cylinder gear tooth alignment

After reading the previous discussion about a misaligned cylinder causing the grippers to smash the form, I thought about the SP20 I’m currently going over (and on which we have not yet printed) and noted that when I received it, the gripper bar was not at 12 oclock when the cylinder was home at the feedboard. I had assumed this was an error, so I rotated the cylinder by one tooth (counterclockwise) to get to 90 degrees, which is (seemingly) the proper position of the gripper bar on my SP15 when the cylinder is parked (never smashed anything on it). There were myriad other odd problems on this press when I received it, so I just assumed this reflected the previous owners idiosyncratic maintenance regime.

But a quick check with a piece of type and a peak under the cylinder, on trip, revealed that the grippers would smash type if used in this (now “fixed”, 12 oclock) position. So last night I reset the cylinder, took another peak– looks proper after all. Two questions: what is the spec on the proper angle of the gripper bar mounting surface on an SP20 when the cylinder is home? And why would this offset (one tooth off from 90) be designed into the cylinder– why not 90, which seems to me to allow for easier feeding to the grippers?

Hope that was clear, and thanks in advance for clarifying.

One more thing: Maybe this is old news, but to adjust the cylinder gear, I simply removed the mid sections of gear rack (which I had just been cleaning) on both sides of the bed and eased the cylinder foward on trip until the last tooth just cleared, rotated carefully, and then remeshed the teeth/rack and reversed. I did this adjustment once on my SP15 and removed the entire cylinder from the bed to do it. Now I know. Don’t know if this is inadvisable, or even applicable, to other models and their specific rack arrangements.

Duncan Dempster
University of Hawaii
Department of Art

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Eric Holub
17 years ago

Paul, aren’t there dead horses in every blog?
I found that drawing worth a bit of study with caliper and protractor, and for the first time imagined the press from the designer’s rather that the user’s perspective.
The axis of the gripper bar points to the center of the cylinder (where it contacts the activating rod). But because the bar has width and parallel sides, the vertical face of the cylinder is made parallel to the axis of the gripper bar, which is on an arc 5 degrees forward of vertical. The top surface of the gripper bar may appear to be flat because its forward swing follows the arc of the cylinder.
As words, that is quite a muddle. Fritz’s drawing on the other hand is illuminating of the actual geometry of the press.

Paul Moxon, Moderator
17 years ago

Not to beat a dead horse, but … while we now know from the drawing that it’s not technically correct to say the gripper bar on SP models is true 90° it does appear to _almost_ be when actually looking at this model (at least the one’s I’ve seen). Fritz has written more than once about engineering changes for this series (e.g. two piece and single piece gear racks, form roller bearing block assemblies.)

Eric: For what it’s worth, there are 64 teeth on the cylinder gear for the No.4.

Eric Holub
17 years ago

Thanks for the graphic explanation Fritz. I’ve been visualizing this the wrong way (that the gripper bar is placed one tooth forward). Positioning the line between cylinder and gripper bar at top center is a much better way to think of this.
From the drawing, it seems the axis of the gripper bar swings along a 5-degree arc from the center of the cylinder, with the lead edge of the cylinder undercut to accomodate the thickness of the gripper bar. (My 325 appears to have the very same relationship between cylinder and gripper bar.)
360 degrees divided by 5 degrees is 72. The 325 has 52 cylinder teeth, which divides to 6.923 degrees, so the actual angle of the gripper and teeth are not exactly equivalent. But now I am curious if that 52-tooth configuration holds for other models?

Fritz Klinke
17 years ago

No, on the SP-20, at least, the lead edge of the top of the cylinder touches a 90 degree line drawn through the cylinder center that’s 90 degress from the bed. Rather than trying to verbally describe it, see

and I think a careful look at the drawing will show how the gripper bar sits.

Eric Holub
17 years ago

That means that the line between the lead edge of the cylinder and the gripper bar is the actual top-center spot? But that the gripper bar is still at 90 degrees vertcal, its working face 0 degrees level, but it sits off-center?

Fritz Klinke
17 years ago

OK, I have pulled out the SP-20 Carriage Assembly print X-19360. and this is what it shows. With the cylinder at the start position, a vertical line, or a line perpendicular to the bed, drawn through the center of the cylinder, touches the front edge of the cylinder casting on the top edge of the cylinder. Note that this is the main casting, and not the gripper bar. The gripper bar is not level, or parallel to the bed at the start position.

Now on to the SP-15. On print X-20401, the exact same relationship of cylinder edge to a vertical or perpendicular line through the cylinder center holds true. The print for the #4 that Paul posted previously does show the #4 to have the top edge of the gripper bar parallel to the bed, an alternate method as to that built into the SP series.

The SP-15 and -20 here in the shop both have singel piece bed racks. But as these presses were being redesigned as they went, split racks, or floating racks, could have been added, and without a lot of digging, I can’t verify that or at what point in time.

Mike Magnesi
17 years ago

Hello Duncan,

I too have an SP-20. The gripper bar is not at the 12 O’clock position. I would guess that it is one tooth past 12 (clockwise).

I have not had any problems getting the paper into the grippers so I do not think the gripper bar position is an issue.

My press also has the sectional gear racks. There are 4 sections with the end two being spring loaded. The press was made in 1966 ser #26395

The head deadline is 2.25 inches from the bar at the head of the press.

Good Luck!

Paul Moxon, Moderator
17 years ago

Like most models , 90° is the proper position for the gripper clamp bar on SP series presses. Your press should have a head dead bar in the press bed that is of a width that aligns with the postion of the head deadline. Head and foot deadlines are scored on the press bed. To locate the head deadline remove the dead bar (and the bedplate if the press is galley height). After-market bed plates are not scored to show deadlines. It may be filled-in with grime-ink-rust, but it is there.

All SP series I have worked on have had a single piece gear rack for each side of the press. So there must have been an enginneering change from a two section to a one section design. Perhaps Fritz can tell us when this happened. My No. 4 has two sections on each side the the press.

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