Coaster thickness for Heidelberg platen printing?

Matthew Reynolds
on 29 Mar 12 (07:31)

Hi all,

Having survived my last job (with significant help from folks on Briar Press), I’ve decided to try printing some coasters on my Heidelberg. I’ve read the related posts, but wanted to double check a few of my assumptions before taking the leap.

The recommended packing is 1/25”. This includes packing, tympan and the paper being used. My assertions include:

1. 1/25” is 40 pt (where 1 pt is 0.001” when measuring stuff like coaster stock).
2. This packing recommendation is designed to provide ‘kiss’ impression.

So far, so good?

My coaster supplier is able to provide 40 pt, 60 pt and 80 pt thicknesses. In a perfect world, I’ll be printing both sides with minimal to less than moderate impression; I want these to be distinguishable from offset coasters with a subtle and tactile impression…but your pint shouldn’t wobble! :)

I’ve run a bit of Crane Lettra 220# through the press in the past (approximately 43 pt) and it was pretty thick stuff. The feeder did a pretty good job of it after some tweaking, so I’d feel comfortable going with the 40 pt coaster stock. While I like the idea of having a thicker coaster, especially if I’m printing it on both sides, I don’t want to buy the stuff and not be able to feed it, etc. Am I silly to even think of using anything more than the 40 pt? (I’m a sucker for a thick coaster…but not at the expense of the press)

This supplier sells pre-cut coasters (square). I know that many people have issues with the pre-cut coasters and prefer to get sheets and die cut them. That really isn’t an option at this point in time (mainly because I haven’t found a reasonable source for parent sheets…and also because I’d like to avoid learning two non-trivial things on a given job to limit my risk). I don’t think the size of the coasters (4” x 4”, rounded corners) will be an issue. I’m more concerned with the gripper denting the stock. As I didn’t get any denting when running the 220#, I’d think running the 40 pt coaster stock would be safe; yes?

Finally, should I try using gripper/commercial register for these (it’ll likely be a single colour pass on each side) or do I need to use the guides? (which is fine, just not sure what the variables for this sort of job would be which would lead someone to choose one or the other)

Thanks all!
Matthew

Matthew Reynolds
on 17 Apr 12 (12:01)

Updated 17 Apr 12 (12:02)

Hi all,

I ended up purchasing some 4”x4” 60pt pre-cut coasters to play around with. With some tweaking (and some #22 suckers), they feed quite well.

The problem I’m having is bruising caused by the grippers. It is obvious to see that the gripper angle causes the coaster to be bent slightly as it is carried down into the press. The pressure exerted by the gripper dents the coaster somewhat.

What are my options at this point? I realize this is the reason most use sheets of stock, then die cut.

My grippers currently don’t have any rubber inside (where they grip the paper). Should I try experimenting with different rubber/tape/etc. to see if I can make the gripper softer?

Thanks,
Matthew

Peter Luckhurst
on 17 Apr 12 (18:20)

the heidelberg manual shows simply how to replace the rubber in the grippers.

Pressingtheadana
on 18 Apr 12 (03:05)

Updated 26 May 12 (23:56)

Peter Luckhurst
on 18 Apr 12 (06:55)

I will have an investigate this problem ,i know the answer is press limitation but there could be ways of minimising the marks but i need to see for myself before i offer any solution , i know packing thickness when running the job gripped all through can cause buckle along the length of the grip edge if the surface level of the packing is higher than the grippersurface while in the print position , probable indication of bent grippers (one higher from the platen surface than the other} , as i said wont try to answer this till ive had a play or you will start to think bills and things disastrous .