How often do you check tracking force?

I agree with audphile1. It depends on how often you use your turntable.

I also agree with billstevenson. If you are removing the headshell and changing cartridges then you are essentially starting from scratch every time you do that.

What I don't agree with is that once your tonearm and cartridge are set up "the variables do not change."

VTF will change a little over time because as you play records, your cartridge's cantilever assembly will soften, and eventually it will sag a little, and when it does the VTF and VTA have both changed.

So has the overhang. Sort of. Your cantilever will tend to bend toward the spindle as it wears, so it may help tracking to adjust for this variable every so often.

The good news is that, assuming you can raise and lower your tonearm pivot, you can adjust the arm height and the tracking force to this new position of the cantilever and restore the sound you had before, more or less.

The bad news is that once the cantilever sags to the point that you see a noticeable change in arm height and VTF, you're nearing the end of your cartridge's useful life, or at least the end of the period during which it will sound it's best..

That's the long answer to your question.

The short answer is: check it every 3-6 months. If the VTF has changed, reset it, and then if your tonearm allows for azimuth adjustment, that is the time to make that adjustment.

And markcasazza, don't worry about using a microscope to check your stylus. If you have your overhang and anti-skate set well you will wear our your cantilever assembly well before you wear our your stylus.

Spring applied VTF arms in my opinion and experience deserve a more frequent check.. also certain cartridge designers specify some very tight requirements… think J Carr and Lyra.

If you have your overhang and anti-skate set well you will wear our your cantilever assembly well before you wear our your stylus.
 

@thebrokenrecord I actually haven’t worn a cartridge out yet. I upgraded after couple of hundred hours a few times and didn’t give it a chance to wear out. But I was always under the impression that the stylus will wear out first. Interesting…

@markcasazza I apologize for taking so long to respond to your question.  My wife and I have been traveling from our home in FL to our home in NH.  Anyway, the first thing to know is that @thebrokenrecord is incorrect that the cantilever is likely to give out before the stylus is worn.  In fact, I have been checking stylus assemblies since working for a high end hi-fi shop in Seattle during my college years beginning in 1970 and I have not ever seen that happen.  With that said, I suppose it is possible, particularly if the cartridge had been stored in an environment that was deleterious to the elastomer that the cantilever is supported in.  So I will never say never.  Anyway, the way to check for stylus wear is to fix the stylus under the microscope so that the tip is facing up directly at the lens and you are looking down at the tip.  Then focus first on the tip to see if it is even.  As it wears there will usually be wear points on each side of the tip that can be discerned as shiny spots.  This will be easiest to see looking at a conical or an elliptical stylus.  Fine line and Shibata and similar more complex profiles are much more difficult to spot wear on.  This is because there is less surface area at the tip.  Proceed by looking down the sides of the stylus.  The better your microscope, the better the depth of field will be even at high magnification.  Over the years there as been much discussion and debate concerning the effects that a worn stylus might have on the vinyl groove.  In my opinion, shapes like Fine line, Shibata or similar, which have sharp edges when new with relatively large contact area with the vinyl wall tend to wear smooth and so as long as you replace them in a timely manner the potential to damage your vinyl should be minimal.  Conical in particular, but elliptical as well, tend to start out smooth, and importantly have relatively small contact area with the vinyl groove walls when new and tend to wear with sharp edges, which I believe are more likely to damage vinyl.  How often to check is a function of rate of use.  As a rough starting point, I recommend checking your stylus every 6 months. 

@billstevenson  Thank you for the details. I run a Shibata stylus on my primary turntable. In the garage it is the original that came with the Pioneer which is where I want to start with inspections. My microscope is an antique, but the eyepieces are all new. My depth of field is okay at lower powers, but pretty tight as I crank up the power. https://www.facebook.com/share/p/16m754VXHU/  

It is fun to use and perhaps this will be the first time I use it for serious work. My Shibata has about 300 hours on it with every record always cleaned prior to playing. Some not so great as it was before I had an ultrasonic cleaner, but at least with a SpinClean. I got the Pioneer used so it is anyone's guess the condition, but then again, it is in the garage.