Flycutters: help to understand 3 different types

Hi BW,

All the fly cutters seen in this thread will work ! The only one that I would not use is the boring head.

The primary requirements are rigidity, and balance ! Out of balance forces cause various issues, vibration being the least desirable. A fly cutter has to be able to encompass the work area or you have to make multiple passes. Clearance, you don't want to collide with any protruding obstacle, hence the angled cutter type.

This is one of mine. 3" inches in diameter, 20 mm thick, 20 mm spindle. A heavy rigid body and spindle. Well balanced, and a good flywheel effect. Particularly important if making interrupted cuts. I can take a 1 mm DOC in mild steel at a 150-200 rpm. The tool bit in this one is 5/16" square HSS.

Edited By John Baron on 06/12/2018 19:19:27

You might also consider the angle of the cutter and the profile of its end if you contemplate cutting up to a shoulder.

Thanks a lot for all of the tips and especially the photos - really helpful to see what others have done. Especially that one by Mick, thats amazing - would never have dreamed of trying that.

Went up to the shed yesterday and came straight back down again .......... 38C+ thats almost 100F in oldspeak and its the same today so I wont post anything more until its cooled down a bit. Opening the doors and windows doesn't help.

At the moment you can feel the tin roof acting like a giant radiator as its dark green exterior absorbs the sunlight and it radiates out heat on the inside of the shed. SWMBO doesn't want me to paint the shed roof white - I guess it would turn into a dirty grey and look awful.

Bandersnatch - cutting up to a shoulder ? Am gonna learn how to cut a flat surface first - do you chaps commonly cut up to shoulder with a flycutter ? I'd be a tadge nervous.

I have seen that german website metallmodelbau - he makes diy flycutter dovetails see here

http://www.metallmodellbau.de/pictures/Ausdrehkopf/FRW-26.jpg

I guess thats cutting a shoulder rather than cutting up to a shoulder.

Waiting for the cool trough that the weatherman promised.

Bill

Edited By BW on 07/12/2018 03:40:59

Nothing is sweeter than a flycut lump of 2034-T4 aluminium alloy under a well sharpened and honed HSS tool with a flush of kerosine, Try a backcut if you are brave enough to check your tramming or just check the dials, wind the table back and start again.

Keep the rpm low, that little bit covers a lot of surface at it's radius.

'Softly, softly catchee monkey'

* Danny M *

You don't need to stop at dovetails, any profile can be done as the flycutter is really just a single point tool, I have also done dovetails though single sides.

I agree ! All sorts of things can be cut with a flycutter.

This is a couple of pictures of a dovetail slide that I made that way. The really hard part was making sure that both the male and female parts fitted together properly.

I admit that I did cheat a little. After making the male half, I took a slice off the end and used it as a template when making the female half. They are a nice fit and slide together well.

The brass screw on the left of the top picture is for locking the slide.

The screw on the bottom picture drives the two parts.

Edited By John Baron on 07/12/2018 12:10:44

Well done, but isn’t that what Gib keys were invented for? One side could be made as a straight edge if the key was retained in the other plane. An infinite number of attempts could then be made to make the key at just the right shape.

Well, thanks for the nice words there. I videoed the second-to-last pass with that overextended flycutter. The component fitted after one more cut of 2 thou.

Of course, I reserve the right to be less forthcoming about demonstrating my failures...

Edited By Mick B1 on 07/12/2018 15:02:20

I agree ! But at the time I had only recently got the mill, so it was very much an exercise to see if I could make one. I've had a Myford S7 for a long time, so making a suitable fly cutter was the easy part.

Hello Again,

Tried to copy what John Baron did. Didnt get any mirror finishes - more like a dirty smeary streaky mirror.

