Face mill size

[Martin Shaw 1Participant @martinshaw1]

I'm after an opinion, I have a SX2.7 which swings a 50mm 4 insert face mill without any bother and gives a decent finish in steel and cast iron, so I think it's not stressing anything. Does the panel think it would take an 80mm 5 insert face mill comfortably? I believe Jason has one this size but thoughts are always useful. I know 63mm is available but I need to face a 70mm block and the finish invariably looks better if it can be done in one pass.

Regards

Martin

Edited By Martin Shaw 1 on 28/11/2022 22:22:34

[Martin Shaw 1Participant @martinshaw1]

[JellyParticipant @jelly]

Depends what you're doing with it.

Mitsubishi's handy cutting power calculator suggests that to use the "optimal" feeds and speeds (430 rpm and 0.48mm per tooth), the SX2.7's 750w motor would be limit you to a depth of cut of 0.1mm per pass, taking a full width cut (in alloy steel)

if you reduce the feed to 0.1mm per tooth, you could increase the depth of cut to 0.5mm per pass, effectively sacrificing tool life for a (marginally) higher material removal rate.

Given that the calculators are generally a bit optimistic when it comes to hobby machine performance, it seems safe to say that you will be pushing it a little to use an 80mm cutter to best effect… But that it wouldn't be impossible to run one if you sacrifice depth of cut or feed rate, you just have to accept the limitations imposed on that tool by the motor's output.

​

I have a 160mm face mill which I can run on my Harrison, and that tool is not used even remotely close to the limits of it's abilities…

But it's able to do exactly what you describe, and face a large part in a single pass giving a better overall surface, as long as I stay within the limits of what my machine can do… 50, 63 and 75mm cutters are all much more practical for most tasks, and can end up offering a higher material removal rate depending on the exact configurate of the job.

[Martin Shaw 1Participant @martinshaw1]

Thanks Jelly

I did a test with a 50mm cutter with 4 SNMX1206 inserts, 480rpm and a DOC of 0.25mm and a fairly slow feed, and it provided a decent finish. I have block of CI 70mm sq by 40mm high. Two sides and the top and bottom just need facing off, the other two sides need 2.5 mm taken off so I reckon I could get away with a 63mm dia cutter which it seems would be closer to the machines capability. I have never minded buying tooling for a specific job but all but £100 to face a block seems a tad expensive.

Thanks

Martin

[SteviegtrParticipant @steviegtr]

I have quite a few face mills 50 to 63mm. They are great in use on the Tom Senior with 1hp motor 3ph with inverter.

But the finish with a cheap fly cutter takes some beating.

Steve.

[JasonBModerator @jasonb]

Put some inserts intended for aluminium into a 6 insert 80mm head and it will need a lot less cutting force than using the steel/iron inserts. Put the speed up so the motor is running nearer it's sweet spot say 750rpm for the larger 80mm head. keep cuts shallow and feed as the machine allows.

SX2.7 will just stall at anything like 0.48mm chip load, you want 0.01 to 0.02mm/tooth There is also the problem that your arm will never go round fast enough to feed at over 1000mm/min which is over 500 turns of the handwheel in 60secs

The other option is just stick it in the 4-jaw

 

 

This is the SX2.7 with standard inserts on 50mm wide CI and the 80mm head, it would cut better with the non ferrous inserts.

 

 

Edited By JasonB on 29/11/2022 07:44:37

[not done it yetParticipant @notdoneityet]

With an odd number of cutting edges it is rather difficult to run with fewer inserts. 4 and 6 insert cutters are easily run in a balanced form with fewer inserts?

[Mike HurleyParticipant @mikehurley60381]

Posted by Steviegtr on 29/11/2022 00:40:40:

I have quite a few face mills 50 to 63mm. They are great in use on the Tom Senior with 1hp motor 3ph with inverter.

But the finish with a cheap fly cutter takes some beating.

Steve.

