As the cluster idea will take a while longer (making it a summer project), to pass the time, why not bolt a cutting disc to one of the spare drill motors without the gearbox?. I understand I won't give optimal torque, but it seems easy enough and would b great to slice into HDPE. the question remains, vertical or horizontal? vertical can concentrate a cut into a smaller area (putting less strain on the disc and cutting deeper potentially) or going horizontal (larger area but less effective cuts)