Designed a new cutting tool - questions

[Bob W.]

In reading an earlier post regarding helical milling it reminded me that some time ago I designed a cutting tool for just such a purpose. It has sat idle because its nature is very specific and I don't know if there is already a solution or even a demand for such a tool.

 

I'm not sure how many people are aware of this, but using a 4th axis it is impossible to cut a TRUE helical surface with a rotating cylindrical cutting tool. If you rotate the part and feed in the X direction while making a cut the results will be close, but not a true helical surface/ groove. I guess in short, you can't use a fourth axis to machine accurate load bearing helical cams, threads, etc... without some surface machining.

 

Using a rotating cutting tool to cut threads will always be a compromise unless the tool is designed specifically for the pitch and diameter of the thread. Threads cut on a lathe with a single point tool, with a tap, or with a die will produce the most accurate threads from a surface contact perspective.

 

Rather than go on and on about this I'll go ahead and illustrate the reason. The angle of a helical surface changes as the diameter of the cylinder changes. Imagine a 1/2" diameter threaded rod with 8tpi. The thread's angle would be pretty steep. Now picture a 10" diameter threaded rod. The threads would be nearly horizontal. The surface's angle increases as you get closer to the root and a cylindrical cutting tool can't compensate for that. Only a specifically contoured tool can. Is there a need for something like this?

 

Sorry for the long post. This has been sitting on the shelf for a few years now :-)

 

Bob