Windmill losing impressional strength

I was running a die cutting job on my windmill today and kept having to increase the impression every 15-20 sheets because the die stopped cutting through.

Also, the press was making a faint clunking sound that seemed to go away, but when it did that was when the impression went too.

What could be causing this and what do I do to fix it?


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Check the shear collar at the rear of the machine, just below the access door.
Does the centre bolt move more than the width of a coin, when the machine is running on impression?
If so, the shear collar needs replacing.

If you check your impression lever, grab the ball and try to turn it to the right, sounds like it is loose as it loosens the impression gets weaker, back impression off if this is the case. I have a windmill that does this and i have to check to make sure its not backing off. If this is not doing this than refer to Bern, shear collar. Dick G.

@Bern - We did exactly as you said and the nut is not loose at all

@DickG - Turned the impression lever as you suggested and it isn’t loose either.

I typically run fine text/line art at a little greater than 1, and large solids, a little over 2.5. I don’t run too deep of an impression usually and I use hard packing.

Is there any way this could still be the shear collar? Or is this indicative of a larger, much more expensive problem?

Does this problem occur when you are printing as well?—or only when die cutting? Have you done much die-cutting? In my experience, when die-cutting, it is usual for the die to “bear-off” at the start of a run; that is, to be cutting completely the first few sheets, and then, usually within the first 125-130 sheets or so, to stop cutting and require more pressure. I do not know why this is, but I have experienced it on a number of small and large Heidelbergs, and think of it as normal. Same for kiss-cutting (face-slitting). After 125 or so sheets and re-adjusting impression, things are fine—the job is “run-in”.

It is quite typical of a die-cutting job to “pop”—that is, to make a popping noise while running. In fact, I listen for this as a sign that it is cutting—if it stops, I know that it has stopped cutting, or run a double.

Hope this helps, Brian

Are you using a cutting jacket on the platen?
If not, what exactly are you cutting onto?
The receiving surface needs to be steel.

Thanks for your reply, Brian. As far as I can tell, it hasn’t backed off while printing. It does, however print somewhat unevenly left to right on a 5”x 7” -ish solid – the impression is heavier on the left side of platen and lighter on the right.

I haven’t run a ton of die cutting jobs, mostly business card stuff. This is the largest die I’ve used (5.5” x 8.5”) yet.

If you die cut you must use a die cutting jacket or you will ruin your platen. If you are cutting into a hard packing it will stop cutting after a few impressions. Dick G.

Yes, I use a die cutting jacket always. The hard packing comment was made in reference to printing. I thought that maybe it was pertinent to add that I don’t overdo it with the press and have never locked it up.

I apologize for being unclear and thanks again for the replies.

Did you put anything behind/underneath the die in order to level impression? If so this stuff might have gotten compressed or the die worked itself through the material. There is leveling tape (“shim tape”) made out of very thin stainless steel (0,05mm) for that purpose. Completely unsuitable is paper or scotch tape…
So, this was blind guess no. 1 and here goes the next one:
As stated before, the windmill looses impression power during the first sheets. This is due to the fact the all the oil gets pressed out of the large bearings until only a thin oil film remains. Usually one only needs to readjust once or twice. Anyway: is your windmill oiled everywhere it needs to be? Remember opening the rear door and filling the reservoirs. These are IMO the most important spots as it gets really expensive when these large bearings are worn.
So, no more blind guesses for now. Hope it helps…

Another one: besides from the complete handle becoming loose (which you checked already) it can occur that the ring you turn for +/- impression just turns backwards. As the ring is split into to halves hold one ring tight and turn the other ring so that it gets fastened. To check if it moves during the run, just use a felt marker and draw a line on the ring and the shaft…

Heidelberg platens use .918 type and about .040 packing and stock to print. When diecutting you have to go through the sheet adding too much behind the cutting jacket puts the feed grippers at risk of damage. I run small dies type high and sell dies type high to my customers that use letterpress to die cut as they are used to .918”
However my own dies that I make for the H platen are often made with .927 cut rule. The advantages are feed gripper clearance when using matrix and a more balanced die load.
Of note many of the unconverted H cylinder diecutting problems are caused by using type high rule. In order to get the sheets cut the diecutting jacket has to be packed up to about .040”. This causes the cylinder surface speed to exceed the speed of the forward and backward action of the type/die bed and the usual solution is to nick the H out of the die or leave out the head rule.
Marco great advice.
For those who doubt the use of other than .918” cut rule do the math it will make sense.

Wow, thanks guys! Okay, now I see what the problem may have been…

I did have some mylar packing (~.10) behind the die so I wouldn’t overpack behind the jacket. I didn’t think it would compress that much, as it came out pretty much as it went in – without cuts or denting. Per @Mike’s comment, it would definitely make sense that I need the die to be .927. Awesome, thanks Mike!

@mob - I did give the press a pump or two of oil as I began, so that may have been added to my problems. I’m kind of paranoid about not oiling enough, so I probably overdid it. Also, I did think about that impression ring unscrewing, but kept checking it and it wasn’t the problem.

Again, thanks SO much for all the great advice!

As long as your sheets don’t get transparent and you’re wading in a sea of oil, you definitively can’t overdo it :)

@Mike: Leveling impression and stuff that raises the jacket is always a challenge. We do extreme blind embossings (most extreme was 12mm deep - no kidding, figures and unit checked) and therefore need to find a way to have the grippers lift off and get over the counter by building skids for the grippers. Of course this hasn’t to do anything with die cutting, but it shows how creative one can be in shortening a windmills life…

Great that we could find the problem by our guesses. In Germany it’s easy for us as the correct height is standard here. But as Mike outlined it’s most important to have dies with the correct height. For die cutting I never put something underneath the jacket, I’ld always go for shim tape underneath the die. And another one: stop increasing impressional power right when the first part of the die already cuts through the sheet and start applying shim tape where needed. Increasing overall power is the fast and lazy way that will result in a partially dull die and therefore fuzzy edges. Don’t do it!!!