I'm a bit confused about the fly cutter comment, There was a lengthy discussion here recently ('Flycutting' 18 Nov 22) from which the concensus appeared to be at odds with the statement (no critisism intended, jus an observation Steve). I've made a couple of these, including the 'tangential' one featured in MEW many moons ago, and find the results variable to put it mildly. Even with the mill trammed as good as humanly possible and cutting speeds relevant to my light machine (Warco WM14) I could never get a very accuratey flat surface. Pretty much given up as a consequence, and now use normal cutters – tends to take more time backwards and forwards with the table (no power feeds!) .

Regards Mike

[Martin Shaw 1Participant @martinshaw1]

Thanks for all the thoughts chaps. I am going to follow Jason's lead, the end result will be displayed on here in due course. Bits ordered from Arc so probably do the job on Thursday. I have a flycutter which I've never got on particularly well with, probably my inability to grind bits well, or at all really, but I can get near mirror finishes in most materials so I've never bothered too much about learning. Shame on me I suppose but in all honesty I'm not too bothered really.

Regards

Martin

[old martParticipant @oldmart]

The 80mm shell mill will work with your mill, but the bore might need an arbor for it rather then being able to share with the existing one. You will soon notice the sound of the motor struggling if you try to take too big a cut rate. You will find that having some inserts for aluminium as well as for steel is a boon. With an even number of inserts, you would not be out of balance much using it with one cutting on its own, and even less if a worn out insert with its edges ground back a little was fitted opposite. With an odd number of inserts with only one cutting, you could turn up a couple of steel thick washers to attach using the insert screws on the opposite side. I have never run one with only one insert, it might not be noticable at the speeds these mills can achieve.

If you can get one that uses the same type of insert as your existing shell mill, all the better

Edited By old mart on 29/11/2022 21:05:50

[Martin Shaw 1Participant @martinshaw1]

I'm rather confused, where has the idea of using one insert in a face mill arisen from, it could be likened to a fly cutter, but I haven't suggested that for this application either. Whatever since a 50mm mill with 4 inserts seems to work fine I can only assume an 80mm with 6 inserts will do just as well with lower feed and smaller DOC, as has been suggested.

Martin

Edited By Martin Shaw 1 on 29/11/2022 22:50:37

[JasonBModerator @jasonb]

I can't see the point in it either if you are going to run with one insert you may as well just use a flycutter with an indexable lathe tool in it if you want to run with carbide.

The big advantage of a multi tooth head is that you have at least one insert cutting all the time so it is a lot kinder to the machine than the thump, thump, thump of a single tool. Plus you can also feed faster which is easier to keep a constant feed rate by hand than hardly turning it to get the same chip load when there is just one insert.

Maybe those suggesting it can enlighten us?

[Nigel McBurney 1Participant @nigelmcburney1]

I would not consider using a 80mm facemill on such a small machine,its cruel, if you do need to face off a workpiece 70mm wide workpiece do as Jason says face it off in a four jaw chuck , or if it has to go on the mill why not use a flycutter ,with Hss toolbits the rake and clearance angles can be adjusted easily by hand grinding and finishing the cutting edge with an oilstone and it costs virtually nothing,I have never bought a commercial fly cutter,just make one,

a good fly cutter can be made using a disc of steel with a shank to suit your largest collet, dril/ream a hole in the face of the disc and secure the toolbit with one or two skt head grub screws,the weight of the disc acts like a fly wheel and smooths the cutting action. I have a couple of top quality industrial face mills ( these came free) and as I am a bit tight with my cash if I do need to cut something tough I use just one cutter it may take a bit longer and why buy 5 inserts when one will do the job. when instrument making long ago now the companys practice was to fly cut all instrument straight scales using fly cutters to get superb finishes which required very little further finishing by straight graining,some scales were a metre long.

When making the disc and shank flycutters the best ones are made in one piece from a billet of steel ,quite a bit turning and swarf production but well worth it.

[JasonBModerator @jasonb]

So what's the difference between using an 80mm facemill compared to a flycutter swinging a similar diameter that makes the facemill cruel?

