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.

Pull Guide Sensor

After a while (many years of use) you may start to get repeated double sheet errors when there are no double sheets on the feed table. Then you may start to get sheet thickness errors when transferring over a new program and the press will disagree with the measured thickness of the paper, making you put in a false reading to get it to work. The likely cause is the double sheet sensor within the pull guide. On our press the nearside sensor was the problem, mostly from all the fount spillages it's had over it in the past causing a build up of crap on the tip of the sensor. Heidelberg will relieve you of a lot of money to clean it up or offer you a replacement upgrade. However, it's not so hard to fix yourself, you just need an allen key set and a bit of time. Strip down the feed table (remove the belt assembly, and the two plates with the feeder rollers on them) until you get to see the body of the pull guide. If you move the pull guides (using a program with paper size of 200mm width) you will get to see the back of the pull guide. Right down the bottom there'll be a wire going into the back of a cylindrical sensor, this is the culprit of the problems.

To remove it is a bit fiddly and if you’re clumsy with tiny bolts then you might want to give it a miss as you’ll be dropping them deep into the crap under the press and you probably won’t seem them again. Take off the mounting for the feeder wheels (the pole that holds those brush wheels), the two allen bolts on the feed table side of the pull guide. Remove the two allen bolts holding the outer cover which will reveal the sensor housing. There is a silver cable guide, you’ll want to remove the upper allen bolt and loosen the bottom hex bolt to swing it out the way. There is a tiny allen bolt holding the sensor housing in place, undo it and slide the sensor out of the pull guide.

Clean the end, hopefully there was a blob of crap on it, give the pull guide a good air blast then slide the sensor back in and tighten up the retaining bolt. Now the fiddly bit and the setting up of the sensor. Go into your CP Tronic pane, on the spanner button (I forget what the correct name for that is). Navigate your way to the “Analogue Engagement” page. The right hand column of figures is what you want to look at, Number 1 is the operator side pull guide sensor reading and Number 2 is the drive side pull guild sensor reading. Rotate the press to 20 degrees and engage the pull guide (no need to do it on the program, just mechanically engaging them on the top of the pull guide is enough). You want to get a reading as close to 570 as possible but it’s incredibly sensitive and it doesn’t help that the pull guide and the screen is at opposite ends of the machine, you may want to get someone to call the figure out to you while you adjust.

There is a hole in the top of the pull guide, put a 2.5mm allen key down that hole and into the locking bolt, undo that and you either screw the sensor into or out of the mount. Very small adjustments are needed, do up the locking nut and take a reading. Doing up the locking nut will change the reading so only take a reading when it’s done up. If you get anywhere near 570 then call it a job done and leave it alone. If you’re getting readings of 3800 or so then you haven’t engaged the pull guide or haven’t rotated the press to 20 degrees.

Rebuild everything you've taken apart. Once adjusted it should fix the double sheet problems and behave itself.