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Face Mill for lathe

Advice sought, again (sorry)

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Terry Kirkup14/01/2020 19:30:04
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Following my first dip into milling on the lathe (Warco WM290) I thought rather than using a spindly little end mill to flatten things I'd go up a few sizes. I ended up with this from an Amazon shop:

facemill1.jpg

It's an R8 50mm 4-cutter job. However, my thoughts were that the extra load imposed on the lathe spindle would require a decently heavy toolholder for it, so I decided to use it inside my largest ER32 collet, a 20mm one. So I set about cleaning off the insubstantial "thick" end of the R8 shank plus some off the whole length to get it down to 20mm from around its original 23/24mm.

Unfortunately, although I got it sliding through the collet nicely I wasn't happy with the keyway cut into the shank as it was causing substantial runout due to the 70mm or so interrupted cut making the job bounce off the cutter (the arbour was fairly hard and I ruined several carbide inserts). It took another three hours of very careful and painfully slow machining and cooling off time to dispatch the slot, by which time the arbour was down to 17mm so I now had to use a 17mm collet instead. No big deal, I hope?

facemill2.jpg

Sticking it into the hex collet block it showed just 2 1/2 tenths runout on the dial gauge so I'm happy with that, but my question to the Old Hands today is this - with such a hefty stickout from the chuck, do you think I should also lop off the R8 taper to pull it back into the collet another inch or so?

facemill3.jpg

And one more question if I may. If I turned it down another millimetre it would fit into my HBM keyless chuck so I could use it in the tailstock and spin the workpiece instead. Is that a bad idea?

Edited By Terry Kirkup on 14/01/2020 19:30:46

Terry Kirkup14/01/2020 19:34:51
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This is my attempt to get around the issue that "she" won't let me buy a milling machine!

JasonB14/01/2020 19:50:09
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Would have been easier to have bought a 4MT arbor ( or 3MT and reducing sleeve) rather than R8 and simply mounted it into the spindle taper.

Tailstock idea is a bad one as it will just make a circular depression in the work as they axis is fixed, may as well spin the work against a lathe too as that is how they are meant to be used.

Howard Lewis14/01/2020 19:55:58
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The WM290 has a 5MT spindle bore, and presumably comes with a 5 MT to 3 MT sleeve?

If so, would it not be better be better to buy a 3MT Shell Mill Arbor, to minimise the number of parts between the spindle and the cutter, to minimise the risk of run out. One possible supplier of such a fitting is Arc Euro, with a M12 drawbar thread, and probably RDG or other suppliers would also be able to offer one.

I hope that you were not contemplating fitting the hexagon block into the 3 jaw chuck! That would probably give you a much greater run out!

Howard (aka Fat Fingers )

Edited By Howard Lewis on 14/01/2020 19:56:59

Andrew Johnston14/01/2020 20:00:23
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Good grief, that's going to be flexible. I don't think you need worry about spindle loads, any sort of cut and you may well get more chatter than an Islington luvvie. And there was me worrying about whether a 50mm face mill would be too big for a Bridgeport.

Andrew

Terry Kirkup14/01/2020 21:03:27
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Ooh, that fettles me then, thanks to all three of you! I just have this thing about removing the chuck, it's such a tedious operation I'd do anything to avoid it. A bit lazy of me I suppose. Jason, thanks once again for ever more enlightenment, tailstock thing is very obvious to me now! Howard, I do indeed have the 5MT to 3MT part, always wondered if I'd ever need it. And yes Andrew, it was going in via the 3 jaw. After the hassle I've had getting this to where it is now I will try it v-e-r-y tentatively on a piece of nice, small, soft aluminium just to scare myself off the idea.

What a great forum this is.

Howard Lewis15/01/2020 12:38:27
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Especially if i want to transfer a job from the lathe to the Mill, such as gear cutting, I use the 5 -3MT sleeve and M T collet chucks. Hopefully, that keeps everything in line as much as possible.

The Collet Blocks only get used for work holding in a vice on the milling machine

Howard.

Martin Kyte15/01/2020 13:47:16
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What I would suggest for your lathe setup is a two point fly cutter. Make an arbor which you can hold in your chuck with a thick disc attached. Couple of 6mm holes in the face side of the perimeter with one at a slightly smaller radius than the other with a couple of tapped holes suitably placed in the perimeter to hold a couple of round cutters. Form the cutters in the usual way and arrange that the innermost cutter is slightly proud of the other. You then have a tool that you can stick in the chuck in seconds and will take a rough cut with the outer cutter and a smoothing cut with the inner. George Thomas did it with a bar holder in the four jaw but you said you didn't like taking your chuck off.

regards Martin

Terry Kirkup15/01/2020 20:13:02
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Cheers Howard, if I get the shakes with this setup I'll probably go that way.

