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A program to calculate clearances between machinery parts.

Project description

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This program’s purpose is to allow engineers and designers to verify clearances between moving or stationary parts within a machine. This check becomes more critical when one recognizes that all the features of machined parts are machined according to an allowable tolerance range. These accumulated tolerances can close operating gaps and thus result in malfunctioning machinery.

It should be obvious that all the features of all the parts will not be at the maximum of their tolerance range, nor at their minimum. This program, in addition to calculating gaps based on max/min tolerances, will also calculate clearances based on the probability of features being at some median size. This probability calculation is used by a majority of the major manufacturers today (six sigma).

What other sources are there for a program of this sort? That’s a good question. I have not been able to find any that are publically available. Most large companies write their own program and it is for internal use only.


This program is free for home use. That is, you can learn how to use this program at home. But if you use it in a professional environment, i.e., to design a machine, this program cost $25 per seat. You may pay for this program per the link set up on the website This program is “donationware”, meaning I depend on you good grace to pay for this product. (See the license agreement for more information.) This product has not been altered or impeded in any way pending your payment.

After initial payment, updates are free. I appreciate your support!

How it works

This program works within a Python [2] command prompt window (or more preferably, in an ipython command prompt window). This program works very similarly to Python’s standard “list” command, which is a basic, fundamental feature of Python, and therefore this program will be easy to learn. YOU DO NOT HAVE TO KNOW THE PYTHON LANGUAGE TO USE THIS PROGRAM!

The fundamental element of the stackups program is called a stackunit, which is comprised of a dimension related to a machine part, a tolerance for that dimension, and a few other items related to that dimension. A group of stackunits are used to define a stack. The majority of times many stacks are evaluated within a given machine. It is beneficial that these stacks are managed as a group. This program does that.

During the course of building up stacks, it is very often necessary to adjust dimensions to obtain proper clearances. In such a case the same dimension may have been used in multiple stacks. This program will automatically make the necessary changes to all stacks.


If you have never done a stackup, no problem. A tutorial has been created to show you how to do this, along with showing you how to use this program. It can be found at


  • version 1.0: intial release


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