View Full Version : Creep formula

NazRaQ

09-09-2008, 12:50 AM

Anyone have a better formula than # of pages / 4 * thickness of stock for Creep ? this Always gives too little of a number because it does not take into account the "bow" of the stock... I currently have to build a mock up with the actual stock for every job which is a pain... but accurate. Thank you in advance.

I usually add 10% to this calculation, but our books are usually less than 200 pages.

mike1

09-09-2008, 05:14 AM

Download this excel spreadsheet,

It's in GSM and mm, modify for your own units

http://www.optimapress.com.au/downloads/Creep_Spine/

deananderson

09-09-2008, 08:27 AM

Anyone have a better formula than # of pages / 4 * thickness of stock for Creep ? this Always gives too little of a number because it does not take into account the "bow" of the stock... I currently have to build a mock up with the actual stock for every job which is a pain... but accurate. Thank you in advance.

We always use that formula then round up to the nearest whole millimetre, it works for us!!

michael.berry

09-09-2008, 03:02 PM

Naz,

I think you are on the right track with pages/4 * mil. However let me add a little with what we use.

# pages/4, but then -1 (you don't shingle the outer most leaf)

Then * by the paper thickness, but also * 2.3. (This little multiplier compensates for the additional loss from the folding.)

This is tried and true, you can test it by laying out a saddle stitch piece and comparing the inner leaf size to the outer leaf size.

Regards,

Michael Berry

NazRaQ

09-10-2008, 01:45 AM

Thank you all... I will try all the suggestions and test against mockups to see what works best for us... I'm sure it will need tweeking based on # of pages.

brian.cupp

09-15-2008, 02:39 PM

There is one thing all of the shingling formulas do not have. That is the use of pie (3.14). Since we are dealing with something that actually curves at the fold, pie should be part of the formula.

Below is the formula using pie. NOTE: the Creep Correction Factor is for paper tolerances/roughness of paper and for how tight or loose a folder is.

Steps to produce good shingling

1.) Total Number of pages (p) divided by 4 is the total number of sheets (n)

2.) Thickness of 1 sheet of paper (t)

3.) n * t * 3.14

4.) Take the value of step 3 and divide by 2

5.) Take the value of step 4 and multiply by the Creep Correction Factor of 1.2

The formula should look like this

(((p/4) * t * 3.14)/2) * 1.2

NOTE: This formula came from Scenic Soft Engineering.

sequoyah

09-16-2008, 05:37 AM

That's interesting. Does Kodak still make that available, or is it something you got in a tech support call back in the day, or from the old Preps newsgroup?

That seems like just a starting concept for developing a model of the behavior of how sheets wrap around a spine. But the radius of curvature of even a single sheet is not constant, and the variation for each as the number increases is not linear. So a lot more is missing than just Pi and a fudge factor of 1.2.

But before getting carried away with mathematical models, don't lose sight of the real world in which the folding of real sheets of paper has variations of may causes, which lead to errors in predicting the position of the front and back pages of the signature. A slight miss fold causes a shift in one direction for the front pages, and shift in the opposite direction for the back pages.

I use Preps and I also run a Stahl 3 unit folder with add-on needle wet scoring. In my opinion, simple creep formulas are as adequate as can realistically be expected.

Al

digital@sig-1.com

09-29-2008, 05:01 PM

I was always told that it is the total number of pages (incl. cover) divided by 4 times the mil of the paper times 2. I.e. a 48 page book on 80# stock would look like this: 48 / 4 = 12; 12 * .004" (mil) = 0.048; 0.048 * 2 = 0.096" for your creep. I have been using this formula for about 6 years without issue.

________

GL1500A (http://www.cyclechaos.com/wiki/Honda_GL1500A)

roger

09-29-2008, 05:55 PM

Ever have to calculate the amount of shingle for a crossover spread somewhere in the job in order to 'Un-do' the creep via a Geometry move in Workshop? If so, you'll want the attached excel file (originally written and recently updated by one of our employees.) Read tabs 2+3 for info on the program.

note: this program doesn't calculate creep for the job, but rather tells you how much shingle there is for each specific page.

Roger

brian.cupp

07-06-2009, 06:00 PM

That's interesting. Does Kodak still make that available, or is it something you got in a tech support call back in the day, or from the old Preps newsgroup?

That seems like just a starting concept for developing a model of the behavior of how sheets wrap around a spine. But the radius of curvature of even a single sheet is not constant, and the variation for each as the number increases is not linear. So a lot more is missing than just Pi and a fudge factor of 1.2.

But before getting carried away with mathematical models, don't lose sight of the real world in which the folding of real sheets of paper has variations of may causes, which lead to errors in predicting the position of the front and back pages of the signature. A slight miss fold causes a shift in one direction for the front pages, and shift in the opposite direction for the back pages.

I use Preps and I also run a Stahl 3 unit folder with add-on needle wet scoring. In my opinion, simple creep formulas are as adequate as can realistically be expected.

Al

Al,

I received the document because of a question on the old Scenic Soft/Preps Newsgroup.

As I remember, the Creep Correction had to do with paper having a texture to it. Which doesn't show up when getting the thickness of the paper.

For our use, I created a Filemaker application where the user put in the number of pages and Type of Stock. When the user selects the stock, it fills in the thickness of 1 sheet of paper. The "Inner Shingle Amount" is shown and they can print this out to keep with the job. This has simplified the process for our imposition people.

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