. It is not a good to have an iron on the same circuit as the sewing machine. The machine is constantly getting high and low power going to it like a wave as the iron heats, stops, heats again to maintain the temp setting. Especially the irons with no auto shut off that sit and go off and on constantly to heat. I don't think any machine has a power regulator installed.
The machine will be harmed before the iron will. This is important if you plug a iron to the same ext plugs at a class as your machine.