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Saw Filing 101: Cuts like a knife

One of the biggest breakthroughs in our time, or certainly my time, for sawmill and lumber production and manufacturing, may well be knives and their applications for chipping.

Once the old bent knives and round back knives were replaced with disposable knives, the market was open to faster speed feeds, increased lumber production and yield. As most remember, the old bent knives and round back knives would push and pull cants causing thick and thin lumber, and other issues and problems. 

Equipment manufacturers quickly jumped in and made these disposable knives a very important mainstay in lumber producing mills. New mills being built changed from modular to straight line mills because of the high recovery and faster feed speeds this new product and process allowed. 

Today, the vast majority of lumber production is made from these new mills. The new conical heads and chip heads allowed the chipper knives and the saws to work side-by-side manufacturing lumber efficiently. This breakthrough with the knives allowed for attack angles and knife angles to be changed as needed. Also, the precision that the heads and knives are manufactured to today create smooth running heads that will operate very well, producing good sawn lumber and quality chips at fast speeds. Because these new disposable knives are smaller and thinner than the old bent knives and roundback knives, they are manufactured much more precisely, and with better heat treat process that allows for better knife quality. Correct hardness for knives increases knife life.

Although it may sound easy to pair the knives and the saws to run together, there is a process. To pair the chipping knives with saws together for best results, it does take some orchestrating and knowledge of RPM, feed speed, log diameter and maximum depth of cut to determine exactly what is required for best performance. The quality of chips produced is critical for both production and profits.

There are many different types of chipping heads with a growing number of manufacturers getting in the business of also manufacturing the knife itself. I have had the privilege to see different heads and knives manufacturers get started and create success for themselves and the wood industry. Most of these manufacturers are successful and can help any mill with chipping issues, including producing the correct chip size needed for optimal profits.

Smith Sawmill Service saw this breakthrough for our sawmill industry in the late 1990s and helped to introduce Key Knife in the South; changing bent knives and chip-n-saw knives over to the disposable Key Knife system. This worked out well for us and the customers for a few years until Key Knife went direct. We then came up with our own system. The knife was as small as disposable knives, but could be sharpened and babbitted. This ensured the knife location would be the same after every change. Now, we are a part of the BID Group and working side-by-side with Comact providing saws to pair up with Comact’s new knife system. It’s our belief that each company suppling these conical, cylindrical and profiling heads with their knife systems will all have their own advantages. 

If any mill is having problems with chipping, knife life, yield and lumber quality, I suggest you reach out to some of these knife manufacturers for help. I personally see pros and cons for the different knives offered today in the wood industry. Depending on the application and your needs, it will be possible for you to select the knife and heads that will best perform in your mill.

Most equipment manufacturers will let you pick the knife of your choice to be in their equipment. Make sure you get all the information you need to help determine the knife you choose to use. Of course, if you decide to mix the equipment manufacturer with a different knife and head manufacturer, I suggest you have them in the same room to determine what will be expected from both. Most knife and equipment manufacturers will work very well together for your best interest. 

Paul Smith is a saw filing consultant and founder of Smith Sawmill Service, now part of BID Group. You can reach him at Paul.Smith@bidgroup.ca.

This article is part of CFI’s 2023 File Week. Find the File Week landing page here.