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Increasing Repeat Length Through Plate Cylinder Build-Up
Author: Frank Burgos, FlexoExchange
I think it would be fair to say that most of us don't have multiple sets of all of the possible cylinder sizes our flexo presses are capable of using. Our plate cylinder inventories tend to reflect the repeats that we most commonly use or expect to use, adding sizes only as needed. As a result, it is not uncommon to have a customer request a repeat length that we don't have on hand. When this occurs, we are faced with the following options:
- Hope that the customer will accept a different repeat length.
- Buy cylinders and gears for the requested repeat length.
- Miss the opportunity of printing the job in question.
Often, packaging is designed to precise specifications and a customer simply cannot accept any compromise in repeat length. Buying the correct cylinders for the job produces the best results, but may not be the most economical and may take longer than our customer is willing to wait. And, finally, few of us want to turn away work.
What I'd like to do here is offer another way of meeting our customer's needs in a pinch. This method works best when the difference between available cylinder repeat and the requested repeat is not too great. Also, it is usually only possible to increase our repeat length, except in cases where cylinders are greatly undercut. What we do is to build up our plates with mounting tape or some other similar material to the correct height and invest only in gears of the corresponding size.
Allow me to illustrate:
For CP geared presses:
Example:
Supposing that you operate a wide web press that uses 1/4 CP plate cylinder gears and your customer requests a repeat length of 14.000" (56 tooth gears). The closest cylinder repeat size that you have is 13.750" (55 tooth gears). The difference is 0.250" in printing circumference and one additional gear tooth. It's extremely important to build up to printing diameters that correspond to whole number gear teeth quantities. Not doing so may result in "bottoming out" of gears or insufficient gear mesh depth.
Increase in repeat length: 0.250"
Divide by pi to determine increase in diameter:
0.250" / 3.1416 = 0.080"
Divide by 2 to determine increase in radius:
0.080" / 2 = 0.040"
This is the amount of build-up to use on your 13.750" repeat cylinders.
I've found that dense mounting tape in layers no thicker than 0.020" works well for me. Obtain 56 tooth gears to use in place of the 55 tooth gears on your 13.750" repeat cylinders.
For DP geared Presses:
Example:
(Note: Pi / DP = circumferential pitch per tooth)
Supposing that you operate a narrow web press that uses 32 DP plate cylinder gears and your customer requests a repeat length of 9.820" (100 tooth gears). The closest cylinder repeat size that you have is 9.624" (98 tooth gears). The difference is 0.196" printing circumference and two additional gear teeth. It's extremely important to build up to printing diameters that correspond to whole number gear teeth quantities. Not doing so may result in "bottoming out" of gears or insufficient gear mesh depth.
Increase in repeat length: 0.196"
Divide by pi to determine increase in diameter: 0.196 " / 3.1416 = 0.062"
Divide by 2 to determine increase in radius: 0.062" / 2 = 0.031"
This is the amount of build-up to use on your 9.624" repeat cylinders.
I've found that dense mounting tape in layers no thicker than 0.020" works well for me. Obtain 100 tooth gears to use in place of 98 tooth gears on your 9.624" repeat cylinders.
Your situation may not lend itself to the method outlined above. It's up to you to judge how or if it may apply to your process. If you have different CP or DP to the above examples, simply modify the values accordingly. If you have any questions, please don't hesitate to contact me.
Author: Frank Burgos
E-Mail: frankb@flexoexchange.com
Web Site: http://www.flexoexchange.com/
© 1997-2003 Content of this article is original and may not be copied or reproduced without the express written consent of Frank Burgos, FlexoExchange. Personal, educational, non-commercial use is allowed provided this article appears in its entirety. This copyright notice must appear on all copies made and/or distributed.
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