Harbor Freight has a sale on their digital calipers right now. A 6" will set you back a whopping $10-15, which is a very worthwhile investment. WRT your problem, there are manufacturing tolerances that may come into play, as well as variation between kits manufactured by different vendors (may or may not be the problem here). For the tolerances, remember that the bushings are made to within +/- some amount (e.g. .005" - I'm making this up, I don't know the exact value). Similarly, the kits are made to within some tolerance. I'd guess that this tolerance is about the same as the bushing tolerance. So, while .005" may not sound like much, if your bushings are too big by 0.005", and your kit is under by .005", then you're off by a total of 0.01". This doesn't sound like much, but it's enough to feel. Plus, if the tolerances are a little "sloppier", you can imagine that it can be more noticeable.
Then, like I said, different manufacturers use different sizes as their defaults. Slimlines aren't EXACTLY slimlines - there's a tiny variation between them. Not enough that swapping components is usually a problem, but it may be enough to further exacerbate the problems described above. For example, if you bought your mandrel at Woodcraft and have the default bushings they provide, but are using Penn State kits, there is a slight difference in the sizes. Once you get your micrometer, you'll start to see these things more clearly.
everthing was IMO simple but nuthen fits right close BUT no cigar .
