User:Jstapko/EngLab/ScrollSaw/HotWire

Heating Element
The heating element is a component of the scroll saw hot wire cutter project, and currently consists of a thick piece of nichrome wire that was taken from a replacement element for an electric stove. Previously, several varieties of steel wire, including guitar strings, were tried, but were found to lack the tensile strength required to withstand the tension needed to prevent bending of the wire while cutting. Efforts were made to use the steel wire at reduced temperature and tension, but this resulted in a slower cut, the element bending and distorting the cut, and generally breaking after a few minutes of use even if it worked well when starting out. It is hoped to exchange the current nichrome stove top wire with the element from a hair dryer, which is also nichrome, but smaller in diameter, which will reduce saw kerf and thus make improved, tighter fitting cuts. Each element is discussed in detail below.

Early Attempts With Steel
The first heating elements were made of mild steel wire of .023 inches diameter. With just slight tension, the wire would bend when pushing foam through the cut, deforming the cut edge. Increasing the wire tension caused the wire to break when hot. Additionaly, even if the wire cut foam well, if it was allowed to idle under power, it would soon overheat and break. Discussing this problem with another lab aide and prof. Foerster led to a suggestion to use guitar string wire, which happened to be in stock. Guitar string wire, while suffering the same drawbacks as the .023 steel wire, came with a small ring, or "ball end" for attaching it to the guitar, which proved admirably suited for anchoring the lower end of the heating element to the scroll saw without requiring the removal of the lower blade holder.

Nichrome Electric Stove Element
Following the failure of several steel heating elements and a few of wire made from unknown material, an element was fashioned from .034 inch diameter nichrome wire from an electric stove heating element. The new nichrome wire had plenty of tensile strength even under the maximum tension of the compensator spring and at temperatures far above that needed to cut foam quickly. It has the drawback, however, of being larger in diameter than needed, causing a larger cutting kerf.

Nichrome Hair Dryer Element
In an effort to retain the extra tensile strength of nichrome, but mitigate the saw kerf problem introduced by the electric stove wire (see above), tests are currently being conducted on .021 inch diameter nichrome salvaged from a hair dryer in the late 1990's or early 2000's. A new tensioner spring that exerts less force is being used in current tests, but results thus far suggest the new element may be compatible with the larger, stronger tensioner spring currently installed on the scroll saw.

Next Steps

 * check to see whether or not 6.3 volts AC will bring 5 inches (blade length, per scroll saw manual of the .021" nichrome to cutting temperature
 * search for sources of still smaller nichrome
 * search for inconel, or other wire materials, per the suggestions that the wikipedia page on foam cutters links to
 * check the .021" with both the old tensioner spring and the new tensioner spring
 * measure the exact amount of force that the different wire types can withstand with different amounts of current passing, possibly by using a scale or smaller objects that can then be weighed

Things This Page Needs

 * a link to the page on testing the .021" nichrome (which needs to be created)
 * links to things such as a page on nichrome or general resistance wire
 * links back to the engineering lab projects page
 * possibly a link to a source for replacement stove elements, an image of them, or a source for smaller nichrome wire
 * possibly a link to the discussion of wire options that the wikipedia page links to, particularly the wire end twisting and the discussion of inconel
 * possibly a link to a page describing inconel
 * pictures of the different wire options, including the hair dryer element before dismanteling

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