when doing this as small particles can be propelled through  the air and can get into the eyes. At the very least, the dirt  can be blown onto other machines and work. pulley that fits the shaft on your motor. You do have to know  the make and model of the machine.  Another way to slow a machine is to replace the clutch  motor with a rheostat motor. They operate the same way as  a dimmer switch for a lamp. The operator sets the speed of  the motor, and it does not run faster than what it is set at.  When finished sewing, always place a piece of fabric under  the presser foot in order to keep the feed dogs from causing  damage to the presser foot. After cleaning, each machine should be lubricated to  ensure smooth operation. For those machines that are self- lubricating, check the level and condition of the oil in the  reservoir. For these machines, a number 1 white oil that has  a higher viscosity should be used. Depending on the amount  of use, the oil should be changed every 6 months to a year.  In no case should the oil be changed less than once a year.  For machines that require manual lubrication, a number 2  white oil should be used as it has a lower viscosity to better  adhere to the moving parts. This should be done daily at the  end of the workday. Oiling the machine at this time allows  the oil to seep downward through the mechanisms and collect  on the bottom.  If the machine does not sew correctly, consult the troubleshooting  guide to determine what the problem is and how to remedy it.  [Figure 6-81]  If the machine jams, it is very important to not  force it, as you can cause damage to the machine.  The most important part of maintaining your sewing  machines is to keep them clean and lubricated. Each machine  should be wiped down daily with a clean rag to remove oil  and dirt. The amount of use each machine gets dictates the  cleaning required. However, on at least a weekly schedule, the  moving parts should be cleaned with a small brush to remove  dust, lint, dirt, and threads. An air hose or bottle is useful in  blowing dirt out of places the brush cannot reach. Be careful  In the morning before use, take a clean rag and wipe off the  excess oil so it does not stain the parachute materials. Pay  particular attention to the shuttle race. Keeping this well  lubricated ensures smooth operation and a quieter machine.  One item that tends to get overlooked is the bobbin winder.  The shaft of the winder has a small hole in the top and a drop  of oil should be added at least once a week to keep it free. Machine Maintenance Troubleshooting Chart for Light Duty Drop Feed Machine Trouble Probable Cause Remedy Needle breakage  Incorrect class and variety of needle being Use correct class and variety needle used Needle loose in clamp Tighten needle clamp screw Needle too small for fabric Use larger needle Operator pulling on fabric Allow machine to feed material Needle thread breakage Thread too heavy for needle Use larger needle or smaller thread Right twist thread being used Use left twist thread Machine incorrectly threaded Check machine for proper threading Needle thread tension too tight Loosen needle thread tension Thread take-up spring out of adjustment Adjust thread take-up spring Burr on bobbin case, shuttle point, or Smooth with emery cloth tension discs Thread rubbing against presser foot Adjust presser foot Needle is bent or has blunt point Replace needle Bobbin thread breakage Bobbin tension too tight Adjust bobbin tension Bobbin incorrectly threaded Thread bobbin to revolve clockwise Bobbin wound too fully to revolve freely Remove some of the bobbin thread Rounds of bobbin thread lapped over Ensure bobbin thread is straight when  one another bobbin  winding Bobbin case is dirty Clean and lubricate bobbin case Skipped stitches Machine out of time Time needle to shuttle Thread controller spring out of adjustment Adjust thread controller spring Drawing of seam Both needle and bobbin tension too tight Loosen needle and bobbin tension Stitches piled up Stitch regulator out of adjustment Adjust stitch regulator Pressure on presser foot too tight Loosen presser foot adjustment screw Feed dog striking Feed dog set too high Lower feed dog to correct height throat plate Figure 6-81.  Troubleshooting chart for light-duty, drop-feed sewing machines. 6-23