Sewing Machine Tension Problem

[Fredathetortoise]

I have a Frister and Rossman sewing machine, 20+ years old but not heavily used. For some years it's had (or I've had) problems with the top thread tension being too low, even when the dial is right up to 9.

I had the machine serviced recently, everything was fine, did one small hemming job, all OK; second project today (new canvas handles on a shopping bag), top tension is loose again.

Does anyone have any suggestions as to what I'm doing wrong, please? I'm using medium weight canvas, and a medium cotton thread with a normal needle.

Many thanks for any suggestions.

Can you ask the place that serviced it? If it worked just after they had it then stopped working I would assume they tightened something (tension disks?) that has loosened off again so either they didnt tighten enough or the part needs replaced.