Martin, thank you for the input too. I have no experience of round cutters, and I'll never use anything other than carbide inserts on bought tools as they seem much more effective and tougher than anything else. I've been given the impression, mainly from the Youtube folk that the more cutters spinning the better, assuming they are all aligned correctly. And I must try to conquer my fear (!) of chuck swapping

Hopper16/01/2020 06:49:07
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Way too much overhang, as Andrew pointed out. I would look at cutting off the tapered section all together and grip the cutter by the larger-diameter parallel section on the end in the three-jaw chuck. The closer you can get the cutting tips of the inserts to the headstock spindle bearing, the more successful your cutter will be. IE less chatter.

Hopper16/01/2020 06:54:29
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Posted by Terry Kirkup on 15/01/2020 20:13:02:
I've been given the impression, mainly from the Youtube folk that the more cutters spinning the better, assuming they are all aligned correctly.

This is the problem with using YouTube as a source of knowledge. Who knows what the You'Tube folks' background is, or what their priorities are. Yes multiple cutting points are good if you want to remove metal quickly, and you have the power to drive them all at once and the machine rigidity to hold things steady at the increased rate of metal removal. That's great if you have heavy duty industrial machinery and want to remove metal at industrial rates.

Old-style fly cutters, like the one of GHT's described above, were designed to be simple to make at home and remove a reasonable amount of metal at a reasonable but not fast rate on the typical home hobby lathe.

You'll have to play around with it and find which suits you and your machine best.

JasonB16/01/2020 07:43:05
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Not sure I would totally agree with that Hopper.

Although the machine will dictate the depth and width of cut to some extent the indexable heads can be fed faster than a fly cutter for the same given cut as there are more cutting edges, the one in the photo will be able to be fed 4 times faster than a single point flycutter while still giving the same chip load.

Added to that being carbide tipped they can be run faster than a typical HSS flycutter toolbit so that can be multiplied by the number of teeth and you can soon be looking at feeding 10 times faster. There is the added bonus on hobby machines that the faster rotational speed also puts the motor into a better torque band so increasing what can be cut and there is no worry about keeping things balanced like you may have to do with a fly cutter

This does depend on having all the cutters cutting which depending on the accuracy of the OP's 3-jaw may not be the case as is the poor fit on some of the very cheap heads on the arbor

Edited By JasonB on 16/01/2020 07:46:46

Howard Lewis16/01/2020 10:48:04
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A greater number of teeth allows a faster feed rate, since the feed should be per tooth (often about 0.002 inch/tooth )

So an eight tooth cutter can be fed at twice the rate (mm/minute ) of a four tooth cutter, although the feed per tooth is the same, and the surface finish should be the same.

Rigiidity is essential. You don't want the workpiece moving (DON'T ask! ) since that may well be curtains for both work and cutter. Also, even if disaster does not strike, there is less chance of chatter.

Rigidity entails the workpiece being clamped, the clamping arrangements (A vice that shakes is not good news), and the cutter and the spindle and machine driving it.

Our hobby machines are lightweights, which is why the feeds and speeds quoted by tip manufacturers may not be directly applicable. they will have have been developed for massive and powerful industrial machinery.

A 500 watt, 50 Kg machine will not match a 5 Kw 2 Tonne industrial mill for rate of metal removal., nor should we try so to do!.

Howard

Terry Kirkup16/01/2020 13:27:20
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Howard, I would have thought, conversely, that if you keep the feed rate the same, the surface finish should be twice as good with twice as many cutters hiting it, they are obviously cutting much closer to the previous cut each time and therefore reducing the gap between cuts? (a simpleton's eye view!).

Let me raise another query based on your reemarks about rigidity; I only have a four inch angle plate/vertical milling vice thingy with my 290, would it be better to increase them both to 6"/150mm? I won't be cutting anything larger than about 100mm square/long/cubic stuff.

JasonB16/01/2020 13:37:33
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Terry, Howard said "feed per tooth" (chip load) not feed rate which is generally regarded as how fast the work is moved. But as you say if the work were moved at the same rate then a finer cut would result as the number of inserts increases.

