On Friday 20 November 2009, John Harris wrote: >Hi All, > Back in the late 50s when, as a young apprentice, I was turning > knobs on a milling machine as part of my education, the shop foreman > replaced the flood system on the mill with a new-fangled mister. The > mister feed tank was filled with the same stuff that was used for the > flood system. That is water with 15(?) percent soluble oil. > >The foreman told me that the mist cooled the part and the tool by > evaporating the water, and the oil gave some lubrication to the cutting > action. Also misting greatly aided the water evaporation compared to the > flood system. > >As the foreman is by now no longer with us, I feel safe in raising the > question, was what he told me true? If it was, why are you now using only > oil that is much less efficient in absorbing heat by evaporation than > water? > >Regards all. I love reading the chat.
Warning: This is personal opinion, subject to revision. 1. in this instance, I'm cutting alu. This makes a huge diff in the chemistry involved. If in the target operation I was cutting steel or cast, I would have a different idea, although the last cast iron I cut, cut very well with a squirt of ace cutting oil on the side of the mill while I was cutting 1.4" deep with a 1/4" 4 flute TiN mill whose flutes were only an inch long. 3 passes to get to full depth while widening the center clearance in a starter nose housing for an old Olds diesel, and whose starters are by now made out of pretty much pure unobtainium. 2. Alu is a VERY actively oxidizing metal when the bare metal is exposed to oxygen from any source, including both air and water. The oxide film so formed then protects it from further "rusting" at that high (about .001 seconds) rate, but does continue forever at ever slower rates. 3. This rapid oxidation can raise the temp of the part being machined if its a small part vs the area being machined. In this case a 2" square of 1/8" thick alu is sitting on top of a block of sweet gum machined flat for a sacrificial substrate so I can cut a few thou below the bottom edge, so there is not the close contact with another block of metal to act as a heat sink. 4. Any rise in the temp of alu rather adversely effects machining as softer alu will tend to push out of the way of the mill as it moved, and it sticks in the flutes of the mill like it was welded. A cube of dry ice sitting on it would help, but would raise the available oxygen too. However the lower temps would slow the oxide formation so that particular item could possibly be a plus factor. That of course isn't going to be compatible with the chip flushing air blast. If one could afford it, dry nitrogen would work even better but a T2 bottle refill was about $100 the last time I filled ours at the tv station. Not everyone has a Cardox in their back yard. :) 5. Oil contains much less free oxygen and very little in compound so it protects the cut surface from this oxidization IF the oil film can be made to cover the cut surface in a thousandth of a second or less. This latter I'm not convinced can be done really effectively without an enclosure and 500+ psi pressures feeding the coolant. So for little machines like mine, it seems the idea to keep the cut surface wet, along with the mill so it tends to leave an oil film on the cut with the back side of the cutting edge, or as wet as I can get it, and not using a fluid with any free oxygen, can only be a plus. Alu oxide is the 2nd hardest substance we have readily available, and is quite capable of eroding the edge off a carbide tool considerably faster then the average ferrous material can. For this same reason, one uses all the rpm the spindle has in order to bring the next cutting edge to the work face before the oxide can form. But my little toy mill can only do 2500 revs, so I have 2500/60 to get rps,then *2 for the number of flutes & take the reciprocal to get the time=0.012 seconds between flutes, many times longer than optimum so there is plenty of time for the oxide to form if left uncovered. So that is the reason I use straight oil. Vactra #2 since I have it, safflower when I get to the store. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> Don't try to have the last word -- you might get it. -- Lazarus Long ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
