Today we’re talking guillotine cutters with Dave Double of Double Equipment, a bindery equipment repair specialist based in Ohio.
Andre: Thanks Dave, for bringing up this topic. You’re out there in the field nearly every day servicing all kinds of bindery and finishing equipment. I suspect you get some good insight on what people do right and what they do wrong. What’s one of the biggest mistakes you see made in guillotine cutting operations?
Dave: I find myself repeating the same thing over and over again when servicing a paper cutter; “You’re not replacing your dull knife blade often enough!” Many owners and operators of guillotine cutters do not truly understand how the type and condition of the knife blade affects the quality of the cut.
It’s amazing how many times I service a cutter that isn’t cutting so well and all I have to do is install a sharp knife. Presto, the machine cuts great. Most operators however, will cut until they have problems and only then decide it is time to change the knife.
Well that’s probably way past the point the knife needed changing. Power cutters today are extremely strong and will cut though a lift of paper with a very dull knife. What operators don’t realize is how much wear and tear this puts on the cutter.
It’s hard on the hydraulic cylinders and clutch systems. Operators will run the maximum clamping pressure in an attempt to compensate for excessive draw on lift of paper. It’s also hard on the clamping linkage.
With repeated use of dull knives, you cause a lot of premature and expensive damage to the machine. And of course the cut quality also suffers with a dull knife. This could all be avoided by simply keeping a sharp knife in the cutter.
Andre: How long should a sharp knife last?
Dave: Here’s my rule of thumb, using 50# Offset as the standard:
- Standard Steel Knife Blade: will cut about 8 hours or about 1,200 cycles
- High Speed Steel Inlaid: will cut about 16 hours or about 3,000 cycles
- Carbide Knife Blades: will cut about 10-20 times longer than High Speed Steel
One of my favorite tales of woe is this: A client is cutting about 2-3 hours a day, everything from plain paper to chip-board. They say, “I don’t understand why we’re having problems…we just put a sharp knife in the cutter.” When I ask, “How long ago?” they respond, “Last month”. Now you do the math…if they’re using a standard steel knife, it probably should have been changed at least 6-8 times!
Andre: What other factors affect knife performance?
Dave: Some other factors that can affect your results:
- The expertise of your sharpening service
- Types of paper or other substrates you might be cutting
- Knife angle
For example; cutting chip-board will dull the knife rapidly to the point it will need replacing as soon as you are done with that chip-board job. Another example; your sharpening service doesn’t do a good job and you assume you’re installing a good sharp knife. I have run into this many times.
The grinding angle on the knife also greatly affects the performance of the cut. Generally, printers use a 24 degree angle. But a 24 degree angle will create draw when cutting spongy or NCR stocks with low clamp pressure. Many cutter manufactures include some guide lines on knife angle in the manual. These guidelines vary by manufacturer. Generally speaking you can look at it this way:
Knife Grinding Angle
- Soft Spongy Paper: Smaller angle, 19 – 20 degrees w/low clamp pressure
- Regular Paper: Med angle, 23 – 24 degrees w/med clamp pressure
- Hard Paper: High angle or double bevel up to 30 degrees w/higher clamp pressures
Always refer to the OEM manual or discuss this with your sharpening service and the manufacturer. There are far too many different configurations and materials to list here to give a one-size-fits-all answer.
Andre: According to Polar, in their manual Cutting in Practice, 70% of all cutting problems are due to the “wrong knife angle, or the knife quality does not fit the material to be cut.” Then they go on to list over 50 types of material with suggested knife angles. I counted at least 17 different knife angles, with combinations of single and double-bevel, including a variety of angles and lengths.
Dave: What is important to understand is that most of us get along fine with the standard knife. When trouble strikes, we should not always blame the machine for problems caused by the knife. Instead, we should have that conversation with the knife vendor or cutter manufacturer. Printers will rarely change a knife based on the stock they will be cutting. Most don’t even know what angle they use. They just wonder if the knife is sharp or dull.
Andre: When I first started in the bindery, we cut an awful mix of SBS, chipboard, cover stocks and then mixed in a lot of book weight papers. And we did it with standard steel knives. After some years of ‘education’ from a good knife guy, we finally added an inventory of knives to include 2 or 3 knife angles and high speed steel to match what we happened to be cutting. The right knife with the right paper gave us a huge boost in cutting productivity and the upgrade paid for itself quickly.
Just to summarize, it sounds like three simple practices will keep your guillotine cutter humming along:
- Keep a sharp knife in the machine at all times
- Use the right knife steel to suit your operation
- Use the right knife angle for the job you’re cutting
Thanks Dave for you input on this topic. You can reach Dave Double online at http://dblequip.com. If you want to do some more some in-depth reading on the subject of guillotine cutting practices, download Cutting in Practice here. (pdf opens in new browser window)
And as always, we welcome your comments and experiences below!