Face Milling Experiment

Following a recent, somewhat intemperate, thread on face milling, and having just got the vertical attachment for my horizontal mill running I thought I'd give a face mill a real run for it's money.

I used a 7 insert 80mm diameter face mill. Parameters were 420rpm on the spindle and a feedrate of 430mm/min giving a chip load of 6 thou per insert. Width of cut was ~75mm, say 3", and DOC was 2.5mm, say 0.1". The parameters equate to a removal rate of 5 cubic inches per minute. My horizontal mill has a 5hp motor. Cut in progress in some scrap low carbon steel:

I thought the mill might struggle a bit, but the cutter went through like a knife through butter. I'm at a loss as to what I have to do to make the mill struggle on a cut.

Andrew

The only way I could do that is with a slab of butter.

Steve.

Impressive demo Andrew. My milling machine wouldn't cope with that job either, but it only has a 1HP motor with electronic speed control and probably weighs 1/10 of your horizontal.

Thor

Thanks Andrew, good to see what is needed to get the inserts to work at around the published chiploads and DOC.

Thanks; are the Miteebites all there is in terms of a 'stop'?

The two conventional clamps offer some resistance to twisting, but are there primarily to hold the work down. To reduce the risk of the work twisting I added the offset hexagon clamps. There are two on the left and one (hidden) on the right. The hexagons and offset head screws are commercial items, but the T-nuts they fit into are homemade.

Andrew

Most impressive and obviously a much larger machine so expectedly taking larger bites. I'm sorry you found my thread intemperate, having reread it I don't think it any more than some strongly held views, however my apologies if I've caused you or indeed any others upset.

Regards

Martin

Hi Andrew

Do you have a 3 phase supply or is your horizontal mill inverter fed at 240V? It would be interesting to know what current the motor was pulling during your experiment.

Regards

Dave

I'm asking so i know what I could get away with.

Edited By David Davies 8 on 04/12/2022 23:08:53

Here in NZ, 5hp is a 3phase for sure, as maximum power on single phase is 3kw.

With that amount of power, things are very different compared to a hobby mill with 1 kw to 1.5 kw. Are those the mighty bite clamps you used Andrew? Looks very good all round and a great result too.

Now we need someone to try the same depth of cut and feed rate with a hobby mill!

Not sure how my 1100W WM18 would take it. I'd reduce the depth of cut by two-thirds to load the motor equivalently, but wouldn't be surprised if it didn't go well! The machine has an electronically speed controlled brushed DC motor, and I'm not sure how much power and torque it actually delivers at 430rpm : it's not a optimum setting, and a heavy sustained cut is likely to overheat the motor and electronics. Potentially damaging.

The drive train is steel-geared, no belts or plastic, so should cope.

I'm most dubious about the mills rigidity. It's a vertical mill of the simple hobby type, that is rather light and spindly! It's not a metal muncher. I confidently predict a 430rpm, 0.8mm deep cut at 430mm/minute would cause the head to flex and vibrate,  reducing accuracy and spoiling the finish.

Probably a good thing I don't have a face-mill or a big enough lump of mild-steel top try the experiment, but don't let me put others off.

I'm very happy with my WM18, but it does have to be driven within it's limitations. It's not a good choice for removing a lot of metal quickly. It is a good choice for hobby work, where it gets time to cool off between a series of moderate cuts that don't overstress anything.

Dave

Edited By SillyOldDuffer on 05/12/2022 11:41:14

I have a 3-phase supply for the workshop at 100A per phase. It makes life easier when dealing with two speed motors and rapid reversing of motors. Most of the time the house just runs on one phase. I've got a clamp-on meter so will try and have a look at current draw this afternoon.

In the UK 3kW is about as much as one can draw via a single phase 13A 3-pin plug. However, it is possible to have much larger loads on single phase. I have a 32A single phase outlet in the workshop. My oven/hob is on a 40A breaker and the 10.5kW electric shower is on its own 50A breaker.

The key to taking heavy cuts is not just power but also rigidity. The horizontal mill weighs nearly twice as much as the Bridgeport and is much more heavily built. The Bridgeport is a versatile mill but is quite flexible, in more than one sense. There's also a limit to the power than can be transmitted via the R8 taper, especially as it relies on friction.

Andrew

I have a 160mm 10-insert, face-mill I would be happy to loan you for an experiment.

I'm not able to drive it at optimal settings with my mill's paltry 2kW, your mill with nearly double the power might have a small chance of doing so (in some materials).

Let me know if you're interested in having a crack.

I guess that is the Adcock & Shipley hoizontal with a vertical head? They are a very solid machine.

Martin

Correct, the A&S 2E with vertical attachment:

I bought the vertical attachment many years ago on Ebay for £50 but have only recently cleaned it up and fitted it. I also made a M16 drawbar and new drive dogs as one was missing.

Andrew

I' ve measured one phase current. With the mill off phase current was 0.03A, which is an offset in my meter. With the spindle motor running, but no cutting, phase current was 3.6A and taking the same cut as yesterday the phase current went up to 8.6A.

Assuming the mill was pulling the same current on the other two phases that gives a total power draw of about 6kW. The spindle motor in high range is 5hp (3750W) and the table feed motor is 1hp (750W) for a total of 4500W. Assuming both motors were running close to full power that means the power factor was around 0.75 which seems a little low. Anyway, that answers the question about power draw.

I also have a confession to make. When I did the cut today the mill simply went through with very little cutting noise and no fuss at all. The finish was very consistent. Yesterday there was a tiny amount of chatter in a couple of places and the finish varied a bit. Turns out that was because at the end of the cut the milling body fell off the arbor, as the SHCS that holds them together had fallen out. I'm amazed that it caused so little drama and the cut generally progressed as if nothing much had happened. Lesson learnt though; always make use of the workshop gorilla.

Andrew

Interesting to see the measured currents Andrew. Yes the PF is poor, one would hope for 0.8 to 0.85.. Are they 4 pole machines? I The magnetizing current can be higher on 6 or more pole machines i believe.

Not knowing much about the A & S mill I assume it takes a 40 int arbor going by the drawbar diameter. Is this true?

Cheers

Dave

The spindle motor is 2 pole in the high speed range. I don't know about the table feed motor; it isn't even mentioned in my copy of the manual. Both horizontal and vertical modes use Int40 tapers.

Andrew

Thanks for the offer and from a curiosity viewpoint I would be keen to have a go. But I am very wary about borrowing tools. If I fudge them I feel obliged to replace them and I suspect a 10 insert face mill isn't going to be peanuts.

Andrew

It was mixed in with with a big box of gun-drills I bought in an auction, so as far as I'm concerned it was free (the gun-drills were decidedly not free, but were still a very good price for what they are)...

It only gets used once in a blue moon anyways, so I'd be entirely happy to lend it on a "loan-er (lessor?) beware" basis if that assuages your nerves, as I am very curious to see what you can push it to do on your mill.

The inserts are about £15 a pack (of ten)

(I would also be shocked if you could actually cause real damage the main body without causing altogether more serious damage to your mill, especially as the inserts are held in by replaceable wedge-type cartridges and each pocket is supported by a good +20mm of steel.

"Expression of interest in seeing the results"

..maybe we can crowd-fund the electricity..?