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Sunday, 6 February 2011

Basic Scroll Saw


Type of scroll saw

Scroll saw can be broadly categorized as either floor models or bench-to machine, they can also be categorized according to the way tension is applied to the very fine blades to keep them taut and stiff so they cut properly. one of type is called a strained or rigid arm saw. It has a spring housed in a fixed over-arm that pulls at the top end of the blade with an increasing force as it moves on the down stroke. This type of saw was popular between the 1920's and the 1980's until the modern reengineered parallel-arm saws appeared. The major objective of the rigid-arm saw was to provide a true, vertical stroke. Problems revolved around using very thin blades with the spring. The primary limitations of these saw are:
1. The driving mechanisms devised to convert rotary energy into a true up-and-down blade motions are complex.
2. The blade is fully tensioned only when it reaches the bottom of the srtoke, and tension is substantially less at the top of the stroke when the spring compresses



Constant-Tension Saws

Constant-tension saws are of various types and designs. they all, however, have blades that are consistently keep taut at the same level throughout the entire stroke, so that unlike rigid arm saws, the tension at the same at the bottom and the top of the stroke. Today constant tension saws are overwhelmingly the most popular and available in the following styles: parallel-arm, C-arm, double parallel-link, and oscillating loop.


Parallel arm saws

The parallel-arm scroll saws is the oldest type of constant-tension saw. it firs appeared 130 0r more years ago. parallel arm have two pivots incorporated into a general parallelogram design. This creates a blade-reciprocating action that keeps the blade in a vertical position. by and large, saws of this type are favored because of their few operating parts, and their design is such that the cuts are vertical and square to the table.


C-Arm Saws

C-arm saws are definitely in the minority, They are , however, favored by some production scroll sawers because of their faster and more aggressive cutting action. The C-arm design may be of one or several connected pieces assembled in a C-shape, but the common factor is that all C-arm saws have only one one major pivot point. One shortcoming of a C-arm saw is that the blade is not consistently vertical throughout the stroke. Therefore, the C-arm saw is not usually the first choice for highly detailed work od curved cuts in thick material that must be square to the table. Another concern is that wher a blade breaks, the upper arm does not automatically lift as do the arms on parallel arm saws. This means that a broken blade may be reciprocating wildly and dangerously until the power is shutdown

 
Double Parallel-link Saw

The double parallel-link saw, the news of the stand  tension scroll saws, has probably the most complex drive system of all. it is also the most difficult saw in which to understand how its reciprocating action is generated. The major advantage of the "link" drive system is reduced vibration. It also provides a vertical blade action. This blade is held between the short upper and lower rocker arms.  These  pivot  in reaction to the push-pull motion of the linkage, thereby creating a reciprocating movement of the blade at the ends of the hollow and fixed arms enclosing most of the moving parts.  Because  the pivoting rocker arms are generally much shorter  than  the arms of parallel or C-arm saws. The result is a blade action with more  front  to back movement during the stroke. This may create some problems of accidentally "over cutting" when making tight, highly detailed cuts. And, there also exist the ever present danger- also likely with C-arm saws- that a broken blade will continue to reciprocrate,  with a stabbing action, until the power is shut down.

Oscillating Loop Saw

An oscillation loop is simply a blade connected to the two ends of toothed flat belt that form a loop and moves ( oscillates) back and forth.  this concept was applied to scroll sawer  over 100 year ago using leather and still belts to generate a reciprocating action



2 comments:

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