On Tuesday 10 May 2016 15:41:57 andy pugh wrote: > On 10 May 2016 at 14:28, Roland Jollivet <roland.jolli...@gmail.com> wrote: > > I once watched a contractor dry cut rebar with a diamond blade using > > a cut-off saw. I wanted to tell him you can't do that, > > http://www.husqvarna.com/us/construction/products/diamond-blades-for-p >ower-cutters/di5-ductile-iron-blade/
If I can put yet another oar in this water, it seems to me that Husqvarna et all, is far more interested in selling you another blade at quite a nice profit margin than in doing a job correctly. Diamond, spinning at those speeds, will shatter from impact, and if not adequately cooled, will get hot enough to ablate/evaporate the diamond, both of which will result in the premature destruction of the blades ability to cut anything. Unfortunately, when you are paying the person who needs to cut such by the hour, it quickly becomes expedient to buy the fresh blade to replace the one destroyed by the pressure to "get the job done". It becomes a C.O.D.B. By running it wet, you can somewhat alleviate the heat that evaporates the diamond. But note the "somewhat" because the heating is localized, confined to the actual contact of that grain of diamond with the material being cut, and at the rim speeds of a modern power saw, there is 100x more air at the contact interface than water as its carried into the slot being cut by the rapidity of the rim, which itself is busily throwing that water away from the blade and generally makeing a huge mess of the environment up to 15 or 20 feet away. At nominally 400 revs on a 10" wheel, the impact shock that shatters the diamond is reduced by 10x, reducing the cutting degradation rate by an estimated 10,000%. And if not pushing the blade, but just letting the diamond carry away the cutting dust its making, the heating will also be reduced. In making those two cuts thru a solid casting about 4.25" in diameter, I watched the rim temp with an IR thermometer, and never saw it exceed 120F at about 3/8" in from the blades edge. It appeared the actual edge of the blade was running 15F cooler. Yes, it took a long time to do those 2 cuts. Had I been physically able to attend to the mill full time, about a day a cut. But that blade can do that, at that cut rate, probably another 100 times. Running that slow and easy, wet or dry has relatively little effect on blade longevity because there is not enough heat, or a high enough impact shock to damage the diamond. All of this seduction of the canine could have been alleviated had I been able to back the clock up to about 1948 when an uncle of mine landed a contract to cut the mounting bosses off an eyeglass lens makers cast iron forms so his forms would be usable in a newer machine. My uncle built the first abrasive cutup saw I ever saw, and he didn't have any lawyers telling him what he could not do. In '48, the abrasive wheels came in 10 or 11", you wrapped them on a shield of steel about 1/4" thick to catch the shrapnel as the recommended rpms for those wheels was pretty close to 9500. So he first used a pulley ratio that gave about 7500, but it wasn't fast enough to easily start the fire. So he went to town and got the next smaller pulley, which gave it almost exactly 10 grand. Bringing the wheel to the casting, it only took 3 or 4 seconds to start the fire, and it literally fell thru the 1.25" square block of cast they were cutting off in another 2 or 3 seconds. He blew up one wheel in cutting about 200 of them off that way. But can I buy an abrasive saw that will cut like that today? Not no, but hell no, at least not without putting 5 grand or more into it. The best OTC saw turns a 14" wheel about 4 grand, and it cannot get the fire started in a 1/2x2" bar of cold roll without 3 or 4 minutes of leaning heavily on the blade just to get the fire started. The damned lawyers and bean counters have caused the wheel speed to be reduced (14" wheels are rated for 6500) and the shrapnel catchers are a piece of Prince Albert can. Scary. Modern tech, by the time the lawyers get thru with it, sucks. My Dad worked in '52-55, in the tool & die room at a place in Des Moines called Solar Aircraft, that was making jet engine parts out of SS and titanium. Somebody shaved the JIT schedule and they ran out of bandsaw blades on Thursday, with the next shipment due in Monday next. While those blades did have teeth, the teeth were intended more for carrying air into the cut to carry away the molten metal as they actually cut by friction heating. Daddy picked up a steel shipping strap, welded it up at the length needed for the bandsaw. It worked fairly well so he made about 40 more with each one lasting about an hour. That kept production going until the new blades arrived. And he got a nice little present for saving those 2 days downtime. First, we kill ALL the lawyers, still sounds like a heck of a good idea... Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Mobile security can be enabling, not merely restricting. Employees who bring their own devices (BYOD) to work are irked by the imposition of MDM restrictions. Mobile Device Manager Plus allows you to control only the apps on BYO-devices by containerizing them, leaving personal data untouched! https://ad.doubleclick.net/ddm/clk/304595813;131938128;j _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
