Home | Up

Tools...

The Mill...Modeler's Best Friend

By Robert Anderson

Eventually, every modeler aspires to have that "ultimate" machine tool on which he can fabricate most any part. For model rocketeers, more often than not, the first "ultimate" tool that he thinks of is the lathe. This is natural because most model rockets and their components are revolutions of some particular shape and consist of round parts like cylinders and cones...which can be easily made on a lathe.

However, there is the first cousin to the lathe that I believe is even more useful and can be easily used to drill, shape irregular parts, and to "turn" parts just like on a lathe. In fact, this "cousin" can be used entirely to replicate itself...something you would be hard-pressed to do with a lathe. Furthermore, this family member usually costs only marginally more. This cousin to the lathe is the milling machine or more simply, the mill.

Lathe vs. Mill

The primary differences between the mill and the lathe are that the lathe typically spins the part that it cuts while the mill spins the cutting tool. Though the difference seems almost abstract, it gives some very significant advantages to the mill.

Think of the mill as a very precise hand holding a rotary grinder or cutting tool with a very precision bit. The mill can very precisely (frequently in sub .001" increments) move the cutting tool around the part (or, as with most mills, move both the tool and the part that the tool is used to cut) and remove and shape material on at least five sides (those being the top, bottom, front, left, and right sides).  The part to be machined is generally mounted on a table which can move precisely to the left and right (the "X-axis") as well as to the front and rear (the "Y-axis"). The spinning cutting tool (or "bit") moves up and down (the "Z-axis"). The spinning tool is mounted to the headstock which moves up and down on the Z axis. Frequently, this headstock can also move in and out along its own Y axis as well as tilt from side to side...though these features are generally included only on larger and more expensive mills (but are coming to be seen on small hobby mills more and more).

By removing the tool bit and its holder or chuck and replacing them with a chuck to hold a part, the mill can effectively become a sort of lathe. The non-spinning cutting tool can be mounted on the table that would normally hold the part and since the table can move in and out with the cutting tool it is easy to see how you would use the mill as a lathe. For mills that can rotate the headstock by 90 degrees so that the part is held horizontally like a lathe, the use of the mill as a lathe becomes even more evident. However, using a mill as a lathe generally does not allow for the turning of parts as large as can be turned in a similarly sized lathe.

On the other hand, the lathe spins the part during shaping which necessarily means that the part must be round (well, there are exceptions...but nothing that can commonly be done on most lathes). Since the spinning piece is mounted at one end, the cutting tool can cut the sides and one end though with longer pieces that must be supported at both ends, the cutting tool only cuts along the sides. It is the non-spinning cutting tool that moves in two directions...along the length of the piece on the Z axis and in and out on the Y axis. Moving the tool in and out allows the cutting of smaller and larger diameters while moving along the length of the spinning part allows constant cylindrical cuts or any combination of curves and tapers which are a result of a combination of simultaneous moves of the cutting tool along the Z and Y axis.

By removing the chuck which holds the spinning part (or simply "chucking" the spinning cutting tool in the existing chuck) and then mounting the part to be cut on on a secondary table mounted to the lathe's tool cross-slide, it can be seen that the lathe can be used to perform milling functions, though typically the ease of cutting or the size of the part is not as great as could be accomplished in a mill of similar size.

Though it seems that you can accomplish basically the same operations on both the mill and the lathe, the mill will hold the advantage in that it typically can be used to make individual parts that are as large or larger than the mill itself whereas doing the same with a lathe would be significantly more difficult.

There are two popular variations on the mill and lathe which combine the functions of multiple tools. One is the drill-mill which is basically a drill press with special bearings on its spinning shaft that allow it to remain precise during side-loaded cuts during milling operations (the typical drill press is not equipped to remain precise and rigid when doing side cuts). Instead of a stationary table, the drill-mill is usually equipped with a table that allows moderate movements along both the X and Y axis. The second is a lathe which is equipped with a larger than normal tool cross-slide to which a part can be mounted and a second headstock that holds the cutting tool horizontally or, optionally, is equipped with a lathe headstock that can be removed and mounted vertically as on a mill. Both are compromises with the drill-mill usually being disappointing in all but the most basic of circumstances. On the other hand, the convertible lathe is generally still a much better lathe than it is a milling machine and generally costs as much as individually purchasing a lathe and a mill by the time you add all the special fixtures and tools.

Hobby Mills

Before I get too deep into mills that are manufactured specifically for the hobby industry (or at least for milling smaller parts) I won't rule out the use of full-sized mills. Sometimes a used full sized mill in good condition can be obtained for about the price of a new hobby mill. The disadvantage is that full sized mills are larger and have greater power requirements...and by their very bulk and appearance are generally not a welcomed addition to an in-the-house workshop but would be better suited in a garage or dedicated workshop structure. As a rule both hobby mills and full sized mills use the same cutting tools, and in spite of its size, full sized mills can generally make parts that are just as small, delicate, and precise as can be made on hobby mills. The largest advantage of a full sized mill is that it can handle much larger parts with ease whereas there are lower limits to the size of the parts that hobby mills can handle (though with a bit of experience and imagination a hobby mill can make parts larger than itself).

