Contour Milling

Alas I am a beginner...:abnornal:
I tried looking up West Virginia Tracer and found tracer bullets! I wish I knew what DTI meant.

I do have a CAD program but even with that cutting a profile seems like a tedious task. The curves are not simple arcs but splines, like the french curve templates used in ancient manual drafting.
I agree that stacking and shaping the plates would be the way to go.

As an experiment I made a touch probe some time ago, and might try attaching this to my 3D printer to gather coordinates. My Rong Fu has too much backlash with its non ball screw table, while there is almost none with the printer.

Thanks for help!
-Jay-
 
West Virginia Tracer is a name given to a process using a “Dial Test Indicator“ following a pattern to move the Y axis of the mill while the X axis is power feeding very slowly to make a copy of the pattern. The pattern is mounted on the table alongside the work piece with the indicator resting on the profile pre-loaded and set to zero. Usually you would mount your magnetic base with indicator on the column. You visually have to watch the indicator and move the Y axis to keep it “zeroed “. HTH
 
OTmachine, that's neat but must take a steady practiced hand, thanks!
-Jay-
 
Unfortunately, spline (bezier) curves are impossible to replicate on the manual mill. Beziers are parametric equations with precedent and antecedent vectors on top of the three point plot, that movement can only be done by computer or by following a pattern, using a ground form tool cutter, or approximating using the West Virginia tracer, stepwise movement, etc. Mathematical curves based on rotary parametrics are possible on special universally synchronized machines like the K&T 2D and piece curves can be strung together for complex shapes, but that is a super specialized example.

Sometimes, when you get beyond what can be plotted with a square and compass it takes a lot of resources or a computer. It gets remarkably difficult to copy curves manually. The best example of a complex curve that I am aware of is the wing profile of the British Supermarine Spitfire. It represents a constantly changing curve. It was hell for production to build, and they hand formed each wing using dozens of sectional profile patterns. Pretty amazing that they flew consistently, and they still built them fast enough to stop the Luftwaffe.
 
Something else to mention about pantographs is the sizing issue of the machine itself: they're not small, and neither are most CNC machines...but given some exterior dimensions, the CNC has more working room. That's why I passed on the pantograph; it was a steal, but for 9 square feet of floor space I can have a CNC with ten times the working area of the pantograph. It's a very cool machine, for sure...but Pontiac is correct: CNC killed them, and for good reason.
 
While spline curves are impossible to replicate exactly on a manual mill, It is possible to get a fairly good approximation with either a stepwise motion or with a series of arcs. The machining is tedious and requires a good deal of patience, particularly when the approximation becomes closer to the true curve.

In fact, this is exactly what a CNC mill does. All moves are collection of simple linear or arc movements. My main driver for buying my Tormach CNC was a need to machine some complex curves. Our newly remodeled kitchen had a number of mathematically complex curves in the upper cabinets. The under cabinet LED lighting was designed to sit directly behind the fascia so as to not be visible.

I had three choices for making the lighting fixtures; use the above technique of approximating the curved paths, farming the job out to a CNC capable machine shop, or buying a CNC mill. Had I elected to use the first option, I would probably still be machining some fifteen years later. The anticipated cost of the second option would most likely have pretty well covered the cost of A Tormach CNC. So I opted for option #3.
 
I looked at the 9 sq foot solution, it truly is a magnificent looking machine! Alas my work area would not have room for me if I added one of those. I'd love to see one though.

I'll have to look up Tormach, I've been doing things the old fashioned way so far but I'm intriqued by the possibilities. Since I don't do production jobs I've dismissed the idea of applying CNC to my Rong Fu, but for specialized work I'm becoming more receptive!

Thans for humoring me and my odd problem, I've enjoyed very much reading your ideas.

-Jay-
 
Jaylab said:
I looked at the 9 sq foot solution, it truly is a magnificent looking machine! Alas my work area would not have room for me if I added one of those. I'd love to see one though.
Click to expand...

I used that number as a basic approximation of the size of the pantograph that I was considering; it was about 36" square, and 48" tall. Sorry if I didn't make that clear; all I was saying is that for equal area/volume, a CNC is probably a more capable machine.
 
Jaylab said:
I looked at the 9 sq foot solution, it truly is a magnificent looking machine! Alas my work area would not have room for me if I added one of those. I'd love to see one though.

I'll have to look up Tormach, I've been doing things the old fashioned way so far but I'm intriqued by the possibilities. Since I don't do production jobs I've dismissed the idea of applying CNC to my Rong Fu, but for specialized work I'm becoming more receptive!

Thans for humoring me and my odd problem, I've enjoyed very much reading your ideas.

-Jay-
Click to expand...
I considered the addition of the Tormach mill as enabling me to be able to do work that couldn't be done in any other fashion. I bought the 4th axis at the same time, figuring that it would complete the ensemble. In 2011, the total package was $14K. I had some available cash at the time and figured it as my retirement present.

A year later, I purchased a seat of SolidWorks as I would be retiring soon and lose access to my seat at work. That was another $4K. Some sort of parametric CAD program is necessary to fully utilize the capability of a CNC mill, I use SolidWorks on an almost daily basis from modeling things for this forum to a designing a complete kitchen with custom cabinetry. Both were a huge expense upfront but greatly my quality of life. To put it in another perspective, I spent $7K on a new outboard motor, $2500 on a trolling motor, and $2K on electronics for my fishing boat which I use about once a month on average. Our toys aren't cheap.
 
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