A tip for signature folding.

[Al Ferrari]

Some times it seems as though in spite of having folded and scored squarely on a prior unit, the folding on the next unit varies a bit more at the foot than at the head, which suggests that the paper stop on that unit may not be square.

But before resorting to adjusting the split dial to cock the paper stop, try small adjustments to the over all setting in either direction on that fold plate to see if there is an improvement in the consistency of the fold at the foot (trials of 10 to 20 sheets are recommended). You may find that consistently square folding can be attained with this over all adjustment alone.

The explanation for this follows:

The purpose for scoring in preparation to folding is to weaken the stock at a location corresponding to where the fold will take place. Accurate folding depends on having the two correspond precisely.

At the ideal combination of score and fold plate settings, the weak point location = the fold setting distance for both head and foot.

But for signatures, a prior fold imparts a stiffness to that edge of a folded sheet which is lacking at the opposite edge if there is no fold there.

Thus this greater stiffness contrast at the head of the signature allows for some non correspondence between the fold plate setting and the location of the score or weak point on the signature compared to the stiffness contrast at the foot. This is why this tip works.

But none of this diminishes the importance of square folding and scoring on the prior unit, or of the squareness of the cross carriage side guide on the next unit. It is always best to start with all side guides square to the next bank of rollers and the paper stops square to the witness marks on each fold plate.

 

[princecraft24]

Please help me having problem perfing. The perf. is very inconsistant. Have tried arranging marbles in s.g. roller tension is good. folding on a mbo 26. Older but not sure how old. there is a new belt on the s.g. any thoughts?

 

[Al Ferrari]

Sorry that I was not able to respond sooner, but I spent all afternoon, you guessed it, running the folder. That's not my full time duty, but it was what I had to do today.

But let's see if we can solve your problem:

Are you running text or cover stock?

Now you must check to see that your side guide is square to the rollers. Do not just assume this: check it by hand feeding an 18" wide sheet with square corners at the lead edge and adjust the angle of the s.g. as the sheet is just about to enter the rollers.

There should be an open grove about an inch or so in length at the end of the side guide, just before the sheet enters the rollers, so that you can watch the edge of the sheet as it runs through the s.g. Generally you can observe the variation right in this slit when the stock is not guiding properly. Run several batches of 10 or so sheets at various speeds while watching the edge of the sheets go by at this slit.

There two ways for the stock to vary at this point:

1) either it is not pulling over consistently, because your feeder pile is too far away from the guide or

2) it is pulling excessively because you are using too many heavy balls on light stock, and it is tending to bunch up into the s.g.

For problem 1), build your feeder load closer to the s.g. A 3/16 to a 1/4 inch is a good range. If your problem is this one but with heavy stock, then use more, or all heavy balls.

For problem 2), switch to light balls and again, build your pile close to the s.g.

For the amount of information you have provided, this is what I can offer. I hope it helps.

Al

 

[princecraft24]

Thank-you so much for the reply.I was observing, the sg today. And noticed that the guide belt is moving around, from side to side. I think that this is part of the problem. The stock that Iam using is 60# gloss. I think that the roller bearings in the guide belt are bad. The belt should not move from side to side. Correct? The belt is a new belt. Again thank-you so much for the help.

 

[Al Ferrari]

That was a keen observation. That could very well be the whole of your problem, if that belt movement is severe enough. The intended function of the s.g. belt ,working together with the marbles, is to create a constant pressure on the sheet in the direction of the guide.

So if the belt were to move away from the guide AFTER the sheet has already settled against the guide, it could move the sheet away from the guide producing the observed inconsistency.

You should get those bearings on the belt rollers fixed before trying anything else.

Al

 

[princecraft24]

yes I will get the bearings fixed asap! It is so nice to know that there are people like yourself. Out there that are willing to help. Again thank-you for everything!

 

[ondemandbindery]

Do yourself a favor and look at your sideguide for a groove on the inside where the paper runs. Depending on the age of the machine you may very well want to consider replacing that also. This is typically the single biggest problem I see people deal with on folding machines when the registration in inconsistent.

Good luck,

JW

 

[princecraft24]

I will look at that more closely. Thanks for the great advice!

 

[Jedo]

I havr similar problem, ever sheet either slips position and on job where i use perf 9 times out of ten will always be squint. The rollers are new and genuinly set ok but to square perf up have to sometimes run it at 4k and tighten one side rollers up alot tighter and then will still vary. Can this be caused by the belt on side lay?