Truck/Roller sizes and slurring on Platen presses
Hi all-
I don’t often pose questions, but I have one for you. This has possibly been covered somewhere but I have a sort of specific reason for asking again.
I am attempting to settle a discussion with a friend. We are talking about rollers and slurring due to differences in size between the rubber of his form rollers, and the trucks he has.
In his case, the trucks are actually a little larger than the rollers. About .020” larger.
He has the idea that if he raised his forms .020” to compensate, and backed the platen off a small amount as well to also compensate, that he’d be able to print.
I have suggested that either A. - He needs to have his delrin trucks ground down to the same thickness as the rubber form rollers (which are perfectly true and flat, having apparently been recently re-ground), or B. have his form rollers re-cast and re-ground down to the same size as his trucks, and that either will be the solution to his problem.
Personally, I’d have the rollers re-done, but it’s such a small difference I doubt it would significantly effect print due to a shorter ink train/the lap-rollout of the rollers if he did have the trucks ground down this small amount instead.
After going over all this with him physically, and then suggesting to him that an underlay that thick and backing off/leveling the platen on an old style C and P is going to be a bit annoying (mostly the backing of the platen/leveling), he is still under the impression that for the time being not spending more money may be the better idea.
So what say you? His rails were very close to type high before, and were leveled off with good tape - and going further, he had rollers that were the same size as the cores before being ground down, so presumably making up the difference with an underlay would be the only adjustment to the inking/form area of the press- the rest is platen work.
Will this work? Or is it a fools errand?
thanks!
There are more ways to kill a pussycat than kissing it to death. Whatever works is OK. His cheap trial for a first go may work. Underlaying the form .020+/- to bring it up to kiss inking is the first step. Total packing is normally about .050. He may not have to mess with the platen screw adjustment and may be able to merely remove .030 of packing. Messing with the platen screws should be avoided if it can be.
If that is not satisfactory, I think the next step would be to machine the delrin trucks to the same diameter as the rollers. Pretty inexpensive at the machine shop.
Your trucks should only be the same size as your rollers if the bearers of the bed(rails to you ) are the same height as your type , any difference between the bed bearer and type high will be reflected in the difference between the roller and the roller bearers(trucks in your language)
If your bearers Rails are higher than type high then your trucks will be smaller than your rollers and vice versa ,
There is not an exacting rule as long as the relationships are correct and you allow a thou or two for the rollers to meet the forme with a light pressure. .
As I understand it, if the trucks & rollers differ in diameter, the roller will slide a small amount on the forme.
In the following illustration, a difference in .02” roller diameter will result in .105” slide of the roller across 10” of forme.
Discussed here: http://www.briarpress.org/21589
RollerPuzzle.png
Why so many negative vibes, post after post, re the height of rollers and trucks etc. To purchase from graphic suppliers,? to contact parts distributors,? (breakers or parting out specialists as you would say)? or contact Engineers?>>> Occasionaly I speak from the correct orifice, this may be One time!!! Middle of last year, (just as a feasability excersise, fun and learning curve)!!! Bought 3 billets of material, Brass, Aluminium, and industrial grade nylon.?? Overnight in the peaceful atmosphere of my shed, produced, 5 examples of trucks, 1st one, straight aluminium,>>>2nd one, straight brass,>>>3rd one, compound, aluminium/brass, I.E. base in aluminium to accomodate roller stock/shaft, with slip on tyre/ring, like slip on wedding ring!!!! With 2 different size rings ONE to give standard specified roller clearance/contact and, ONE at plus .005 or plus .010 thou, to give extra clearance!!. Think about it!! >>>4th one (As virtually every smaller older machine, appears to have a wide gap, between the compound of the roller and the roller hooks) it was not exactly rocket science to turn a single truck with 2 different dimensions, slipped off and reversed in milliseconds???>> 5th one, Industrial Nylon COMPLETE FAILURE, my lathe only goes to approx 800, R.P.M. max, nylon would appear not to Turn at that speed, Grinding is beyond my sphere at present!!!>>Obviously impractical to suggest such, from this distance, but given the challenge and the dimensions in imperial measure, and spec for material, I could produce TRUCKS to an accuracy within .002, for (compared to graphic suppliers) comparative peanuts???>>>AND one more, with apologies, (of course) for correct orifice etc, is it such a hard concept to, instead of consuming column inches on B.P. and similar “To Tape or Not to Tape etc etc etc, Ad Infinitum” to simply make 2 say, stainless steel “L” shaped slippers, to go on top of the rails to carry the rollers, at maybe original, accurate height , with then, the option of normal packing beneath the form???>>>Rails attached via Chemical Metal, Superglue, Epoxy Resin, Grub Screws, ETC.>>> Please by all means Have a laugh, but study the concepts FIRST. MICK
Friends,
I am constantly amazed by the discussions of delrin rollers and tape on the rails.
A good set of Morgan expansion trucks works like a charm.
Even if you have to make adjustments during a run, which you shouldn’t, it is possible to adjust for changing conditions with the height of your form or th humidity in your shop.
s
I use the morgans and love them, i see what you are saying Mick, your slipper idea sounds great, but that would solve a lot of problems and wouldn’t give us as much to discuss here.
Anonymouse, that’s basically the information I was looking for. So sliding (and thus some possible slurring) during the inking portion happens if the rollers and trucks are (significantly) different in diameter. I assume this could lead to some otherwise inexplicable problems.
Hey Steve, my friend doesn’t have Merts, but thanks for the suggestions. I have a set but I’m not parting with them and my buddy doesn’t live close by enough for me to just ‘lend’ them ;-)
Thanks for the info, all of you. I’m glad to be part of this forum and to receive practical answers to practical questions as well as theoretical answers. You’re a swell bunch of folks.