support member 69 is provided opposite the backing layer l from the clamps 70 to provide support for the backing layer the support member 69 is controlled by cam member 73 and is cleared from its support position as the backing layer l is advanced the yarn bit clamp 70 is shown having hollow shields 71 into which extend the needle 30 of each needle pair which is closest to the yarn adjuster 62 the shield serves to prevent impalement of the yarn by the shielded needle 30 as it descends in close proximity to the yarn adjuster 62 the yarn adjuster carrier bar 66 is shown having channels 68 through which the bit clamps 70 are permitted to reciprocate as does yarn adjuster carrier bar 66 although independent of each other the bit clamps 70 are secured to bit clamp carrier bar 72 which is shown housing spring means 74 supported by flange support 148 for each of the individual bit clamps 70 as shown in fig1 cam 75 provides the vertical reciprocation for carrier bar 72 a laser 76 is shown which will be positioned on one extreme side of the machine while a photo detector 78 will be positioned at the opposite side of the laser aligned therewith so that the laser beam may be used to.