With a few mentioning having the same issue, then yes it seems that would be a manufacturing error. Phase II has a fairly good reputation, I'd say at least equal to or possibly better than something like the Vertex tables. The cause of the actual problem would depend a lot on it's internal design. Some have the main worm wheel gear teeth hobbed and then high precision form ground directly on a hub below the main table. Others like my Vertex have a separate bronze worm wheel that uses that hub below the table as a location point for the tables center of rotation, and through bolts in the face of the worm wheel to fix that gear to the table bottom surface. However those Phase II's are done, any half decent rotary table is or should be designed and built with very high angular precision on those gear teeth. When you start talking minutes and seconds of degrees, it's not something you can easily fix in a home shop without drastically altering that same precision your paying for. In this case, not knowing exactly what your doing can and will hurt your wallet.
If it is being caused by any contamination, then yes that's obviously an easy fix. Most of us are buying these Taiwanese and Chinese rotary tables because of there much lower price. That almost guarantees the manufacturer's have little left for proper operation checking and assembly in anything like clean room conditions that something more upscale like a Moore, Walter, Leitz, Nikken ect would be. I figured it out myself long before his videos, but just like Stefan Gotteswinter on YT points out, anything like this requires a proper and through disassembly, cleaning, adjustments and re-lubrication before it's put to use. A bit of casting sand isn't impossible to find, but in my experience, most of what you will find would probably be some metal chips, disgustingly poor lubrication products, and at least a little to maybe a lot of grinding dust mixed in with that lube. The exact same holds true for the lathes, mills, chucks, vises ect. And none of that is at all good for tool longevity, it's functional operation or accuracy.
Simply because of the high precision, I most certainly can't agree with using hand scraping or even worse sandpaper to relieve that tight spot. Yes a highly trained person could probably do it, but most of us aren't. And if you were, then a forum post wouldn't be needed. And the instant anyone does so, you've lost any warranty against manufacturing defects and without question introduced unknown amounts of rotational and indexing inaccuracy. Return it to the dealer it was bought from for a proper repair or replacement. It's also not impossible the material stress relieving on the worm wheel or even table was incorrectly done. If so, that could have caused either to go a bit out of round or out of square after the teeth were hobbed and ground. But again, that would be a manufacturing defect and needs to be corrected or replaced by them. If your lathe has a large enough swing, then just the table with it's worm gear attached could be set up between dead centers, and the tops of the worm teeth at least checked with a 10ths or metric equivalent test indicator. It's also not impossible it's not the worm wheel at all, there's fairly tight tolerances on these tables, any after the manufacturing part warpage of the table bottom, the main outer casting body, or the table axle to it's lower bearing could also be enough to cause some partial drag or eccentricity within the assembly. You have to first identify what the real cause is before trying anything haphazard that may or may not fix it. To me anything that relates to machining is mostly about using logical thinking and problem solving as your first priority.
Since I've never used a Phase II table I'm unsure of how there set up. On my Vertex, the worm gear rotates through an eccentric bushing. That allows adjustment of the worm to the worm wheel to reduce the gear backlash to the bare minimum, or to fully disengage that worm from the worm wheel to allow quick hand positioning of the table to your rough starting point, the worm is then swung back into position to re-engage with the worm wheel. However... and like almost any gear, there not designed to operate at a zero backlash condition. If those Phase II's are like my Vertex, there will be a threaded and usually designed for hand operation without tools positioning lock on that eccentric bushing that's designed to set the amount of backlash you find acceptable. Very hard to explain with just words, but a Goldilocks situation, not too tight, but not too loose. If your trying to operate these tables and that eccentric bushing swung over to a very tight and with zero backlash position, your operating them incorrectly and that eccentric bushing needs to be backed off by at least a few degrees until there is a very small amount of backlash. But even operated incorrectly, there still should be no real tight spots over the full 360 degrees of rotation if the worm wheel is correctly located to the tables center of rotation and with the gear teeth and it's gear center as round as they should be. As I said in my first post in this thread, a whole lot more information and descriptions of the exact issues are needed, adding detail pictures would help even more. Without that, it's all at best guessing what the real cause might be.