[BazParticipant @baz89810]

Posted by JasonB on 30/11/2022 13:02:15:

So what's the difference between using an 80mm facemill compared to a flycutter swinging a similar diameter that makes the facemill cruel?

The face mill is far kinder to the machine than a fly cutter.

[old martParticipant @oldmart]

For home use with a low powered machine the large diameter shell mills can only take small cuts, but as the user is not usually expecting to make a living out of their work it does not matter at all if the cutter is lightly loaded and takes longer.

[Chris MateParticipant @chrismate31303]

Some time ago I tried to make a flycutter like out of the brazed cabide facemill 80mm that came with the mill.

In the process I fit every toolholder I had from the lathe with an opposing one as ballance to see how they cut.
-Some of them with negative config and inserts cuts the best.
-I have a indexable 10mm set which give a beautiful finish in aliminium or metal, they are neautral configured, and to my surprise they all deliver a horrible finish here.

-So maybe one should find out the geometry of those flycutters that give a perfect finish before making one.

Edited By Chris Mate on 30/11/2022 19:42:17

[JasonBModerator @jasonb]

If your inserts have a neutral edge they were probably rubbing when used as a flycutter as there is no clearance behind the cutting edge. You also really need a left hand tool to put the cutting edge at right angles to a line drawn through the ctr of the flycutter as anything else will in effect make it a negative top rake.

Edited By JasonB on 30/11/2022 19:47:59

[Martin Shaw 1Participant @martinshaw1]

Well some interesting comments today which haven't changed my mind. I can well understand following the flycutter route if low cost is a primary requirement, it isn't necessarily so in my case nor do I wish to spend time making tools to do something, they are a means to an end that I can either afford or not. I'm well into retirement so without wishing my life away it is necessarily finite and the application of finance to solve a problem will probably win over other considerations ,mostly.

I have had considerable success with face milling at 50mm dia, it works far better in time than a flycutter and if the machine is properly trammed the end result is on a par, certainly adequate for my needs. One of the most difficult lessons I have had to learn in many life aspects is that perfection is not achievable and rarely needed, it would appear that an 80mm face mill will do what I need.

Regards

Martin

Edited By Martin Shaw 1 on 30/11/2022 21:42:40

[Anonymous]

Posted by Martin Shaw 1 on 30/11/2022 21:42:10:

…application of finance to solve a problem will probably win over other considerations

I think the elephant in the room just sat on you.

Irrespective of how much money you throw at the problem the metal removal rate will be dictated by the horsepower available and the rigidity of the mill. Running a bigger cutter doesn't help. Some of the chip loads and DOCs mentioned are tiny, well below those for which the inserts were designed.

On my Bridgeport the maximum diameter face mill I use is 50mm. Even then I am limited to a DOC of 1mm or so. On the horizontal I can let rip with 63mm and 80mm face mills and make full use of DOC and feedrates. But the mill has a 5hp motor.

Andrew

[Martin Shaw 1Participant @martinshaw1]

No the elephant hasn't sat on me at all. What you have done is taken my statement out of context to make a point and frankly if all a Bridgeport can handle is a 50mm face mill then somethings wrong. I bet my job turns out just fine, if not then I'll acknowledge you were right. I asked a simple question and even amongst the supposed experts there is a complete lack of concensus so it rather begs the original question.

Best wishes

Martin

[JellyParticipant @jelly]

Posted by Martin Shaw 1 on 30/11/2022 22:31:52:

frankly if all a Bridgeport can handle is a 50mm face mill then somethings wrong. I bet my job turns out just fine…

 

A standard "J-Head" Bridgeport only has a ¾ hp motor, giving it less power than your SX2.7's 0.75kW. The later "2J2-Head" models with variable speed have a much more gutsy 2hp, and the difference is very much perceptible if you get a chance to run both types.

On a standard bridgeport even running a 50mm facemill at optimal speeds and feeds is pushing it, and requires the operator to hold back on DOC, or run at below optimal speed.

