SP-20 No Impression

I’m working on the rebuild of my (previously) dismantled SP-20 and I’m finally ready to test the impression. After calculating the correct amount of packing for a .019″ sheet (.024) on a cylinder with an undercut of 040 I proceeded to attempt a blind proof. There was nothing, not even when I added another .006 packing. Upon closer inspection, the cylinder bearers are not in contact with the bed bearers by about 3pts or .0417″. When I put the press into trip, that distance increases further. So far, I can’t seem too close the gap by adjusting the carriage bearings that ride the under rails or any of the bearings for that matter. I’m not as familiar with the SP series, but I would imagine that the cylinder bearers are supposed to touch the bed bearers. Of note, the trip plungers are working and retract when switched to print mode, so I don’t think that’s the issue. Thoughts on what would lift the cylinder  out of contact with the bed bearers?

 

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Paul Moxon, Moderator
Admin
4 months ago

I was chatting with Dave Seat, who said he adjusts the top bearings first with a .003″ gap and then bottom bearings at .015″, nearly the opposite of what I do. We agreed that it might not make a difference whether the gap is greater on the top or bottom but that the elliptic of the bearings should initially be parallel to the bed and outward. And that the side plate are kept parallel to the bed.

Paul Moxon, Moderator
Admin
5 months ago

Jess and I have been discussing her press restoration since the beginning of her adventure. Originally, the eccentrics on the SP20 were parallel to the bed, with the apogee (or long node) for each bearing facing outward. See the attached image. In my experience, adjusting the bottom impression bearings is easier than the top trip bearings.

The Arm NYC
5 months ago

Here are the pictures that show the eccentric positions on an SP-20 at Cooper. I am not sure how close these would be to the ideal positions on your press as they are adjusted to compensate for wear and subtle differences in the machining. Is there anything else I could document for you that might be helpful?

DGM

The Arm NYC
5 months ago

You should definitely have bearer-on-bearer contact on print. Is the issue eccentrics settings? I am unfortunately not back in the company of an SP-20 until Monday of next week at Cooper Union, but we can compare photos then.

DGM

Eric Holub
Editor
5 months ago

My SP-20 was .918″, and I’ve only seen one .968″ out of a dozen in the SP series.
Setting the impression bearings that hold the cylinder down on impression and the bearings that hold the carriage up in trip is a very tricky business, and mis-adjustment increases wear. But I haven’t made this adjustment in over a decade, so I can’t give the best method. I will say that when both sets of bearings are set correctly, the form rollers will be at the same level on both trip and print.
A pox on all disassemblers.

The Arm NYC
5 months ago

Most SP-20 Vandercooks are .968 bed. Did you check your bed? It is usually stamped near the bed pin on the operator’s side.

DGM

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