End mills are used for cutting and shaping a variety of materials, from steel to plastic, to wood. An end mill looks something like a drill bit, except that drill bits are designed only for cutting downwards, while end mills predominantly cut sideways. Some end mills have cutting tips for making plunge cuts, too. There are a wide variety of end mills available, depending on exactly what they will be used for.Whether using a hobbyist mill at home or working at a professional machine shop, end mills are an important part of a serious tool collection. This guide covers the different types of end mills and how to buy end mills on eBay.
Types of End Mills
End mills vary primarily in size, in material, and in number of flutes, or cutting edges. End mills can also come with a variety of coatings. The shape of the tip and the angle of the cutting edge also vary. While end mills can be altered to be customized for specific tasks, it's also important to understand what types are available ready-made. Depending on how precise and how varied the user's needs are, it may be possible to get by with a single, all-purpose end mill, or a collection of end mills may be necessary.
Size and Material
End mills range in diameter from almost hair-like all the way up to more than an inch across. The larger the diameter an end mill has, the more material it can remove with each rotation. To some extent, a smaller end mill can make up the difference by simply being run faster, but small end mills can break if run too fast. However, small diameter end mills do have the advantage of being able to cut more precise inside corners.
End mills also vary in length. They are classified into stub length, regular, and long. The longer an end mill is, the more likely it is to bend with use. Of course shorter end mills cannot cut as deeply. In general, it's better to choose the shortest tool possible for the job, especially if the job will involve feeding the material in with a great deal of sideways pressure.
Number of Flutes and Shape
The flutes, or cutting edges, of an end mill usually vary between two and four flutes. However, six- and even eight-fluted end mills are used in some cases. Everything else being equal, fewer flutes mean there is a lot of room for chips to be ejected, while more flutes mean the chips will be smaller and the cut surface smoother. Different flute numbers can be used for different tasks. For example, an end mill with six or eight flutes can be used at the very end of a project, after most of the material has been removed, in order to improve the finish, This is something like shifting to a finer grade of sandpaper to put a final polish on wood. Different materials will also call for different flute numbers. For example, aluminum, fiberglass, and plastic require higher numbers of flutes, while steel and titanium require end mills with lower numbers of flutes. Some materials, such as iron, are more varied in their requirements.
Rake angle and helix angle both refer to the end mill's shape. These angles also influence how efficient an end mill will be for different kinds of milling for different materials. End mills also come in a number of styles or shapes suited to a variety of jobs. Center-cutting and drill-point end mills can cut directly downwards, just as drill bits can. Non-center cutting end mills are designed only to cut to the side, and can be damaged if forced to cut downwards. Ball-end mills have rounded tips, and have several applications, including cutting holes and slots with rounded bottoms. Ends may also be single or double. Some end mills have left-handed spirals which direct the chips away from the working area. There are also other variations.
Materials and Coatings
End mills themselves can be made of high speed steel (HSS), HSS-cobalt, or carbide. HSS is the standard, basic material, and will work well in most cases. The addition of small quantities of cobalt produces a steel that is both harder and more expensive than basic HSS. These harder end mills can be run faster, and therefore can improve productivity. Carbide end mills are harder and more expensive, though the greater cost can be more than offset by substantial increases in output. Carbide is more brittle, however, and is therefore more more likely to break. Given this brittleness and the high speeds at which these cutters can be run, carbide end mills should only be used with tools able to handle them safely.
A variety of coatings can also be used to make end mills even harder and more efficient. Coatings include titanium nitride (TiN), titanium carbonitride (TiCN), titanium aluminum nitride (TiAIN), and diamond. Not all materials and coatings can be used on all projects. Of course, the end mill must be harder than the material to be cut, so while high speed steel will work well for most jobs, it cannot cut carbide. There are some other considerations, not all of them immediately obvious. TiAIN contains aluminum, and therefore does not cut aluminum well. Diamond should not be used to cut metals, but works well on graphite and composites.
Using and Maintaining End Mills
If an end mill is not cutting properly, make sure it's actually the right one (the right size, shape, material, and so forth) for the job. Make sure the end mill is held tight in its holder, so it can't wobble or "chatter." Make sure there are no dings or chips in the end mill itself, and that its cutting surfaces are sharp. For small diameter end mills, it may be necessary to use a loupe to be able to see damage.
It is possible to re-sharpen end mills, but doing so will change the shape of the mill, and therefore change its performance. In most cases, it is both easier and cheaper to get a new end mill than to re-sharpen a damaged one. The major exception is if the damage or dulling is near the tip of the end mill, in which case the damaged portion can be cut off and the new tip ground to shape.
Buying End Mills
Once the buyer has a general idea of what kind of end mill is needed, it's time to go shopping. Here are some tips on how to find and purchase end mills through eBay.
Finding End Mills on eBay
To find an end mill on eBay, go to the Business and Industrial page, and start searching. Category lists will help in narrowing down the listings by item type. For example, to search for end mills, start by clicking on Manufacturing and Metalworking, then click on Metalworking Tooling. Under Metalworking Tooling is Cutting Tools and Consumables. You will find end mills listed under this category. Narrow the listings further by condition, location of seller, and other variables.
Search eBay listing titles for specific keywords. For example, type "diamond coated carbide end mills," without the quotation marks, into the search box and find every end mill of that type currently available through eBay. If a given search yields no results, try varying the keywords slightly, or maybe you're being too specific and so more generic keywords may be in order.
If you try searching with categories and keywords and you find that the right end mills don't appear to be listed on eBay, there here are three further options: browsing for end mills on eBay Stores; create a post on Want It Now, to ask the eBay community for their help; or save a search on My eBay, and eBay will send you an email when the right end mill gets listed.
Buying End Mills on eBay
Before making a purchase on eBay, you will have to register as an eBay member. It is important to understand what is being bought and who you are buying it from. Carefully read all the details in the item listings. This way you'll be sure you've found the right end mills for your needs. As mentioned above, you will need the right end mill to work on certain materials. Remember to figure delivery costs into the final price. If you have any questions about the end mills you are thinking of buying, you can contact the seller by clicking on the Contact Member link in the seller's profile. You should also discuss shipping insurance. If you are confronted by a choice of sellers, the easy choice is the one who has been rated as a top-seller on eBay. Such a seller has a good history of successful transactions behind them. This isn't any different from buying something in a brick and mortar store, where the buyer would want to examine the merchandise and know something about the store.
A Note on eBay's Buyer Protection
The eBay Buyer Protection program will cover the purchase price plus the original shipping costs in the unlikely case that the item never shows up or is not as the seller described it. However, this program is only available for transactions completed through eBay, by bidding or using Buy It Now, or Best Offer. Before you go through with the transaction, make sure that you have read up and understand how eBay's buyer protection program works, in case you ever need to use it.
End mills are relatively specialized equipment, but nothing else really shapes material in quite the same way. They are one of the tools where, when you need them, nothing else will really do. If you're looking for a selection of end mills to browse through or you have have a specific end mill in mind, you are sure to find what you are looking for on eBay.