TPT January 2018

AR T I C L E

Advanced Machine & Engineering/AMSAW

Innovative devices to maximise carbide saws’ blade life By Willy Goellner, chairman and founder – Advanced Machine & Engineering/AMSAW, and Christian Mayrhofer

and spindle. If the backlash of the spindle gear is only 0.05mm (0.002") and the spindle gear is 300mm (12") in diameter, the backlash increase on a 2,000mm (80") diameter saw blade is

Proven methods for minimising backlash and reducing vibration during the carbide sawing cycle, to reduce the cost of carbide sawing.

0.05*2000 = 0.33mm (0.013") 300

The sawing process It is nearly impossible to design a perfect machine that will eliminate all vibration problems and negative influences in the machine structure. However, many negative influences can be overcome with innovative devices, which will minimise the problems. In previous articles we analysed the effect of torsional vibration, the compliance in the drive, and proved mathematically the negative results. In this article, we will demonstrate how machine designers have introduced devices which will help to improve the cutting process. The most damaging aspect of the sawing process is the entering and exiting of the circular blade into and out of the material. The circular blade enters and exits the material with only one cutting tooth. So, when the first tooth enters the cut, before any cutting begins, the tooth is momentarily halted while the backlash and part of the compliance of the gear train in the head is eliminated. This is comparable to winding up a torsion spring, and the actual cutting does not happen until the spring force exceeds the tangential force required to cut the material. When the stored energy (the torsional spring windup) of the first tooth is released, the next tooth of the blade accelerates into the material, causing it to hammer into the material. This “hammering effect” at the beginning and ending of the saw process can be very damaging to the carbide teeth. When there are more teeth in the cut, the fluctuation in the gear train is reduced and the sawing process becomes more stable. Saw designers have come up with several different devices with varying complexity and cost to minimise these problems. Method 1 – backlash reduction by a split spindle gear (Metalcut) A saw spindle is always running slower compared to the drive motor and requires several gear reductions between motor

Therefore, the backlash effect on the carbide tip of the blade is more than six times the gear backlash and is very damaging to the carbide teeth. The teeth of a helical gear contacting the mating gear must have a slight clearance to function properly. Holding a tight tolerance between the pinion and gear centres in the gear case and the tooth tolerance of the gears is costly and must be avoided. A relatively simple and less expensive way to minimise the backlash is to spread the helical-gear teeth against the teeth of the helical solid pinion gear. By spreading the split gear section, the backlash between the pinion and gear sections can be reduced to nearly zero. Using a spacer between the split gears allows the backlash to be set to a desired minimum value, and the two split gear portions can be locked with the locknut.

Figure 1: Backlash elimination by spreading the spindle gear with a spacer (used on the first Metalcut 12 carbide saw)

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JANUARY 2018