Fly Cutter Rough Surface Finish on Carbon Steel

cfoxx911 · Feb 20, 2018

I am having trouble obtaining a nice, smooth surface finish on carbon steel using an indexable fly cutter with my mill (pictures attached). The surface is very rough like sand paper and I can't figure out how to get a smooth finish. The fly cutter's cut diameter is 4in (2in radius) and I've tried running it at 600rpm starting with feeds from 2 Inches per minute up to 16 ipm, and then at 1300rpm with feeds from 6 ipm to 30 ipm and still no success. I tried depths of cuts from .002 to .010. I have been cutting with no lubrication and. I'm looking for what is causing this rough surface finish and how to possibly fix it.

My observations are: I don't hear any chatter, I haven't seen any sparks, cutting insert is brand new and I don't see any signs of ware after use, my mill is sitting on 4x4's (vibration?).

My machine's limits are 160-600rpm (low) and 1300-4600rpm (high) with feeds from 0-34 ipm in the x-axis only (all other axis's are manually adjusted). The mill is Kent USA KTM-5VK.

I'd like to point out I am a novice in the machining world so I apologize if any of my terms seem odd. I am excited to learn as much as I can from you all and I appreciate all those who see this post and provide information. Also, can we please keep this discussion on this topic and avoid any unnecessary comments/off-topic discussions.

Thanks!

Cody

dalmatiangirl61 · Feb 21, 2018

In the last pic it appears your feed is too fast, you might also consider reducing the stick-out of the tool in the flycutter. Have you tried using HSS, interupted cuts are hell on carbide. Is material steel, or cast iron? Swarf in pics looks like cast iron.

Conrad Hoffman · Feb 21, 2018

Agree tool is way out there. Remember if you try HSS you have to check SFPM and probably slow way down. If it's cast iron, dry may be OK, but if it's some sort of CRS or something, you need oil. I'd probably do it with a 3/4" end mill and live with the pattern you'd get. Or get that grinder you always wanted.

JRIowa · Feb 21, 2018

This is a first for me. I've never seen anybody use a turning tool in a fly cutter.
JR

Pete Deal · Feb 21, 2018

I have always used either brazed carbide tipped tools or hss, very sharp.

BobM3 · Feb 21, 2018

Hard to see but it looks like the cutting corner of your tool is quite worn. There's also a big exit burr which would indicate a dull tool.

redlee · Feb 21, 2018

Try the same tool in a lathe with overhang the same and it will probably give the same results.3

SilveradoHauler · Feb 21, 2018

Fly cutter is way too small. Too much overhang with the tool. Wrong tool bit geometry. Feed to fast. Spindle RPM too fast.

If you have much of this to do, buy a big fly cutter. Below, 3 inch A36 flat bar, the fly cutter is 3" in diameter. With a little tool projection the cut is made in one pass. I am using 3/8" HSS tool bits in the fly cutter. Note the cutting oil.

2+

For my operation in the photo:

4 times the cutting speed divided by the diameter:

A36 steel cutting speed is 100

diameter of the tool about 3 1/2 inches say 4 for simplified calculations

4 times 100 divide by 4 gives me about 100 RPM

In addition to the 8 speeds in my mill I have a 3 hp DC motor on it with variable speed drive controller. I set the gearing/belts to approximate rpm and fine tune with the speed controller

So I am saying your 1300 rpm is way too high.

HuFlungDung · Feb 21, 2018

No tip clearance for the cutting edge. It's a lathe toolholder, so it would appear, and the way you're using it would be equivalent to having the tool set about 1/4" above centerline: it's going to rub like crazy beneath the cutting edge, because that's where the maximum sweep of the tool is.

SilveradoHauler · Feb 21, 2018

Pete Deal said:
I have always used either brazed carbide tipped tools or hss, very sharp.

Yes Yes Yes. Tool bit grinding is the most important skill in a Machine Shop.

Tyrone Shoelaces · Feb 21, 2018

JRIowa said:
This is a first for me. I've never seen anybody use a turning tool in a fly cutter.
JR

You've never lived JR ! I have but normally it's not a throw away tip tool.

Regards Tyrone.

plastikdreams · Feb 21, 2018

Head trammed? Really though who uses fly cutters anymore?

Try running 300 ripems and an inch per minute. Copius quantities of cutting fluid of your choice brushed on the part.

crazygoat · Feb 21, 2018

Lathe tool will not work in a fly cutter. Geometry is all wrong. Also, I can't really tell from picture, your slot in the cutter needs to be offset from the centerline by whatever size tool you are using, so your tool tip will be on the centerline of the cutter.

Rstewart · Feb 21, 2018

A lathe toolholder/insert will work Great, but you have to make the fly cutter!
I made one a few years back, it worked amazing facing hardened 4130.

atomarc · Feb 21, 2018

Agree, a lathe tool fixtured properly will work fine..but that picture sure looks like cast iron to me, and cast iron doesn't finish exactly like regular old carbon steel. If your feed speed was lower the finish would look much better.

Stuart

Spruewell · Feb 22, 2018

That definitely appears to be cast Iron, which will not require lubrication. Your tool is sticking out way too far, reduce the cutting diameter as much as you can. It is in the fly-cutter head backwards (you will also need the reverse of that tool holder style). That fly cutter is meant to turn the other direction. Cutting edge of insert should be about centerline of the tool. Lower your RPM to between 100-200 rpm and you should be able to get a decent finish at about 2-4 i.p.m. With anywhere from .01 to .04 depth of cut.

Tyrone Shoelaces · Feb 22, 2018

I had a little 4 insert positive rake throw away tip milling cutter about 1-1/2" in dia on the " Bridgeport " I worked on. I can't recall the make now but it was great. Did everything I wanted and didn't beat up the machine.

Regards Tyrone.

steve-l · Feb 22, 2018

As others have stated, your tool geometry is wrong. You are rubbing not cutting. Just like on a lathe, your cutting edge must reside on the center line. You need adequate back rake and cutting clearances. You have neither. I assume you have an R8 spindle, is so, you have questionable stiffness at that diameter, this is especially true and aggravated by that extreme hang out of the bit. If you must use indexable carbide, there are inserts designed specifically for this. The one you are using isn't. Can this be done on an R8 machine? Yes, but you should be using HSS. You need a larger, stiffer fly cutter, you need to go slower with lighter DOC and slower feed (watch your tool loading). Also, your head tram must be spot on or your result will not be flat. if your tram is correct, you will have a very fine cross hatch pattern as a finish. If you don't, it ain't flat. The tool's nose radius should equal 1.5 times the advance rate per revolution for the best finish. The greater the nose radius, the greater the tool loading and the greater the tool deflection. It is a delicate balance. In any case, it's good training. Just as others have stated, you are better off using an end mill and living with the tool marks.........the machine will be happier and the end result will be achieved faster and better.

JRIowa · Feb 22, 2018

Tyrone Shoelaces said:
You've never lived JR ! Regards Tyrone.

Oh, I have lived. I have several flycutters that I use on very, very rare occasions. I learned many years ago how hard they are on BPs and that a good insert cutter will out perform them 99.9999% of the time.
JR

Tyrone Shoelaces · Feb 22, 2018

One shop I worked in got the job of facing both sides of some cast aluminium cover plates. They were about 3ft by 2ft by about 1.25" thick. Flat on one side and with several bosses on the other side. There were about 50 in the batch.

After trying several milling cutters without great success the guy doing the job opted to fly cut them. That method turned out ok but in spite of trying to box the job in we were finding the chips up to 50 feet away for weeks afterwards !

Regards Tyrone.

Fly Cutter Rough Surface Finish on Carbon Steel

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