Flycutters: help to understand 3 different types

Hello,

Could you please give me a hand to better understand these 3 different types of flycutters ? Have become confused and perhaps misinformed by my internet searches. Would appreciate any commonsense comments debunking any known urban myths that us newbies may not have the skills/knowledge to dismiss.

Alternately any known links or previous threads greatly appreciated.

Flycutter 1 : Utilises a standard boring head, seemed to me to be a clever idea but have read that it can wreck the dovetail on the boring head and that the total amount of stickout below the quill isn't a good thing either. Possibility of the lower dovetail block getting loose and getting thrown off becoming a dangerous projectile ? Would be fairly easy to make this from a solid cylinder of steel thereby avoiding any of the dovetail associated problems.

Flycutter 2 : Traditional shape plus HSS left hand grind toolbit. How/Why did the angled shape evolve ? Is there a best angle ? Why is this better than the orientation of the cutter in Flycutter 1 ? Does this simply relate to your preferred way of grinding the cutting tool.

Flycutter 3: Single carbide bit mounted on a bar, fairly easy to make. Could use a circular carbide insert as well to give more cutting "points". Even easier to simply remove 2 teeth from a standard facing bar , although this seems to be very rarely discussed as an option - why is that please ?. Also possible to use a piece of HSS instead of a carbide insert - this leads to the idea of putting a piece of HSS in a tangential orientation and people claim this can give a much greater depth of cut in small machines.

I have also seen Flycutter_2 using a toolholder that holds a circular carbide bit. Seems to me that if the insert is circular the angled toolholder shape of flycutter_2 isn't necessary.

First anything that uses carbide was originally done with HSS, and before that plain carbon steel. Not everything that can be done with HSS can necessarily be done with carbide though.
Secondly it is often difficult to understand which way the tool is cutting, and hence the required geometry. It looks like it cuts downward (for your photos) but the cut is actually sideways.

Number three is the starting point - dead simple and the tool is anything to hand either screwed into a hole or under a clamp.
Then when you have thought about the cutting direction and want to be posher using a full new square piece of HSS the angled version in 2 reduces the amount of grinding if you get it right.
Number 1 is 'cos you've got one and haven't got round to making 2 or 3.

The heavy cuts and interrupted cuts of a flycutter are not what a boring head is designed to cope with. I would not use that idea except maybe for light cuts in a pinch if I had no alternative.

Not sure I completely agree with you but I do see your point. Boring and facing heads which are just boring heads with more gizzards are often used in the facing mode on areas producing an interrupted cut and do not seem to suffer unduly but I would completely agree they are not good for ploughing off 1/8"! A lot of the "hobby" boring heads are pretty well built though with a good area of slide so as long as the slide is not extended beyond the body (as shown in the picture) it should be fine. A shorter tool would be good though.

As to the OP any design that holds the tool rigidly in the right orientation is fine. I have a couple of examples of a fourth version to muddy the water further! Lumps of round bar, reduced at the top for a suitable shank and profiled (mine are bevelled) at the bottom to give a bit of clearance, drilled at 45 degrees at a suitable size to take old centre drills with a tapped locking screw hole to clamp. Good use for knackered centre drills!! They work fine too. Grinding the right profile on the tool will have a far greater impact than the lump that is holding it!

Strange how everyone says carbide tips don't like interrupted cuts on the lathe but there are plenty of tipped fly and milling cutters about that do that every day..........

Paul.

I"ve often wondered about that.

Bazyle Hopper and Paul - thanks for your help - am off to the shed to see what I can do.

Bill

I have a small fly cutter which is a piece of 1 inch silver steel turned with a 1/2 inch shank. It is cross drilled for a 6mm diamiter carbide cutter held in place with a 6mm grub screw. I have ground the end of the carbide so that I can slightly rotate to give different angle of rake more for aluminium less for cast iron it works well for me.

I wondered about that too but in making my flycutter I used the boring head with a carbide tipped tool (side mounted) to flycut the 20 degree angle on the head of the cutter. It was a brazed tip tool though not an insert tool and it worked absolutely fine, in fact it made me wonder as to why I,m making a flycutter as the boring head with a suitable cutter works a treat. However I would rather not use the boring head for fly cutting and keep it for its intended use.

Picture below of the boring head with a modified carbide tipped lathe tool, as mentioned it works and cuts really well but it is only a stand in until I finish the flycutter.

Edited By Ron Laden on 06/12/2018 08:12:36

Two more pictures of my fly cutter.

David

I made a flycutter similar to your third photo, but with a replaceable/adjustable bar. I used TNMG160416 inserts, tried with 08, 12 and 16 radiuses but found the larger one gives the best finish. It is a negative rake and good for interrupted cutting, the downside is that you have to machine the cutting clearances in your bit holder bar.

Also it will vibrate at higher speeds if you go oversize.

