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]

Reply to RGP

Reply to RGP

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]

Re Alferrai

Re Alferrai

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]

re John and Al

re John and Al

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

 

[ondemandbindery]

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

For purposes of consistent makeready's on the folder you should change the paper for every job. With that being said, there are plenty of gray areas in the topic but for your sake we have to go to basics. As for the second caliper, it absolutely will make a difference. But yes, you answered the question properly and that is what I was after. Remember, you need a correct amount of pressure to pull the substrate out of the plate and not cause a potential wrinkle. All rollers needs to be set properly for each job as they can all have cause and affect on any given substrate. Here is an example of proper caliper settings for a Trifold using the 1 and 3 plate respectively. The would be for a 4 buckle plate folding machine like the one in question:

caliper 1- 1 sheet
caliper 2- 1 sheet
caliper 3- 1 sheet
caliper 4- 3 sheets
caliper 5- 3 sheets
knife shaft- 3 sheets

Do a time study and watch 100 sheets go through the guide keeping your eyes on the notch where you can see the sheet edge as it goes into the folder rollers. Just want to make sure we are absolutely on the same page.

John Weaver

 

[RGPW17100]

By adjusting the infeed on my original post I meant the adjustment that scews the sheet going into the folder. If gates are square and fold is crooked it should be adjusted using this instead of scewing the plates. This will insure the sheet is going into the folder straight. You might want to go back to putting one sheet of thin stock in all the calipers again. Then take three thin strips of the same stock and put one on the operator side one on the non operator side and one in the middle. Check all the rollers this way including the slitter shafts. You might have a bent roller and may not be getting good grip in the middle. Also remember on a stahl with the rubber segmented rollers you want very little pressure on the sheet when setting the calipers. Setting them too tight will wear them down faster and can cause bad folding

 

[Al Ferrari]

"Point 2/3 Not totally clear about this."

The numbered collars I referred to are illustrated on attached pictures 3 and 5.

Picture 5 also shows the approximate location of the witness or alignment marks used to set the paper stops to square for each fold plate.

"The fold plates on a Stahl do not appear to have any means of setting the two halves of a plate apart."

See attached picture 6. There two of these knobs on each fold plate. There are also scales along the sides of the fold plate to show the amount of movement, but I was not able to find pictures of these on the web.

These screen captures are from YouTube videos about folding machines with my call-outs added in Acrobat pro and new screen captures made to include the call-outs. You may need to zoom in/out to improve the focus.

There are an impressive number of such YouTube videos. Unfortunately they are of very poor quality and with little or no voice over commentary, so that one is left wondering what these well intentioned posters were hoping to accomplish with their efforts.

Al

 

[Leedsprinter]

Hi Al,

Yes the knobs you show on pic 6 are for setting the throat, so yes I know those. Your point 3 refers to spacer washers. That I am not clear about.

Thanks for all the trouble you are going to on my behalf.
Peter

 

[Al Ferrari]

Peter and others,

I am assuming that since you say the rollers were professionally resurfaced and reinstalled, that the bearings were also replaced as new. Therefore we are investigating operator settings that may be incorrect in the use of an otherwise sound machine.

Please disregard that point 3 of the three points under fold plate. I forgot that in Stahls the back part of the fold plate, or pan, fits inside grooves in the main plate, and that the gap between the two fold plate halves is generally not changed.

But the knob in picture 6 is entirely relevant to crooked folding. There are two of these on each side for each fold plate and it is possible with these to have the pan set crooked, causing the problem.

Also, do you catch on now about the numbered collars which are easily disturbed and useful only for immediate small adjustments and not to be relied on for resetting the roller gaps to a zero or standard position?

Likewise with the paper stop on each fold plate. Use the factory set alignment marks, or witness marks on picture 5, to set that square. Do not rely on the marks on the two halves of the overall fold depth adjusting knob to set the paper stops square. There are two of these marks at 180 degree on each knob, and when one is on, the other is off a small amount. Like the numbered collars, these are only useful for gauging small local moves.

Al

 

[Al Ferrari]

Re-reading the first post in this thread, I now see that a "professional" install of the rollers with the new rubber was not actually mentioned, and it may have been unwise for me to assume that. So if none of the operator suggestions made so far yield substantial improvement in the consistency of squareness of folds on the first unit, we should consider the possibility of one or more of the rollers in that unit having end play (side to side play).

Al

 

[Leedsprinter]

Results of work on folder

Results of work on folder

Hi guys,

I have been working on the folder today applying the sum of your advice, with encouraging results. I have been running test paper of the weights and sizes we usually use and have got good folding. I have found that contrary to my expectation the fold is better at higher speed, also that steel balls work the best. I have been concentrating on getting the paper square on entry as you seem to suggest. I also believe that two or three thicknesses in the calipers, opening the rollers a bit more is better. I intend to run the next few live jobs myself so I can apply what I have learned. I will let you know how I get on. Thanks for your advice as I feel now I have somewhere to go.

Once again I am very impressed by your willingness to help as well as your obvious technical knowledge.
thanks,
Peter

 

[ondemandbindery]

I am still waiting for his response about the consistenct of the sheets in the side guide in a 100 count or so cycle. I have not seen where this has been verified. Just a side question to all this. Is your coated substrated really poor in quality as compared to an uncoated stock? By saying that if you speed the machine up the quality improves is of concern but atleast you are working on some different ideas.

John Weaver

 

[Leedsprinter]

Hi John,

Yes I have watched 100 sheets going in and all pull over well as far as I can see. All the paper is of good quality, though I hear from one of the lads that that the more ink on a sheet the more probs. I am sorry I haven't tries a larger sheet yet as you suggested, but as that will go with the grain my guess is that it will run ok. That fold is where I have least trouble-ie with the fold running parallel with the grain.
Best,
Peter

 

[ondemandbindery]

Hi John,

Yes I have watched 100 sheets going in and all pull over well as far as I can see. All the paper is of good quality, though I hear from one of the lads that that the more ink on a sheet the more probs. I am sorry I haven't tries a larger sheet yet as you suggested, but as that will go with the grain my guess is that it will run ok. That fold is where I have least trouble-ie with the fold running parallel with the grain.
Best,
Peter

For the moment I will say that everything is in order prior to going up into the Rollers. So lets talk about grain direction. If you have 20 jobs you are processing through the folder, how many of them are against the grain? What is the weight basic of the substrates you are trying to fold against the grain.

John Weaver