TECH TIP - End Preparation Squareness

Tri Tool Inc. designs all standard ID mounting weld end preparation products to machine the end square to the mounting surface within .002" per diameter inch and flat within .005". Tri Tool does not test and certify each tool to meet the criteria, but the initial production lot is verified to meet the criteria and random samples are tested thereafter. A squareness factor of .002" per diameter inch is equivalent to about 1/8" of one degree. If a customer requires a certification of squareness and flatness then Tri Tool will test a machine at time of sale and provide the certification at a nominal fee.
There are several factors which can give the appearance of a machine cutting out of a square, when in actuality a machine is not at fault.

• Comparing the squareness with the full length of pipe/tube versus the mounting length. If the pipe/tube has a significant bow in its full length, the ends will appear to be out of the square; whereas, the end relative to the length in which the tool mounts is still machined square.
• Not setting the tool correctly in the pipe/tube. A three jaw mandrel with relatively short mandrel mounting block lengths as compared to the pipe/tube diameter, can be set in the pipe/tube up to about 1/2 degree out of square. The operator must bring the mandrel jaws or blades into contact with the ID and jiggle the machines slightly as the mandrel is tightened to set the machine for optimum squareness.
• Mounting a machine with a jaw block or blade setting on a seam, a flat spot or dent in the pipe/tube or other non-uniform surface . The mandrel can only mount square to the surface point with which it makes contact.

To perform a squareness test with an ID machine select a short length of pipe or tube ( length to be about 3 to 6" for the small bevelers) with a reasonably good ID surface and proceed as follows.

1. Mark an axial line on the side of the pipe/tube.
2. Install the sample with the line indexed over a mandrel blade or jaw block.
3. Use a facing bit to cut the tube.
4. Remove the sample and reinstall with the index line over the same mandrel blade or jaw block to cut the other end.
5. Cut the second end flat.
6. Measure the length of the sample in several places to find the high/low points either with Verniers or on a surface table.
7.  

The difference between the shortest measurement and the longest measurement divided by the actual diameter of the pipe/tube is equal to twice the out-of-squareness factor. By indexing the sample to mandrel blade any misalignment will be in the same plane on each end. This makes the length measurement differences double the actual out of squareness factor per end.