Tech Talk
How can we "Optimize Router Production"?
Some time ago, a wood worker, at the time unknown to us, called me and asked if the router bits we carried were "any good". My natural response, of course, would be to assure him that we sell only high quality tools etc., etc. But I must be getting a little crusty (tr. cynical) because I through it right back at him, wondering what prompted the question. He then proceeded to tell me how no one in the business made a decent straight flute router bit and I was his last hope. My ego was only slightly bruised that he had used everybody else before calling us, but in reality, we are often better off being the last hope for a solution. Often then, even the most stubborn will come to realize the truth lies in the first, and least wanted answer. The problem was that every bit that he purchased broke. He had used brazed tools, solid carbide tools and insert knife routers with almost no success in terms of tool life. As the conversation wore on it became obvious the set up was wrong, not his tools, so we agreed to send a rep in to look at what he was doing, before selling him any of our router bits. It turned out to be a simple feed rate problem. No tool can bite more than it can hold, or discharge. He had been told this several times, but either couldn't or wouldn't understand.
I have written several articles that relate to feed, but to put the concept in it's simplest form, router bits should feed as fast as you can go without one of three things happening. If the tool breaks, and subsequent tools of the same style break as well, you can make a pretty safe bet they simply can't withstand the load you are putting on the cutting edge, and you must back off. It may be that a different type of router bit will run faster but consistent breakage with the same type of tool will be temporarily solved only by slowing down. Secondly, if the material moves during the cutting action then, again, the feed rate must be reduced. Changing the tool style or boosting the hold down system may stop the movement, but until this is addressed, you must slow down. And finally the third circumstance that will dictate a reduction in feed is poor quality of cut; chipping, tearing, or roughness.Often the comment from the user is "get me a better bit - the same style- that I can run faster without having these problems", indicating that a stronger bit won't break, or a sharper bit won't move the wood across the table, or chip the laminate. Rarely this is the case. Surely, there are some bits that are better than others, but this usually relates to precision of manufacture and grind, or carbide type rather than strength of body. The problem is usually in the marriage of feed/ speed and tool type, as opposed to tool quality.Different tools will react to incorrect feed in different ways. Small diameter bits tend to break before anything, and it is with these that there is the most skepticism about quality. But small tools not only have smaller surface speed, but smaller capacity to carry a chip, and much less body strength than larger ones, and when pushed too hard they can't move the wood, but something has to give. Small diameter tools tend to be used more often in grooving slotting or etching applications where the problem is exaggerated because the tool is cutting on a 180 degree arc and not just trimming the edge, multiplying the capacity requirement, and also they are often cutting at the extreme bottom of the tool, increasing the leverage on it.Larger routers may not break in overfeeding situations. Because of the increased body strength they will often move the wood or just tear at it as opposed to cutting it cleanly. But breakage can happen, particularly with solid carbide bits that do not have the tensile strength of steel bodied bits. Getting back to my statement about simplifying the feed rate problem, if any of the three aforementioned problems occur; breakage, bad cut, or material movement - slow down, but if none of these has happened then I would speed up the feed until one of them did, and then back down.It may seem like an unsophisticated, and unusual way to maximize your production and it may cost you a bit, but the fact is there is no exact calculation that takes in all the variables that affect feed rate. We can come close, but materials vary, as do thickness' amount removed, hold down, tool size and type, machine type and condition, finish required, etc. You will optimize your output and tool performance by doing in house controlled, and sometimes destructive testing, utilizing the guidelines that your tool supplier has given you. The cutting edge on router bits, like most cutting tools, will last longer when running cool, and high feed speed will usually keep a tool cooler than feeding to slow. And at the risk of repetition if any of the conditions change, the feed rate must be reviewed. by: Doug Reid, President, B.C. Saw
