The techniques, tools and bits required will vary drastically dependent on the job. Tools can range from pin vices to precision drill presses, mills and lathes. Bits may include augers, Forstner, spiral or spade and even hole saws, fly cutters or lathe boring tools. Only you pocketbook, ability and necessity define the limits. Other determining factors are the material to be drilled, the hole size and depth and the accuracy required. However, though tedious, almost all work can be accomplished with simple hand tools and common bits.
BITS
MATERIAL
Abrasion by molecular particles can "sand" away the edges. Even the chips contribute to the process. Common plastics as styrene are more abrasive than brass, aluminum or zamac. While fiber glass and glass filled circuit-boards are particularly bad. Proper lubrication can alleviate the problem by providing a coating over which the particles may ride away from the edge.
A direct result is heat, which in turn aggravates both wearing processes by agitating the molecules. Increased cutting speed increases heat produced. Lubrication can help remove some of the heat. Only breaking or bending can destroy a bit faster than heat.
At the low end of material are CARBON (steel) bits, normally found in hobby-shops. For hand and low speed power drilling, they are the most practical, since they have a little more spring, which reduces breakage. Even though their durability is lower, probably more are broken than worn out. They cut very well in the common hobby substances excepting harder steels and glasses.
For faster power drilling HIGH SPEED STEEL (HSS), translated as higher heat resistance, provide a higher priced, more durable, but more brittle choice. These can handle all but the hardest steels. They are the standard hardware store bits, more recently introduced into hobbyshops by Mascot in select sizes.
Although normally considered industrial or production materials, some of the following have trickled down to the consumer market. Chromium, tungsten and tungsten carbide alloys offer higher durability and heat resistance at a much higher price.
Very durable Solid CARBIDE bits are used for high production of harder steels, glass filled circuit-boards and other abrasive substances. They are readily available in the 61-80 range, but with standard 1/8" collet shanks. Since they a very brittle, bit lengths are usually relatively short and only precision machine drilling is recommended.
STYLES
The most common SIZE series in the USA is FRACTIONAL or fractions of an inch, ranging from 1/64" (.015625" = 3.96875 mm) to many inches with 1/64" increments.
More common among machinists, are the NUMBER and LETTER series, ranging from #97 (.0059 = .15 mm) or more commonly #80 (.0135" = .343 mm) up to #1 (.228 = 5.7912 mm) and A (.234 = 5.9436 mm) up to Y (.377" = 9.5758 mm) with some half sizes at various places. Unfortunately the increments are irregular and do not follow any standard progression. Sets of 61-80, common in most good hobby-shops, will serve most needs, excepting larger tap and clearance bits for commonly used screws. General's steel model railroad scale lists the latter commonly used. Other sizes are found in many handbooks with variations for different work materials and thicknesses.
Harder to find, but more preferable for precision sizing, except in the smaller sizes, is the METRIC series usually starting at .1 mm (.003937") to many mm with .05 mm (.00197") increments in the smaller sizes. For most uses, tap drill diameters are:
ASME: nominal diameter minus 1/pitch
metric: nominal diameter minus pitch.
For ideal sizing a judicious selection from all might be considered, since many sizes overlap or are too close to differentiate. Many handbooks list all three together, in ascending order, for quick comparison and possible conversion.
Unfortunately it is very difficult to find inexpensive bits smaller than #80 (.0135" = 1.176 HO in. = 1.89 N in.) to drill holes for handrails, grab irons and small piping.
These require a set of collets or adjustable chucks, quite frequently a keyed Jacobs or key-less variations. Sizes over 1/4" to 1/2" are offered with cut down 1/4" shanks for 1/4" chuck usage. Lengths are usually proportioned to diameter but extra long jobber's bits are available in larger sizes. The remaining shanks are more specialized for industrial or production use. Numbered bits less than .125" (#31 - #80) are available with 1/8" shanks for collet usage. Larger sizes use standard 1/4", 3/8" and metric collets. Recently hexagonal shanks were introduced for cordless screw diver usage. Machine shops use Morse or other tapers with flattened tang extensions.
For general usage, standard cutting lips form a wide vee of 118 degrees total angle, usually with a small flat chisel tip. However other angles are used for more efficient drilling in brass and other materials. Recently pointed tips were introduced, replacing chisel tips, to supposedly eliminate center punching.
Wood augers are a variation of the spiral bits, having a wood screw type tip and outer cutting edges extended beyond the lips. Usually they have a sort of pyramid shank end that fits into a chuck on a hand brace.
Similar, larger earth augers are available for drilling wells and post holes.
Special carbide or diamond tipped bits, sometimes driven by hammer or air powered drills, are used for glass, masonry, concrete and rock. These can prove useful when supporting benchwork from masonry walls.
