The motor, the feet and the order you set the tension in. None of it is glamorous and all of it decides whether the machine is a pleasure or a fight.
The motor
If a machine feels uncontrollable, this is usually why, and it is the cheapest thing on the machine to put right.
Clutch motor
How it works
The motor runs continuously at full speed whenever the machine is switched on. The pedal engages a clutch that connects it to the machine.
In its favour
- Robust, and they last
- Plenty of power for long continuous seams
- What most older industrial machines came with
Against it
- Speed control means slipping the clutch, and the usable range is narrow
- Genuinely hard to learn — the machine tends to take off
- Draws its full rated power whenever it is switched on, needle moving or not
- Hums constantly and gets warm
- Heavy, and some want three-phase or 220V
Servo motor
How it works
The motor only turns when you press the pedal, and its speed follows how far you press. Most have a dial to cap the top speed.
In its favour
- Fine control at low speed, which is what upholstery actually needs
- Silent when you are not sewing
- Uses power only while driving, so no heat and no hum
- Much lighter, and usually runs on ordinary single-phase mains
- You can set a top speed and simply not exceed it while learning
Against it
- Some lose torque at very low speed — the point at which a speed reducer starts to matter
- Cheaper analogue ones are less precise than digital
Changing a clutch motor for a servo is the single best thing you can do to an older industrial machine. It is a bolt-on job, it costs less than a set of feet and a few cones of thread, and it turns a machine that bolts away from you into one you can walk a stitch at a time. Upholsterers who have done it are close to unanimous.
Slowing it down further
Two ways, and they are not the same.
A smaller pulley on the motor is the cheap one. It slows the machine and costs a few pounds.
A speed reducer is a second pulley stage between motor and machine. It slows the machine and multiplies the punching power by the same ratio, which is why it is the answer for very thick leather where a servo starts losing torque at the bottom of its range. Fitting one may mean drilling the table for the bracket and buying two new belts.
Do not fit one before you need it. A reducer makes the machine very slow indeed, and upholsterers who fitted one early report finding it maddening once they got quicker and wanted to actually get through the work. Fit a servo first. Add a reducer only if you are still short of power at low speed on genuinely thick assemblies.
Presser feet
The foot is doing two jobs at once: holding the material down, and staying out of the way of whatever you are sewing next to.
Standard set
Everyday seams.
On a walking foot machine, feet come as sets — an inner and an outer that work together. You cannot swap one alone.
Welting or piping foot
Running piping, and sewing it in.
Sold in sizes matched to the cord: 1/8, 5/32, 3/16, 1/4, 5/16 and 3/8 inch are the usual set. The groove has to suit the cord or the stitching will not sit tight against it.
Zipper foot
Zips, and anything you must stitch close up against.
Comes as a single left toe or single right toe. Which you need depends on which side of the needle the obstruction is, so most people end up with both.
Roller foot
Leather, vinyl and coated cloth.
Rolls rather than slides, so it will not drag on a sticky face. A rubber roller also stops the foot marking soft leather, which matters more than the feeding on a show surface.
Teflon or non-stick foot
Vinyl, PVC, laminated cloth.
Cheaper answer to the same problem as a roller foot: a steel foot grips vinyl and stalls it, a non-stick face slides over it.
Feet with teeth, or smooth
A choice, not a type.
Toothed feet grip and feed better through thick assemblies. Smooth feet do not mark. On anything where the face will be seen — leather especially — smooth is worth the poorer grip.
Edge guide
Consistent seam allowance.
Either a foot with a guide built in, or a bar that bolts to the bed. Cheap, and it does more for the look of a seam than most things costing more.
Setting the tension, in the right order
Almost every tension problem is solved on top, and almost every tension problem made worse is made worse by starting at the bobbin.
- Rethread with the presser foot up. The discs only open when the foot is raised. Thread it with the foot down and the thread sits outside them, and no setting will fix that.
- Leave the bobbin alone. Bobbin tension is set and rarely wants moving. If you have already been turning that screw, put it back to where a full bobbin case just holds its own weight when you dangle it by the thread and gives line with a small jerk.
- Sew a test seam on an offcut of the actual material. Two layers, same thread, same needle. Not a scrap of something else.
- Read which side is losing. Loops underneath mean the top tension is too loose. Loops on top mean it is too tight.
- Adjust the top only, a little at a time, and re-test after each change.
The maintenance that actually matters
- Oil it. Industrial machines are built to be oiled and they will wear out fast if they are not. Follow the plate on the machine; most want it daily in regular use.
- Brush the lint out of the bobbin case and race. Lint under the bobbin tension spring changes the tension noticeably, and it is the cause of a great many faults blamed on the machine.
- Never blow compressed air into it. It drives lint further in, past bearings, where a brush cannot reach.
- Change the needle when the work tells you to, not on a schedule. Skipped stitches, a change in the sound, snagging in the face, or straight after it has met a tack or a staple. Cheapest insurance in the workshop.
Also in this section: selector · thread · needles · machines · troubleshooting · setup · everything.