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Sewing Machines Technicians Corner

(edited by Mindconnection)

Has a customer ever asked, "Why should I pay someone to clean and oil my machine, when I can do it my self?"

The answer to that customer’s questions is simple. There is far more to proper maintenance than just cleaning the shuttle area and putting a few drops of oil here and there. This is especially true on today’s sophisticated machines. In fact, I would be willing to bet that the majority of users could not even get the covers off many of the newer machines.

I can’t tell you how many times I’ve had a customer insist her machine doesn’t need cleaning because she does it herself often. The expressions on their faces are priceless when I remove the covers and show them just how much fuzz and gunk is really in there. So much for "I did it myself."

The thousands of makes and models make it virtually impossible to detail all the particular maintenance requirements of each and every machine. However, if you have a question about a specific model, please write to me and maybe we'll answer it in a future column.

I like to start with the repair tag or work order. Look at the customer’s complaint. Why did the customer bring the machine to you? Is it skipping stitches? Poor tension? Does it break needles or thread? Does it sound like it has indigestion? Such information gives you an idea of what to look for, but don’t limit the inspection to just the complaint. Many things can be at the root of specific problems.

1. Remove the needle. Is it obviously bent? Is it dull or burred?

2. Turn the machine over by hand and check for binding. Does it move easily and freely? Does the hook or shuttle move? If you sense it is binding, determine why. Is there an accumulation of old oil, grease, or dirt? Check the belt: is it too tight? Check behind the hand wheel and motor pulley: Is thread wound around the shaft? If the hook or shuttle didn’t move, check the gears and or timing belt. If it is an oscillating shuttle, check the connecting link. Is it loose or broken?

3. If you experienced no binding and the hook or shuttle is moving, install a new needle and turn the machine by hand again. Is the needle hitting? If so, check the needle bar height and hook timing and needle clearance. Are they to the specifications in the repair manual? Check for broken and/or burred hook points. This is also a good time to check the thread guards and/or race cap and shuttle driver spring. Don’t forget those position brackets.

4. If you can turn the machine by hand without causing damage, plug it in and run it. Or remove the needle and run it. Does it actually run? Are there any unusual noises? Is the speed correct? If you hear a noise out of the norm or the speed seems incorrect, then find out why.

If the machine doesn't run, I start with the cord. If the machine is an older style with an AC motor, you can use jumper leads to "hot wire" it. If this causes the machine to run, you’ve eliminated a motor problem, and can now focus on the cord and foot control.

Caution do not "hot wire" a machine with a DC type motor or an electronic speed control. You will damage these parts beyond repair.

If it doesn’t run by hot-wiring it, connect your leads directly to the motor wires. If it still doesn’t run, then the problem is in the motor. Check the brushes. If they appear to be good, then replace the motor. If the machine does run by connecting leads directly to the motor, check the switch (if it has one) with a meter. If there is no switch, check the connections in the terminal block.

If the machine is electronic or uses a DC motor, start swapping parts with known good ones to find the source of the problem. The same goes with the lead and foot control. Although you can use your meter to narrow the problem down to either the foot control or the cord, most machines will have a manual for troubleshooting problems. Use the book!

If the machine runs too slowly, start with the foot control: attach a new one. If the result is proper speed and range, you know it is the controller. If the result is still slow, check the belt. Is it too tight or too loose? If the belt seems satisfactory, check again for binding in the machine; then try replacing the motor.

Unusual noises can be as simple as poor lubrication or as complex as loose or worn parts. Many times, a trained ear is all it takes to find and eliminate a noise. Other times, you can spend a great deal of time finding the source. Start by listening closely. Is it knocking, grinding, squeaking or squealing? Locate the source of the noise check for excessive wear. If it is not readily apparent where the noise is coming from, place a screwdriver between suspect parts and your ear.

Note: do not put a screwdriver on your ear and a moving part! Place it adjacent to the part on a stationary portion of the machine. You’ll hear the noise transmitted through the case.

If you haven’t already removed the covers and the needle and slide plates, do so. Check the needle plate. Is it bent, burred, broken? Is the hole enlarged from previous repair or damage?

Many times, you can straighten a needle plate with a few light taps of a hammer. If the hole has burring from repeated hitting of the needle, you may be able to smooth it with a file or polish it with emery cloth. Be careful not to remove too much and make the hole too large. Doing so can cause flagging resulting in skipped stitches.

Visually inspect all the parts in the machine for looseness or wear. Check to see nothing is bent, cracked or broken. Cracked or broken parts are usually obvious; bent parts can be difficult to spot. Often, bent parts are those that protrude from the machine surfaces. These include take-up levers, bobbin winders, presser bar lifters, tension assemblies, thread guides, stitch length levers and various control devices. I’ve encountered bent needle and presser bars, assorted driving shafts, connecting links, and screws. Sometimes you can straighten bent parts, but the reduction in strength usually means replacement.

