Introduction: Precision Hot Wire Station
As a hobby metalworker, sand casting aluminum of my own custom parts is very rewarding and fun. There are two basic methods in use for this endeavor; reusable hard patterns and lost foam. Each has it's own advantages and disadvantages, but since my wants are 1- offs or very short runs, I prefer lost foam and so I constructed a cutting unit that reflects my needs. Using lost foam I can cast a project to what I call near- net shape, and pre- processing foam to a high degree of accuracy helps produce it. Based on established tooling geometry like a tablesaw or bandsaw, this project incorporates largely the same functionality; rip to width, crosscut to length, miter cuts, bevel cuts, compound miter/ bevel cuts and rounds, even template cutting. Care in construction will be repaid with a tool that will render yeomanlike service and reliable results, coupled with ease of use.
Step 1: Safety First
Unguarded hot wire may be contacted, always keep your eyes on the workpiece proximity to the cutter.
Step 2: The System Mockup
I had no plans other than a concept of what I wanted it to accomplish, so regrettably I have no drawings to share, but then again these type of units are always free-form in the builder's mind anyway, and tend to be constructed from what's available close to hand and based on necessity. Once the basic dimensions were arrived at, fleshing out each feature's details began as illustrated in the first image, followed by refinements to the accessory items.
I wanted a decent rip fence that would track precisely so a bit of aluminum angle, wood bits, and a Plexiglas- laminated fence came into being. The fence holding device is as simple as can be — a spring clamp, and it works remarkably well too.
A miter gauge was next, and I used a cutoff piece of plastic channel for the “head”, and a length of acrylic from an old monitor screen as the “bar”. I drilled two holes for locking into a 45 degree left and right miter— I can slot a half circle later if it other angles becomes a desirable feature too. Resetting the miter head to a perfect 90° is easily accomplished by butting it up against the rail when inserted upside down in the track slot and tightening the screws.
Step 3: Determining Power Needs
I used nichrome wire salvaged from a $2 thrift store hair dryer. It is cheap, plentiful, and since it is a very mature product, much technical information is readily available for designing a supply scheme based on the intended use. Inside, I found the following wire sizes: 28 gauge (.013”) 24 gauge (.020”) and 22 gauge (.025”), a nice selection and in lengths likely to last my lifetime. I used about an 8” [203mm] length of 24 gauge for my design, wanting to try and stay in the preferred heat range of about 600° F [316°C] and powered it with a switcher wall wart. In use, it does not perform like “a hot knife through buttah!”, that action is in fact undesirable to me since it will cut a much wider and irregular swath than wanted. More importantly still, is that a much better tactile feel is had when a slight resistance to cutting is given, yielding a more manageable outcome thanks to a limited heat. Finally, the resultant workpiece's cut edge has a nicely glazed, smoothed surface and shows much less evidence of chatter or dwell markings.
More about nichrome wire data and a calculator can be found here:
Step 4: Control Wiring
I used a typical 2.1mm diameter Barrel Connector with a 5 amp d.c. rating so I can swap power sources in and out depending on what I'm doing. To keep wiring trim, I shopmade staples by cutting off the heads of brads and bending them to a “U” shape and simply pushed them in with pliers. A basic on/ off switch mounted on the frame's top rail gives quick and comfortable action.
Step 5: Hot Wire Installation
A simple spring loaded upper tensioner for the wire accommodates the heat induced stretch and contraction, and a slot hacksawed in the headless bolt end facilitates quick engagement/ disengagement for doing enclosed cuts. The lower connector is a brass wood screw with a shallow groove cut halfway around the shank, this keeps the looped end of the wire locked in place yet freely allows for pivoting during bevel settings.
Step 6: Basic Operations
Ripping: It has a throat capacity of about 7” [178mm] deep, that's quite sufficient for my needs, however longer rips can be done by simply flipping the stock end for end up to 14” [356mm] long. Anything much greater can be had by feeding right or left across the table but a temporary fence has to be employed, and I do not anticipate much need for that in my work.
Crosscutting & Mitering: The “T” gauge guides the stock through the cutter leaving a clean, linear face with no falloff on either the start or finish of the cut. Locking holes provide accurate stops for left and right 45° miter angles.
Bevel Cuts: Using a simple protractor, up to a 45° bevel angle can be set for either left or right orientation, again using the rip fence or miter gauge to guide the workpiece through. The Plexiglas fence extension is re-mountable to either side of the main body to accommodate this need.
Template Cutting: Since wire temperature is closely controlled, ordinary cereal box stock can be used as a pattern without fear of scorching through it, thus many replicas can be generated with unusual profiles or shapes.
Step 7: Parting Thoughts
Versatile, accurate, portable, and a joy to use, this little shop tool is expected to get quite a workout in it's lifetime.