Filament dia. problem

Hi everyone,

I make polymer filament using my home-made version filament making machine (with a small winding machine).
The problem is that the filament diameter varies from 1.5 - 2mm, and it's not good for the printing. I plan to make a tube which has 1 end is 2.5mm and the other end is 1.75mm so that the filament will be squeezed to 1.75mm when it still hot.

I'm using shape memory polymer, polyurethane.

Anyone has an idea for this problem, please feel free to share.

Thank you for your time.

I read into filament making, and from what I remember people where having the best results when they had a very exact rpm on the winding machine and were pulling the filament through water. Faster rpm= thinner filament, slow= thicker. Though you probably already know and do this..

I suppose a tube could work but how is it leaving the second tube any different from leaving the primary extruder? Would the filament be cooled already at a larger diameter then cold extruded through the tube, or still warm? An interesting project, if it works out well I may look into one of my own.

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If you need some help, or don't understand what I just said, feel free to send me a PM anytime

Printer: Prusa i3, 2 E3D v6 Hotends, Arduino + RAMPS 1.4 with a Bypassed 5V Regulator, 400w Insignia ATX PSU, Custom Designed Bowden Extruders