Rainer Schmidt wrote: > I can vouch for the problems the us imperial system is creating. > There is not a single day in a custom shop I know off where there are > no parts messed up because of conversion problems which simply would > not exist with the metric system. Instead of simply shifting the > decimal point one has to be aware of the 12 the 3 and the fractions to > the respective decimals. At time the US imperial unit system is like a > rubics cube which has to be solved before the emergency exit can be > opened compared to a button you can press blindly. I know I am > exaggerating but the pile of little cut off's next to the chop saw is > telling a story. It's the 'Dohhhhh' pile. > Rainer > > ------------------------------------------------------------------------------ > Crystal Reports - New Free Runtime and 30 Day Trial > Check out the new simplified licensing option that enables unlimited > royalty-free distribution of the report engine for externally facing > server and web deployment. > http://p.sf.net/sfu/businessobjects > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > > There are American standards for threads, gears and other things like bolts etc. These are fixed and in every case are determined by best practices. The Germans have have a set of metric standards the English have ISO standards and the Spanish have still another. We here in the US have come closer to standardizing the metric system for screw threads than anyone in the world. We specify a metric screw and never say which standard, as a rule the the machinist makes it to one of the three. The Chinese don't work to any standards and at the same time they try to work to everyones. Imperial bolts are designed to break before the threads pull out of the parent metal. The best thread pitch is picked for the bolt diameter to achive this partially by having a smaller or larger root diameter. Europeans after WWII tried to copy this into the metric system for bolts and did a pretty good job. I am not sure this is true but I was told in apprentice school that prior to then they only had fine threads and determined whether the threads would strip out in the parent metal buy how deep the thread was. To a degree we do the same if the bolt and drilled an tapped whole are not in the same kind of metal. For example, a hardened steel bolt and a drilled and tapped hole in an aluminum engine block. The first rule in mechanical design is no sharp corners. Dig some bolts out of the drawer and look at them the all have sharp v threads they are not to any standard. Every standard in the world calls for a radius or truncation in the root of the thread. As a result nobody can calculate the strength of the bolt. The metric thread system is a kind one size fits all. There are only a couple threads for each size. Very convient but there is a reason we have so many threads and that is they all serve different purposes. The metric system has traditionally put more concerned itself with fitting the threads into a convient metric system instead of being the best thread pitch for the job. Since the metric system uses decimal places the same as we do I don't see where it's any easyier to use than imperial. Most of the fractions come into play because a machinist says in his own mind .493 Hmm that's about a half inch. More than likely a half inch shows up on a drawing as .5 or .50 or .500 it's all the same thing. It sounds like an excuse to me that a guy cut a piece of steel wrong because there were three decimal places instead of one. Does he also mistake a centimeter for a millimeter? Most parts are dimentioned on cad why in the heck would anyone be using fractions on cad cam? So if metric is not standard the world over and imperial is not why are we knocking ourselves out over this. For me this is not really about metrics or imperial. I think a huge majority of Americans think that anything that takes place in Europe is somehow wonderful. We are ashamed to drive an American car, just not enough prestige. What ever it is if it's US made it is somehow inferior to European. Their parliamentary governments are better, their health care is better, and we Americans are crude and unwashed. This of course is not a scientific argument it's a machinists argument and an American argument and they are both real , says me. Geeze, I have finally worked my way around to my pet peeve. I guess this is really where I'm coming from :-) Sorry guys, I started to delete this whole thing and changed my mind as there might be something here for somebody . Doug
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