Fly Cutter Build

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seal killer
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Fly Cutter Build

Post by seal killer »

All—

I needed a fly cutter better than the one I had, which holds the bit at a 45* angle. I don’t like it.

I started off wanting to build it from 12L14, thinking I had a 3” diameter chunk of that material laying around. It turned out to be an inch. But, I found a 2.25” diameter piece of 1018. I decided to go with what I had on hand.

The first thing I did was to figure out how to hold the workpiece at a 10* angle in the mill. I settled on 10* because I had seen a fly cutter build on YouTube that I liked that held the cutter at that angle. (Blondihacks or Joe Pie?)

I didn’t pay attention to how they held the workpiece at an angle. Eventually, that bit me. Here is the setup. Looks good and it worked well for cutting the 10* angle. I used a ¾”, 2 flute, TiN endmill.

Milling 10 degree flat.jpg
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It also worked well as I was creating the half-inch slot, initially. My procedure was to cut the middle of the slot first using a 2-flute, 3/8” TiN end mill. That worked well down to the ½” depth. (I stopped just short of a half inch DOC. I wanted the bit to stick out a little bit beneath the face mill.)

Cutting slot.jpg
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Next, my plan was to side mill at the full DOC on the centerline side. I needed to take off 1/8”. I thought I could take 1/16” fairly easily and then clean up that side with smaller cuts.

I thought wrong.

My work-clamping failed. The endmill dug into the side of the slot and yanked the workpiece up creating a divot in the side and in the bottom. I shut the machine down and nothing had broken.

But I had no other way to hold the workpiece. I (very laboriously) reset it at the 10* angle and took 0.010” cuts. The divot in the side disappeared as it was much less than the 0.125” I needed to take off. The small divot in the bottom did not, but it is insignificant other than to my ego.

I took the other 0.125” off the back side of the slot without issue. I had learned my lesson.

Slot with bit.jpg
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Now it’s time for the set screws. But you can see the bit fits.

I wanted to use 5/16” set screws. But after looking at it, I thought there wasn’t enough meat in that half-inch slot sidewall. (Right or wrong?) I could have made the slot ¾” deep, the bit would have been buried a quarter inch up in the slot, but that would not affect its function. But to do that the top angle of the workpiece would need to be greater.

I went with 10-24 set screws.

Set screw holes.jpg
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At this point, I have a fly cutter with a 2”+ arbor!

The first thing I did after sticking the workpiece in the lathe was to cut a relief to help me in the next operation, which is creating the arbor by turning down the 2” workpiece to 7/8”.


Relief cut.jpg
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Since I have been having pretty good luck grinding my own lathe bits in the last few months, thanks to monumental help from Harold and others, I faced off my 1018 fly cutter workpiece and cleaned up the diameter with HSS. I didn’t like the finish, to put it mildly.

So I broke out my Dorian half-inch tool holders and used a CNMG 432-NN insert.

CNMG 432-NN.jpg
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I don’t have a lot of experience with carbide. I did remember that it needs to be turned faster than HSS and that it likes deep(er) cuts. Machinery Handbook was my guide on SF/M and I took .0.050” DOC on the way down to my desired arbor size of 0.875”. (I chose 7/8” because I have never used that R8 holder and it also saved me a bit of wasting the 1018.)

(Continued in next post.)

--Bill
You are what you write.
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seal killer
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Re: Fly Cutter Build

Post by seal killer »

(continued from above)

First, I center-drilled my workpiece so I could use a live center in the tailstock for extra support. Then I started making chips. They were blue. I switched from Viper’s Venom cutting fluid to Rustlick cutting and tapping fluid. It seemed to work just as well and produced a lot less smoke and odor. (My new shop is not ventilated, yet. To get the smoke and odor out I have to open the door of the shop enough to put a fan in it to blow the smoke out into the garage.)

Blue Chips.jpg
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I turned the arbor down to 0.9”, then had to swap out the live center for a dead one. I greased the hole and the point of the dead center with some white lithium grease I have laying around.

Making Arbor.jpg
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My turning skills with carbide are not that great. I managed to get a good finish as long as I kept the speed up and took healthy cuts. (When I had turned it down to about 1.25” diameter, I boosted the RPM up to regain good SFM for the carbide insert.)

But now I was going for the big finish. I took 0.020” off the 0.9” diameter. Now I am at 0.880” on the way to 0.875”. I probably should have switched to HSS. But I didn’t and you see the less than ideal finish.

Fly Cutter.jpg
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I wanted to be a “wee bit” under 0.875”.

Micrometer.jpg
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I tested the new fly cutter on a piece of aluminum scrap.

Test Scrap.jpg
Test Scrap.jpg (229.7 KiB) Viewed 1358 times

I have a fly cutter!

