# fly cutter help



## gilessim (Mar 21, 2008)

I'm just making a fly cutter for the mill from a chunk of 35mm SS that I had, I was going to use drill rod for the cutter, I have some 3/16" and some 1/4" but then I found a piece of 8mm HSS, does anyone think that 8mm is too big for the cutter? ,I am going to drill in at 45° and does anyone have any thoughts for the best shape for the cutter?

Giles


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## Mcgyver (Mar 21, 2008)

Giles, good call on the hss - isn't worth using drill rod.  making cutters from tool steel is great when you need something special, but hss will stand up much better, is cheap and will last forever.

On the second page of this thread I show a facing tool with a chip breaker - this is what i use in the common cheap fly cutters that hold the bit at what, maybe a 20 or 30 degree angle? 

http://www.homemodelenginemachinist.com/index.php?topic=1494.15

This will work for yours or you could angle the edge slightly if you're at 45. The common mistake people make is to use geometry as if the cut is a plunge from the z axis - to become dexterous at sharpening any tool, think of where the cutting edge is, then visualize where the rake needs to be, then where clearance needs to be so only cutting edge contacts the work. In the example i gave, the rake is formed bu the sloped side of the chip breaker


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## rake60 (Mar 21, 2008)

Giles

In the very early days of this forum I had a thread in the "Tools" about my
own homemade small flycutter.





There are plans for it in the thread: Mini Flycutter
It was made from 1" CR steel and uses 1/4" HSS bits, but it could 
easily be scaled to any size.

Rick


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## gilessim (Mar 21, 2008)

Thanks guys!

Mcgyver, that's great info!, I did see that thread when it started but somehow it didn't really sink in (duh!) that's me thinking I'm a smartass, I'm not bad with the grinder ,I used to grind my own profiled wood router cutters for tiny mouldings on harpsichords, I should take more notice!

Rick, I wish I'd seen yours before I stated mine!, I got the idea from a book by Arnold Throp and it's just about done now, so I can't go back, I'll post a pic when it's done, BTW I have round bar for the cutter, we'll see how it works!.

Giles


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## tattoomike68 (Mar 21, 2008)

I made the flycutter a while back, mine does a fine job.


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