Straightening

A blade’s back should logically be straight. The straightning is checked thanks to a 1.20 or 1.50 meter rule.

For single cut blade, it is possible, even it is recommended, to curve slightly the blade’s back. This would allow to lenghten the back of the blade respect to the toothed part, so the part would be more tensed on the pulleys. Moreover, when the blade works, it becomes overheated on the teeth side consequently the blade lenghtens.

N.B : Straightening has an influence on the tension. It means that this two operations are indissociable.

A straightening defect will be corrected more easily if the blade is sufficiently tensionned. It is better to tension more than necessary on the side where the straightening will be corrected. This excess will disapear when correcting the straightening.

When the rollers pass over the blade it must be at least at 15 mm on each side.

Clearanced back

Curved back

Correction of the clearance

Correction of the curve

Correction with files

When reparing a blade, it can have a defect named « out of true ».

This defect show that a part or a side of the blade is lenghtened consequently the blade takes the shape of an helix.

To check the defect, it is necessary to raise the middle of the blade.Then we realize that the sides are crossed.

RIGHT UPPER SIDE COMING TO THE SAW DOCTOR

If the toothed part is longer than the back : there is a bad out of true. The toothed part raises on the levelling bench

LEFT UPPER SIDE COMING TO THE SAW DOCTOR

If the back of the blade is longer than the toothed part, there is a good out of true. The left upper side comes to the saw doctor.

To true a blades, it is necessary to pull out of true the upper roller.

For picture A :

= lower roller B = upper roller

For picture B :

= lower roller B = upper roller

Then tension and straight the blade.