 

I think you're right that your job will be fine, if you heed Andrew's point… material removal rate (in m³/min or in³/min) is directly proportional to the power of a machine…

So for a given design of facemill insert, you can strike different balances between diameter and depth of cut but ultimately the relationship:

"Diameter × D.O.C × Feed Rate = Power × k (for some constant k)"

will always hold.

So if you choose to have an 80mm facemill, that will push you to compromise more on DOC or Feed Rate…

If you don't strike that compromise correctly and try to take too much in one go then you will stall the cutter, possibly damage inserts, and most likely damage your workpiece.

 

However, so long as you work with that constraint, it will function perfectly well, as my comedically large 160mm facemill has proved in the past.

Edited By Jelly on 30/11/2022 23:46:30

[Martin Shaw 1Participant @martinshaw1]

Thank you Jelly, I do understand the relationship between DOC and diameter but all I'm doing is facing two sides of a block square so I doubt more than 20 thou needs to come off, it can take two or three passes to achieve that. I acknowledge I'm pushing the limits of the machine and ordinarily two or three smaller diameter cuts wouldn't matter, but the bits are ordered so I'm sort of committed. I didn't realise the Bridgeport had such a small motor, I am surprised.

Martin

Edited By Martin Shaw 1 on 30/11/2022 23:54:25

[JellyParticipant @jelly]

Posted by Martin Shaw 1 on 30/11/2022 23:54:07:

I didn't realise the Bridgeport had such a small motor, I am surprised.

I'm on record as stating that the original Bridgeport isn't even the best Bridgeport Clone…

The variable speed head was a major jump forward, but still doesn't match the improvements that Czech, Chinese, Taiwanese, and Japanese made to the basic turret mill concept in terms of power, rigidity, and capacity.

[JasonBModerator @jasonb]

On difference between a Bridgeport and the hobby machines is that the Bridgeport has belts so you are getting the full beans out of the motor at all times, not so with a variable speed motor which won't have the same guts at low motor rpm as it doe sat full rpm which is where the quoted wattage is measured..

So lets take a hss flycutter at 25m/min surface speed thats about 100rpm, so notor is running at 5% its optimum speed. Don't know what thatreally equates to in watts but I expect it is more than 5% of the quoted 750w so lets say 200w so as dia goes up wattage and therefor removal rate comes down which does not happen with a belt drive machine be it separate pullies or constantly variable(mechanical) speed adjustment

Going from a HSS flycutter to a carbide cutter be it a single flycutter will allow the spindle rpm to be approx 3 times greater or more so simply by going to carbide you put the variable speed motor closer to its optimum.

With the chip loads mentioned by Jelly and that Andrew uses as I have said you will likely stall a small benchtop mill or trip the overload worse kook the board or strip gears. But with 6 inserts rather than the single flycutter you can feed at upto 6 times as fast with the 90mm head than you can with a single carbide flycutter for the same load so although you will have to tale smaller cuts some of that is negated by the number you can take per rev.

As and example with an 80mm swing HSS flycutter I would have to run at about 300rpm and feed at a painfully slow 25mm per min. with a fairly shallow say 0.3mm DOC. I can take the same DOC with the six inserts but run at 750rpm and feed at 150mm/min so that means the insert head can be upto 15times faster than a flycutter on the same job.

I've also mentioned that a multi insert head will mostly have an insert cutting all the time which keeps a more constant load on gearboxes of hobby machines that have a hi/low option so again kinder than the interupted cut a flycutter gives.

Whatever type of cutter is being used on the hobby benchtop mills they will never have the removal rates of a Bridgeport, even if motor rating is similar rigidity certainly is not so best to find ways to get the most out of what you have and get on with making swarf even if it is going to be less per pass.

To me a non brainer. If I get a chance I'll go and waste some cast iron to show how the SX2.7 cuts with the 80mm head. but may not be today.

Edited By JasonB on 01/12/2022 07:23:15

Edited By JasonB on 01/12/2022 07:39:21

[Author]

Posts