Sheet Timing - Gripper Issues

Hi All,

I have been having some serious issues with paper feed recently and we narrowed the problem down to the impression cylinder grippers being badly worn out.

We have since replaced the grippers (huge improvement straight away). However, there are 9 grippers where the screws have been stripped. What is the easiest / best way to remove these screws in order to fit the new grippers (these old ones are still causing some feed issues every so often.

Secondly, we have been having problems where the delivery gripper bars are damaging the sheets at the feeder end. See attached picture. Can anyone explain what is the cause of this and how we can rectify the problem.

Any input would be greatly appreciated.

Kind Regards

Shawn

 

The damage could be caused by your sheet arrival timing, turn the dial near the paper feed height control to move & adjust the timing, or the delivery chains may be slack if they have stretched over time and may need adjusting or changing.

 

To get the counter sunk gripper screw out I used to use an automatic center punch with good success. If that did not work I used a Dremel tool with a cut wheel to cut a slot in the screw and take it out with a screwdriver.

Are the tears facing up in the delivery? if so the impression cylinder grippers are holding on to the sheet to long. If the tears are down the delivery gripper bars are getting there to early in which case you would have dropped sheets. Also, is it happening on every sheet? Have you had a major jam in the delivery lately? It is possible the taper pins on the on the delivery gripper sprocket have sheared.

The chains could also be loose as mrheidelberg mentioned, but if they are that loose they typically hit the delivery jam switch causing the press to stop during imaging.

 

Hi Mrheidelberg,

Thank you for your feedback! Adjusting the sheet arrival timing did help. The problem does not occur all the time but sometimes more frequent than others.
The chains do need replacing and this sometimes adds to the problem. I think once the chains are replaced we should see this problem go away.

Thanks again - at least I know I am looking at the correct possible causes.

Regards

Shawn

 

Hi Paul,

Thanks for your reply - you always seem to have invaluable input that makes life so much easier. Thanks for taking the time to respond whenever we have queries that may seem trivial but can certainly make life difficult.

I am not sure what you meant by "automatic center punch" -please could you elaborate. I could also try the Dremel Tool option if I cannot come right with the punch. How would the punch work if you don't mind my asking?

With regards to the tears on the paper - as I replied to mrheidelberg - I think that problem is a combination of slack chains and sheet arrival timing. Remember, we are over compensating on the sheet arrival timing to make up for the 9 remaining impression cylinder grippers that still need to be replaced. We are running the press with the sheet arrival advanced so as not to miss the bad grippers and go up onto the blankets or into the rollers.

I must add that since we got most of the grippers replaced the feed problems have been greatly reduced. It's just that every so often, a sheet will hit a bad gripper and get kinked or nicked on a corner and then misfeed.

Thanks again for the advice. Please let me know about the center punch.

Regards

Shawn

 

The automatic center punch is a device used to make a pinpoint identification in a hard material such as metal or plastic. It perform the same function like an ordinary center punch but without the used of the hammer. When pressed against the work piece, it stores energy in a spring eventually releasing it as an impulse, the drive punch producing a dimple. The indentation provides a more stable starting point for a drill to cut the material. It is used for a wide variety of other applications these include ; letter stamps set, glass breaking tools, pin press for electronic assemble and other. The automatic center punch resembles a short screw driver but instead of a having a tip like a screw driver, it has a round shaft shortened to a conical point. It is made up of six basic parts such as the handle hammer mass, intermediate rod, return spring and the point.

The handle is containing a driver assembly which consist of a very stiff spring and a releasing hammer which resembles that of a screwdriver is approximately 1 1/2 inches in length and 13/16 inch in diameter. The handles plastic exterior permanently encases a stiff spring and a releasing member. The spring is the part that drives the point to the material.

The hammer mass is a spring loaded from the back of the punch by a large spring. The spring's preloaded compression can be adjusted by loosening or tightening the end cap at the back most portion of the punch. A stopped hole drilled in the front center portion of the hammer mass facing intermediate rod acts as a receiver for the rod and as an anvil for the punch action.

The intermediate rod which provides the automation, when preset, a provision is made such that the rods is cocked slightly so that it is resting position is skewed and tip contacts the hammer mass, This is commonly done by using special bent end on the intermediate pin spring or using an out-of flat face or bottom end of the pin or top of the punch. It bears of the hammer mass and pushes it back against its spring. The punch is pressed storing energy in the hammer spring. The punch is further pressed against the work piece, the intermediate rod travels back until a certain point where its mid-section begins contracting surface and as it continues back becomes aligned toward the center axis.

The return spring is a steel spring not much different from the type used in most ballpoint pins. It returns the points to its normal position after the tool has been used.

The retainer is a tubular piece of steel which contains the return spring and the point. Its inside diameter is 17/64 inch at its wide end and 5/32 inch at its narrow end. The retainer is 43/64 inch from end to end and has 32 threads per inch at its wide end,which screws into the based of the handle.

The point is the steel bar 1 5/16 inches long which is machined and polish to a main diameter of 0.1532 inch. The end opposite the point measured 0.0923 inch in diameter for a distance of 3/8 inch. Twenty-five thirty seconds of an inch from this same end, a groove is cut completely around the shaft. A separate piece of wire wraps around this groove to old back the return spring. The pointed end of this shaft is sharpened to a 60- degree angle and hardened to resist wear.

That might be overkill on the description. I got it from google.

 

Hi Paul,

Thank you for taking the time to explain. Would you then use the punch to make an indentation on the screw head and use that point to drill into so that one could use an "easy out" extraction tool?

Could I attempt drilling slightly into the center of the screw head? Please advise.

Thanks again for your feedback.

Kind Regards

Shawn

 

You don't have to drill at all, you just use the punch to remove the screw. It takes less than a minute. Go to this link and watch the video at 5:47. This is how to do it with a punch and a hammer. With an automatic center punch you do the same thing. https://www.youtube.com/watch?v=i39N-LukmQo

Here is a video on an automatic center punch. https://www.youtube.com/watch?v=TsY8U4exqOE

 

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