Stahl folder inconsistent folding

[Leedsprinter]

I have a Stahl folder, B2 size with 4 parallel plates and a crossfold which I rarely use. We use it mostly for the simplest folds, a single fold A4 to A5 or a roll fold A4 to DL. The problem is that the folding is inconsistent, never consistently accurate. It will throw out slightly top and bottom throughout the run. This happens on all weights and finishes. The machine is probably 20 - 25 years old but I can see nothing wrong with the engineering, no worn gears etc. The rubber segments on the rollers have been recently replaced and the feed belt is not old. I have tried various combinations of balls.
Thanks for any advice.

[ondemandbindery]

You are giving a broad statement that it will not hold any type of fold which even the worst of worn out folders can make some type of magic happen on atleast one type of fold. So lets get the basics out of the way. And the age of the machine has no bearing on your situation. Just the condition of a few parts.

1-Was a qualified person responsible for reparing the rollers as well as the side guide belt?
2-Have you watched the sheet in the side guide to see if it is consistently holding and is the guide square to the rollers?
3-Has the side guide been replaced (a groove will develop over time)?
4-Are you having this problem when folding with the grain?
5-Does this change with run speed?
6-Are you positioning the side guide to the substrate so that it has adequate to correctly get into the side guide.

Some of these are basic questions but we all can not see the forest for the trees sometimes. Most of the problems people have begins in the side guide. That truly is the first step. Moving the balls around absolutely can have an affect on the consistency and quality of the folding. But there are many variables to that. A good rule of thumb is to not have all steel balls in the guide on the roller end of the unit.

If you have a groove problem in the guide, you can run the machine at minimal speed and it will most likely still fold ok. Start to put some speed to the machine and this problem will quickly show up.

Past that, there are other questions I could ask but you have to make sure the sheet is consistent and correctly getting to the rollers before anything else can be looked at . There are some other things you can look at once the substrate goes into the rollers but lets make sure this is not a sheet guide/control issue prior to folding.

Good luck,
John Weaver

[RGPW17100]

Look at your lower fold plates and make sure they are in all the way. I have seen where one is slightly out and it can cause the problems you are describing. Also there should be etching in the fold plates that you can use to square the fold plates. Verify these are straight then with the delivery scewing make sure that is centered. Is the fold straight or do you need to cock the fold plates or screw the delivery to make the fold square? First and the most important make sure the sheet is square. If your cutter is not square you will not be able to fold very well.

[Leedsprinter]

Dear John,
Thanks for your amazingly prompt reply. I am impressed!! I agree that the age of the machine shouldn't have any bearing as long as parts are not worn out. Our strength lies on the printing side and we are all a bit weak and inexperienced with folders, hence the request for help.
1. The probs antedate the re-rubbering and I put it down to worn rubber. The rollers were re-rubbered professionally by a roller company and taken out and refitted by me. I set the roller pressures and I have tried all sorts of settings. The feed belt was changed by one of the lads, not an engineer. It appears to be self-tensioning. Am I right?
2. I have paid careful attention to the sheet entry at the notch on the guide and it looks perfect to me. I have centred the guide and also tried it at different angles.
3. The side guide has not been replaced. It is almost certainly as old as the machine.
4. We do have the problem folding with the grain but I think to a lesser extent and I think it is less with lighter paper eg 80gsm. Inevetably as we print B2 A4s are always cross-grain. Mostly we fold 130 - 170gsm, usually silk.
5. It seems no better even at the lowest speed (or the top speed)
6. I have been careful to have the paper in the feeder the right distance to pull accross into the side guide, and I have adjusted the distance of pull to no avail.
Originally I put the problem down to lack of grip in the rollers, hence the re-rubbering, then I have tried any combination of plates, then I have looked at sheet entry. Can't see anything wrong but I am convinced that a solidly built and engineered machine like mine should fold beautifully. Our Heidelberg presses of a similar vintage print excellent work every day, but as I say they are operated by professionals, which I admit is not the case with the folder, though we do at least know how to set up a simple roll fold. I have had a general print engineer have a look but he just said 'well what can you expect with an old machine?' I don't buy that myself.
Thanks again for your help.
Peter

I have tried a mixture of some steel, some plastic and all of each type to no effect.

[Al Ferrari]

@RGPW17100: Can you please amplify your comments about the influence of the delivery on the folding?

@Leedsprinter: I agree with ondemandbindery's insistence that you assure that the sheet is traveling straight before entering the fold rollers. Use the sheet viewing slit at the end of the guide to follow the travel of the sheet. Make sure that you do not have an over guiding condition due to an excess of heavy balls, and/or the sheet entering the guide too far away to be effectively guided.

Post back when you have eliminated the sheet travel along the side guide as a source of the problem.

Al

[Leedsprinter]

Thanks also to RGP for your fast response.
I have checked that the plates are well home and that all the settings are square. The problem is in evidence even with only one plate in use. I have tried swapping plates and different routes through the folder. I am sure the cutting is square and as we have 2 guillotines you would think work off one might be out but not both.
Thanks again
Peter

[Leedsprinter]

Dear Alferrai,
Thanks for the advice. The help from the forum is very impressive!!

I will pay particularly close attention to the guide/entry if that seems to be where I should be looking for the cause. It all looks ok to me but...
Thanks again,
Peter

[Al Ferrari]

From your 2:56 PM post it sounds as though your side guide use is not the problem.

Let's go on to the fold plates and rollers.

In addition to being set squarely in the machine, there are at least 3 concerns about the fold plates:

1. Each fold plate needs to have the paper stop set square to the witness marks on the top of the plate. Variations from this can be made to compensate from some other source of trouble, but should be returned to squareness at the start of each job set up.
2. Each fold plate needs to have the the lower part, called the pan, set square to the top part, and set at the middle of its range (unless there is particular reason to set it differently).
3. Each fold plate needs to have the spacing between the two halves even from side to side and front to back. this is accomplished with spacer washers.

These last two are often ignored by inexperienced operators.

Now the fold rollers:

1. Each fold roller gap needs to be set even from side to side with ONE sheet of stock in the gap sets without regard to the numbered collar position.
2. After this is done, the numbered collars can each be set to 0 without altering the gap setting itself. This "calibrates" the gap sets, which can now be used to set the gaps for the required number of stock thicknesses that will pass through that roller gap in the particular job.
3. In the case of uneven length legs from a prior fold, each gap should be set to the least number of stock thicknesses passing through that roller gap in the particular job, so as to achieve proper drive force into the next fold plate. This will result in a roller bounce for that gap, which is OK.

Post back to report if attention to these points does not result in an improved performance.

Al

[ondemandbindery]

Ok. Let me ask you another question. If you are absolutely sure that you are consistently holding into the guide and you were to take a 11x17 and fold it to 8.5X11 (half fold) with a 50lb offset stock will the fold be inconsistent? Also, if you have the rollers set properly please tell me the sheet thickness in your 1 and 2 calipers?

John Weaver

[Leedsprinter]

Thanks guys.
John-50lb is 130gsm? I will try and let you know. 1 sheet in 1st caliper,2 sheets in second.
With 1 fold, the second caliper is irrelevant, right?

Al- Witness marks, I am afraid i don't know the term but I will have a look and double check all is sq.
Point 2/3 Not totally clear about this. The fold plates on a Stahl do not appear to have any means of setting the two halves of a plate apart. The two halves can be moved front to back relative to each other and that is centred.
Rollers are set with 1 sheet as you describe. Then the relevant thicknesses in each caliper. I think for the simple folds we do only 2 sets have any effect on the fold. ?

I will have a play tomorrow and report back.
Once again thanks to all for your advice.
Peter