# My Finishing "Fly Cutter"



## Cedge (Aug 20, 2008)

It's no secret that I like making tools. When i first began machining metal, most of my projects were either tools or mods to my machines. Both are great for learning the ends and outs of different metals and techniques. I often looked through tool catalogs for things I could not only use, but make myself. It gave me some satisfaction to end up with a $200.00 gizmo from a couple of dollars worth of scrap metal.

The tool shown below began its evolution from just such a project. Travers Tool catalog had a tool designed to cut larger circular holes from sheet and them plate. The listing also gave enough specifications to make it easy to duplicate the tool. It had a "hook shaped" cutter which trailed behind the center line of the body. The hook "cut/scraped" the metal away, leaving a nice clean walled hole and a round center core. It worked much like the typical hole drill we all bought for use on a drill press, with wood.







The surface that you see has not been polished in any way. A light wipe down with carburetor cleaner and a soft cloth is all that was done before the photo was taken. The surface is flat enough that .0005 shim stock will not slide beneath a parallel sitting atop the cut. (smaller than I can accurately measure with the tools I have)

I also built a 2 inch fly cutter, which used a stationary round tool steel cutter, with the same basic trailing angle. It worked great but was limited by it's small diameter. I still use it often on small pieces and it never fails to give me a nice clean surface. With a bit of experimentation, I found the adjustable tool also functioned quite nicely for "fly cutting"

Yesterday, I scored a large piece of 6061 aluminum that is destined to become an elevated work surface for use with the swivel head on my SX3 mill. This will give me the ability to use it as a Horizontal mill when the need arises.

Back to the tool.... I began squaring the 4 x 4.5 x 5.5 inch block today and decided to see if I could "fly cut" it for some nice slick, square faces. I picked up the expandable version hole cutter and put a fresh pound of HSS in the holder. The tool is not made for making deep cuts. In fact, .005 in. is pretty heavy with the reverse rake the attack angle gives. What it does well is shallow cuts with minimal tool marks when run between 150 and 200 RPM with a slow feed and lots of WD40. The finish is such that a light lapping for 2 or 3 minutes will remove virtually all the swirl marks. 

I've never seen this particular tool offered anywhere and I've tested it for quite a while before having the nerve to post it here. I'm not sure whether it would be considered a proper fly cutter, or perhaps a burnishing tool, but it works great for large flat surfaces. One caveat.... the mill has to be adjusted pretty stiff and it has to be in near perfect tram or the surface will "cup". 

I'll be happy to post more detailed photos if anyone is interested.

Steve


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## Mcgyver (Aug 20, 2008)

Steve, whats the material? can't tell if its AL or Steel. what is the business end of the tool like just a flat end on a cylinder? From what you say it might described as a tool with a alot ot negative rake and very large tip radius....surprised you were abl to take 5 thou with it, but that must have been AL, right? I'd say if its making a chip then its shearing, same as any cutitng of metal, not burnishing but maybe the geometry provides a little of both? shears ahead but with the negative rake its pressing down downwind of the shear plan??? I dunno, interesting though.

the all time ***** to get a decent fly cut finish on is regular old 1018 - have you tried on that? we'll all be building them this weekend if so 

thanks for sharing it, and look forward to more details


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## Cedge (Aug 21, 2008)

Mcgyver
It's 6061 aluminum. I've not really given it a try with steel since I usually work in aluminum and brass, unless I'm making tools like this one. I suspect a carbide round would work in steel. I have a piece laying around somewhere, so maybe I'll have to rig up a steel version and give it a try.

The tool peels up nice 1 inch long curls when everything is going just right. Lighter cuts make lots of very nice little 6's and C's. You might be right... it could be doing both functions at once. 

I'll do a tear down and shoot a few shots tomorrow.

Steve


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## BobWarfield (Aug 21, 2008)

It looks odd, but it is not unlike the round insert turning tools in its action. They give a very nice surface finish too. While it does have negative rake, it may have the advantage that based on how the rigidity works it doesn't "dig in" but rather flexes to a shallower cut.

I've got an HSS cutter for fly cutting that one of my mentors Widgitmaster gave me. It has some really unique geometry as well. He gets a wonderful finish with it. One thing to note about it is it has a very large curved radius tip, so it is also similar in some ways to this tool.

The PM crowd swear PCD inserts give the most fantastic finish when flycutting aluminum. They're normally ridiculously expensive, but I got a few to try for cheap on eBay. At some point I'll make up a cutter that uses them.

There are, BTW, fly cutters and face mills that use the round inserts together with positive rake that I've heard a lot of good things about.

Cheers,

BW


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## Bogstandard (Aug 21, 2008)

Bob,

Try putting your round tipped profiling tool into the flycutter holder and see what happens.

Ever since I was shown how to do it many years ago. I always grind my flycutters with a large radius.






This allows me to take deep cuts of up to 0.1" in non ferrous at a good feed speed, and still end up with amazing surface finishes.

John


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## BobWarfield (Aug 21, 2008)

I probably will, though I just ground a radius like you show on my brazed carbide tool and it's pretty nice already.

If I'm patient with feeds my Lovejoy indexable facemill produces nearly as nice a finish. I largely use a flycutter when I want a single pass (for cosmetic reasons) on a part wider than the 3" face mill can accomodate.

Cheers,

BW


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## SmoggyTurnip (Aug 21, 2008)

Bogstandard  said:
			
		

> Bob,
> 
> Try putting your round tipped profiling tool into the flycutter holder and see what happens.
> 
> ...



I'd love to seee a shot of that from another angle so I can see the rake and relief.


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## ScottM (Aug 21, 2008)

Steve,

any chance of a closeup of the sharp end of that cutter?
In the picture I can't tell how it's ground.

Thanks - Scott


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## Cedge (Aug 21, 2008)

Scott
It's not sharpened at all. It's just your average stock " as bought" round HSS. It's just angled so that only the corner makes contact with the work surface.

Steve


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## ScottM (Aug 21, 2008)

Steve,

Wow that is some negative rake!

Thanks - Scott


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## ksouers (Aug 21, 2008)

Steve,
That's a pretty cool tool.

Have you played around with the angle? How does that work out, is there a "sweet spot"?


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## Cedge (Aug 21, 2008)

Ksouers
When I built the tool, I set the angle as described in the Travers catalog. The extendable shaft has a V cut which accepts a pair of pointed set screws to hold everything rigid, making the cutter angle a fixed item. Since it works to satisfaction I've not tried to experiment with other angles. Sort of "If it ain't broke, don't fix it.....(grin).

It will extend to cut a 5.5 inch diameter, so I'm not likely to build another one as long as this one performs as it does.

Scott
That was what surprised me too. I would have thought it would have had problems lifting metal, but it makes lots of nice clean curls as it goes about its business. Bob might just be right in his thoughts about the "spring effect" allowing it to ride out the tough spots.

Sorry guys... I didn't get the free time to do the photos today. I'll try again tomorrow.

Steve


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