Thanks for your input!

Indeed I struggle a bit with the low torque on "larger" steel parts. When I bought the VFD for this project I chose a model with vector control since I read that this type of control would allow for near full torque at low rpm. Unfortunately I don't see much difference with it on or off, hence my assumption that something could be wrongly configured on the VFD. I will try your advice to go back the original pulley ratio and increase the VFD frequency to still maintain the top speed. Do you also have an EMCO 120?