Some of the common causes of slipstitches with a sewing machine are :-

• Using a blunt needle
• Using a bent needle
• Using a needle which is too thick for the fabric being sewn
• Using a needle which is too thin for the fabric being sewn !

A bent needle will be carried away from the point of the stitch forming device under the needle plate and prevent a stitch from being made.

Particularly with a fine, knitted fabric, using a thick needle has the same effect as a blunt needle - it will push the fabric downwards. This is usually worse when using a zig-zag machine with the wide slotted hole in the needle plate. If you don't have a thinner needle you may have a plate with just a plain round hole for the needle, try using that.

If you are sewing heavy material, such as denim, too thin a needle will be easily deflected and have the same effect as a bent one. You should use at least a size 16 (100) for this, if not 18 (110).