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Occasionally we receive questions from our customers about the proper use and performance characteristics of our products. Below are some of the more common questions about our products and answers to them.
What is wrong when I make an oblong or egg shaped pencil?
Check that the hook angle marked on the knife matches the cutter head angle. If the cutter has been re-sharpened, make sure the new grind is parallel to the front and back.
How often should I change my cutters?
Sharp cutters are always the best to use but watch for raised grain or tear-out. The cutters should be changed before this happens. Using properly maintained cutters, most manufacturers change them two times per shift (8 hours run time). For more information on cutter maintenance, click here.
What is an acceptable number of cuts per inch (or cm) when shaping pencils?
When using Incense-cedar slats, one should not encounter machining problems shaping pencils at a minimum of 25 knife-marks-per-inch (9.84 marks per cm). This number may be higher for other species. The formula for determining this number is below:
Knife-Marks-per-inch =
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(Number knives cutting) x (Spindle speed RPM)
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(Slat length) x (Feed rate - slats per minute)
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For more information regarding optimal pencil manufacturing techniques, click here.
Why is it important to keep my knives in sets?
After a cutter is re-sharpened, it becomes narrower from top to bottom, because of top clearance angles. When it is installed on the head, it doesn't protrude the same distance as before sharpening. If they are not matched precisely, only one cutter will be grooving or shaping.
What can I do about raised or torn grain?
Keep the cutters sharp. Make sure the hold-downs are tight. Check feed roller pressure. Reduce slat feed rate. Increase spindle speed if possible. Check moisture content of slats. Raised grain can become a problem if moisture content is consistently greater than 15%.
How long should cartons of slats be allowed to equilibrate in the warehouse before the production department uses them for grooving?
Though temperature and humidity are different for each manufacturing environment, we recommend storing the slats in a warehouse for at least two weeks and an additional 24 hours in the production area prior to use. The two slats in a sandwich that have significantly different moisture content can cause warped pencils, also known as "Banana pencils". When the affected pencils equilibrate to the local relative humidity, one pencil dries more quickly than the other, bending the pencil. This defect can be avoided by allowing for adequate equilibration mentioned above.
How can paint bleed-through be prevented?
The occurrence of bleed-thru is relatively rare. Nitro-cellulose lacquer solvents can loosen natural wood extractives (most of which are dark in color) found in stain-treated slats, which migrate to the surface and blend with the lacquer. Switching to water-based lacquers or some other non-solvent based finish system can usually prevent bleed-through. With solvent-based finishes such as nitro-cellulose lacquers, bleed- through cannot be prevented in all cases unless an impenetrable solvent barrier is placed between the wood and the upper coats of finishes. However, this solution is not yet available. Some proprietary undercoats are said to help but there is no industry-wide consensus on this point.
How can end chipping be prevented during grooving?
Ideally, the cutting tool moves through the wood, parallel to the grain with cutting forces localized near the cutter. When wood grain moves severely away from parallel at the end of the slat, a chip out may occur. End chipping can be prevented by reducing the cutter angle (for example from 25° to 15°), maintaining sharp cutters, reducing feed speed and/or using wood with less cross grain in the mix.
I need to change and sharpen my cutters often and this reduces efficiency in my Production Department. How can I minimize changing cutters?
Check the type of tool steel from which your cutters are made. Your cutter manufacturer should be able to provide this information to you. If you are using M2 tool steel, a material commonly found in pencil cutters, you might need to switch to stronger tool steel, such as CPM-10V. Cutters made of stronger tool steel will require sharpening less often but are likely to be more expensive.
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