Fly Cutter questions

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Wino1442

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Hi all... I need to make a fly cutter for an upcoming project and I would like to hear your opinions to may questions.

1. Is there any particular steel that you would use or not use to make it?

2. I was thinking of making it a 2 piece unit ..mainly to save on wasted material from machining the shank from a large diameter ...I would make the shank a press fit into the tool holder....would there be a problem doing it that way.

3. how does one determine what diameter to make the cutter?...the large diameter

Thanks
 
2) I would not recommend that, there is a lot of force on a flycutter, especially on steel.
3) depends on what you are going to surface.
 
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That is still a lot of hammering.
 
I made a 2-piece cutter similar to what you're talking about. To join the two pieces I cut a slot in the piece that holds the cutter, and the end of the arbor has a rectangular profile that fits into the slot. This way you don't need to worry about the holder spinning due to cutting forces acting on the fixing screw, which is a hex drive flat-head type. I have a rotary table I used to mill the end of the arbor, but it also could be done if you have a square collet block (or you could make something like it out of a piece of square stock).

Cutter A.JPG
It was designed to be a miniature fly cutter/face mill. The photo was taken before I drilled the hole for the cutter, which is a short length of HSS rod. It has one cutting face I ground on the end. This particular cutter geometry (and the way it's presented to the work) can only remove a few thousandths at a time. but in that range it produces a nice surface.
 
1. Unless the flycutter will be heat treated or made from prehardened material, the grade of steel makes no difference.

3. While it might be tempting to make the cutter as large as practical, large flycutters create vibration and chatter problems unless well balanced, especially on less rigid mills. 4 inches is a practical maximum for BP type mill, but even that creates vibration problems at speeds appropriate for aluminum.
 
I just bought one of these for surfacing cylinder heads:
www.flexbar.com

Fly Cutting Tool

Large Capacity combination roughing & finishing fly cutting tool system for CNC and conventional milling machines. With Flexbar's Simul-Cut fly cutters you can now expect better surface finish and increased productivity over conventional fly cutting methods. Tool cutting instrument
www.flexbar.com
It is a 2-piece construction, pressed and welded. It was trued on a lathe after welding if you believe the tool marks. These are 2-point cutters, but can be run as a single point if you back off the second cutter. I haven't used it yet, but have plans to.
 
2 piece would be fine if you can make it a press fit, AND then weld it in place. After welding machine the shank and head to final dimensions so everything is concentric and straight.
 
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