Tolerance

With the new milling machine, I have been exploring some of the internet sites dedicated to machining. One of these sites Industrial Hobbies has a good explanation of the various degrees of tolerance when machining. (How close to the actual design you are -- 0.001" is one thousandth of an inch.) Getting to a higher and higher degree of tolerance is something that comes with work, time, experience and patience. Here is a brief intro and the examples for Tolerance:

In search of Tolerance
Tolerance is without a doubt one of the most misunderstood terms when people talk about CNC. To be exact tolerance has noting to do with CNC, the proper term is resolution (ability to return to a known location) when discussing CNC. But, tolerance is the work that folks like to use.

Maintaining tolerance is the ability to produce something within specifications, no more no less. In the hobby (and small business) arena this is a loaded question, because for the most part you the �designer�, the �machinist� and the �quality inspector�; the tolerance can be whatever you want +/- 1� (one foot) +/- 0.000050 (50 millionth) or anywhere in between. It�s your call.

Reasonable Expectations

0.050 With a tolerance of 50 Thou� you can produce most things that are used around the home and shop, some model projects but nothing too serious. Some of your friends will be amazed with your results, some will not. Basically, you threw the machine on the bench, threw down a few beers (not a good idea) and �fired it up�.

0.020 With a tolerance of 20 Thou� you�ll be able to do some of the more difficult hobby stuff but still nothing too serious. You did everything as above but without the beers.

0.010 With a tolerance of 10 Thou� you�ll be able to do most hobby stuff, except engines and extremely complex mechanical projects. You trammed (squared) the machine and played with the gibs (adjustment bolts). You think about machining more than once a week, and look for ways to improve your tolerance.

0.005 With a tolerance of 5 Thou� you�ll be able to do some simple engines and fairly complex mechanical projects. From time to time you re-tram your machine. You realize that more expensive cutters will more than likely help and you think about popping for a �good� set of gauges. Your CNC code now includes a finish pass. Your friends are impressed.

0.001 With a tolerance of 1 Thou� you�ll be able to do most model engines, except turbines. You can check the square-ness of you machine in less than 5 minutes and adjust as necessary in another 5. Your code now has �lead in�s and lead out�s� and you know whether you need to use a climb or conventional cut. You�ve lapped, scraped, or re-ground the ways of your machine and know when it doesn�t �feel right�

0.0005 With a tolerance of half Thou� you�ll be able to complete any model in any book you find new or old. Your CNC code is poetry in motion and you are considering leaving your real job in order to be a machinist. When you read Home Shop Machinist, and say, �I can do it better�

0.0001 With a tolerance of Tenth� you have left your day job and do this full time. You know what temperature you machine needs to be at to �hold tol� and you adjust your machine accordingly. You are considered a skilled craftsman. Your friends have no idea what you�re talking about anymore.

I love that last line... And no, I have not trammed the mill yet (building up the workspace for it) but the old Southbend I have works reliably at one to five Thou' when I'm anal about it.