{HEAD ~ Each sliding frame} is provided with {TAIL ~ a pair} of rack gears with teeth facing each other and cam surfaces facing each other in parallel with a pitch line of the rack gears 
{ HEAD ~ Each sliding frame } is provided with { TAIL ~ a pair } of rack gears with teeth facing each other and cam surfaces facing each other in parallel with a pitch line of the rack gears
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH