What Cutter For Big Cuts On A Small Mill?

Getting more confident using my first mill, a Chester 626 and experimenting with heavier cuts now the novelty of it all is being overtaken by a desire to get the job done in reasonable time. I'm wondering what people would recommend for shifting metal fast on a small mill? For instance I've just been making big square nuts for an old plough and needed to take approx 8mm off the edge of some 25x50mm hot rolled steel bar. I found I could take a 1 mm cut with the big (60mm diameter maybe) brazed carbide tipped shell mill that came with the machine but once that is blunt I'm thinking to invest in something with replaceable inserts but would appreciate any advice on how big to go, how many inserts and what type will give the best performance?

Thanks, William.

Hi William,

I use a cutter with carbide inserts; 30mm dia. It is very handy when removing the hard scale on Cast Iron etc. I usually use HSS cutters for the finishing cut. I do have a 60mm cutter with carbide inserts and I use that mainly for facing cuts. If you have a collet chuck try to use a HSS or carbide endmill so you can use high speeds and feeds and see if that works well on your milling machine.

Thor

Edited By Thor on 22/06/2021 17:33:40

50mm shell mills with APMT 16 inserts are easy to get hold of and will cut to a shoulder. 50 and 63mm 45 degree shell mills which take SEKT 12 inserts are good for facing and are easier cutting.

William

Machine spec states 63mm max face cutter so you need to look for an MT3 arbor to fit the face cutter to, unless you can get an integral unit.

With a 2HP motor you should be able to remove material in a timely manner but remember the more metal you are removing the greater the force is applied to the vice or other material to table securing method.
You may also need to lock all slides not being used to prevent vibration causing a poor finish.

Emgee

Edited By Emgee on 22/06/2021 17:41:44

Bandsaw?

A shaper would hog 8 to 24 inches of bar at a time for free

I reach for one of my trusty 12mm Dormer TiCN Coated 3 Flute Rippers when things start to get tedious.

There are cheaper options which work just as well, but I got a deal on the Dormers

Somthing of an oxymoron?

To take big cuts you need a big mill with plenty of power and rigidity. Here's my experience. Last year I bought 50mm, 63mm and 80mm insert milling cutters from Arc. Overall I'm impressed with them. On the Bridgeport I only use the 50mm cutter. The Bridgeport doesn't have the power or rigidity to utilise the bigger cutters; if overloaded it tends to lose tram. I have recently been trimming up a lot of hot rolled steel on the Brdigeport. With the 50mm cutter parameters were as follows - 800rpm, width of cut 25mm, 1mm maximum DOC and 350mm/min feed rate. The mill seemed happy with little cutting noise and the chips coming off blue. Note that the Bridgeport has a mechanical varispeed head so even at 800rpm I get full motor power. If that isn't the case the OP might be better running a 10mm 3-flute carbide endmill at around 2500rpm, the full 8mm DOC, 1-2mm WOC and 500mm/min.

The Bridgeport cannot fully utilise the insert cutters, although they are convenient for milling large surfaces and the inserts seem to be lasting well. When I first got the insert cutters I used the 63mm one on the horizontal mill on some hot rolled steel. Parameters were 450rpm, 50mm width of cut and 450mm/min with a depth of cut of (wait for it) 4.5mm - the maximum recommended. The cutter went through the steel like a knife through butter, throwing chip everywhere, and left an excellent finish. But the mill has a 5hp motor, geared spindle and weighs nearly 2 tonnes.

By all means get an insert cutter but accept that it probably won't be possible to run it to the limits.

Andrew

With a 2HP motor ...

Is it? It claims 2HP in the specs but lower down it ‘features’ a 1.5HP motor. Forked tongue hype advertising, methinks?

As a fellow Bridgeport user I agree with Andrew re rigidity, if I need to shift metal I use a 40mm three tip cutter. Light cuts and a high feed rate work for me. I once went on a course to use a Deckle copy mill and the mantra of light cut high feed rate was taught and has stayed with me.

I've not been milling more seriously for long but its pretty obvious they excel at the small cut high speed high feed stuff which is far less stressful on the machine and cutter

So take the faster rate small depth route, not the more depth lower speed route

Think flycutter and how do I make it hog more material

Good words of wisdom here

I haven't yet learnt the art of tramming the mill head with 50mm face mill resulting in (I think) one of the inserts cutting deeper than others - any advice please? could be the inserts are not equally seated and slight angular displacement on head position

Tram won't make one insert cut deeper than the others but it will give a slightly concave surface.

Gently rotate the head backwards against a dti and compare the position of each insert.

I use the same approach of shallow depth of cut and as fast a speed as the cutter will allow hence carbide over HSS and then the more inserts you can get the faster you can feed for a given chip load. Though the downside of more inserts is an increase in cutter dia which will need more power from the machine to drive it hence I tend to keep my 80mm cutter for aluminium which is easier to cut.

...in theory

Once you get up to speed More mass on the outer edge of a wider face cutter, or a heavier cutter mounting, will give you more momentum for maintaining the cutting RPM under load

Like a flywheel effect

As long as your machine can cope with the higher side loads you can use a faster feed rate at the same depth

Edited By Ady1 on 23/06/2021 09:59:58

And to cope with higher side loads you may be able to mod the nose of your spindle like with the Drummond M series mod in this thread, which gives the stiffening effect of a bigger spindle

Jason, you are absolutely right - thanks - I am not seeing any dishing so probably my head is aligned correctly

Ady - I havent got the nerve (or space right now) to use my shaper in anger yet, the few test cuts done a year or so ago were very impressive though

Disagree with the supposed ‘theory’. Flywheels only supply energy as they slow down. To recover the decreased rotational speed, more energy has to be supplied by the moter. Only useful for intermittent operations (like ‘hit and miss’ engines). The only thing a flywheel will do in an overload situation is slow the rate of slowing!

Just occurred to me today that it might have been better if I had faced mine towards a wall or facing into a corner

It fires swarf all over the place, and it's quite chunky spiral swarf

Plasma?

Dave,

I don’t have a plasma cutter - I might get one of the lidl offerings if I ever get the opportunity (some hope of that happening in my local lidl!) but no chance of cutting 25mm. Certainly I will never need a machine capable of a clean 25mm cut.

The bandsaw (with a kerf of about a mm) might at least offer the opportunity of making an approx 5mm ‘waste off-cut’ that might be useful sometime.🙂

I am wondering how William is currently cutting his 42mm pieces from his 50mm (42mm) bar.... and how he intends removing the 8mm (from the long bar, or a stack of short pieces clamped securely together🙂 .

Edited By not done it yet on 23/06/2021 18:51:50