form cutters

[loose nut]

I just finished a milling job that required 3 operations with 2 different set ups, milling out a rectangular area, reset job to a 45 deg. angle, mill another section out and finish by using a ball end mill to radius the area were they meet. Sorry no pictures. When I was almost done it donned on me that a form tool of the required shape, a lathe tool in a fly cutter holder shaped properly maybe, would have finished the job in one set up and a single milling operation and have been a lot faster also.

Now for the problem, when ever I have tried form cutters before I have had difficulty with chatter and the tool feels like it's hammering the machine apart. Has anyone used these much and what is the proper procedure IE: proper speeds and feeds, what type of rack etc. There isn't much documentation available on this subject that I can find.

[wierdscience]

I've used various types in both the mill and the lathe.The simplest way to make one for the mill is by turning it from drill rod on the lathe.Turn the profile you want,then mill two or three flutes in it providing for some back angle,then harden and hand grind the back relief.The smaller diameter means you can spin it faster and reduce the chatter.If the profile is fairly large or radical then removing as much material first by normal milling is best.

I've also made form cutters for the fly cutter,just did a layout and gorund to the line finishing up with hones.Still kept the diameter as small as possible.On those it helps to chuck the fly cutter in the lathe and clamp a machinists scale to the toolpost with it's edge 90* to the cutters axis.Move the scale's edge along the profile you have ground and rotate the cutter in the chuck checking the back clearence at various points on the profile.

Profile cutters on the lathe I make out of A-2 flat stock that I bolt into a tool holder.I layout,mill and file to shape,then heat treat and surface grind the top to sharpen.I've made these up to 3" wide and 1-1/2" deep,still hogging off the majority before using the form tool to finish at the lowest rpm.

Radius form tools for the lathe are easy to make,just a square piece of A-2 clamped in the mill vise on a 5-7* angle and a endmill centered on the corner and plunged through is it,surface grind top to sharpen after hardeneing is the usual.

[loose nut]

thanks Wierd, I hadn't thought of doing it like that, I'll keep that one for the next job.

[Evan]

If you do make a form cutter don't post it here. I got yelled at for doing that a while back.

[ScottM]

Evan,
I'm curious, can you explain what you meant?

- Scott

[Evan]

http://bbs.homeshopmachinist.net/showthread.php?t=26316

[ScottM]

Evan,
Thanks - I remember that post now.

- Scott

[quasi]

Frank Ford on Frets has a very well written and photographed article on making a form tool out of O-1.

[loose nut]

Thanks for the warning Evan, I don't see why posting a thread about something that you made, as an example to others, should annoy others but sometimes it does. Any way I keep it to myself, I just need info on why I have had trouble with them.