Milling - What am I doing wrong

That's wrong; you can take whatever width is required, although 50% is about the worst value to use. Width of cut should generally be less than 40% or more than 60% to minimise shock loading of the teeth. For shallow facing cuts I normally use around 75-80% WOC.

However, if you need to take off a depth of 12mm I'd be inclined to take pretty much full depth each pass and use smaller widths of cut. You're paying for the full length of the cutting flutes so you might as well use them rather than always use the bottom millimetre or two.

There are several rules associated with cutting tools:

1. Don't buy cheap cutters, they are often badly ground, will never give a good finish, and don't last

2. See rule 1

3. Cutters are consumable items -don't tiptoe about trying to make them last for ever, you'll just wear them out quicker

4. As mentioned above feedrate is single most important parameter - most people run too slowly with the result that the cutter rubs rather than cuts

For your case of a 14mm cutter I'd be running at 800rpm and 200-250mm/min feedrate.

Give it some welly! The same rule applies to chatter. Many people instinctively slow down, often the solution is to increase feedrate and make the cutter work. You're inevitably going to break cutters at some point, it's part of the real world learning process. Get it over with quickly and learn from it.

Andrew

Hi John, thanks

What be a good size rough cutter to buy?

I have ordered the book

Hi

FYI ...



​... from Model Engineers Handbook... Tubal Cain, 2nd edition

George.

Thanks, rotated so other may read it

Strange advice from TC. Clearly practice has changed, as tooling and machine technology has evolved. Plenty of examples of end mills taking much deeper cuts out there, including slotting at 100% width.

For what it's worth, Mercans don't recognise the concept of the "slot drill" - everything on the other side of the Atlantic is an end mill although of course they have centre-cutting versions and the same choice of numbers of flutes.

Part of the learning process is exploring the limits of your machines. I suspect that machine could remove a lot more metal if the width and depth of cut were increased. At some point the motor will stall or the possibly the tool will break but before then it's likely that a glorious rate of removal will be seen. One clue might be the rating of the motor - how could you get anywhere near the rated power without taking enough of a cut?

My Bridgeport clone has a fairly modest 1.5hp motor but I have made full width slotting cuts with 12mm 3-flute HSS cutter at a depth of 15mm or so, using power feed for a consistent load. That was pretty much the limit and I used coolant otherwise I suspect the tool might have overheated before the full length of the lot was completed (about 300mm, roughing out a tee-slot). You may be surprised what your machine can achieve.

As pointed out, you should try to use as much of the flute edge as possible, otherwise most of your cutters will wear out near the corners and you will be paying for something you aren't using. And failing to take a heavy enough cut will increase wear due to rubbing, particularly if you use conventional milling. Climb milling isn't a problem if you tighten up the gibs just enough to overcome the self-feeding.

Murray

When Tubal Caine was writing no amateur had a one ton Bridgeport but would be using a 1/2 HP lathe with vertical slide or if lucky a Dore-westbury. Yes, times have changed.

A word of caution. When you move down to a 3mm cutter don't go hell for leather late on Saturday if you haven't got a few spares already in stock,

If you can afford it, buy the full set....

I got a bit of discount doing it that way...

It's about the cutter climbing into the cut in the X or Y plane, nothing to do with Z axis on a vertical mill

Edited By Nick Hulme on 04/03/2017 11:27:47

Too true!

The rule of thumb is that if you have a spare cutter you won't break the first one. If you don't you will. The smaller the cutter the firmer the rule.

I've recently made some bevel gears using a 1mm ballnose cutter. In all 20 hours of machining with the same cutter; but of course I had a spare.

Andrew

.

Been there, done that. .....................

Nick

See above, use my tip about grinding the corners to 45 degrees then relieving them.

Feeding a cutter too slow or taking too shallow a cut can rapidly blunt them as they end up rubbing not cutting and the tips do all the work.

If you don't want to feed at manic speeds, slow the rpm.

Neil

I'd get another HSS ARC one probably 12mm, one thing I do find with the ARC ones is that the shanks are a fraction smaller than other brands and they are loose in an untightened collet so you have to make sure they don't drop out and hit the table when fitting as this will chip the corners off.

Either go 7mm wide and say 2mm deep or as Andrew says full depth and come in 1 - 1.5mm.

The advantage with full depth and shallow cuts is that you spread the wear over a lot more flute.

The advantage with shallow depth and wide cuts is that all the wear is on the end so easier to resharpen the cutter.

Neil

Thats what I did, finished the other side with no movement of the quill this time.  Have orders a replacement 14mm and also bought a 10 and 12mm roughing cutter

Nice swarf?? Mind its bloody dangerous as it went all overe the floor and is very sharp

Edited By petro1head on 04/03/2017 14:52:48

I made a test piece a few years back for an injection mould tool here's a pic of one half, its quite dirty now and is only used as a paper weight but you get the idea, the finishing path was also around the 20 hrs mark, 0.3mm ball nose cutter these aint cheap!!, the figure is approx 52mm kneeling down, with an eye loop you can see the knots in his boot lases, I remember the split line was a nightmare to draw, bit it did shut off ok with no flash, I later went on to machine 20 odd of these in differing poses and uniforms...........

Pen top to show depth

Project finished, 6 T nuts made, 2 for the vice and 4 for general work/rotary table

Next job is cutting a large hole in an aluminium front drive wheel cover on the Harley

Guys you have been so helpful, many thanks

Grenade.......

X and Y axes can cause chatter which may lead to a cutter or Z axis loosening and/or moving.

One tip that has been overlooked (I think) is that of machining with the minimum quill extension. Far better to move the table up or head down (as long as the column is not a round one!)

Its a Warco WM18 so the table does not move. The head stops quite sort of the table due to the gas ram in the column so I have to use the quill at full reach if I doing work bolted to the table

Edited By petro1head on 04/03/2017 20:52:10