Most hobby mills and lathes are typically classified as "micro mills" and "micro lathes." I've always felt that the "micro" term might lead some to underestimate the ability of the devices both in function and size of components that can be worked. Surprisingly, if you look at the ratio of the part size these "micro" machines are able to handle to the actual size of the machine you will discover that they are really the ants of the machine tool world in that they typically handle proportionally larger parts than can their full-sized counterparts.

Unlike hand tools such as saws or knives it is hard to address micro mills as a generic brand. There are three major manufacturer/sources of mills generally thought of as hobby mills. These are Sherline, Taig, and the Chinese manufacturers (there are several Chinese manufacturers which manufacture mills [and lathes] that are essentially identical and marketed through outlets such as Micro-Mark and Harbor Freight and brands such as Microlux (the latter of which equip their mills with custom features unique to them).

Sherline

The Sherline mill is the smallest and simplest of the three and is generally the more expensive by a slight amount. At first, it would seem that the Sherline is the less capable and not as good a "deal" as the other two but don't let that fool you...the Sherline is generally considered the Corvette of the group. There are two general models of the Sherline mill. One offers four motions...three conventional in the X, Y, and Z axis and a fourth by allowing the headstock to be rotated through a full 360 degrees.

The Sherline is notable, perhaps, for the features that it apparently lacks. It almost totally lacks all but aluminum metals for its construction. Even the gibs and ways (think of these as "sliding bearings), which on most mills are of brass and steel (or iron) are of a plastic material for the gibs and aluminum for the ways.  There are no fancy "ball screws" (the screwlike devices that move the various parts of the mill that are designed in such a way as to prevent "slack" or backlash in the moving parts) and the only place you will find ball bearings are in the headstock spindle...small hardened steel "thrusts" (thrust plates) contain the ends of each of the 3 axis lead screws contain no formal bearings or bushings but utilize simple washers to act as bearings. None of the components are cast but all are themselves milled and machined from solid aluminum billet. Secondly, every aluminum component is black anodized. The table and the bed are cleanly laser etched with scales on the X and Y axis. The only significant non-aluminum component is the vertical way along which the headstock travels and it is a conventional steel beam type of structure with ground ways as on full-sized mills. However, the ways on the table and the cross saddle are the aluminum itself. Sherline relies on the hardness and the durability of the anodizing (which is, in fact, harder than most steel) to provide the bearing surfaces of the ways. And rather than being ground, the ways are precision milled...to an amazingly accurate degree. One might think that wear might be a problem but after ten years of use in my workshop the anodizing looks as good as new. Due to the low wear aspects of the Sherline the unique adjustable plastic gibs (which are shaped to a very long taper and adjust by sliding parallel to their bearing surface) are more than up to the job and reduce friction compared to metal-on-metal gibs. As a result of its black anodized aluminum construction with integral ways Sherline mills are mechanically very simple, very easy to maintain, and make use of a minimal number of components.

Some people may be concerned about the fact that both the Z axis lead screw and the Y axis lead screw are fully exposed. The X axis screw is basically open but is shielded by being located in a trough on the underside of the milling table. The exposure of the Z axis screw is of minor concern since it is located in a vertical trough on the backside of the milling column. However, the Y axis screw is fully exposed to falling chips from the machining operation. If you use conventional lubricants, the screw acts as a magnet for any chips and the smaller ones will inevitably be drawn into the leadscrew nut mechanism which can cause rapid wear. Dry Teflon lubricant greatly minimizes this but many would still like to have the screw protected. It is fairly easy to fabricate your own protective cover but it would be nice to see Sherline offer it as an accessory or option for those who are nervous about the exposure. However, I must point out, that after ten years of machining with an exposed Y axis lead screw my own unit shows no sign of wear in excess of the lead screws on the other two axis'.

The motor which drives the spindle is unique. It is a 90 volt DC unit that can be plugged into any AC power from 110 to 240 volts over a range of cycles from 40 to 70 without any adjustments or setting of switches. Also, for hobby use [even with hard metals] the motor is very strong and powerful...surprisingly so even at lower speeds. It has two general speed ranges controlled by shifting a drive belt on its pulleys with a constantly variable motor speed range controlled by a dial.

From an aesthetic perspective, the Sherline is unique and attractive in its stark black anodized finish. It is incredibly simple and easy to maintain as well as to keep clean. One other advantage, particularly from an indoor cleanliness perspective, is that a dry Teflon lubricant is recommended which offers two advantages. First, you will not get your hands or clothes stained by oil and secondly, because the lubricant is dry, it does not attract dust or offer small metal filings a surface on which to cling.

