Press packing enigma, would love ideas!
I recently brought my C&P 10x15 out of storage and gave it the full court press – new skids, floor level, rail height, and platen level. To level the platen I used the very clever setting gauges from Stark Press – once the platen was snugged up to them on all 4 corners, it sat at a perfect, calipered .958 from the press bed, leaving .04 for packing. Great, right?
I was very surprised to run a job and find that somehow .04 was well shy of what I needed for a clean impression. I was running a 110c lettra, so if anything I’d expect to need less packing, not more. But to get a clean impression I ended up needing two sheets of red pressboard and probably a dozen of 20# bond, as well as the drawsheet. My packing calipered at more than .08! I would have thought this way too heavy, but once I had the makeready done I pulled an impression on bond paper and it isn’t even visible from the back (pictured). It’s textbook perfect, just with WAY too much packing – the packing was even too thick for my grippers to lay flat at impression. I have no idea where the empty space is coming from and I don’t really want to have to run that much packing if I can help it.
Things I’ve tried:
- Re-check the platen level with the gauges. At impression they all skate freely but do not knock or tap at all, there is zero slack, so the platen is absolutely set at .958
- Calipered my form just in case it’s sitting low. It’s a perfect .918
- Checked roller height in case they were not inking for some reason. Also perfectly at height.
- Changed stocks, no change
- Adjusted packing order to experiment with pressboard over bond and under drawsheet, vs. bond over pressboard under drawsheet (would always prefer the former). Nada.
I’m fairly at a loss to explain this. I figure I could re-level my platen with the packing I want on it, and just eyeball impression until I’m happy, but it’s hard to convince myself to do that when everything is mathematically ‘correct’, just not doing what it should be – I’d be very glad for any ideas from anyone!
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Additional troubleshooting: removed all packing and rollers, and turned the press over by hand, looking for any slippage or play. Hauled on the flywheel, drive shaft, and platen at all points of cycle. Zero play whatsoever. Went around and checked every possible bolt head for snugness, again found no play.
I am only the third owner of this press so it is in really excellent shape, I’d be surprised if it were a mechanical issue.
Not questioning anyones products, but did you double check the guages with a mic? Make sure they’re at 0.958”
Absolutely valid, I triple checked with calipers, all 4 in the set are perfectly flatted .958
A little inexperienced with all the type out there, but you wanted .958? instead of .918 or .937?
Have you tried printing any other forms? The form pictured is on the larger side. I’ve always understood the standard .04 packing setup as a sort of calibrated starting point so you can make job-specific adjustments in a measured way. Standard packing should produce a kiss impression on book weight paper with no visible impression, but with solid ink coverage for a pretty average form, maybe a dozen lines of 12pt roman weight type. Larger forms tend to require more pressure, so it’s common to add additional packing. The density of your form is also a factor, the more solid a form is, the more pressure is required.
Your form is both on the larger side, and is fairly dense, so it’s not surprising to me that you’d need additional packing. What is your form made of? I’ve also found both linoleum and photopolymer to be a bit “soft” so they compress a little bit during printing which can throw off your impression settings. I’ve had better luck using softer packing with large forms, subbing out the bond sheets for 32# lettra, or even the press board for a 110# sheet. Dampening your paper can also help.
I guess what I’m saying is that there might not be anything wrong, this form just might need this much pressure. I think you should see what happens with a smaller form, just a few lines of type and go from there.