Pre-Press Counter Plate Validation

Written By Mark Batson Baril

What is the best way to validate the accuracy of the counter plates produced, to the die, without the benefit of a press or XY coordinate inspection machine?

There are several parts of a typical counter plate that need to be checked before it goes to press. Those parts include:

• The thickness of the counter plate material
• The width of the channel that was cut
• The depth of the channel that was cut
• The size of the locating holes that were cut
• The actual image that was cut
• The size of the image that was cut

How each of the parts is passed through Quality Control varies from shop to shop. The most common are outlined here. Specifications for each tool set must pass with the tooling through the QC process. Your quality control people are only as good as the information they are provided with. Training in what's important to inspecting a counter plate is also vital to the quality control.

The thickness of the counter material
This is very important as the overall thickness controls the overall emboss we get when the creasing rule enters the counter. Typically a spot check is made of two or three points on each counter with a vernier. ±.001" (±.025mm) is the standard thickness deviation allowed within the industry.

The width of the channel that was cut
The width will typically vary with the grain of the board you are working with. Both the with the grain and against the grain width should be at least spot checked within the counter plate. Again a vernier is typically used to check this width. The channel width should fall within ±.002" (.052mm) of the nominal dimension.

The depth of the channel that was cut
Again an extremely important factor in how well a tool set will work together. More than any other variable, this is the one that may be out of tolerance. Any up and down movement of the material during production will produce results that may not work. Unlike the width of the channel where the constant tool produces a fairly constant channel, the depth relies on the up and down tolerancing of the machine head and the ability of the machine to hold the material in place. Spot checking the depth with a micrometer is standard practice. Typical tolerancing is ± 10 % of the overall depth of the channel.

The size of the locating holes that were cut
Here's a simple one that really matters to the press person. If the holes are to small it's a nightmare to get your pins in the plates. Nobody wants to have to take the time to ream out the holes in pre-make ready or worse yet, on press! If they are too big you'll have to be a magician to get them to stay with the die long enough to make that first impression. You can use a vernier to measure but that's tough to be accurate with a round hole. One of the actual pins that will be used on press is often the best bet for a great and practical QC. Spot check all your plates. The standard deviation allowed is ±.002" ( .052mm). Another excellent measuring device to use is a standard gauge pin. This especially works well if you are a commercial shop and your various customers use various sources for their pins. Set-up the size you need to give them and go with it based on the gauge pin.

The actual image that was cut
The actual image we refer to here means differentiating between creasing / cutting / perfing / cut scoring / etc.... Making sure that there are no channels missing and that all of your cut backs stay far enough away from the cutting areas. Again spot checking is most commonly used by putting in few locating pins and actually laying the plate on top of the knifed die (it's easier before the die is rubbered). Check that everything that should be there is there and that areas that should not be there are not. There's no standard tolerancing on this, it's either right or wrong.

The size of the image that was cut
An XY Coordinate measuring machine is a great tool to have in your shop for many reasons - measuring counter plates is not one of the reasons. The amount of time and effort that would be spent measuring each and every counter plate would slow your inspection department to a halt and there are not too many customers that would be willing to pay for this service. So how do we get comfortable with the fact that we really are not checking each and every channel in our plates?

Calibrate your Counter plate machine as you would your laser, your bending machine, or your XY coordinate measuring machine. When you're comfortable with the fact that your laser and your counter plate cutter are cutting within tolerance, then you can start to relax about you final product.

Most companies again perform a spot check by laying the finished plate over the finished die. You will be able to see whether it lines up or if it's questionable. This is done at the same time you are looking for discrepancies in the image that was to be cut. Again this is the fast down and dirty method for checking your tooling.

Two other methods used in practice include:
1). Produce a one up vinyl of the carton or product to be produced and use it as an overlay to check the plates. Make sure you are comfortable with your plotter accuracy by calibrating it along with the rest of your equipment.
2). Take the laser cut die board before it is knifed and lay it on a light table. Take the counter plates and fit them to the die board. Because phenolic counter plates are see-through at the cut channel, you will be able to see whether the light coming through the die is locating to the plates. This method only works for steel counter plates if you have Superman working in your QC department. The only company that we have been able to find that has this ability is Metropolis Die Company.

We hope this has helped in your quest for the best possible checks on your system. As always, quality leads the way in being the best at anything.