Overall, the Sherline is very well suited as a "desktop" machine tool in that it is small, light, and clean. It is best suited for non-metallic materials though it is fully capable of doing some surprisingly heavy-duty work on aluminum and other soft metals. With care, it can handle harder materials such as steel or even Titanium but I wouldn't use the Sherline as a "production" unit for such materials.

Another plus for the Sherline is that the Sherline web site is very comprehensive, all manuals and much more are available free online, and every single part for every Sherline model made is available from Sherline. Almost every accessory and component for the Sherline tools is made by Sherline...including many items that most would consider "off the shelf" such as the various chucks or even "generic" items such as their milling vice and rotary table. As such, these are all more expensive...but once you buy the Sherline tools the obvious higher quality of all its tools and accessories becomes addictive and you find yourself more than willing to pay premium (though still reasonable) prices especially when many of accessories have the same look (anodizing), feel and fit as the mill itself. However, there is nothing about the Sherline that forces you to use their tools and accessories exclusively...most functionally equivalent items can be found on the general market at discount prices. There are also a number of dealers (web and brick-and-mortar) which carry Sherline parts. Sherline also updates components as "better" ideas and designs come along and almost all of the updates universally retrofit earlier models.

There are several Sherline mill models though I would (as with any tool) look to any possible future needs and go with the models which offer the greatest flexibility and growth path. I personally favor the 5400 model because it has slightly more capacity than the other models. However, the Model 2000 offers 8 axis movement/adjustability though this comes at the expense of reducing its ability to handle more heavy duty operations. For hobby use and non-metallic materials the 2000 will work just fine. Expect to pay between $700 and $800 for a manual Sherline mill (the Model 2000 is about $1000).

The Sherline also comes in a CNC (computer numeric controlled) model as well as one that is equipped with the stepper motor mounts for those who wish to do their own CNC conversion. Even if you get one of the "manual" versions of the Sherline it is the easiest mill that I have found to perform your own conversions on.

Taig

The Taig mill is, from a design perspective, in a class of its own. It uses a rather unconventional tubular steel structure to hold its table and headstock which, for its weight, it is surprisingly strong and rigid. Though it is a much more industrial machine in appearance and complexity it is still a relatively simple device when compared with full-sized mills. Most of its components are "in the open" and there are not a lot of areas that need messy lubrication. Though I don't know Taig's position on the matter, I suspect that the Taig can be lubricated effectively with dry Teflon lubricants like the Sherline.

Unlike the Sherline, the Taig is largely of steel construction with some aluminum. The ways are ground steel and the gibs are more conventional brass that are adjusted via conventional set screws and lock nuts. Though it is more traditional it is also a bit more difficult to precisely adjust than the Taig. The leadscrews on the Taig are twice the diameter of those of the Sherline though the amount of movement per rotation is the same. Typically, this means a bit more efficiency in the amount of leverage that can be applied and also means larger bearing surfaces on the threads which has the potential to reduce wear and "backlash" in the system over the long run. The Taig also has more conventional handle-type handwheels for manually moving the table and spindle.

Like the Sherline, the Taig uses the same headstock for the mill and their lathe. The headstock is an extruded block containing a pair of preloaded bearings which are very durable. A rather large (almost overwhelming) AC motor provides the power to spin the milling tools. Speed adjustment is via stepped pulleys rather than via an electric speed control (AC motors aren't as suitable for speed controls as DC motors).

The Taig mill offers a degree of movement that is not part of the standard Sherline mills in that its Z axis column can be tilted from side to side (different than the headstock being rotated) though, unlike the Sherline, the headstock itself cannot be rotated. It should be noted that an $80 add-on for the Sherline will give it the ability to tilt its column. This extra degree of motion is not as commonly useful as you might at first think as there are rarely situations where its use is mandated or convenient (the biggest "downside" for such a tilting column is re-truing it back to an exactly vertical position which is critical to proper milling.

The Taig comes with a rubber flap type cover over the Y axis lead screw. However, its use is probably more beneficial to the other components of the mill table as they are more complex and have more nooks and crannies that might collect metal chips and dust than does the Sherline machine. Frankly, though effective, the rubber flap cover is not a very elegant solution and sometimes gets in the way as it bunches or folds upward during table moves.

The Taig is very capable of handling harder materials like steel as well as hobby materials such as plastics, resins, and aluminum. However, because it is a slightly more "industrial" design there are more nooks and crannies into which metal shavings and dust can migrate making the machine a bit more difficult to clean and to keep clean (though by no means difficult...just a bit more diligence is required).

