I seem to be having an issue with one of the bearers (is that even the right term?) on the rear form roller on my SP-20. I can’t lower the roller height to type-high on that side. I can on the user side, but not on the opposite end. No problem with the front roller. In the video you’ll see the assembly is loose while the others are not. Any ideas?
(I’m taking Paul’s maintenance workshop at the end of April, so hopefully I’ll get my terms down then!)
Attached video: SP20_rollers
I think Paul has the problem diagnosed correctly. The bearing is held in the ring by 2 methods. Locktite was specified by Vandercook to glue the bearing into the ring, or “staking,” a commond machine practice, was used. A cold chisel is used to put a nick in the outer ring on opposite sides of the bearing and that will hold the bearing in place. A roller undersize by 1/10th of an inch is a lot and may indicate an older roller that has shruken, or was possibly over ground when made. We sometimes see an attitude of “well, it’s just for letterpress” from some roller makers who think all we do is use numbering machines, so finishes and tolerences are unimportant to them when it is actually just as critical as in making an offset roller.
The roller can’t be lowered any more because the gear teeth are seated at the bottom of the gear rack, 0.10 of an inch is significant. You have to recover the rubber on the cores.
I checked the thickness and the rollers are about 2.9″ in diameter, so you are right about them being undersized. Is there an adjustment or part replacement that needs to be done to get that side of the roller to type-high? I’d imagine this could present a problem if I’m printing a large form that requires a fair amount of coverage.
“Quick Change” form rollers used on Universal and SP series presses allow the diameter to be undersized to a greater extent than on older models where both rollers are bracketed in a frame, e.g. the No. 4.
The other factor in determining whether rollers need to be recovered is their hardness called durometer. I’ll have my gauge to measure this with me in workshop.
It’s a common failure of the Universal and SP20 roller adjustment assembly for the bearing to slip out of the ring. Your shims won’t effect the height adjustment, but telfon plumbers’ tape make for a more snug and uniform fit. Replacement assemblies are available from NA Graphics. http://order.nagraph.com
By “the rubber,” I assume you mean the rollers. I’ll have to check that out. If it’s less than 3″, does that mean I should have them re-covered?
Additionally, that particular knob and the round outer ring would come dislodged from the assembly after 8-10 impressions and I’d have to wriggle it back on to the bearing. (again, terms…sorry). I put a few knicks into it and crammed a copper spacer in and now it’s tight and doesn’t come off during a press run. Could I have done something to affect the roller height in this process?
Jonathan, I fixed the link in your post.
This is a common problem: the diameter of the rubber is undersized. If you take a pair of calipers, I trust you would find it to be substantially less that 3″. What’s happening is that the gear is bottoming out against the gear rack. The looseness demonstrated in your video is a result of having turned the adjusting knob, left to lower, beyond its effectiveness.
I’m not sure the video is easily viewable via this post. Here’s another direct link to it on my server: