The Importance of Chip Evacuation

All of us in the metalworking industry always talk about the importance of chip evacuation and for good reason. Perhaps the single most important aspect in good metal removing techniques is the ability to effectively get chips out of the way so that a tool does not overwork itself by re-cutting chips. Re-cutting chips causes a tool to wear out prematurely and typically leave a rough and non-polished surface finish on the work piece.

Chip evacuation comes into play in many other things as well. It is the Fall Season here in Michigan and I planned on spending this Saturday in the woods in my backyard sawing up some of the numerous large oak trees that had fallen during our summer storms. The participant in this case was a 35” diameter by some 200 foot tall Black Oak that sadly now lay in a horizontal position on the ground.

Any of you who have used a chain saw to cut wood know how hardwood trees such as Oak will quickly dull even the sharpest of chain saw blades. This particular oak was so hard that, at times, I actually saw sparks while I was cutting. I found myself sharpening/retouching the saw blade about every two or three cuts. About halfway through the tree I started thinking about how the wood chips were ejecting out the back of my saw. (Yes, tooling is too much of my life) Many times they were getting gummed up and clogging. Not only was this tree hard but it was green and the chips were damp and gummy. Does this remind you of any materials you’ve worked on in the shop lately? Now, as any good tool-man would do, I shut off the saw and looked at the situation with a metalworking mentality.

The problem was that the wood chips were not ejecting fast enough or effectively enough to keep the area clear for the blade to do its work properly. I needed a chip slot to help get these wet and gummy chips out of the way faster. So, I created a chip slot in the log. I cut on the top of the log and then lifted the saw tip up to cut down the opposite side of the log thereby creating a slit in the wood. So far this isn’t anything new to anyone who’s cut wood. But what I did next was to step to the other side of the log and do the same thing. Now the cut I made the first time was working for effective chip evacuation. The chips flew out of the slit and the saw cut faster and without binding up. I didn’t generate nearly as much heat either and I was now able to cut 6-8 logs before re-sharpening the blade. This equated to a 3-4 times tool life for my chain saw blade. Not bad at all and yes, still a bit sick for my "day-off" work. You may not be able to convert this method to quicker metal removal with your favorite Carbide End Mill but the theory is there.

There are several keys to proper chip evacuation with an end mill. First of all, make sure you have the right end mill for the job such as using a three flute end mill in aluminum rather than a four. The three flute end mill offers better chip evacuation due to the chip gullets being deeper than a 4 flute design. The 3 flute also offers a larger core diameter. Typically, a three flute carbide end mill designed for aluminum has a higher helix. This also aids in chip evacuation. Please visit toolinghouse.com for more information and costs. (To get back to the blog you can use your back button or from the toolinghouse website click on the link located in "Toolinghouse Blog")

If you are working with hard (Rc52+) or tough to machine materials such as Stainless Steel, Inconel, Hastaloy, Waspaloy or many of the aircraft or medical materials you should consider using a variable helix end mill. A variable helix end mill offers a chip ejecting flute form for enhanced chip evacuation at high speeds and feeds. It is also practically "chatterless" because of the unequal flute indexing and the helical transition that typically takes place on the flutes at about 50% of the tools diameter. This unique flute transition also assists in chip evacuation. It is very important that a variable helix end mill be TiALN coated. It is virtually useless to use one that is not coated. The reason is that these hard materials generate a lot of heat and that heat needs to be released into the chip and not into the end mill. Also, TiALN coating actually needs heat to work properly and in these hard metal applications is a perfect match.

For more, please visit the toolinghouse website at www.toolinghouse.com.