The print co-op I belong to recently had the form rollers for our SP-15 recovered by Pamarco. After reinstallation, I adjusted both roller heights to achieve proper strike on the roller gauge. When the rear form roller is set to a proper height, the roller gear skips along the gear rack, barely making contact. When I lower the rear roller far enough for good meshing between the gear and rack, the roller sits at an unusably low level. What simple thing am I missing?
recovered roller diameter: 2.54″
form roller gear diameter: 2.62″
gear rack height: sits 3–6 points below the bearer. Shims in place.
the press bed is galley high with a bed plate.
impression is normal with a normal amount of packing for 0.040 undercut
Thanks in advance! Happy to supply pictures if needed.
Well, the gear size did seem like a long shot.
Last weekend I was at the Gaspereau Press Wayzgoose and one of the Vandercooks there seemed to have a problem with the form roller gear skipping as well. Sometimes it would skip right from the start, but other times it would start to skip partway down the bed, beyond the end of the forme. I think the problem is exacerbated by tacky ink, since this gear has to drive four rollers in mutual contact.
Maybe some of these problems are just caused by worn gears…
Your response made me hopeful, but I counted 40 teeth on the roller gear. Thanks so much for your thoughts.
How many teeth are on the form roller gear? There should be 40 teeth to go with the standard 2.5″ roller diameter. On my press I found the form rollers to be 1/8″ under diameter, and rather than splurging on recovering the rollers I fitted a 38-tooth gear, whose pitch diameter exactly matched the 2 3/8″ roller diameter. Note that for gears the pitch diameter is less than the outside (major) diameter. These gears (and the rack) have a diametrical pitch of 16 teeth per inch of pitch diameter (and the rack tooth spacing is pi/16 inch to match), and you want the pitch diameter to match the form roller diameter to get optimal gear mesh and minimal slurring.
Perhaps at some point someone installed a different form roller gear on your press…
Here’s a photo of the starting tooth under pressure. It springs upward when released, but sits slightly unevenly with the rack (photo 2)
Here are a few images of where the roller gear falls on the rack with a little heavier strike.
I always get my SP-15 rollers at 2.515 diameter. You might be having trouble with these because of the oversized outer diameter. I’d also check the starter tooth on the gear rack as well as the corresponding spring.
I would suggest either trimming the Nyliners you have in order to use them in pairs, or getting some which are not as deep. If you only use one Nyliner per side, you will slowly either wear out the journal edge of your cores or your end screws will cut into the side of the adjusting blocks. Nyliners are far cheaper than either of these, though Fritz can provide either if you need them already.
I’m using a .918″ roller gauge. The gauge sits level with the bearer when it is in the press bed with bedplate.
When I reinstalled the rollers, I placed a nyliner between the collar and the bearing block. Two nyliners wouldn’t fit in the block, so I guessed this was the best position?
I won’t be able to take pictures of the press until Monday (I’m out of town), but will post them asap next week.
Thanks a million!
Paul’s question is a good one. Did the person who put it all back together remember to put in the Nyliners?
Photos or a video might help. Confirm that you are using a .918 roller setting gauge and not a .968 gauge with the bedplate.