Tool durability

[freddo1]

Does anyone know if taking lots of small cuts with a milling cutter makes it's sharpness last longer than taking fewer bigger cuts?

Obviously speed, heat and lubrication come into the equation too, and the same question about sharpness applies - can one cut TOO slowly with a cutter?

[chameleonrob]

I doubt that you could run a cutter at too low an rpm but beyond a certain point you would see no advantage as the heat levels would be so low. however in my experience taking lots of little cuts will reduce the amount of metal cut in the lifespan of the cutter, although the life span in hours will be increased slightly, you are effectively cutting all the bits of metal twice not once. another way of increasing your tool life is to use as much of the cutter as possible, say you are cutting a 10mm x 10mm step go to full depth straight away and the largest width of cut to allow any one tooth to cut at any one time (to prevent chatter, deflection and cutter breakage), follow this with the highest feed the cutter and mill can cope with. the only problem with this is the heat generated so cutting the spindle speed is a must.

rob

[baggo]

I'm sure I've read somewhere that taking too light cuts with such as endmills can rapidly blunt the cutting edges. They prefer high speeds and heavy cuts. Just how heavy a cut you can take will obviously depend on the rigidity of the setup.

John

[jgb7573]

Tubal Cain has advice on this in his "Model Engnineers Handbook". If I recall correctly, the feed rate must not be too low or the tool rubs rather than cuts and loses its sharpness. You can reduce the depth of cut but the feed rate (how much travel per rev of the tool) needs to be maintained. This seems to work in practice for me. It is also very obvious the difference between using my mill/drill at home and the industrial mill in the club workshop. Having a decent solid mill makes a tremendous difference.

[freddo1]

I've been looking around too, and have had a variety of differing advice. It seems you can take a cut (on the side of an endmill) up to 1/3 it's diameter, and the recommendations I have also heard are of speeds of around 800 feet per minute.

Before I waste a perfectly sharp 12mm end mill, does this sound reasonable without suds?

[Noddy]

Again from Tubalcain that is the theory, but, depending on what you are using, the rigidity of your work and the machine might be your limiting factor.

One piece of advice that I've heard is to:

set the spindle for appropriate surface speed for the cutter diameter and material.

Width of cut the max for that style of cutter (so 1/3 diameter for the end mill, or with something like a slitting saw, so that at least 3 teeth are cutting at any time)

Depth of cut not too ambitious but not too cautious.

feed as fast as it will sensibly take, without choking teeth.

If it chatters, reduce depth of cut

If it seems happy, try a bit deeper cut.

Machine shop questions and answers suggests that chips should be tan coloured as they fly off. he says not to worry if they turn blue after landing as the heat for that is from shearing within the chip, not from the tip -tool contact.

He suggests reducing spindle speed to cool the chippings if they are getting brown or blue.

I think the implication is, if the chips are silver or slightly yellow, not tan, then you are probably cutting too fine a chip (your tool is cutting too many miles of surface to get the same volume of metal off).

Keith

[chameleonrob]

keithanderson said:

If it chatters, reduce depth of cut

Keith

the tool can chatter if the depth of cut is too low as well, with a less than rigid setup (or cheap mill) and there is a period of time between one tooth finishing cutting and the next starting