Economics of a Defecting Saw

      For a big investment, you can get smart equipment that senses and cuts out knots in accordance with your cutlist. But that cost isn't worth it for every operation. May 23, 2007

I am interested in an automatic defecting saw but I'm not real certain how these machines work. I've noticed a couple of different companies that make these. Dimter is one and Grecon is another. Do these machines automatically detect defects in the wood, or do they require an operator to mark the defects with a crayon? Let's say I have a product spec that requires every moulding strip to be 96" long PET. Do these saws automatically detect an end split, compensate for it, and still give me a 96" long clear strip? Or does it require an operator to mark the defect with a crayon? My cuts will be a minimum 6' length and maximum 16' length. I've read all the bells and whistles, but I'm really only interested in this machine for defecting, cutting to length, and sorting. The optimization is of no importance for my purpose. Also, if this defecting saw does recognize defects, can you select how sensitive it rejects?

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
Both manual and automatic systems are available. In the manual system, your operators mark defect with a fluorescent crayon which is scanned by the saw and then cuts are made. Most of the higher end saws can take your cut lists and optimize where they cut to improve yield. The fully automatic systems use a scanner that can scan optically, with ultrasound and a couple other methods. Tells the computer where the defects are and the process continues as described above. At IWF there were two systems I saw that did the defect scanning. I believe they were around $300-350k for the scanner plus the saws, which range from about $100k up, depending on speed and other capabilities. One other brand you may want to look at is Paul saws - they can integrate with crayon marking or the automatic scanner.

From contributor R:
I believe Dimter & Grecon are now owned by the same company. The Weinig Group would be able to help with those models you're talking about.

From contributor C:
You made the statement that optimization is of no importance to you. If you understand how that term is used in the industry and are certain that you do not need optimization, then you are throwing money away to purchase an optimizing saw. A scanner that can see defects such as small knots, splits, bad wood, etc., will cost you $500,000 to $700,000 just for the scanner alone. Now you have to feed it with chains and a feeder, buy the saw for another $100,000, and a sort line. Pretty expensive. Worth it if you are optimizing and defecting. But if you are not optimizing, a good operator with an air or clutch operated knot saw will cut defects as fast as he can mark them with the crayon. The optimizing saw's purpose is to measure the strip and take the mix of product you are looking for and divide that strip, taking its defects into account, into the most valuable parts. If you are going to cut certain lengths regardless, or if you have only a few lengths and not a realistic mix of lengths, you are throwing your money away. Optimizing is the keyword. If you don't need it, don't buy it. That is why it is called an optimizing saw. A perfect example of where optimizing is worthless is in a flooring mill running strip flooring where random lengths are standard. Many moulding operations are similar.

From the original questioner:
Thanks for the responses! I think with improved material flow, I could make the defecting go much faster. Besides, I can hire an employee for several years for 700,000.00!

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