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View Full Version : Does It hurt the collet to leave the tool in it?



danlb
05-16-2009, 10:30 PM
I have a bad habit of leaving my cutter in the Mill collet as I finish one step and move to the next. This is likely due to the way my mind works... Once it reaches the required dimensions I'm already thinking of the next setup. If that setup is somewhere else (like the lathe), Then I might not get back to the mill for days. Thanks to my tunnel vision (mental, not physical) I only notice what I concentrate on when cleaning up.

So the end-mill might sit in the collet for days or weeks before I finally notice.

Does this hurt anything?


Dan

websterz
05-16-2009, 10:35 PM
No rust no harm. I have endmills in holders that have been there for weeks at a time with no problems.

danlb
05-17-2009, 12:35 PM
No rust no harm. I have endmills in holders that have been there for weeks at a time with no problems.


Thanks. I appreciate the feedback


Dan

Evan
05-17-2009, 01:37 PM
I have left tools in collets for years at a time. No harm done.

danlb
05-17-2009, 02:07 PM
OK, here's a harder question....


Does it cause any deformity in the table when I leave my 55 pound vise tightly secured to the left of center of the table? Does that distort the tslots? Does the off center weight of the vise do anything to the gibs or ways?


:)

Thanks for your insights.

Dan

David Powell
05-17-2009, 02:07 PM
I am sure that you are unlikely to do any damage to a collet by leaving a tool in it, however, I was always urged to remove the tool before cleaning the machine or removing or adding tooling. Should your hand slip, when for instance lifting a vice on or off, the hopefully still sharp cutter, in your collet is just waiting to slice at least a bit of skin off. When I was young and invincible I didnt listen, now I am old ( and thankfully only slightly scarred)I wish I had listened more enthuiastically to suggestions regarding safety. Regards David Powell.

derekm
05-17-2009, 05:59 PM
I am sure that you are unlikely to do any damage to a collet by leaving a tool in it, however, I was always urged to remove the tool before cleaning the machine or removing or adding tooling. Should your hand slip, when for instance lifting a vice on or off, the hopefully still sharp cutter, in your collet is just waiting to slice at least a bit of skin off. When I was young and invincible I didnt listen, now I am old ( and thankfully only slightly scarred)I wish I had listened more enthuiastically to suggestions regarding safety. Regards David Powell.
I've got those scars as well :)

Evan
05-17-2009, 06:07 PM
To the vise question, no. Steel or cast iron or metal in general doesn't take a "set" just because it has been elastically deformed. As long as the elastic limit is not exceeded it will spring back to exactly where it was before the stress was applied. The only way it will deform permanently is for it to be "bent" beyond the elastic limit into the region of plastic deformation. That happens, if it is going to happen, at the moment the elastic limit is exceeded.

MaxxLagg
05-17-2009, 09:12 PM
I have a text book (Technology of Machine Tools, Krar . Oswald) that says not to leave the vise to one side for that very reason.

Evan
05-17-2009, 10:16 PM
I suspect they mean because of the uneven wear it will cause, not because it will somehow deform the metal. If they really do say it will cause the metal to take some sort of "set" then throw the book away.

Carld
05-18-2009, 02:53 PM
The vise question is one I have had for a long time. I don't leave the vise on either side or the table moved to one side just because I don't want a sag issue. I have also seen a lot of mill tables that are high in the center and low on the ends. Where did that come from?

Evan
05-18-2009, 04:47 PM
How exactly are you measuring the "low on the ends" condition?

John Stevenson
05-18-2009, 05:04 PM
The Bridgeports with the older heavy mechanical feed box were notorious for bowed beds.

.

philbur
05-18-2009, 05:12 PM
Sample quote:

"Cast Iron is very imperfectly elastic, that is, even a very small load will produce in it an appreciable permanent set."

I find it's always best to Google before giving answers to things I know little about.;)

If you are going to throw that book away please throw it in my direction.

Phil :)

bborr01
05-18-2009, 05:58 PM
I don't think you will damage the table at all. The reason the tables seem worn in the middle is because the ways get worn in the middle from most of the machining being done in the middle. Like Evan has stated, unless you exceed the "modulus of elasticity", the steel will go right back to its original shape.

Evan
05-18-2009, 06:13 PM
"Cast Iron is very imperfectly elastic, that is, even a very small load will produce in it an appreciable permanent set."


That really is nonsense although I am sure there are many well informed people that believe it. To take a "set" the material must slip along the crystal boundaries. That won't happen until a certain degree of stress is applied. Cast iron is quite brittle meaning that it is very elastic. Elastic doesn't mean stretchy like most people think, quite the opposite. Glass is a perfectly elastic material meaning that it has no zone of plastic deformation and if it doesn't fail it always return exactly to the shape it had before stress was applied. Cast iron is imperfectly elastic as are nearly all metals because they do have a zone of plastic deformation in response to stress.

Elasticity in the context of material response to stress means that it will deform under stress and when that stress is removed it will return to the previous shape.

Try bending some cast iron. You will discover that it really won't take a set. It will however warp from built in strains that are residual from when it was cast, if it hasn't been aged or heat treated properly. It is not unusual at all for strains produced in manufacturing of metal to almost equal the rupture modulus of the material.

John Stevenson
05-18-2009, 06:47 PM
Evan,
Years ago I had a big old Herbert lathe, about 3 tonnes.
it had stood for years on an uneven floor but never fasted down.
The bed had warped and although I fasted it first to the floor, then to large steel channels I couldn't get any of the twist out of it.