Various flat bits with no flutes are available. In very small sizes starting at .004" (1 mm) relatively expensive, jewelers spade or pivot bits with vee tips are very useful for the modeler in drilling accurate holes in nonferrous materials. Larger versions with pointed tip and arched or straight lips are available for drilling wood.
Very expensive Forstner wood bits are available in medium sizes, if you are well heeled.
There are many non-standard bits for drilling other than standard sized cylindrical holes.
Useful for benchwork are, commonly flat, wood screw pilot bits. They provide a tapered hole section, slightly smaller than the screw root, a cylindrical shoulder section for easier insertion and an adjustable flathead countersink depth.
STEPPED BITS are commonly used in thinner sheet metal. Each succeeding cutter is an increment larger, permitting trial and error hole fit,
Stepped sized hole saws are useful for larger shallow drilling in thinner materials like plywood. Essentially an arced hacksaw blade in a grooved holder, they have an extended pilot bit to start the drilling and help in centering.
Similar in function, borrowed from machinist usage, is the continuously adjustable FLY-CUTTER with 1 or 2 specially ground lathe tool type bits mounted on a cross-bar. There is also an extended centering pilot bit. More commonly it is used without a centering bit on a mill to plane large surfaces or to cut concave troughs in blocks. An example of the latter is enlarging or lowering the saddle on cast steam cylinder blocks.
WARNING: This tool should
only be used with a drill press or vertical mill with the work piece
securely clamped. Especially with the unbalanced single bit, the side
thrust is uncontrollable , possibly leading to damage and serious
injury.
Similar again is the lathe boring bar, used to bore and thread larger holes. It clamps a tool bit at its end, which is inserted into a pre-drilled hole with the bar mounted on the crossfeed for adjustment. It can bore any contour circular hole.
Various conical or cylindrical COUNTERSINK BITS are used to recess screw heads and nuts. Hobbyist sizes are usually available for screw sizes #1 on up at industrial suppliers..
Often overlooked, one of the most useful and precise hole enlargers is the TAPERED REAMER available in very small to gigantic sizes. Mascot offers a set of 6 square 4 edged hand reamers ranging from almost 0 to about .1" (2.5 mm). With their long tapers, they are ideal for precise enlargement of through holes for mounting grab irons and lugged details. Available in many sizes are long taper, manual or machine reamers for enlarging bores, often in bushings, to very precise tolerances. Shorter tapered hand reamers are common in hardware stores and machinist's suppliers.
DRILLS
>Basically there are 3 classes of drills, hand, portable powered and fixed machine tools. All are available in useful modeller sizes.
HAND POWERED
The simplest, least expensive and probably the most useful is the PINVISE, which has many variations. Basically it is a cylindrical rod with a collet type bit chuck at one or both ends. Bits and other rods may range from .00 - .25", with some storing extra collets inside. Normal drilling is accomplished by twirling the rod between the thumb and finger(s) using one hand. The index finger is used to apply cutting force and to stabilize and guide drilling. Some have a stationary or swivel knob on one end for comfort. A lubricated swivel is best for most applications.
For faster and lazier cutting, various spiral fed push drills are available. These have very low pitch spirals with a meshed "nut" which translates pushed longitudinal motion into turning torque. In general, they are more awkward in use, requiring 2 hands, and must be used very carefully to reduce wobble.
Available in modeller and larger sizes, a hangover from pre-portable electric drill days, is the "egg beater", using a knobbed, geared handwheel to rotate the bit. In general it is much faster but rather clumsy.
Another hangover, the brace is sometimes useful for drilling larger holes in wood, when power is lacking. The ratchet type permits drilling when a full revolution of the crank handle is not possible.
Although not drills, PUNCHES are frequently used to make holes in thin material. Drilling clean, larger holes in very thin material is often very tricky and punching may be a better alternative. With limited size ranges, even paper punches can eliminate drilling. Leather punches can provide a wider range of holes. NWSL offers various sizes of matched dies for the Sensi-Press. An over-sized hand, paper punch like, unit can produce a wide range of holes in fairly thick metal. Electronic suppliers offer larger screw driven Greenley chassis punches, which require a pilot hole for the screw . Commercially, most punch presses are hydrolic or pneumatic.
PORTABLE POWERED DRILLS
Used for freehand drilling, these come in many sizes, power sources and guises. The most important factor is speed control, unless you prefer to melt or burn your way through the hole. Next few have good true running bearings for precise drilling. And last, most are too bulky for delicate work, since their mass disguises the "feel" required. Today most are available battery or line powered and some, not very useful for modeling, are air powered.
CAVEAT: A spring loaded foot
switch should be used with units lacking spring loaded power switches
to obtain instant stopping in emergencies.
ROTARY GRINDERS OR MOTOR TOOLS are readily found in good hobby shops from a variety of sources and in sizes and quality. Most are overpowered, too fast and too bulky for fine work. For delicate drilling a small, speed controlled unit with little runout (wobble) is best. A pencil type grip has a more natural feel and is more controllable than the pistol grip.
