Fly Cutter

I need a fly cutter to square up the 1.812"x2.000" block for the stirling. I could buy one, but I can also make one pretty easy. Id rather it be from tool steel, and I have a piece of 4140PH that would be perfect, but with these ball bearings in the spindle there's just no way. So aluminum it is! The first challenge is getting a piece cut off the hunk of stock I have. Since I have no bandsaw, part off is my only option. I used the part off tool down to about .6" diameter then finished it off with a hacksaw.

You can see how close everything is. Had I not milled that one part down so I could flip the compound around I wouldnt have been able to get the travel out of it.

Look at the crappy fine chip. The chatter is unreal. I need to put those tapered bearings pretty soon. Why they don't already do that when they build these is the one and only serious gripe I have with this machine. 

Finally, a piece I can work with. Now let's make it look like a fly cutter. Below is a short clip of me roughing the OD down.

I decided on .75" shank. First side is done!

Picking up center with the ol' trusty edge finder.

Now we're making a bit of progress. This is one of the first 2 or 3 cuts.

Thats all we need, three 1/4-20 drilled and tapped holes where the lines are, and it's done.

This is the angle the tool will sit. I could have gotten by with a smaller angle, but this'll work just fine.

Here you can see how the end mill dug in on a few of the beginning cuts. To clean it up, I would have had to take too much off that face and it would've blown my centerline by .04" at least, likely more, to get all that out. It's not gonna hurt anything like this. I struggle with rigidity on this little thing. Between the shoring block and tightening the gibs way down it did okay, but its a bitch to turn, because everything is so tight. I do plan to do some rework or whatever it takes to squeeze a bit more rigidity out of this thing.

Ill probably make another one. I think .5" might be a bit much maximum capacity on a little two inch aluminum fly cutter. Not too much to work, it'll still work fine, but mill it for 1/8" HSS blank, which I have a few. I think it would do a much better job. This will work for now, though. I can fit any tool I have in this one, though. The tool I plan to use is a 3/8" indexable(surprise, the one in the pics), but I'm likely to throw a chunk of HSS in there too depending on how well the indexable tool cuts. I haven't been real pleased with them so far and never use them. Im hoping to redeem them by finding they work perfect for a fly cutter.

That finish isn't the greatest, but it's because of wobble in the milling attachment, it too needs some attention to make it more rigid. But its cutting great. It sounds good, no chatter, just all around doing a great job. I am going to make another, though. I've realized some things that are important that I didn't realize before, for instance, making it to use 1/8" HSS blank and also to have a 3/8" shank so it can go in my end mill holder. Those two things alone will make a huge difference for the next tool. 3/8" shank wouldn't be nearly beefy enough if you were whacking at something with a tool like what I have in there now and taking a decent depth of cut, but 1/8" HSS blank, nice and sharp, shiiit, be perfect. I didn't have set screws, so I had to use those big honkin' socket head cap screws.

Now I can square up the main block of the stirling easily. Below is a short clip of it cutting. Listen to that cut, that's just how you want it to sound.