock Global (in Japan) invented the home serger. Almost every patent related to the improvement of the home serger belongs to Baby Lock Global. It contracts out the manufacture of Baby Lock sergers and coverstitch machines to a single Japanese factory in Yamagata. Babylock Global sergers feature jet-air threading and a really fancy alternative to tension control, and surprisingly these features work very well.
I have a Babylock Evolve BLE-8 combo. It's 25 years old. It does 2/3/4/5 thread overlocking and 3-needle coverstitch. It can do overlock and chainstitch (with up to 5 needles) simultaneously. Jet-air threading and automatic thread delivery are amazing.
Babylock importers/distributors around the world sell these machines and also machines they have made themselves by other companies under the Babylock logo. Not every serger (and no conventional sewing machines) with the Babylock logo are made by Babylock Global.
Until the end of the 90's Babylock sergers were manufactured by Juki. They’re easy to thread and adjust. I got an old (Juki) Babylock 2/3/4 model at a rummage sale for $50. It had none of the problems the Singer did. I gave it to a friend for Christmas when I decided I needed a machine with cover-stitch and differential feed. It’s still running strong. Kevin owns a later (Juki) Babylock with differential feed that he bought new. It's still running strong.
Modern Babylock machines (with BLE model numbers) hold their value well. If you're lucky you can get some real bargains, but they often sell for as much as a new serger from another manufacturer.
Babylock Global is the most machine you can get, period, but they're expensive.
Bernina: I shopped for Berninas for quite a while. They’ve always been made by Juki. The average Bernina salesperson will try to convince you that because it’s a Bernina it’s better than a Juki. I haven’t seen the difference (other than in the price).
Elna/Janome: The Elna brand is owned by Janome. I’ve got an Elna 704DEX 2/3/4 from about 1997. Elna features a lower-hook blade, easy threading and needle changing, and a large work area. The 704 is really sturdy. The outer case is plastic, but there are huge aluminum castings under it. It (and the current 744 model) includes chain-stitch and cover-stitch. The “automatic” tension system actually works. The 600 series doesn’t include cover-stitch; the 900 series is a 2/3/4/5 with everything. On the other hand, the earlier “Elna Pro 5” 2/3/4/5 model does not have a good reputation. You may find the equivalent Janome model to be a smidge cheaper than the Elna, but there may be small feature differences.
Singer: My first serger (well, it belonged to a housemate) was a Singer 2/3/4. I hated it. It always drifted out of tolerance, requiring constant adjustment, and a gorilla wouldn’t have the strength to screw down the fixed knife clamp. From what I’ve seen, the design and build quality haven’t improved. Really early Singer sergers (from the early 80's) were made by Juki, and had a white and blue crackle finish. They're sturdy and reliable machines. Singer is now owned by SVP Global (Singer/Viking/Pfaff).
Pfaff: Pfaff is now owned by SVP Global (Singer/Viking/Pfaff). I shopped for Pfaffs 20 years ago, they had a lower-hook blade like the Elna, and a large work-surface.
Husqvarna/Viking: Viking is now owned by SVP Global (Singer/Viking/Pfaff). I haven't paid a lot of attention to older Viking Huskylock sergers, but I have friends who are happy with them.
SVP Global: SVP Global holds the trademarks for Singer, Viking and Pfaff. The general consensus is that since this buy-out/consolidation, the quality of Viking and Pfaff machines has dropped significantly.
White: One of the shops I frequented sold White sergers. White Sergers were at the time made by Jaguar (not the car company), but I’m not sure if they still are. They have a lower-hook blade, but it’s not retractable. The store owner had nice things to say about them, and since he’s one of the best repairmen I know, I’ve got to trust him.
Jaguar: See above, but probably a touch cheaper.
I can't stress this enough. If you have never owned a serger, buy your first serger from a sewing machine shop with a reputation for providing good start-up classes. Having someone guide you through the threading process the first few times will get you over your initial worries about how complicated this new machine is. If you don't, you're just going to have an expensive machine sitting unused in a box.
Your local sewing machine shop may also be a good source for used equipment. I’m actually a big fan of buying reconditioned used machines (as long as there’s a repairman I trust nearby). If I was starting over cheap, I would look for a used Juki (or Juki-manufactured Bernina or Baby Lock) 2/3/4 model with differential feed. They are easy to thread, easy to convert, and needle-changing is not too much of a hassle.
If I was starting over expensive, I would buy a new Juki MO-654DE. It's a good 2/3/4 thread machine with differential feed. There have been many improvements serger design that make threading and adjustment easier now
If I was just buying a new machine for myself without regard to cost, I would buy a Baby Lock Triumph (Gloria in Europe). If I had a bucket of money. But it's dirt-simple to thread, and produces an absolutely reliable stitch both when overlocking and when doing coverstitch.
The more practical (and cheaper) route to all the features you need to work with any materials would be two machines: A Juki MO-655 for overlocking and a Juki MCS-1500 for coverstitching.