what is a reasonable max size flycutter for a CAT 40 knee mill ?

Overland · Jan 5, 2022

I have a Supermax 5 hp knee mill, and I'm making a flycutter for it.
I have a piece of 1-1/2" plate, about 9" diameter.
I good stout tool (did I really right that ?), is good for vibration etc, but it looks massive compared to a Cat 40 shell mill holder.

Thoughts on the diameter, thickness and weight please ?

Thanks
Bob

boslab · Jan 5, 2022

Your massive stout tool should have the stiffness you seek, in fact you could go bigger, mines an old brake rotor of an Audi 80, stiff enough but requires some bravery, big tools can be intimidating
Mark

dian · Jan 5, 2022

what are you going to do with a fly cutter?

gustafson · Jan 5, 2022

People use flycutters on bridgeports because the head won't stay trammed enough to make a surface in more than one pass without a notch. I have a machine almost as stiff as your machine and rarely am tempted.

bill jones · Jan 5, 2022

---here is some pictures of the one large cutter I built specifically for milling heads

Bill Jones Page 1

---I used a cast iron flywheel because I didn't want any vibrations and I felt the cast iron would dampen out vibrations
------but even then I was still getting some odd cutter patterns---so I installed the aluminum bowl piece as it was something I just happened to have
--made that aluminum bowl to fit all preloaded nice and tight--and since then this set up has worked perfect

---at first I had made 12 mounting points for my 12 solid carbide bar pieces that I was making for the cutters---but after a while I tried just 6 cutters and that works excellent and doesn't require near as much set up time

------------------------------------
---later on I came across the large diamond wheel and I mainly use that for some small VW diesel heads that have hardened precups

---biggest issue with it is trying to get the OD and the bottom cutting edges to dial indicate in---but even with it not perfect it stills does a pretty nice job---just need to run it a little slower

Overland · Jan 5, 2022

Thanks for comments.
My thoughts are to create a large diameter cutter for surfacing a large object, rather than multiple passes with smaller diameter face mill.
I really don't know what size face mill my machine will handle; I know on my old BP clone, 3" was enough. So I figured a large diameter single point (fly-cutter) would be ideal, and an interesting project.
High rates of metal removal is not really the point, as I only have 5 hp.
What size and type of facemill do people use on this size machine ? (5 hp, CAT 40 Supermax mill).
Thanks,
Bob

Garwood · Jan 5, 2022

I have some big flycutters, up to around 24" in diameter. I never use them because they're so stupid heavy.

I was making a product that was 5" wide and considered facing it one pass. The flycutter I was going to buy was this: B-52 Fly Cutter - Kristi Tool

I ended up changing the design so it wasn't one big surface so I never bought a flycutter.

My opinion is keep it light. It will be easier on the machine and you when you load it.

Oh, I should add that a couple years ago I had a few extra to spend on tooling and I impulse bought the flycutter that Suburban tool makes and sells. It took 2 months for them to ship it and when it arrived it was a total pile of shit. Absolute joke of a tool, stupid design and the machinework was very sub-par. So I sent it back and they refunded me no problem.

Mtndew · Jan 6, 2022

You can make it as big as you want. You're limited by how you use it. How heavy of a cut and how balanced it is will be the deciding factor.

Hbjj · Jan 6, 2022

My homemade junk
2" square bar T style on 30qc in a bp no problems.

Karl_T · Jan 6, 2022

Just a data point for you. I have a supermax 5hp knee mill manual with nmtb40.

I have a 9" diameter fly cutter with a SUPER SHARP HONED HSS BIT it can get a mirror finish with light cuts, about 5 thou.

plastikdreams · Jan 6, 2022

Fly cutters are antiquated, extremely dangerous tools that have no place in a modern shop.

Bobw · Jan 6, 2022

plastikdreams said:
Fly cutters are antiquated, extremely dangerous tools that have no place in a modern shop.

A fly cutter, by definition, is really nothing more than a face mill with a single insert.