A flycutter's whatever you make it to be, and the workholding conditions are as important as the flycutter configuration itself in how well it works.

I generally use a standard lathe boring boring bar with a 3/16" square HSS toobit set by caliper to whatever radius I'm wanting to achieve - though obviously that's not usually critical when generating flats. Equally obviously it has limitations on depth of cut when doing it in a lathe.

But it will do some quite surprising things:-

... as when I was wanting to cut (IIRC) a 1.407" rad to a specific depth in an arc-shaped reinforce.

I don't think there's any more fixed answer to what's the best flycutter than there is to what's the best anything else - it depends on what you're trying to do, to what and with what. The best flycutter for the job is the one you've got, that you can make do the job.

I’ve got a traditional bought fly cutter on a MT3 shank like this type.

**LINK**

I use HSS in it with a radius tip for cutting alloy and a round carbide cutter for steel. I get a great finish with it.

I recently purchased a face end mill from Banggood after watching a video review. The finish on ali was not as good as I got with my fly cutter but more importantly it seriously overloaded my WM18 mill.

I am now wondering if I can use it with just one or possibly two inserts instead of four?

Surely it's a milling cutter made "on the fly" with whatever you have to hand?

More likely a poor set of inserts, have a read of this thread to see how some better inserts transformed my similar face mill which was terrible out of the box.

I've got an MT2 'angled' fly-cutter that is used for light 'facing' cuts when required, as well as a number of plain shank fly-cutters of various head diameters (from about 1/2" up to 3" ) which use round HSS cutters. For specific diameter cuts I also have (somewhere) a holder that fits on my faceplate.

All of them work pretty well and it's mostly a matter of either convenience or sweep size that decides which one I'll use. When used in the lathe, the plain shank ones can be simply held in the 3-jaw or ER collet - whereas the MT2 one requires the chuck removing and a drawbar fitted.

I'm afraid I thought Micks' 3/16th tool had far too much extension from its' holder - and whilst it might work - It's not something that I would recommend myself.

Regards,

IanT

Of course it did! 

I even tried with the little parting-tool-shaped grind on the tip to sort of trepan out the radius, so I could simply then part off two of the arc-segment reinforces.

I didn't expect that to work, and it didn't. That was when I decided to flycut the rad out, and that did.

My point was to keep your eye on the objective you're trying to produce, and not become too preoccupied with doing it in some procedural manner.

Edited By Mick B1 on 06/12/2018 11:07:28

Everything is a compromise.

The common angled square tool-bit style made in a range of sizes seems to do about as well as can be expected over the general range of our workpiece sizes. Its easily adjusted, holds the bit firmly even when set to the smallest size and keeps the non cutting spinning bits well out of the way of any protrusions on the workpiece or clamping arrangements. Pretty good on balance too and probably requires the least grinding to sharpen the tool.

Boring head version makes good use of something you already have. Best to be very conservative on moving the slide tho'. With the inevitable interrupted cut its advisable to ensure that all (three?) gib adjustment screws are pressing the gib onto the slide. Any overhang and you risk bending the gib which isn't going to help matters when returning the head to its proper purpose.

Flat bar with a bit is easiest for DIY but the spinning non cutting end can be something of a hazard. Especially if you use a direct mounted insert which, of necessity, puts the bar very close to the workpiece. Its very easy to loose track of just how big the device is putting clamps and workpiece projections at serious risk. The one I made, about 10" long, got reduced to produce after completing its job. Next time I shall use a round carrier. Either full diameter or most of it with the tools projecting a short distance whether simple HSS bits or inserts in short holders. I suspect the Bridgeport spindle drive splines would appreciate the flywheel effect of a full circle too.

I'm with Ian in thinking "Sheesh, thats brave!" over Micks' uber projection version. Shows just how far you can push the envelope with appropriate care and knowledge.

The general rules are conservative for good reason. "Rules are made for the guidance of wise men and the obedience of fools." Its deciding whether we are wise men or fools that sometimes catches us all out. As I frequently said to my trainees and work experience students. Its fine to break the rules if you think through properly it first. Usually leading up to a careful contrived example of safely driving a coach and four through what the book said. Followed by a visually and audibly impressive, but actually safe, example of what happens if you don't think it through and do something nearly the same but not quite same enough!

Clive.

Milling carbide is a different grade, if you read the spec sheets some lathe cutters are suitable for interrupted cuts. Most have no mentioned of interrupted cuts, these are the ones that flake after a while, there a photo of a lathe tip after use in a mill - it's not pretty

Here's one I made some time ago...Use a TCT welded LH cutter, works fine with light doc's. I also have a boring head that can be set up as in Paul Kemp's pic, plus a fly cutter, #2 as in BW pic. so am pretty well covered for what I need.



George.

Most things work if you don't try and take off too much metal too fast and take some care with the angles and avoid rubbing.

Neil