Think I am feeding too fast (2.5mm in 8 seconds ? ) and not enough rake on tool, tried 2 different tool grinds but didnt seem to make any difference. Slight difference when I slowed the feed right down _ am using manual feed is that ok ? Finish on Al (short squat lump in photo) seems better than finish on hot rolled steel (long thin lump in photo)

Tried varying rpm from 125 to 300 but not much effect - cut diameter is 2.5"

Will have another go tomorrow - reminds me of my initial attempts at getting a nice finish on the lathe - took me a couple of years to get a good finish with a round nose tool - shear tool and turning a knife tool around to rub worked fine but round nose tool was always awful for me. Maybe I gotta go back and learn how to grind tools properly.

Hi BW,

Very good effort !

First thing I noticed from your first picture, you have far too much tool stick out. Rigidity is the thing here. I also notice that you have the spindle secured with two nuts. Whilst its hard to see on the picture of mine there is no spindle below the bottom of the disc. The spindle on mine was pressed into a bored hole, and I also used superglue to make sure that it did not move. Whilst not absolutely required, I also faced off the underside whilst holding the spindle in the lathe chuck.

I did a lot of playing about with tool bit shapes. The rounded edge seen protruding through the disc is the one that I use for alloys. There is only about five or six degrees of rake and the front face is virtually flat.

The toolbit for cutting steel is quite hooked. I basically copied my lathe tools.

Last thing ! Check your mill tram. Under ideal conditions you don't want the cutter taking more off on one side, this is most noticeable on a long cut when cutting in one direction and the cutter is taking a shave off at the other side.

Don't forget the direction of cut is sideways. With a round tool it is easy to end up setting it to negative rake.
Your speed is 125rpm and for a finishing cut you want 1-2 thou per cut. so 125x2= 250 ie 1/14 inch per minute.You have been traversing a bit fast.

125 is a bit slow, I'd be 5-700rpm on the ali and the skin of the hot rolled may have taken the edge off the tool.

Feed wise at my speed roughly 1 turn of the handwheel per second which equates to 150mm /min

Splash of paraffin or WD40 will help too

Edited By JasonB on 09/12/2018 13:51:13

The flycutter I finished this morning, 40mm diameter, 16mm shank, 20 degree angle tool mount, fitted with an ARC HSS tool bit.

Gave it a test run and it cuts really nice, tried it on some 6082 and I couldnt want for a better finish, very pleased with it. Ran it at 650rpm and feed wise I couldnt tell you but it was steady, I tend to go with what feels and sounds right.

Seeing Jasons figures I roughed out the feed rate I used timing the turns of the handwheel as I used on the test piece. I was running a bit slower at approx one turn per one and a half seconds so somewhere in the region of 100mm per minute.

Good afternoon,

One of the most useful tools in my workshop is a little fly cutter made to a design that appeared in the Live Steam magazine many years ago, it's probably no more than 3/4" diameter and give about a 7/8" diameter sweep with a 3/16" square HSS tool bit. I use it for finishing cuts taking off no more than .001" at about 1600 rpm with a dead slow feed results in a finish like a surface grinder! Wonderful.

Regards

Bob

Popped one of ARC's new flycutter bits into a 2.5" head so swinging a similar 3" radius, 800rpm 0.1mm DOC and about 100mm/min feed finishing cut. Not too bad, maybe the mirror is a bit steamed up but could not be bothered to play about with it any more.

BW, I would say you have too big a curve on that tool which can cause it to start chattering, if you look at John's one I would say the cut is being made by that small angle on the corner of his toolbit rather than the bottom. I'd grind yours more like a lathe tool say 10 degrees across the botton and the edge 90degrees to that then just lightly stone where they meet for finishing cuts, heavy metal removal just leave as ground.

Edited By JasonB on 09/12/2018 16:56:25

A good cutter and the right combination of speed and feed certainly can produce a good finish, pleased with what I got.

A question: how will a HSS bit cope with flycutting silver steel, thought I would ask before I try.

Should be OK, just a little harder going than a low carbon steel.

It might, or will, depend on the hardness. Is your steel in the annealed state or hardened?