Theoretical and practical aspects of circumferential pick spacing on boom tunnelling machine cutting heads

The effects of equally arranged circumferential pick spacing on boom tunnelling machine cutting heads are described, through a series of laboratory and in-situ trials. The equal circumferential spacing is emphasized to be an important parameter significantly influencing cutting head balance and is limited by the total number of arcing picks and tool-lacing. A number of alternative lacing patterns is outlined and then compared in terms of cutting efficiency and manufacturing feasibility. The long-term practical investigations indicated that within the size of the commercially available tool-holders, up to 26 or 27 heavy-duty picks may be laced at equal circumferential spacing on medium-duty roadheader cutting heads. The problem of tool-holder overlapping was further found to reduce with a threestart arrangement employing a higher angle of wrap. The underground trials also indicated that threestart cutting heads laced with a total of 24 arcing picks may not be so efficient at higher arcing speeds as the other heads investigated.