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RSC Tolerances for Case Erectors and Packers

May 27, 2022

Brian asks:

Do you have any printed information, such as TAPPI, PMMI, FBA, regarding tolerances for RSC’s that you can share with me?  We have a customer that purchased a box erector/packer/taper that sometimes jams up and they would like to know what the tolerances are for the boxes that we manufacture for them. Any help would be appreciated.

There are industry guidelines, but they are just that…guidelines. Tolerances can be customer specific and should be considered when estimating a job. Then you consider your capabilities. What tolerances can your equipment hold from feeder through counter-ejector? Probably not your case, but if you’re diecutting RSCs, what tolerance does your diemaker guarantee?

The FBA Handbook discusses these tolerances and provides guidelines for carton tolerances and may be purchased at (Store Products – Fibre Box Association).

The PMMI/FBA publication PMMI B155-TR2.2-2011, recommends that any RSC panel, when measured from scoreline to scoreline should not exceed ± 1/16” (1.5mm). It also recommends that the overall length of the blank should not exceed ± 1/8” (3mm). From specified size of course.

The PMMI document also recommends that slot depth should vary no more than ±1/8 (3mm) from the centerline of the slot (corrugator) score to the tip of the slot. Slots should also be aligned within 1/16” (1.5mm) of the centerline of the aligning (relative) score.

The PMMI/FBA publication PMMI B155-TR2.1-2011 offers some tolerances for the manufacturers joint (MJ) which, as we know, is most important to creating a square box. Measured at the flap (corrugator) scorelines, the MJ should not be less than 1/8” (3mm) or larger than ½” (12.5mm). Skew or fishtail should not exceed 3/16” (4.5mm), again when measured at the flap scores. At no point along the MJ should the opening be less than 1/16” (1.5mm) and the alignment of the flap scores should not exceed 3/16” (4.5mm) at the MJ.

TAPPI has a very wide range of documents and specification available to TAPPI members, but in reviewing the lists we couldn’t identify any document specific to RSC tolerances. (If anyone know of such a document, please share the name with us.)

Now of course, case erectors and case packers are going to want the box as square as absolutely possible. Perhaps equally as important is the consistency in size. We can often compensate if we are consistent. It’s when sizes or tolerances jump around that it becomes difficult to keep an automatic line running.

We also have to be cognizant of tolerance stackup. If we look at the tolerances above, the overall blank length can vary ±1/8”. So that’s a total of 1/4″. Now let’s add in the manufacturers joint. According to the specs we can be as small as 1/16” and as large as 1/2”. Now, we rarely see the MJ vary this much, but it can happen. Then, there is fishtail to consider. Remember that these tolerances tend to stackup, a combination of MJ width variation and fishtail can cause nightmares for case erectors and packers. This is especially true if the stackup causes the flaps to come into contact with each other.

We reached out to a few case erector/packer manufacturers, but it was hard to get a ballpark reference because of the number of possible variables from the squareness and size of the box to the forgiveness of the product being packed.

— Ralph

 

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