Check Your Angles Frequently

Check Your Angles Frequently

As part of the manufacturing process for ScopeRoller's caster assemblies, I first make a rough cut of the cylinders on a chop saw, then square them and trim them to the correct length (plus or minus .002") on the lathe. The last couple of times that I have made a set, I have had a heck of a time getting the cylinders to square up correctly on the lathe--and as a result, when it comes time to center drill the ends of the cylinders, those holes just don't end up very well centered. For the cylinders that I am going to bore out to make a sleeve, this is a nuisance, but not a hopeless one, because I generally use a boring bar to finish the interior diameter of the sleeve. For those that will be turned to an exact outside diameter, it is more than a nuisance--I end up have to turn away a lot more material than I would prefer, and do another squaring cut.

I couldn't quite figure out why I used to be able to do a pretty good job of squaring these cylinder--but not anymore. Then I pulled out a steel square, and checked to see if the chop saw blade was exactly perpendicular to the surface on which the cylinder lies for cutting. And that was the problem. The chop saw blade is adjustable for vertical angle (from 90 degrees to 45 degrees), and it was easily several degrees off of 90.

Squaring a cylinder on a lathe can correct for small discrepancies, but when you get to something that is several degrees from a right angle, it seems to be pretty much impossible to get a perfectly square result. You start with the end that is the closest to square, and chuck that end first. Then make a cut across the less square end. I'm having trouble applying the opposite angles theorem from geometry to a rotating 3-D domain, but my intuition tells me that as the net effect is that the squaring cut makes the less square end at least as square as the end in the chuck--and then when you turn it around, the second squaring cut gives you something darn close to 90 degrees. If worst comes to worst, turning the cylinder end over end again gives you an even closer cut to 90 degrees.

In any case, with the chop saw angle set correctly, I only need to square each end to have a 3.048" long cylinder so square that no matter how carefully I check it, there's only about .001" difference between the length of the cylinder at various points.