Basic formula is number of teeth x chip load  x rpm = feed rate

So for the same chip load and surface finish

fly cutter may be 1 x 0.02 x 1000 = 20mm per min

Your 4 tooth cutter 4 x 0.02 x 1000 = 80mm per min

Or for a finer surface at same feed rate chip load must go down 4 x 0.005 x 1000 = 20mm but then you are starting to rub not cut.

As always the stiffer the better or take lighter cuts and/or use inserts for non ferrous materials which are sharper.

Edited By JasonB on 16/01/2020 13:48:16

Howard Lewis16/01/2020 14:10:25
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Jason has said it!

The feed per tooth will reduce, if the feed rate is reduced, for the same cutter rotation speed.

Feed per tooth is determined by the type of cutter in use, and the material that it is cutting. This, combined with the speed of rotation, will give a MAXIMUM feed rate, i.e. ,the speed at which the cutter traverses the workpiece.

With a feed per tooth of 0.002", a single tooth flycutter operating at 100 rpm will travel at 0.2 inches per minute relative to the work.

An inserted tooth cutter with 20 teeth will travel at 4 inches per minute, all other things being equal. They won't be, in that a 20 tooth cutter will, be larger, and so likely to rotate at lower rpm, for the same cutting speed. So the actual rate of travel is likely to be less than 4" / min..

But it will remove metal a lot faster than the flycutter, and need more power to do it.

If the 6 inch vertical slide is made of parts with the same section as the 4 inch, it is likely be more flexible.

Hopefully, being taller, it will be made of thicker section components. IF in proportion, (say 0.1 is increased to 0.15 ) the individual parts will be 3.375 times as stiff, but being half as large again, the stiffness, overall is only likely to be 2.25 times that of the 4 inch one. Having said that, a doubling of stiffness is to be most beneficial!

Blunt cutters have nothing to recommend them, in my view. A sharp cutter, properly aligned, requires less power, and cuts more cleanly, with less tearing.

Howard

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SillyOldDuffer16/01/2020 14:20:26
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Posted by JasonB on 16/01/2020 13:37:33:

Terry, Howard said "feed per tooth" (chip load) not feed rate which is generally regarded as how fast the work is moved. But as you say if the work were moved at the same rate then a finer cut would result as the number of inserts increases.

...

Maybe, but I'm not sure altering time between cuts makes much difference to the finish. All that's happening is the next cut starts sooner than otherwise, but it's not a different type of cut. Isn't the main benefit of multi-cutters simply that metal can be removed faster? (Provided the mill has the necessary power and rigidity.)

My experience with a WM18 suggests the best finish is produced by a single-point fly-cutter. Not sure why, possibly it's because the relatively light machine tends to vibrate when pushed with larger or more cutting points? Or I could be doing it wrong!

Dave

JasonB16/01/2020 14:47:30
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Dave think of it like threading as you alter the tpi (distance between cuts) the thread becomes finer or coarser. Time between cuts will not alter things if each cut is kept the same (loading)

I can run an insert cutter at 2000rpm (limit of my spindle speed) and feed at 4-500mm per min and get as good a finish as a flycutter run at 1000 rpm but have to feed at something like 75-100mm/min.

I have found the insert cutters run smoother on teh X3 as there is more tooth engagement, with a flycutter I do sometimes get gear noise as the load goes on and off. I have found that poor quality blunt inserts will make the machine vibrate but not so with reasonable and high cost ones.

Look at the rate that the handle is going at in some of these clips, your arm would drop off trying to keep up.

Howard Lewis16/01/2020 14:50:16
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Surface finish is basically the shape of the cut, and the space between the cuts.

So, for the same feed rate,

Using a flycutter ground as if for screwcutting is likely to produce a "rougher" finish than that from a cutter with a small nose radius, because the form of the cut is more pronounced. i.e a V groove versus a flat with radius leading into the vertical face.

After all, is that not what we do with cutters on our lathes?

In my experience, cutting becomes smoother as a multi tooth cutter engages further with the work, so that more than one tooth is cutting at a given instant. Initially, only one tooth contacts the work, but as the feed progresses, a second tooth begins to cut, and so on, providing a steadying influence on the cutter, and reducing any deflection, however small.

Howard.

Neil Wyatt17/01/2020 16:35:43
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One thought, if you have a wobbly set up with plenty of overhang, then the more inserts on your cutter, the more expensive it is when they all get chipped.

I agree with Howard about multiple tooth engagement.

In the early days when milling tools were seen as 'rotary files' they had vastly more teeth, which possibly helped with spindly setups and questionable alignment.

Neil

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