News  :  June 2000

Tips & Tricks By Leonard ...

An Average problem.

I’ve been a machinist and a CNC programmer for over 10 years now and not a day has gone by that I haven’t learned something. Sometimes my daily education has nothing to do with machining. An open mind and a desire to improve always makes my day exciting. Sometimes I feel foolish getting excited about a new math formula or finding a better way after doing it the old way for years.

All machinist and engineers work with high low limit tolerancing. Usually these tolerances are associated with special fit requirements. Thread pitch diameters, bearings, clearance, seals to name a few. As a programmer the center of these tolerances is the most appropriate number to use. If a machinist is careful to cut to size the feature with the closest tolerance then any features cut with that tool should also be correct if all dimensions are programmed in the center of their tolerance.

As a machinist I always want to know the center of my tolerance. Whether it is a dimension on a print or a tolerance out of the Machinists Handbook I like to calculate the middle of the tolerance if for no other reason then my piece of mind. 

I always find this calculation cumbersome especially when the numbers are four place decimals from a thread pitch or a conversion from a metric tolerance. I took a small poll at the shop and found everybody, young and old did the math the same. First they subtracted the low limit from the high limit. They then divided the difference by two. Then they added the quotient to the low limit to receive their answer. None of this sounds too terribly horrific. After all they did end up with the right answer. Most people in my poll made at least one mistake causing them to start over. 

Good machinists always double-check their work. This doubles the number of keystrokes on their calculators in turn doubling the chance for errors. This method requires that you type in at least one of the dimensions twice to receive your answer. You also have to add the correct dimension to your quotient or your answer will be outside the tolerance range. Any way this calculation always interrupts the true task at hand.

The answer is to average the numbers. Add the high limit to the low limit and divide by two. So simple that only took me 9 years to figure it out. I no longer have to juggle numbers on the calculator or lose my train of thought. I no longer do x.xxxx – y.yyyy = / 2 = + y.yyyy =. I just do x.xxxx + y.yyyy = / 2 =.

Here’s an example.

By Leonard Fronhofer V— CNC Engineer

Fronhofer Tool Sponsors Capstone Project at HVCC

Each year Hudson Valley Community College has a new manufacturing technical systems capstone project. The project is worked on by all participants in the program and is fairly in depth.

To sponsor the 2000 capstone project Fronhofer Tool donated $4000 dollars to the program and in return received one of the three completed projects. The project is now on display in the Fronhofer Tool office.

The 2000 project was a scale model of a “Victoria” two cylinder horizontal steam engine which was used to power steam engines in the 1800’s. The model works on compressed air to facilitate demonstrations.

A second model went to the community college while the third went

Office Safety

Did you Know? The average weight of an object that breaks some one’s foot is 7 lbs. So don’t forget the steel toes. There are different strengths of steel toes so make sure you buy the appropriate shoe for the maximum weight you could drop on your foot.

Ahlstrom does final inspections on the MDR Machines

Ahlstrom customers do final inspection with Fronhofer Tool owner Paul Fronhofer (left). Inspectors are Engineer/Designer Ellen Ketchum (center) and project Manager Ron Bunker (right).

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Last modified: November 08, 2007