using milling cutters

I read all the above comments most of which is accurate and helpful. What must be appreciated is that the machine must be adjusted so that all slides move smoothly without vibration. Then you come to the question of cutters. This to the beginner can be a minefield but does not have to be. As you have experienced there are 2,3 and four flute cutters all of which have their place for different applications. The 2 flute is primarily for cutting slots hence why it is referred to as a slot mill. If you used a tri cutter or 4 flute to do a slot you would find that it would cut oversize. The reason for this is that with a 2 flute cutter there is more room for the cut chips to be evacuated which would not apply to both 3 and 4 flute cutters. One then has to take into account the cutting load being applied to each edge of the cutter. For example if cutting steel at say 500 rpm with a feed rate of 30 mm per min with a 2 flute cutter you change to a 4 flute cutter using the same speeds and feeds, then the force on the 4 flute would be twice as much. You then have to take into account the cutter you wish to use. Is it a new cutter or a used one. Is it a HSS one or is it a carbide one. The speed and feed for a carbide cutter will be significantly higher than for HSS. Do you propose using cutting oil using flood coolant or occasional brush applied coolant. You can now see that there is a lot of considerations regarding tooling. The other factor to be taken into account id the material you are going to use. This will have a great bearing on the tooling to be used. Again this is a difficulty when materials are purchased at the shows not knowing exactly what it is. I hope that this will guide you and feel more confident with your future machining operations. I am more than happy to answer any questions you may have.

Ken Price.

One then has to take into account the cutting load being applied to each edge of the cutter. For example if cutting steel at say 500 rpm with a feed rate of 30 mm per min with a 2 flute cutter you change to a 4 flute cutter using the same speeds and feeds, then the force on the 4 flute would be twice as much.

Ken, with the same speed and feed rate wouldn't tooth load be halved if doubling the tooth count ?

Emgee

Something I have never seen written down, but that is blatantly obvious when you think of how a cutter works when making a slot:

When a 4-flute cutter is used to make a slot one flute is cutting across the end of the slot (and tending to pull the cutter to one side while pushing the work the other way) this deflects the cutter right at the moments the other flutes should be sizing the slot.

With a 2-flute slot drill there is no flute cutting the end of the slot (and therefore pulling the the cutter to one side) when other flutes are cutting the edges of the slot.

With a 3-flute this effect is negligible and in my experience most 3-flute cutters will make slots to size.

Neil

Exactly, I've cut slots with both 2 and 3 flute cutters and they're accurate to better than half a thou, as measured with gauge blocks.

Andrew

Sam wrote "Well I met the engineer". RPM @ 188 aka = 1/3 plus fast feed. Cutter sharpened by hand!!! Same lump of steel.

Job done". Several posters here suggested steel might be hard-tough.

1) Does anyone else think Sam's lump of steel was hard-tough steel? I ran the FS-Wizard and consulted the Presto chart.

Both assume coolant and suggest reducing rpm by 1/2 if no coolant. That gets me to around 200 rpm. Sam's tool likely blunted-chipped by too much rpm on hard-tough steel, right-away.

2) Any suggestions on how to identify hard steel before blunting tools? How did Sam's new friend identify the steel?

3) Sam: Will you share your hard-won secret on how to sharpen endmills by hand?

Paul

Neil

If you look at chapter 6 of the Model Engineers Workshop Manual by George Thomas, he explains this in great detail.

Phil

I probably have I have seen it mentioned there then, I just don't recall it.

Neil

Edited By Neil Wyatt on 27/10/2018 16:48:53