how do you set a constant print speed for everything?
Need to print TPU and need to set a constant speed of 15-20
Can anyone please help?
Which printer have you got? Which slicer are you using?
The Prusa MK3s
If you need absolute speed control with every move being at the same speed, set those limits under Print Settings->Speed. If you just want to slow everything down when printing TPU, try reducing Filament Settings->Advanced->Print speed override->Max volumetric speed (MVS). I prefer adjusting MVS for each type of filament as it saves having to tweak a bunch of printer speeds. MVS determines an upper limit for speeds based on filament flow, and will reduced print speeds as needed to stay below that level.
As you make these changes, slice the part, then spend some time in preview mode verifying that the speeds are staying at or below the maximum you want.
What would be a good speed to set it to for most TPU's?
You can always set MVS very low (Colorfabb XT-CF20 uses MVS set to 1) and work up if that works. I'd try a small print at successively higher MVS rates.
Also be sure your extruder tension screw is as loose as possible when printing flexibles.