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Although there are some touchy tasks that must be done very carefully by hand, power saws can speed up jobs and make things a lot easier. Many very slow and tedious can be accomplished quickly with the right tool. Accumulating a large collection can be very expensive. Selection of a few that fit the needs correctly will conserve the budget. The choices today are fairly wide as are the prices.
Among the earliest attempts at developing hobby power saws were some vibrator driven reciprocating types by Burgess and Dremel. At first glance, they appear to be quite crude, but with some experience, they could perform a creditable job on all but the more delicate tasks. Their major limitation was lack of suitable blades. Since good plastics were not developed, during that time, most structure kits were of wood and cardboard along with many rollingstock kits. Most metal parts were soft metal castings of lead alloys. easily trimmed with a knife. Die cast zamac was widely used on locomotive and car frames and on some boilers and shells. Normally only the non-metal parts needed cutting. Since most of the kits in other hobby fields were similar. apparently finer blades were deemed unnecessary.
The Burgess Vibro-Tool set contained some knife blades similar to the Xacto #2 sized blades. These fit well, but with a little tinkering, #1 blades can be adapted, yielding a pencil type saber saw. The stroke can be adjusted, but not the speed; which is not excessive. This tool is used quite regularly with various tips. A newer version, with a streamlined housing, is marketed as the Burgess Vibro-Graver.
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BURGESS VIBRO-TOOL w/ #13 saw blade.
Dremel's offering could have been used as a powered jeweler's or hack saw, but the selection of a pin type 4" blades was limited to coarse wood cutters. Blade tension is derived from a heavy flat spring which also permits longitudinal motion.
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DREMEL VIBRATOR HAND SAW
With the development of new motors, power saws have expanded rapidly in every area, replacing most hand saws. With the exception of band and radial arm saws, miniaturized versions of many have been introduced into the hobby field at affordable prices. Through the use of accessories, most hand work can now be done more accurately and quickly with power.
Each having its own particular advantages, power saws fall into four basic types. The first three can cut curves, while the last is dedicated to very accurate straight cuts.
RECIPROCATING WITH ONLY ONE END OF BLADE ATTACHED. These include the common portable saber saw and table saws designed as such or as accessories of the former. Since blades are usually thicker and wider, these are usually used for rougher cutting and portability.
RECIPROCATING WITH BOTH ENDS ATTACHED, including scroll or jig saws. These are usually table mounted and some can handle very fine jeweler's blades. A few can also accept single end blades. A common problem among most is access to lower clamp and aligning blade with correct orientation toward upper clamp. With very fine jeweler's blades, these can be used for most delicate work,
CIRCULAR SAWS are rotated on a mandrel or arbor. Some are freehand, portable as with blades used in rotary handtools or grinders. Portable dedicated types have guides and foot plates. Others are mounted in tables which may tilt for beveled cuts. Because of the total mass of the blade, heating is reduced, permitting much faster cutting. Unfortunately very thin blades, suitable for fine splicing jobs, that fit table units, are difficult to find.
Generally running cooler than others, band saws use continuous looped blades, mounted oo pulleys, for rapid cutting of most materials, including hard steel. With fences and guides they can make straight cuts; or without them, they can cut curves, with narrower blades yielding smaller radii. Finding blades of the correct length, width, thickness and TPI is a little difficult, but changing bands is relatively easy. Again a speed control is a necessity ,
Only Proxxon offers an expensive, modelling sized, AC unit, with a 5 29/32" throat, 2 5/32" cut height and speed from 395 to 820 ft/min. Four blades are offered: 1/64" X 13/64" with 14 tpi or 42 tpi, 1/64" X 9/64" with 14 tpi and a diamond 1/64" X 7/64". Coolant system for the latter requires a drain below. 7 7/8" X 7 21/32" table tilts to 45 °. Except for speed, most scroll or saber models are better suited for fine model work.
However an inexpensive , small bench unit is very useful for larger pieces and benchwork projects. It can also replace hacksaws to cut bar stock in preparation for lathe or mill work. With the right blade, a band saw can perform the same work as a scroll saw on a larger scale. One limitation is that cuts inside holes can not be done. With care rough shaping can be done similar to a belt sander. Doing both faces at the same time, rounding off the corners of a muffin fan, to fit inside a spray booth duct, it was first sawed just outside scribed circular arcs; then improved with light trimming. Final fitting was done with a belt sander.