Feed dog height and timing.
The feed dogs should rise above the needle plate approximately 1mm. With the stitch length set to the longest stitch, they should have traveled their full distance and be just below the needle plate when the point of the needle has reaches the top of the needle plate on its downward stroke.

Pendulum timing (zigzag machines).
The needle must not start its left or right movement until the point of the needle rises above the thickest layer of fabric being sewn, approx. 5/32 of an inch.

Reverse cycle stitches (stretch stitch).
To test, place a piece of paper under the presser foot and turn the machine over by hand in the operating direction through a complete cycle of stitches, two forward and one back. The point of the needle must penetrate the paper on the reverse stitch in the exact same hole as the previous forward stitch. If it doesn’t, adjust it.

Button Hole stitch.
Are the forward and reverse stitches of equal length? Is the distance between the left and right rows of stitches properly spaced? If not adjust the machine.

On computerized machines.
Do all of the stitch functions perform properly? Try them all; sometimes a problem with a board will affect only one type of stitch or function.

Presser bar height and pressure.
Adjust the presser bar so the fabric feeds without slipping or pushing. The pressure usually is user-adjustable, but if the presser bar is to high or to low this adjustment may not work. Consult the service manual for specific requirements. Usually when the feed dogs are at their lowest point, the presser foot should contact the needle plate and exert enough pressure to keep the thinnest of materials from shifting under the foot.

Needle position.
Is the needle central to the hole in the needle plate? Many machines come equipped with a seam guide on the needle plate. Use a scale to measure the distance from the center of the needle (the point ) to one of the measures on the plate. In case the plate has no scaling, the needle should be either central in the hole, or in the case of left needle position machines. The needle must penetrate the fabric in the exact same place when straight stitching as it does on the left through of the zigzag stitch.

Feed zeroing.
The machine must not, with the stitch length control set to zero, move the fabric being sewn in any direction. If it does, adjust per the service manual.

Upper thread tension assembly and bobbin case.
Inspect for worn and broken parts during the initial inspection. Common problems include excess lint and debris between the discs ( upper tension ) or the under the spring (bobbin case); worn or broken check spring; grooved or rusted tension discs or springs; missing or broken parts.

These steps should provide you with ample information to properly estimate the cost of repair on many machines. Some will require further analysis, some less. Determine as many of the machine’s problems during your initial inspection as possible. This avoids the unpleasant task of admitting to your customer that you missed something. Be thorough the first time.

The maintenance tune-up may very well be the most important part of any repair job. It is also the bread and butter of the service business and the part of the business upon which our reputations usually depend.

1. If you haven’t already done so, remove as many of the covers as practical: the top, bottom, and side covers always, as well as the needle and slide plates. The object is to expose as much of the inside of the machine as possible.

2. Use compressed air (not the same as "canned air"), if you have it, to blow out as much of the dust and lint as you can. You can also use a canister type vacuum cleaner with the hose attached to the exhaust, and a crevice tool. Though much slower, a small brush and some sort of pick can remove the dust and lint, too. Be sure to get in all the nooks and crannies, i.e. between the feed dogs, under and around the hook, in the shuttle raceway.

3. Check for thread wound around the mechanisms. Some common spots: take-up links, under the hook or bobbin case basket, handwheel, motor pulleys. On machines with rotary hooks, remove the gib screws and the bobbin case basket. You’ll usually find an accumulation of gunk in there.

4. Check for loose screws and connections, as well as gears not properly meshing. I use a dental pick to get in between gear teeth and pick out the accumulated grease and lint. This is especially important on newer machines with the fine tooth gears; buildup can cause premature failure.

5. If the machine has a belt, adjust the tension. It should be tight enough to prevent slipping, but not so tight that it causes the machine to slow down.

6. Lubricate the machine. One or two drops of clear white oil on all moving parts (where metal parts contact with each other). Use grease on the gears and cams. I use white lithium grease for this. It seems to hold up well and resists flying (coming off the surface from centrifugal force).

7. Replace the covers.

8. Remove any burrs or damage from the needle plate and replace it and the slide cover if necessary.

9. If you can, disassemble the tension assembly and clean between the disks. Sometimes just blowing air through them won’t get everything out.

10. Remove the spring on the bobbin case and clean under it.

11. Reassemble the bobbin case and tension assembly. Make preliminary tension adjustments.

12. Wind a bobbin to ensure the bobbin winder works properly.

13. Insert a new needle, thread the machine and sew a little. Make final tension adjustments. Ensure the check spring is functioning properly.

14. Sew a sample, include as many of the stitch functions as necessary to be certain they all work properly. Use various widths and lengths; adjust any that perform improperly.

15. Use a mild detergent to clean the outside of the machine thoroughly.

16. Put it back in its case, or a plastic cover. Now you’re ready for delivery or to carry the machine to the customer's car when they come to pick up the machine.

If anything you read here is contrary to the manufacturer’s recommendations as specified in a service manual, defer to the manual.

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