I think I might still build one out of a 3" piece of 12L14.

--Bill
You are what you write.
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Harold_V
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Re: Fly Cutter Build

Post by Harold_V »

Bill,
A couple comments, if you don't mind.

First, it's not good practice to attempt to hold a long object as you did with the long V block. The mechanical advantage created by the length pretty much assures failure (exactly as you experienced). You'd have been far better served to have sawed the piece to an acceptable length to permit a couple facing cuts to bring it to length and held it much closer to the vise jaws, where you have the greatest mechanical advantage.

There are options on how the piece would be machined. I don't see any of them as right or wrong. One chooses a method that suits their experience and equipment.

When using negative rake carbide, avoid lubrication completely unless you can submerge the cut constantly (flood coolant). It provides little in the way of enhancing performance and you risk micro-fracturing the carbide by intermittent rapid cooling.

Negative rake is a poor insert for finish cuts, as you discovered. If you can take cuts of adequate depth and feed that may not be true, but negative rake performs poorly for light cuts. A switch to even positive rake (for finish passes) would have been an improvement.

When shooting for a given size and it matters, it's a good idea to leave enough material for thee uniform cuts. That way you can take a third to smooth out the part, a second third to create the tool load that represents the final pass, and third, after measuring, the final amount that leads to the finish size.

If finish is important and you are achieving a clean cut, it's a good idea to shoot for a finish size that's a half thou over, then spin polish to size. That improves surface finish and allows for some control over a few tenths. Do not assume that this will improve a torn finish. It usually will not. The cut must be clean, free of tearing. Not always easy with 1018.

I read with interest your desire to have the end result "a wee bit under 0.875"". I would NOT have made that choice. Here's why. Collets are ground such that when the proper diameter is gripped, the collet internal bore and the external taper are all in the proper attitude. As you enlarge the part being gripped, the pressure shifts towards the inner end of the collet, and if the diameter shrinks (below nominal) the collet then shifts its gripping towards the outer end of the bore. When it's extreme enough the shank may be gripped by only a very short portion, allowing it to wallow in the collet. It's the same in either direction. So then, when you hope to grip a shank in the best possible condition, it should be sized to the nominal dimension. I like to be within less than a thou.

A thought on fly cutter shank diameters.

It stands to reason that a shank is very best when it is rigid, limiting deflection and chatter. However, the typical drill chuck shank is almost never 7/8". I standardized mine @ 3/4", and for a very good reason. If you are engaged in various operations that include machining as well as drilling, it's far more convenient to just loosen a collet and change a tool than it is to exchange a collet, too. You're better served to use a 3/4" shank for that reason, and my experience dictates that it is more than adequate for the typical fly cut. I don't see any particular advantage in using the 7/8" size.

I hope some of this helps in your decision making in the future.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Bill Shields
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Re: Fly Cutter Build

Post by Bill Shields »

Very good

But there is one point that I have failed to comprehend:

But how do you get flys to stand still so that you can cut them?
Too many things going on to bother listing them.
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seal killer
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Re: Fly Cutter Build

Post by seal killer »

Harold and Bill--

Harold, thank you for the invaluable tips and guidance! Regarding my decision on undersizing the shank diameter . . . I mic'ed several 3/4" and 5/8" shanks on end mills. They all appeared to be half a thousandths undersized. (Maybe my mic is off that much.) So I was shooting for that amount under.

I missed it.

Regarding my choice of 7/8" over 3/4" . . . As I mentioned, I thought 'why not?' It would save me some turning. I also thought that if I really missed my target diameter I could always keep going down to 3/4". After reading your comments I may do just that.

Thanks again for your thoughts. They will help me in the future.

Bill, I'm just an amateur machinist. I'll leave those deep topics to you pros. You could try to explain it to me, but I doubt I would understand. (Superglue?)

--Bill
You are what you write.
Bob D.
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Re: Fly Cutter Build

Post by Bob D. »

Sheesh Bill, it's not for cutting that kind of flies….. Used for the making of pants!
3/4" Juliet II 0-4-0
3/4" Purinton Mogul "Pogo"
3/4" Hall Class 10 wheeler
3/4" Evans Caribou/Buffalo 2-8-0
3/4" Sweet Violet 0-4-0
3/4" Hunslet 4-6-0
3/4" Kozo A3. Delayed construction project

1 1/2" A5 Camelback 0-4-0
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Harold_V
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Re: Fly Cutter Build

Post by Harold_V »

Bill Shields wrote: Fri Feb 03, 2023 8:39 pm Very good

But there is one point that I have failed to comprehend:

But how do you get flys to stand still so that you can cut them?
Meth?
Dunno. Mine just seem to accept their fate! :lol:

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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