My choice, for not too precise holes, is the smaller Maxicraft which is very light by comparison, has an excellent runout and continuously variable speed, controlled by a DC power pack.
Not quite as portable, the FLEXIBLE SHAFT ROTOR TOOL can be used. Although most of my free hand cutting grinding and polishing is performed with a very superior foot speed controlled FOREDOM having a precision Jacobs style handpiece, the shaft stiffness prevents a good feel for drilling.
Although not very useful in smaller model work, the common electric or battery powered hand drill, usually pistol gripped, is essential for benchwork and other larger holes. Again variable speed is best, followed by stepped, while fixed is undesirable. The less convenient keyed Jacobs chuck is far more secure than most key-less . Only slightly bulkier the 3/8" accepts larger bits and usually has considerably more power than the 1/4". In general the 1/2" is too bulky for general use.
Almost any larger layout need can be met, even masonry and I-beam holes, with careful attention to overheating and the proper bits.The secret is to invest in the best quality. My 45 year old 3/8" Craftsman, relegated to drilling screw pilot holes, is still going strong. In conjunction with a newer variable speed using screwdriver bits very rapid screw jobs (no pun intended) are accomplished.
DRILL PRESSES AND MACHINES
Usually a vertical rigid stand supporting a drill with a work mounting table and manual feed, they come in all sizes, precisions and forms, bench and floor mounted. Other than precision, their main advantage to the modeller is more rapid drilling of many holes. Their disadvantages are setup time and labor.
DANGER: Although pieces
requiring very small holes may be hand held and positioned, larger
holes on more powerful machines demand secure clamping. When a bit
grabs, the work piece will be wrenched from your hand and swing around,
possibly causing severe cuts or injury and damage.
Most of the rotary hobbyist tools have a variety of accessories including DRILL PRESSES. The major consideration here is minimum horizontal play. Most are fairly sloppy. Upon examination, play can be acceptably reduced with shims and washers. A little disconcerting to the experienced user, some feed the work up to the bit. Although some have accessory vises, a major problem is finding or making suitable clamping devices. However jigs and stops can be fastened to some tables for alignment of repeated work.
Expensive complete, precision modelling sized presses are available, but most are bulky.
For precision, delicate drilling (and milling), I prefer my 1952 vintage UNIMAT DB 200 with a runout of less than .01 mm (.0004"). Work can be precisely positioned with the screw feeds.
Larger, heavier precision drilling (and milling) is handled by an EMCO C-5 VERTICAL MILL.
Various drillpress accessories are available for the standard powered hand drill, but most are very sloppy and when drill runout is added, lack precision.
For very large work, a floor model drill press may be required. In general the affordable units are not considered precision. However they can handle jobs requiring large bits, hole saws, fly cutters and stepped bits and are much better than freehand drilling.
For concentric axial holes, the LATHE has the best precision, especially when the work is mounted on the headstock and the bit is chucked in the tailstock. There is a tendency for the bit to center itself. Very large holes can be enlarged with a boring bar.
Although it appears to be a toy, the UNIMAT 1 can do some very fine drilling and other work such as turning and milling in non-ferrous materials. Cuts must be light and feed slow, but excellent results can be achieved at a small sacrifice in time.
DRILLING METHODS
As mentioned, methods will vary according to the job at hand, but the basic procedures are the same. First the location is marked with cross hairs, then a guide dimple is made with a CENTER PUNCH to assure proper alignment. Drilling is started very slowly, checking for centering and correcting, immediately after the lightest cut. Bit angle should be set before lips enter hole. Next a lubricant is applied, if necessary. Sufficient force is applied to maintain cutting, but not bend or break bit. Using sight, sound and feel for signs of trouble, proceed slowly and carefully. Removing a broken bit, filling a hole and re-drilling or remaking a part will take much more time than could ever be saved by haste. Most holes must be cleaned-up afterwards by careful deburring.
Although some kind kit manufacturers provide dimples, partially started holes or templates, location of centers may be very tricky. In some cases standard machinists' layout methods must be used, while in others a calibrated eyeball is the only solution. Normally perpendicular center lines are marked accurately with a very sharp draftsman's pencil on softer materials or a sharp hard tipped scriber on harder. Dark blue layout dye (Dykem) is useful on metallic surfaces , where the lines will appear as very clear metal colored strokes.
The tip of a very acute angled PRICK PUNCH is pointed at the line intersection, under magnification if necessary. In many cases, if you have a good sense of touch, the centerlines may be felt with the tip. Once dead center, tap gently with a small hammer. Observe the centering and correct. Reinsert the tip and slightly enlarge the dimple. For all but the very smallest bits, the dimple must be enlarged with a center punch to provide centering of the bit tip. Spring loaded punches may be used, if properly adjusted. If not they can be unwieldy and cause damage. For very accurate work, a small circle may be circumscribed with sharp calipers as a bull's eye to judge centering better.