There is one basic Taig mill model. Though there is a "computer" ready version, it is based on the regular Taig mill. You can expect pricing in the $700-$750 range for the basic manual Taig.

Like the Sherline, the Taig can be purchased both as a full CNC ready-to-run unit or equipped with stepper motor mounts to perform your own CNC conversions. However, if you purchase the manual version of this machine it CAN be modified for CNC though it will require significantly more work than any version of the Sherline.

Micro-Mark Mill

Shanghai Sieg of China makes a "mini mill" model which is manufactured in several similar models which are sold as rebranded units with specific modifications and features depending on the rebranding. The most popular of this type of machine is the Microlux (the Sieg X2 model) which is sold by Micro-Mark and  is the nearest clone of a full sized machine shop mill being built out of several conventional steel castings castings that are machined to make up its individual components. Virtually identical mills with their associated "custom features" are sold through Harbor Freight and Cummins Industrial among others. The primary reason that I recommend purchasing the Microlux is that it comes with feeds that move exactly .05" per revolution of the handwheel on each axis. This machine from other sources comes with either metric feeds (.039" per revolution) or fractional inch feeds (.0625 per revolution). To be fair, I've only seen one of this type of machine with metric lead screws so such a set-up is probably very rare outside of Asia. Believe me, you will very much appreciate the fact that exactly two revolutions is .1", twenty revolutions is one inch, and so on (BTW, both the Sherline and Taig mills use the .05" per rev "standard").

The Sieg is substantially larger and heavier than either the Sherline or the Taig units (hence, its classification as a "mini" unit rather than as a "micro"). However, its travel along the X and Y axis is smaller than the corresponding travel distances on either the Sherline or the Taig.

Like the Taig, the Sieg Z axis column can tilt from side to side and the headstock cannot rotate. A nice feature of the headstock/spindle assembly is that it is equipped with a spring "counterweight" and feels much like a drill press when operating (i.e., depending on how the spring is adjusted, the spindle advances and retracts against a spring much like a drill press). You can use it exactly like a drill press using a large lever wheel on the "coarse" Z axis. For more traditional fine milling, you disengage the large lever wheel and engage a fine Z axis feed which is operated by a small wheel that faces out toward the operator. In this respect the Sieg is more complex and, some feel, a bit more limited than either the Taig or the Sherline. While the Taig and Sherline units move through their entire Z axis range using a single lead screw the Sieg does not.

The Sieg is different from the Taig and Sherline in that it uses a geared headstock working in combination with a speed controlled motor. As a result, this machine is definitely noisier and requires more headstock maintenance (as well as lubrication) than the belt drives of the other machines. Unless you get a more recent model of the Seig through Micro-Mark you will discover that one of the gears in the headstock is of plastic construction. There are reports that this gear shears with regularity and some claim that this is a safety feature that protects against overload.

Down on the table, the X and Y axis handwheels are very substantial units that might be more at home on larger mills. The Y axis wheel is located low on the machine and the unit must be located near the edge of the workbench so that the Y axis hand wheel can hang over the edge...otherwise, the machine will be "jacked up" on  the hand wheel rendering it useless. Unless you are really hogging metal, there is no real need for such large hand wheels and several users have reported equipping the machine with smaller handwheels. The Y axis lead screw has an excellent accordion-type shield which neatly stays out of the way as the table is advanced back and forth. However, the accordions themselves served to collect chips that can cause the cover to bind as it retracts...so the chips need to be occasionally cleared from this area.

The Sieg is also similar to full sized mills in that it requires slightly more messy lubricants with a synthetic motor oil and lithium grease being recommended for the various components.

Like the Taig, the Sieg can easily "hog" (very heavy cuts) hard metals.

The great advantage in buying the Micro-Mark version of this machine is that Micro-Mark stocks an incredible array of accessories for this machine at very reasonable pricing. The Micro-Mark version of the machine sells for an incredibly low $525 and Micro-Mark has been known to "discount" the machine even further from time to time.

Which One For Me?

This is pretty much an apples or oranges type of call. You can do incredibly intricate work on all three of the machines. The Sherline excels at being compact, simple, and clean while at the same time having the capability of having the most easily maintainable precision of the three. Though it can handle metal, it is really better suited for other materials. The Taig is pretty much a good "do all" kind of machine that easily handles metals. However, it is more complex, requires a bit more maintenance, and is not as "clean" of a machine as the Sherline but if you have good housekeeping habits the Taig is really no more of a problem than the Sherline. The Sieg is the more "machine shop" type of machine. It is right at home working with metals but has far more places for dust from non-metallic materials to collect. I know one owner of the machine whose only complaint that he has ever expressed to me is that "its a bear to keep clean." Though it is the largest and heaviest of the three mills here it has the shortest travel in the X and Y table axis' (not a problem for 99% of hobby use) but you can do some VERY heavy duty cutting with this machine.