Tool bit grinding/form?

[cartertools]

I was inspired by your wonderful segment on Made in America to try my hand at rose engine work. Not having a rose engine I emulated the action with my benchtop CNC mill - rotary axis for the rotation, y axis for wobble back and forth, x for tool advance/retract and z axis for tool hight on/above/below center. The setup seem to simulate the action of a rose engine well (and I can use the same setup for a linear engine!).

My question is the form of the toolbit, rake angles etc. Any quick tips? Also it seems that the tool often is taking a shallow, almost horizontal cut, more pushing the work from the side rather than cutting on the end. Is this more a case of optimum rosette design, or does the tool indeed make more of a scraping cut (in the sense of pushing dragging rather than raising a chip) when doing a shallow angle (from horizontal)?

You can see my setup in a little blog post I did, I expect to play more with the whole setup over the next few weeks.
blog post showing CNC emulation (http://mechanicalphilosopher.blogspot.com/2007/01/engine-turning-and-boxed-children.html)

The design shown is 25 iterations of a reducing diameter by .02" per iteration of a simple vee starburst (easier than arcs to program, but I have those figured out now)

Anyway, let me know if I'm on the right track and if you have any tips about toolbit geometry.

Thanks,
Nick

[cartertools]

Not a lot of forum interest, but here are a couple of more pictures of my rose engine attempts:
http://mechanicalphilosopher.blogspot.com/2007/01/just-few-more-pictures-of-rose-engine.html

[johhnymossville]

Maybe you should try a whole dial next, and see what happens. Nice work!

John P.

[Admin]

Thank you for posting and your interest in Engine Turning.

The cutter form is very important, and yes the cutter makes a side to side motion as well as going forward. On round work as you get near the center the cutter moves more side to side then forward. The V nose cutter should have an angle of 10 to 12 degrees with a front clearance angle of 20 degrees.

I would recommend two books.

1. "George Daniels Watchmaking" this book has a chapter on Engine Turning.

2. "Engine Turning 1680-1980" by Martin Matthews. This is the best book.

Also on ebay right now is a very nice Plant Straight-line Engine, this is a very good machine.

I hope this helps,

Best Regards,
R. Murphy

[cartertools]

Thanks for the angle information, that should help a lot, 20 deg is far more than I usually grind tools!

Someone (what about RGM?) needs to reprint that Matthews book, I only found one used copy on the internet for $370! That will have to wait for purchase.

The Daniels book will be purchased shortly. I love any excuse to buy new books.