Miscellaneous

Feeder

The timing of the sheet can be adjusted for better register or to cut down on the amount of mis-feeds (remember I'm talking about the SM-52). This is done by turning the knob on the rear door (where the air bleed nipple is). The ideal and recommended setting is 265°. The way to check if you have the feeder set at 265° is to start the press up and feed a couple of sheets down the feeder and stop the press on the emergency stop button before the sheet gets to the head lay. Inch the press on the inch button on the feeder console and turn the conveyor on. Eventually the feeder will start up and the sheets will continue towards the headway. Watch very closely as the sheet approaches the head lay stops. You should stop the inching the very moment the sheet contacts the stops. This will give you a reading on the LCD display. Advance or retard the feeder to get it closer to 265°.

Ink Tack

Tacky ink is a fact of lithography. The oil based ink is naturally sticky and for that reason it is offset onto the blanket cylinder. The rubber blanket has better release properties than the metal plate. However, although the blanket is there to help with tacky ink it cannot solve the worst cases. In these cases the ink will pull fibres from the surface of the sheet and hold them on the blanket. This will eventually build up and you will find areas on the printed sheet where there is no image where there should be. There is normally a loud 'tsh' as the sheet passes through the nip between blanket and impression cylinder and it's tack that causes this. The answer is to add Tack Reducer (makes sense). The reducer will reduce tack but also reduces the body of the ink which means that is will print lighter than an un-reduced ink. You might need to increase the inking to compensate, and because of this you can overdose on reducer. About 5% is your limit.

The Wash-up Tank

The wash-up reservoirs seem to get a build up of crud. This crud eventually blocks the small filter that's in the hose that goes to the press. The crud builds up to the extent that you have to clean the small in-line filter out to make the spirit flow again. Trouble is, the tank still has loads of crud in it. The only (or I should say easiest) way to get the crud out is to disconnect the hose on the outlet side and very slowly re-pressurise the tank. The re-pressurisation will pump the crud out of the tank and squirt it all over the floor, still it's out of the way. Expect to get about a quarter of a pint out every two years or so.

The Powder Spray Unit

The idea of the spray unit is to put a layer of powder between the wet print and the underside of the following sheet. Left is a close up of that situation. 1 - Wet Ink, 2 - Powder Spray, 3 - The underside of the following sheet. As you see, the lower sheets have been sprayed with a very fine powder (about 1.5R) and the particles are laying on the wet print. The problem is, the particles are so small they are not creating a barrier between the ink and the following sheet. This will lead to set-off and could spoil the job. Towards to top of our pile, the sheets are being sprayed with a larger particle of powder (2.5R) and the powder is doing it's job. There is space between the wet ink and the sheet. In this instance there will be no set off and the print will be saleable. There are a few other variables to consider. The coarser the sheet surface is the higher the likelihood of the sheet absorbing very fine powder. The fine grains will settle into the valleys of the sheet and will not form a barrier. So, generally speaking, glossy art papers require a finer powder whereas course papers require a larger particle of powder. You will also find that you will need less of the courser and more of the finer to achieve the desired affects. Beware though, if you use too much it will cause you problems when you put the sheet back through the press. The powder is pulled off the sheet on the first unit and becomes stuck to the blanket. This will cause a barrier between the blanket and the wet ink on the plate and eventually the blanket will go blind and will need cleaning. In very bad circumstances this can be in around 500 sheets.