feed speed

Yesterday I was doing my first "proper" milling operation on my warco mill. To insert a 3mm wide groove in an aluminium cover plate for an O ring. Plate was mounted on a rotary table

I was using a virgin 3mm HSS end cutter obtained from Warco when I bought the mill. I was rotating the table by hand & not applying much pressure. Depth of cut 1mm, speed was 1125 RPM which is max for the bottom range on the M16 mill- it had not occurred to me to switch to top range

after 1 inch of cut the cutter broke !!!

Was 1mm too much for a 3mm cutter? was I running too slow? are Warco cutters carp? I am sure I was not applying much pressure.Was I using the wrong sort of cutter? Was I just unlucky?

Any comments as to why I may have broken the cutter. There does not seem to have been a build up of aluminium on the cutter teeth when examined through a magnifying glass

Thanks

3mm or less is "watchmaker territory" and you will need to use a lot more care

Weird stuff happens, drills snap in the middle of making a a hole etc etc, a tiny bit of swarf in the wrong place at the wrong time and "click.." your tooling breaks

Higher speeds are usually better but I'm not familiar enough with teeny processes to say definitively

1mm deep with a decent 3mm cutter in Ali should be OK though for now you would do better to stick to the 1/4 times diameter as your max so 0.75mm depth.

You say an "end cutter" by which I will assume end mill or 4 flute cutter. Really for slots you want a two flute cutter or 3 flute as a compromise. Not only will the 2-flute give a more accurate flute width it will also clear the swarf better which may well by why you snapped the cutter.

What grade of aluminium were you milling and did you use any lubricant?. Some grades can be soft and sticky which will build up on the cutter and cause problems. This can be helped with a cutting fluid, on Ali use paraffin or WD40

Sets of cheap cutters can be of variable quality

Higher speed would help.

If I was doing a lot of teeny work I would find a way of "shortening" a drill or mill to its minimum, to maximise stiffness. like putting the milling cutter all the way in to the chuck and just leaving 3mm protruding kinda thing.

The aluminium may have melted a bit and stuck to the cutter, 'it happens. Also with that sort of size of cutter any looseness in the set up, slides etc can cause problems.

Plus as Jason mentioned a slot drill would be a better option than an end mill.

I usually work on a max depth = the diameter of the cutter but a fine feed is needed and I doubt if I would use that on a cutter under 6mm dia - that's end mills too. Slot drills have less flutes so would need an even finer feed or a much shallower cut. Jason's rule is safer.

John

-

I have used plain old suds on aluminium but not at home. It's not to bad and might be a better option for people who don't want to sniff various oil fumes. I've used it for surface grinding aluminium as well.

It works 'cause water has a boiling point of 100C which is well below the melting point of aluminium so can carry heat away. Just like cutting oil it can be applied with a brush but was pumped when I have used it.

John

-

Make sure the x and y slides (and the quill) are locked and also slightly nip up the table lock so that there is no backlash. Use plenty of WD40 etc to prevent swarf sticking to the tool, make sure the swarf is cleared from the slot - and calculate speeds and feeds using something like FSWizard. It's also critical to feed consistently to prevent overloading the tool.

Yes I meant a 4 flute end mill

However, if an end mill will not cut a slot then what does one actually do with an end mill?

ie If I cannot cut a 3mm slot with my 3 mm cutter & need a 2 flute slot cutting bit, then what would I use my 3mm end mill for ?

Sorry if this sounds a bit silly but !!!!!!

Hi Sam,

Difference between end mills and slot drills and their use were discussed here. You also mention in your first post running at 1125 RPM, that is quite a bit slower than I use on aluminium alloys. Have you tried using the top range of your milling machine?

Thor

Edited By Thor on 30/07/2016 18:18:45

Well I might do when I get another cutter !!!!

Use a bit of paraffin or neat cutting oil and it will help stop chip welding, a major cause of cutter death.

You can salvage the end mill by grinding the end at an angle to give it one cutting corner. It's not as good but it may get you out of a hole some time.

Neil

One of the odd thngs about kerosene / paraffin and aluminium is that the term more volatile is often used to explain the advantage. It's also a weak lubricant. Bit more oily than petrol but a lot less likely to burn but the vapours burn easily.

Boiling point 2 to 300C, water 100C, The soluble oils - a lubricant. I'd guess this is why toolrooms etc use suds on aluminium. The thermal conductivity of water is also nearly 3 times higher.

Basically I reckon it's an old wive's tale that offers dubious advantages over other coolant / lubrication methods.

1L of some soluble oils will make between 10 and 40L of suds. Rather a lot of cans of wd40 and more efficient in several respects.

This one gives mixing ratio's.

**LINK**

John

-

I used water based lubs years ago on a Colchester lathe I had for very occasional use in my business. This caused rust build up & was a real issue. Modern ones may have changed, but if not, then I would prefer not to use them

I figure the spindle speed should be 10,000 rpm for that cutter in aluminum. At the speed you are running you are probably exceeding the recommended feed per tooth on your end mill. A 2 flute cutter is best for aluminum. 4 flute cutters do not have enough chip space for aluminum. You can improve performance by using an end mill specifically designed for aluminum. It has polished flutes and a high helix angle in addition to greater chip space. Come type of cutting fluid is desirable to keep chips from sticking. I use soluble oil in a squirt bottle.

I've seen chucks in particular that get a brown patina due to suds but people should clean up their lathes and wipe over with oil fairly regularly and also try and keep it on the work not all over the machine. I've only been involved with suds at work and it doesn't seem to cause any problems there - the machines were generally looked after.

I generally just use neat cutting oil from Morris Lubricants for problem jobs or if I want an exceptional finish. Just a smear via a lightly loaded kiddies paste brush. 5L of it will probably last longer than me.

Having posted about suds though I have ordered a bottle but don't intend to flood things with it. I just suspect that it will be better for some things and again will just use a brush. When people see video's of pumps chucking out huge streams of the stuff it might be worth pointing out that even grinding doesn't need that high a flow rate.

John

-

Edited By Ajohnw on 31/07/2016 00:50:20

My rough and ready cutting speeds are based on a 1/4" drill, 1000 RPM in mild steel. Ali or brass 2 or 3 times faster, other sizes pro rata. So 3mm (1/8" should be a minimum of 4,000 RPM.

Frank

For milling I think this thread has gone a bit bonkers. I suspect Jason hit the nail on the head early on. The feed rate was too high for the speed the cutter was running at. There is no should be as far as cutting speed go other than problems can crop up of various sorts if it is too high. The type of problem will depend on the material that is being machined and the material the tool is made of. There is no too low really other than maybe chip breakers but in my opinion that is more related to feed rate.

Also slot drills must be used when a milling cutter is plunged into something. End mills aren't very good at doing that - try drilling a hole with one. A slot drill will do that easily. End mills are for surface milling.

John

-

.

Exactly that ^^^

It's the relationship between the two that's important.

MichaelG.

I have a feeling of despair every time the cutting speed thing comes up. People just wont realise that the quoted figures all relate to tool life - some one opinion of how long it should be and time to do a job and nothing else and that there can be all sorts of reasons for working well out of them.

Maybe if they looked at old figures based on hardened tool steel cutters they would but I suspect that the myths would still persist.

John

-

Edited By Ajohnw on 31/07/2016 18:05:05

Don't think I ever mentioned feed rate and mearly said speed was a bit slow for that size cutter.