For the home sewer who expects to do a great deal of sewing using heavy fabrics such as denim or canvas, the best thing to do is to purchase a heavy duty sewing machine. Singer makes several and most are moderately priced in the $200 to $300 range. They include accessories for most sewing tasks and can work with normal weight fabrics.
For someone who only needs to sew heavy fabrics occasionally, it may not be worthwhile to have a second machine. There are some things you can do, however, to help a standard sewing machine handle the rough stuff.
First, be sure to use the correct needle size and type. If you are not familiar with needle sizes, do some homework. Needles for heavy-duty fabrics will be at least a size 14 or higher. Also, do not use a ballpoint needle, intended for knits, with woven fabrics such as canvas or denim. Some needles are marketed for special purpose sewing. You should be able to find needles labeled for denim, canvas and leather at any sewing or fabric store. And do not expect the needle to last very long. Be prepared to use a new needle after only a few hours of heavy duty sewing.
Also important is thread size. Look for threads labeled for heavy duty sewing. Upholstery thread, carpet thread or button sewing thread may be appropriate for your task. These threads will not come in the full range of colors you see in all-purpose threads, but you should be able to find a close match.
Don’t expect too much from your machine. If it has a speed selection lever, set it to the lowest speed. If there are several layers of fabric you may need to turn the hand wheel manually to assist the motor. Do not let the machine overheat or you may burn out the motor.
Consider alternative construction methods. If you cannot do a flat fell seam, common on jeans, sew a regular seam and add additional rows of stitches to approximate the look. Use rivets, available in fabric stores, to reinforce stress points and also as an attractive accent.