This may seem like a strange topic for a blog post. Burrs, really? Snorefest, am I right? I understand, trust me. Let me ask you one question before you move on to the next post, what do you do to your parts after they come off the machine? Depending on your coolant you wash them, then are they ready to go to inspection? No sir, nine times out of ten they are not. When the part comes off the machine there is almost always some form of deburring operation. Unless of course the programmer includes small chamfers on your part as a deburring operation inside the program. Either way, when you spend as much time as you do performing a single omnipresent function, how could it be as trivial as everyone seems to think? I have worked from prints dating as far back as 1938, and even that print had a note on it requiring all sharp edges and burrs be removed. This post is intended to shed some light on the often ignored topic of burrs, and perhaps teach you a bit in search of strategies aimed at eliminating, or at the very least minimizing burring on your machined parts.
Burrs are a concern for multiple reasons. First and foremost, they can cause dimensional issues or fit issues. The dimension on your part may be right on, but if there is a burr on the edge then subsequent parts may not fit. Along those same lines, depending on the location of your burr you could have a part that is in fact within tolerance, but measures out of spec because of burring. Another major concern when dealing with burrs is cost. Deburring, like inspection, is not a productive operation – you are not producing parts, simply making the parts that you already produced meet requirements. Since the operation itself is not making money, it must be costing money. You know how it works – if it costs money, do less of it. It doesn’t matter how unreasonable the request may be, just do the same thing you’ve always done. Only, do it faster. And for less money. And with no overtime. I digress – deburring operations can be reduced, which will make you more efficient and your department more profitable. Many studies have been done on the causes of burring, and one of the reports I read was somewhat eye opening. On a part of medium complexity it is estimated that deburring accounts for 14% of the total manufacturing cost.
Sharp tools reduce burrs and for that reason it is a good idea to use a different tool for finishing than the one used for roughing.
There is a lot of money to be made by optimizing strategies and tooling selection. One of the more common culprits is the tool you are using. Always make sure your tools are sharp, since a dull tool can cause serious burrs even with the optimal tool path. In fact, watching for burrs is one of the best ways to monitor tool life, at least until you have a good understanding of how your go-to tools are going to perform. Also, this is one reason it’s a good idea to use a different tool for finishing than you do for roughing – that way you ensure the best finish and also limit burring.
Minimize Burrs in CNC Drilling Applications
When it comes to drilling, many of the same rules apply. A dull drill is going to give you larger burrs on the bottom of your part when you drill through – fresh drills will help with that. One of the simpler causes of burrs when drilling is not drilling deep enough. When you are drilling through your part you need to make sure you make up for the angled tip – the larger your drill diameter the deeper you will need to go. Drilling too shallow will result in what almost looks like a cap on the bottom of your part, not to mention a taper at the bottom of your hole. If you drill deep enough with a good, sharp drill you should be good to go.
Burrs are a frustrating, time consuming problem that you will always deal with on some level. Just take care of your tools, mind your feeds and speeds and make sure you are drilling deep enough. It can be more efficient to utilize your CNC machine to deburr in process, just keep in mind there will always be geometry that you will need to deburr by hand. Get next to it folks, cause it’s never going away. Just keep it under control. Until next time, be safe and mind the numbers.