For more accurate holes, it is common practice to start drilling with a relatively small bit first, increasing sizes gradually until the desired size is attained. By whatever drilling method, the first light trial cuts should be done dry to permit unobscured checking. There are many methods for correcting off-center starts, but most are almost useless with very small holes. Start it right the first time.
Of little consequence in hand powered drilling, speed is very important in power drilling, to avoid over heating and breakage. Plastics tend to melt or gum up, if heat is generated by higher speeds, leading to grabbing, bit breakage and possibly the worst holes you ever saw. Unfortunately, most handbooks list speeds for various materials by surface feet per second or minute. Since most users lack a tachometer and conversion to RPM for the small bit diameters is somewhat of a pain, the simplest solution is to drill slowly at a slight loss in time. Smaller bits indicate higher RPM, but tend to clog faster and thus require lower speeds. A notebook listing successful speeds can save later trials and errors.
Materials such as wood, some plastics and softer metals may be drilled dry, with low speed drilling. However a good lubricant will help chip removal, reduce heating and wear. Sold in bulk at machinist's suppliers and in smaller quantities at better hobby or sewing shops, Bee's wax is excellent for hand or slow power drilling and is easy to clean up. Cutting oils or compounds (Rigid and others) are available at better hardware stores or machinist's suppliers. Even Labelle is better than nothing in a pinch. Many old handbooks recommend lard, soap solutions and other concoctions, but these have been superseded by much better inexpensive synthetics .
Beware: Many lubricants
may soften or melt some plastics.
Start slowly, checking bit angle and centering. Maintain sufficient pressure to assure cutting, but avoid breakage by too much. In most cases two spirals of material will appear above the surface, when cutting is correct. At worst, a steady stream of small chips will emerge. With a little experience, even the sound of proper cutting can be recognized. Especially in deeper holes, back out the turning bit frequently and remove chips from flutes with a brush to avoid clogging. Relube as required.
The greatest danger point is just before break through on the opposite side as the lips tend to bend and grab the material rather than cut. With wood, pieces may be torn from the surrounding surface. In hand drilling, a very noticeable increase in required torque is the signal. While in power drilling, change in sound, motor pitch and feel are clues. Back out, clean flutes and restart drilling with less pressure, feeling the way carefully. If possible, scrap material should be used to backup the opposite face to reduce the effects.
A hole is not finished when drilling is complete. In almost all cases, small ridges remain around the rims. These should be removed on both ends of through holes with a slight CHAMFER applied, usually by hand, with a much larger bit or deburring tool. This definitely eases the insertion of screws etc. and allows joining pieces flushly. Tapping can also produce these ridges.
Drilling small holes with a PINVISE, is probably the most common for modellers, but they do not come with instructions. Three things are basic: steadying the drill angle, applying cutting pressure and twisting the bit. After some trial and error, the methods shown fit my needs best.
Since almost all holes made with a drillpress are perpendicular to the work face, the head should be checked for alignment to the table. This is particularly the case with pivoting heads or tables. This can be checked with a large, straight bit and a machinist's square at various positions. Unimat recommends pressing a flat, spindle mounted face plate against the table, then tightening head clamp. Most machinists use a dial indicator on a spindle chucked holder, rotated by hand to various check points.
centering holes can be tricky, particularly on larger units. Standard practice is to use a wiggler. In practice needles with eyes ground off make excellent center feelers, since they have sharp points and some give. On sensitive presses touching the sides of the punched cone can be felt. Under magnification any slight bending can be noted clearly. Collect various sizes to match bit lengths.
There is a tendency to drill too fast. Make haste slowly, with just enough pressure to ensure continuous cutting, then remove bit to empty chips and check often, Use lighter pressure at the beginning and break through.
Advanced techniques are acquired as part of the learning process depending on application and machine (lathe etc.).
Angle drilling is very tricky and requires some serious thought and planning. Although it can be done by hand, a tilting drill press should be used, if at all possible. The bit tip tends to ride over the dimple rim in the direction of attack. To reduce the effect, first use a prick punch to make a small dimple, the angle it slightly and repeat. to the angle desired. At this angle a standard punch may be used to farther raise rim. Start drilling with a small bit, using light pressure to avoid bending. proceed slowly to establish a guide hole. If it will fit, a center drill bit is helpful here. Entering bits carefully and slowly, repeat drilling with bit increases of one or two sizes until desired diameter is reached. Slower but surer.
Non-circular holes are made by other methods as sawing, nibbling, filing and milling, but frequently pilot or starting holes are drilled for insertion of saw blades or others. Another common practice is to press drill a series of closely spaced holes just inside the perimeter of the hole to reduce hand sawing and material removal.
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