I made a small dipole centre insulator from 10mm HDPE cutting board on the CNC router. HDPE is moderately UV resistant so should survive for some years outdoors.
The insulator is 100mm across its widest points. No provision is made for supporting coax, it is for use with home made open wire line which will fall from the dipole leg ends. If you want to use it with coax or ribbon feedline, then incorporate a tab to secure those lines.
The design was done in Freecad. Note that the holes were chamfered with a countersink bit after the CNC operations. That could be done on the CNC Router, but work would be required to index the part position when turned over… it is just quicker and easier to cut the chamfer with a hand held drill.
The project was more about testing cutting of the HDPE board than a need for the end product.
The insulator could be made with simple hand tools, but even easier with a jigsaw and drill.