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Tolerance for Manufacturers’ Joint on RSC

By Ralph Young

October 12, 2023

Xavier asks:

Is there a formal guideline in Tappi or else, that refer to the tolerance of the in and out on the gluing panel of a rsc on a flexo-gluer?

Most of the case erector maker establish guidelines of their own for single or double wall but is there a standard written.

See the tolerance I’m referring to in the image below attached here,

Looking at your illustration, it appears you are asking about the Manufactures’ Joint. I’m not sure if there is an actual TAPPI rule or specification. (if there is maybe one of our readers can help us out) The general rules that boxmakers in our industry try to live by are,

  • Measuring from the flap score line (A, Figure 1), the width of the gap should not be less than 1/8” or greater than 1/2” inch. 3/8” is typically the target.
  • Skew or fishtail – the tapering of the joint in either direction (Figure 2) – should not exceed 3/16”. This would be the difference of the gap when measured at the corrugator score (A) and compared of the gap measurement of the same gap at the ends of the flaps (B).
    • Regardless of the amount of taper (skew or fishtail) the gap should never be less than 1/16”.
  • The corrugator scores of the two panels forming the manufacturers’ joint should also align within 3/16”.

This last bullet is important because typically when we see fishtail the two panels are either being pushed forward or backward in machine direction, thereby causing a tapered manufacturers’ joint. The corrugator scores may align but the gap is tapered.

However, if sheet control is lost somewhere through the press or when it enters the folder-gluer, this can cause a situation where one panel is folded forward (in machine direction) and the other is folded backward because the blank is not feeding straight through the machine. Now your gap may very well be straight (not tapered) but the corrugator scores don’t align and the box is not square.

Critical measurement points for manufacture's joint on RSC

Figure 1: Critical measurement points

RSC with fishtail at manufacture's joint.

Figure 2: RSC with fishtail at manufacture’s joint.

Manufacturer's joint on skewed blank

Figure 3: Manufacturer’s joint on skewed blank

Figure 3 Close up

(Figure 3 Close up of mis-aligned corrugator scores)

– Ralph

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