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BAND SAW
Speed control is an absolute necessity, since higher speeds can produce heat very rapidly. This can melt or gum plastic, burn wood and destroy temper in blades, causing breakage and loss of cutting ability. Particularly when cutting metals, lubrication is highly recommended. For AC machines that do not have them, BUILT-IN SPEED CONTROLS controls can be added very easily in many cases.
The DC versions often use variable power packs. Although the voltage range on the latter is essentially the same, each line uses a different connector. Although speed changes are infrequent during operation, in general I prefer foot operated controls for more convenient changes, when hands are occupied. Foot switches are used on all machines that run at constant or set speed, for instant starting and emergency stopping. To avoid a large number, they control multiple outlet power strips. For position convenience and due to larger power requirements, the lathe and milling machine use MODIFIED DEDICATED FOOT CONTROL.
For security and stability most benchtop machinery should be fastened to table top. For those that do not provide means for clamping and to avoid drilling multiple screw holes in bench top, individual units can be mounted on fitted sheets of plywood with an extended lip for clamping.
BLADES
Blade selection is very critical based on the task, material, thickness and machine used. The types of blades and their characteristics is very broad, but not all are available in modelling sizes. The teeth are successive chisels that gouge away bits of material as they progress. Each succeeding tooth digs in a little deeper as pressure is maintained . Larger teeth will dig deeper, increasing speed of cut, but tend to produce more jagged cut due to wandering from spring between individual teeth. Finer teeth tend to track each other more closely, since they are more rigid. But chips tend to wedge more easily to clog them. Harder materials place more stress on larger teeth, which may break them, so depth of cut must be limited, requiring closer tooth spacing.
For discussion purposes, blades may be divided into two groups: circular and straight such as saber, jeweler's, knife and hack. Band blades may be treated as straight, since the portion used for cutting is straight.
Measured in teeth per inch (TPI) or other units, the size of teeth is also very critical. By dividing 50 TPI into an inch the spacing would be .020". If a .010 sheet is pushed into the blade, it would enter deeply into the space between teeth behind the chisel edge, where cutting is relatively poor. This produces a chopping action; which results in a very jagged cut, tearing, rapid wear or possibly tooth breakage. At the bare minimum, at least three teeth should be in the kerf at all times. This would require a minimum TPI of 300. The alternative would be a shearing tool. On some larger machines slanting blade permits more tooth contact. To farther complicate matters, circular blades are often rated by number of teeth and diameter. To find the spacing, the circumference must be divided by the number of teeth. It would be much better, if teeth were rated by spacing as in the module system.
In most cases teeth are bent or set at a small angle to either side of the blade to cut a wider kerf in order to provide clearance for the body to reduce rubbing, which may increase heat or cause binding. Pattern may be alternating or in a series of left, center, right, center, left.... or other variations. The theory behind having a centered tooth is that it clears chips between the swath of the offset teeth. In smaller blades the variation are either absent or not discernible . In straight blades, the offset is often increased to permit sharper curved cutting.
The thickness of a blade plus the offset determines the width of the kerf, along with any wandering or wobble. It is very important that latter be held to a minimum through proper mounting and use. Particularly noticeable in splicing and precision cuts, the kerf width is wasted. A .010" loses about 7/8" in HO. While setting a fence, measurement should be done at the tooth offset and not at the body. Too often it is not clear in specs whether the stated thickness is for the body or the offset. Thinner blades are more susceptible to bending from side thrust.
In straight blades, the width determines the stiffness in resisting feed pressure. But increasing width increases the the minimum radius while cutting curves, Some blades are tapered toward the rear to improve the situation. Most saber and hack saw blades are stiff enough to withstand heavier feeds, but narrow jeweler's blades flex a break very easily. Better machines have adjustable guides that can be placed close to the cutting section to resist both feed and lateral pressures. Yet light force should be exerted.
Mounting methods may determine choice of blades, Some clamps use collets which may not be long or wide enough to accept blade. Others use screw pressure and may not secure narrow blades or set fore and aft tilt correctly. Still others use end pins (Dremel ) which restrict the choice in length and mountability with other clamps.
Circular blades present their own problems since the diameter must be large enough to have sufficient extension above table and work to cut completely and small enough to clear all parts of the housing and table. In addition the mounting hole must fit the mandrel or arbor bushing snugly to center the blade. In a few cases, adapter bushings are available to accept larger holes. Drilling to enlarge holes is not recommended.
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