I just noticed, you put the words "Sewing machine motor" in the tags for this question. A possibly better place for these words would have been in the body of the question itself.I asked Google Images to show me "6500 rpm 230 VAC sewing machine motor",https://www.google.com/search?hl=en&site=imghp&tbm...and from looking at some of the the pages it linked to, I am guessing that your sewing machine motor is a universal motor,https://en.wikipedia.org/wiki/Universal_motorAlso guessing that this motor will turn more slowly if you feed it with voltage source, with smaller RMS (root mean square) voltage, and the easiest way to do that is by using a lamp dimmer, the kind that uses a TRIAC, to sort of slice and dice the AC waveform. Wikipedia calls this kind of dimmer, a "solid state dimmer", here:https://en.wikipedia.org/wiki/Dimmer#Solid-state_d...It is convenient to put the dimmer and outlet in a box together, like done in this instructable,https://www.instructables.com/id/10ish-DIY-Variabl...That 'ible uses connectors a NEMA style outlet made for use with 120 VAC mains power, like that found in the Former US, and maybe a few other countries. I am guessing the version of this dimmer box, built for mains power in your country would be made with a 230 VAC dimmer, plus 230 VAC outlet.As anecdotal evidence, I can say that I personally have used a lamp dimmer to slow the speed of some 120 VAC motors. Specifically, I have tried this with a vacuum cleaner motor, and also an electric mixer kitchen tool, both of those intended for use with 120 VAC. There is kind of a certain range over which this trick will work. I mean if you turn the knob on the dimmer too low, the motor will just stall and buzz.Be somewhat wary when trying this out for the first time. By that I mean, be ready to unplug it quickly, if there is evidence of excessive heat, or smoke, or overly loud buzzing with no movement, etc, coming from your motor.