Home made construction of a fly cutter.. That can go either way.

Antiquated, yes.. Though I have used them on occasion. I've also pulled all
but one insert out of a face mill just to get that "perfect" mirror finish.
I've also made them, or things similar to do some oddball things, like a 4.5"
back counter bore through a 2" hole. Basically an up side down fly cutter.

Old school techniques do still have a place.. You probably shouldn't use them
everyday, but sometimes you run across "That" situation where that is the only
thing that is going to work, or at least work without breaking the bank.

Overland · Jan 7, 2022

What I'm building is a 9" disc, almost 1-1/2" thick with a single tool.
So it really is a big facemill with all except one inserts removed.
I don't see any particular safety issues.
Thanks,
Bob.

Mike1974 · Jan 7, 2022

plastikdreams said:
Fly cutters are antiquated, extremely dangerous tools that have no place in a modern shop.

Depends on the type/brand. We have a few un-mentionable brands that take a high positive rake polished insert. The bar has a groove to lock the set screws into as well to adjust the diameter.

dian · Jan 7, 2022

problem: stepover when facing
idea: huge flycutter
result: huge stepover (fortunately its in the air, so invisible)

Mark Rand · Jan 7, 2022

If the head's out of tram in the B axis with the work travelling in the X direction, a fly cutter will produce a less flat surface than multiple passes of an endmill. The difference is that there won't be any steps in it.

Neither is good for things like cylinder heads and flanges, but the stepped surface will take less work to flatten than a curved flycut surface.

michiganbuck · Jan 7, 2022

Overland said:
What I'm building is a 9" disc, almost 1-1/2" thick with a single tool.
So it really is a big facemill with all except one inserts removed.
I don't see any particular safety issues.
Thanks,
Bob.

9" disk might be better served with the tool bit facing down rather than outward so as to be a little safer for an accidental hand bump...and made to be in balance. One might even have two (+) bits cutting.

An end mill is sharpened with a dish at the cutting end so the stepover is more pronounced. I have made end mills with a .060 end flat so the stepover is not as mich pronounced.

Yes the dish starts .06 inside the flat nose.

Overland · Jan 7, 2022

Thanks Buck,
That's a good point about the cutter not extending beyond diameter of the disc, for safety.
Your point about being out of tram, machining a concave surface reminds of a lecturer back in college advocating to tilt the head slightly so the cutter only cut on the front, not the backside, to give a better surface appearance. We beat him up pretty badly telling him you really need both sides to cut (touch) to get a true flat surface.

michiganbuck · Jan 7, 2022

Overland said:
Thanks Buck,
That's a good point about the cutter not extending beyond diameter of the disc, for safety.
Your point about being out of tram, machining a concave surface reminds of a lecturer back in college advocating to tilt the head slightly so the cutter only cut on the front, not the backside, to give a better surface appearance. We beat him up pretty badly telling him you really need both sides to cut (touch) to get a true flat surface.

It was common to use large cutters out of tram so the heal would not mark the finish, the amount of tolerance was considered. Crosshatch may make true flat but then the cycle time had to allow the cutter to full pass the part.

Likely your lecturer back in college knew the What but he did not know the Why.

eKretz · Jan 7, 2022

You can tilt a cutter a small amount and not run into much issue with flatness problems. You'll get a very slight dishing but at max only half as much as the TIR on the tram is out, and sometimes a good bit less due to flex in the machine and whether the cutter is cutting anywhere near full circle diameter on the sides. (Remember the low side is going to get the most tool pressure too because it's cutting the deepest). So kick the thing .002" out and you're only going to see a .001" out of flat surface due to the dish (or less).

what is a reasonable max size flycutter for a CAT 40 knee mill ?

Stainless

Titanium

Titanium

Diamond

Aluminum

Stainless

Diamond

Diamond

Cast Iron

Cast Iron

Diamond

Diamond

Stainless

Diamond

Titanium

Diamond

Diamond

Stainless

Diamond

Diamond; Mod Squad

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