This extruder is schedualed for a complete barrel replacement also. As the condition of a barrel misalignment, that I am unsure about since I do not know when it was last installed/aligned etc.. So far it looks like next week is when the barrels are being changed. At that same time, I'll be able to check motor alignment, condition of mounting etc... From what has been posted/said, I have a rough check list set up when I do start the alignment check. I want to thank you all for your time, and suggestions.

Interesting thread! Alignment issues always seem to get beat into the dirt. Great way to solve a problem. My two cents... Training, training, training! The problem I see these days is that many of the younger mechanics that are asked to perform alignments have never performed an alignment using dial indicators. Some don't even own a set of indicators. Many are trained by co-workers that only teach the laser alignment technique and skip some of the pre-alignment issues. Unfortunately, a bunch of mechanics are pushed by others (ones that have never even performed an alignment, but may have watched many alignments being performed and consider such checks as softfoot unnecessary) to finish the alignment job. To compound the problem, the mechanic skips the softfoot check and the final few thousandths needed to meet tolerance kicks their butts when the equipment is tightened down. Then, after a frustrating stint of tightening, reloosening, jacking over, retightening, only to find that the equipment still hasn't stayed in position, the overseer blurts out, "that's close enough". Lack of experience, lack of proper training, and the acceptance of precision that can be found in a Stanley 12' tape are some of the problems we face today. "Great Job" to the young mechanic that takes the initiative to research and train for their craft.

The most likely 'bent shaft' condition is where the shaft is bent external of the drive-end bearing. Near the bearing, the runnout will be minimal, and will be maximum at the end of the shaft. If you put your alignment bracket near the bearing, you will be aligning the centerline of the rotor (i.e., portion of shaft between the bearings) with the centerline of the driver (or vice versa). However, if you mount your bracket towards the end of the shaft (on the coupling hub for example), you will be aligning the portion of the shaft between the bearing and the end of the shaft, but the rotor centerline will lie at an angle to the driver centerline.

In both cases, misalignment still exists.

This is what I'm talking about: a misunderstanding of the geometry of this model.

The dynamic method of alignment will NOT detect bent shaft and will only measure the perfect imaginary straight concentric centerline of the bearings as they are the mechanism that allows rotation. The bearings are the point of contact and their line is the center of the journal.

Let's say you have a bent shaft - 100 mils on the motor and a perfect shaft on the pump. In addition they are perfectly aligned. Now on transparent graph paper construct the above. Put you indicator bracket and indicator on and note the point. The indicator's button never moves but the indicator head will if misalignment exists. But in our model the concentric centerlines are perfectly aligned but the actual shaft is sitting 50 mils above the centerline. If you take readings you will only have bracket SAG and will not see any run-out, zero, nada. The bend in the shaft is always at the same point and relative position to the indicator's button regardless of position, 3, 6, 9 12 O'clock etc... So the bend at 12 O'clock is in the same relative position to the indicator's button as 6 O'clock and therefore the indicator will not see the bent shaft. Same goes for laser or any system using dynamic alignment. Dynamic alignment being defined as "both shafts rotated together". In the case of dial indicators with our model the readings will represent bracket SAG since perfect alignment is present in our model.

This message has been edited. Last edited by: Sam Pickens,