.

Evan
05-18-2009, 07:37 PM
You have heard of course that cast iron pigs are set outside to age, sometimes for years, before being used to make quality equipment. The inbuilt stress and the resulting strain from casting will make the iron warp with time. An easier method is to normalize the metal by heat treatment.

Cast iron also is different than other alloys in one important respect. The glassy transition temperature from ductile to brittle crosses the room temperature range for many types of cast iron. This changes the properties appreciably as the ductility, what little it has, will vanish entirely at temperatures near freezing. I don't know for a fact but it seems likely that if a piece of cast iron is deformed and then frozen it might actually lock in strains that remain when it is returned to room temperature.

Regardless, as long as the material has been stress relieved and is maintained near normal room temperature there is no way that it should shift to another shape unless the stress exceeds the elastic limit.

[edit]BTW, the fact that you could not remove the twist supports the idea that it won't take a set, doesn't it?

aboard_epsilon
05-18-2009, 08:09 PM
ive heard that even glass will drip after a few million years .


perhaps johns lathe would have unwarped ..given time
all the best.markj

spope14
05-18-2009, 08:49 PM
Regarding the collett, leaving a tool in it may not be a major issue, but over the years I have had problems with humidity and resulting rust when I leave a tool in too long. This is not so much with 5-C colletts, though over a summer I left a 1/2 and 3/4 in two colletts on teo mills (wanting to eliminate set-ups) and they rust in pretty good. The harder part is with end mill holders and the like where you can't get the tool out normally, and when you finally get it out, you have to clean out the bore to put a new one in (rust ect).

Evan
05-18-2009, 09:10 PM
ive heard that even glass will drip after a few million years .


That was the thinking for a long time but according to Corning Glass it isn't true. Glass was thought to be a supercooled fluid but it has been shown that even though it doesn't crystallize it does undergo an energy transition from fluid to solid. Below a particular temperature that depends on the glass "alloy" the atoms are locked in place because they don't have sufficient energy to be mobile. It isn't required that a material be crystalline for that to take place.

lane
05-18-2009, 09:49 PM
Given enough time any thing will sag. You old guy`s have to just look down. And you young fellows just wait.

philbur
05-19-2009, 03:17 AM
But as inbuilt stress and the resulting stain will make iron warp over time then surely external stress will do the same thing.

In the pasted I have seen cast iron specifications that actually quote a permanent set stress value, above which a significant (for structural applications) permanent set will occur over time. The value was a long way below (like half) the normally accepted/used yield point.

A simple Google turns up numerous apparently respectable references to the issue of permanent set (and also creep) in cast iron. They could of course all be wrong but alternatively ……?;)

The fact that John could not remove the twist indicates that he was unable to applying the stress in the necessary places and has nothing to do with the permanent set issue.

Phil:)


You have heard of course that cast iron pigs are set outside to age, sometimes for years, before being used to make quality equipment. The inbuilt stress and the resulting strain from casting will make the iron warp with time. An easier method is to normalize the metal by heat treatment.

............................

[edit]BTW, the fact that you could not remove the twist supports the idea that it won't take a set, doesn't it?

Evan
05-19-2009, 06:16 AM
The fact that John could not remove the twist indicates that he was unable to applying the stress in the necessary places and has nothing to do with the permanent set issue.


How so? If the item in question is fixed so that the shape is changed to the desired degree back to what it was then the stress must be of the same amount but of opposite sign.


A simple Google turns up numerous apparently respectable references to the issue of permanent set (and also creep) in cast iron. They could of course all be wrong but alternatively ?


Alternatively...
The issue of creep is widely mentioned in the literature but it doesn't apply at room temperature.




Creep
The flow or plastic deformation of metals held for long periods of time at stresses lower than the normal yield strength. The effect is particularly important if the temperature of stressing is above the recrystallization temperature of the metal.
Creep Strength
(1) The constant nominal stress that will cause a specified quantity of creep in a given time at constant temperature. (2) The constant nominal stress that will cause a specified creep react at constant temperature.

http://www.principalmetals.com/glossary/cdoc.htm


What is the definition of creep strength?
The ability of a metal to withstand a constant weight or force at elevated temperatures.

http://www.toolingu.com/definition-500210-15802-creep-strength.html

tmarks11
05-19-2009, 06:44 PM
The issue of creep is widely mentioned in the literature but it doesn't apply at room temperature.
Specifically, in metals, creep is not a factor until you reach 40% of melting temperature (which is something like 1570 degrees C for iron).

For polymers, creep will occur at room temperature (this is also called "cold flow").

My materials textbooks won't allow a cast iron table to permanently sag. Unfortunately, the table can't read...

Liger Zero
05-19-2009, 06:59 PM
Ok. I'm starting the betting pool now.

$20 on 350 posts and 3,750 views by Friday.

:D:D

Evan
05-19-2009, 07:42 PM
I don't have time right now for long discussions. I have several new thread topics to post and haven't found time for them either. Too much to do that has little or nothing to do with machining.

However, I did finally get a mig gas bottle for my Miller wire feed. :D

PeteM
05-20-2009, 12:09 AM
Well, just to help the post count along -- I've heard credible accounts of planer tables (the woodworking kinds) taking a permanent set after a heavy weight was set on one end for a period of time. This wasn't creep -- the planers were at room temperature. It wasn't displacement of the gibs -- readjustment was apparently futile. It's possible the cantilevered load somehow exceeded the elastic limit I suppose.