# Practice Posting >  The new Scroll Saw conceptual model

## toma

This is only test model using the step motor.For a practical use it needs a more powerful motor, but it wooorks nicely !

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## petertha

Thought you might find this interesting. If I understand the operating principle, there is a ($$$) commercial version of this 'linear action' type saw that uses much more of blade. Not quite sure if they are using mechanical or electrical direction switching.
Knew Concepts Precision Power Saw - Fine Metalsmithing Saws Designed for Artisans - The Red Saw - Santa Cruz, CA

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## toma

Thank you Petertha for this link...it is a very interesting technical solution (Knew Concepts). I am also wondering about a steel cable direction change, I think it is some mechanical system, because the heavy motors have a considerable inertia, so they can not change rotational direction so fast.
Best regards...

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## petertha

That's my guess. Picture a typical engine crankshaft driving a piston up & down via a connecting rod. Its converting rotational motion into 2 way constrained linear motion. Now if a belt were connected to a slider block (piston component) and looped over 2 sets of pulley wheels and the belt was open to accept the blade holders... I think that satisfies the up & down blade stroke in sawing mode. Larger crank pin radius = longer stroke. This way the motor always goes in one direction, you don't need complicated reversing mechanism. But of course you can vary the rpm for slower/faster stroke. But to keep the belt in tension & blade aligned & easy on-off for piercing the blade into inside pilot holes... thats where the R&D comes in!  :Smile: 

I'm always fascinated that 'good' scroll saws like Hegners seem to be able to cut metal & more challenging materials with precision whereas other saws of the same power & dimensions frame rigidity etc. just don't seem to cut as well. Hegners cost a fortune here so I will never know, but makes me wonder if it has to do with blade action?

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## toma

Yes, this method of transforming a rotational to linear motion one is well known from the ancient times.I only liked to see this particular practical solution of it, in this rather expensive machine. But the expensive machines are- generally speaking-a good ones.
My intention was to avoid this mechanical solution,simply by electronically changing of step motor rotation, but every design has a cons and pros, unfortunately.
Thank you for the time consuming on this topic.

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