Turning & drilling speeds

Whenever I see recommended drilling and turning speeds I have always assumed the figures were maximum speeds, i.e. any speed below that figure is
acceptable, but now I begin to wonder if they aren't also minimums as well. I understand the idea of not turning or drilling too fast in terms of surface feet per minute at the cutting tip to avoid excess heat generation, but can one really drill too slowly?
I do realise that published figures are aimed at industrial applications where other considerations such as down time, tool durability etc. are important, so I must stress that I am not trying to replicate those speeds, I am trying to understand the principles behind them. Can anybody enlighten me?
Cliff Coggin.
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Cliff
As a relative amateur, I thought I'd wait for the experts to respond. However, since no-one else had replied, my understanding is that feed rate is the issue. The recommended speeds include some assumed feed rate, and at speeds lower than those recommended it's necessary to reduce the feed rate in proportion, otherwise the cut/ turn will be too great, and something will jam or break. As an example, with very small drills run at low speed it's almost impossible to manually feed slowly enough, and drill breakage is very likely. Been there/done that.
Mike
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Cliff Coggin wrote:

The right speed for a particular job is whatever you are happy with.
--
Charles Lamont

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23:44:55 +0100 typed in uk.rec.models.engineering the following:

    And the material is "happy with". Taking too light a cut in some materials work hardens the material, making subsequent guts more difficult.
--
pyotr filipivich
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09:23:38 +0100 typed in uk.rec.models.engineering the following:

    Yes - if one cannot get a "toothful" on each pass. Some materials (stainless steels, titanium) will work harden, and if you do not remove that "hardened" region, the drill, or tool, will just skitter across the surface making a lot of noise, but not chips.

    Casting my mind back to tech school, if my memory serves, the speeds & feeds are compromises. At the maximum speed & feed, you remove the most amount of metal per unit time, but you go through cutting tools/inserts faster. For a commercial operation, that may be cost effective. Your mileage may vary - in other words, you may be happier with an effective feed rate "half" the maxi um, with twice the run time, if your tools are lasting last three times as long.
    For the most part, there is an optimal zone of feed and speed which balances out tool wear and metal removal. But there is also an area below that zone, where being cautious is not going to accomplish the task in any reasonable amount of time.
    As the foreman at the Gearworks said "We just crank it up till it snaps off, replace it and back off a bit."
tschus pyotr
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pyotr filipivich
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On Tue, 27 Mar 2012 15:03:12 -0700, pyotr filipivich wrote:

... but can one really drill too slowly?

There is definitely a minimum feed rate for those materials, not necessarily a minimum speed. I had some "fun" recently parting slices off some 2" marine stainless bar, and it was even bogging down the highest backgear speed (on an 80+ year old lathe). Provided I kept the feed rate reasonably high, it kept cutting, even at a relatively low speed.

I also think you can shorten a tool life by not cutting deeply enough - it may make as many chips as it should, but remove much less metal in the process (because each chip is thinner). Work hardening materials are another matter - the tougher chips can damage the tool, and heat builds up in the chip which doesn't help the edge either. If the titanium chips start glowing, stop and re-sharpen the drill!

There are also considerations when using lighter weight tools; we have to find a compromise that works, and it may not be the same as the industrial recommendation.
- Brian
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If titanium chips start glowing, stop and head for the nearest fire extinguisher, fast. It is highly inflammable.
David
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A few weeks ago I parted off a thin Ti chip and held it in the wood stove fire to test this. The oil burned off, then the end ignited very brightly but almost immediately went out and wouldn't relight.
jsw
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Jim Wilkins wrote:

A mate used to work at a place making magnesium alloy wheels and they regularly used to bring the turnings to bonfire night parties and throw a handful in the fire. Nothing would happen initially but it would all go up in a big flash when water was thrown on it. I presume the magnesium oxidised on the surface in the heat and so didn't burn as expected but the addition of water produced a violent reaction with the hot magnesium. I don't know if titanium would behave the same.
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news:4f738a01$0$12259

When I put a small piece in the stove on the glowing charcoal it melted quietly and didn't ignite until disturbed.
jsw
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The fire department's response to an alarm at the Segway factory (Lithium batteries) was truly impressive.
jsw
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On Thu, 29 Mar 2012 02:41:09 +0100, David Littlewood

That article makes the point that fine chips/powder ignite more easily than large solid lumps of Ti. I can vouch for that - I was squaring off the end of a length of Ti tube on my belt sander, and Ti dust was collecting inside the tube. I noticed a couple of bright flashes, then the collected dust ignited - went off like an old flashbulb. Thankfully not enough quantity to do any damage to me or the workshop, but enough to make me treat Ti with more respect in future!
One of the problems is that Ti is a poor conductor of heat, so will heat up locally where the tool is cutting but the heat doesn't dissipate quickly. A good candidate for using flood coolant.
Regards, Tony
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The main reason for this is that Ti very rapidly forms a surface layer of TiO2, which is impervious and inhibits further oxidation; when the Ti melts this obviously ceases to be a barrier. Small particles heat up very easily, so will burn - Ti is actually a *highly* reactive metal - but bulk material is much harder to melt. If it does, though, it is a major matter! And if water comes into the frame it is much worse still. One other unusual feature is that Ti will also react with nitrogen (if hot enough) so has to be protected with argon if melted or heated to high temperatures.
David
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On Wed, 28 Mar 2012 15:10:55 +0100, David Littlewood wrote:

Jim's experience was more like mine - a VERY bright glow for a moment, not quite like an old photo flashbulb - and it went out. But I wouldn't want to bank on it, and cleared the rest of the swarf PDQ!
- Brian
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15:10:55 +0100 typed in uk.rec.models.engineering the following:

    Make sure it is the right sort. Once Ti lights off, water does not help.

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+0000 (UTC) typed in uk.rec.models.engineering the following:

    Lol -If the titanium chips start glowing - slow down or increase coolant flow! B-) Ti fires are spectacular, I'm told.
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