You're welcome. Hope it helps you to bore better.
I am not suggesting that you buy an Aloris tool post! I do, however, suggest you buy an Aloris AXA 4D if you plan to do a lot of boring. And yes, it will fit your import AXA tool post. The boring bar holder you show in your pics is the typical import type that pushes against the bar at just two points with cotters; those cotters contact a steel sleeve inside the bore of the holder. This is not a secure way to hold a boring bar and will contribute to chatter in the bore. In contrast, the Aloris 4D squeezes down on the entire bar so that it cannot move once it is locked down. The only way to get it more solid is to use a heat shrink bar holder. As I said in the article, the holder is more important than the bar and it is worth buying or making a really good one.
The 4D also allows you to make sleeves to fit your smaller bars into it, making it possible to use every boring bar you have in one holder. Not sure that its practical to do that for your really small bars and it might be better to make a tool holder out of aluminum with a smaller bore in the holder to fit smaller bars. I suggest a 3/8" bore if you do this.
There are a number of reasons why a drill will drill oversize. The main one is because the geometry is off. If you take a drill gauge to your drills you will find that many drills are not ground dead on symmetrical, especially imported sets. What brand of drills are you using and are they jobber drills? Other reasons include drills that are not sharp, have improper relief angles, excessive web thickness (required more feed pressure to cut, which can exacerbate any asymmetry in the geometry) and then there is the human factor.
One of the key human factors is improper feed. I know drilling a hole may not seem like a big deal but for all cutting tools, performance is enhanced when the tool cuts continuously but without being forced into the cut. This is a feel thing. You must feed so there is a slight positive resistance to the feed so the tool cuts as efficiently as it can. This also allows the chip clearance features of the tool to work as they should. I have seen so many guys crank on the feed pressure as much as they can, thinking that is the right way to go. The drill comes out of the hole smoking hot and they wonder why their drills don't last long. My drills are almost cool to the touch after drilling but they cut fast and they stay sharp. The trick is to slow down the speed a little bit and feed properly. This allows the drill to cut accurately and your hole sizes will be closer to what they should be.
I'm not surprised your reamer produced an oversized hole but as to why, I can only guess. I suspect that your pre-reamer hole was not straight and not consistently sized for the reasons discussed above. The reamer will try to follow that hole and if it cannot follow precisely then it will cut oversized as it cuts off the bends in the hole.
Another reason for reaming oversize is improper speeds and technique. You will find that for reamers above about 3/8", it is best to slow down. I run my reamers at about 100 rpm and again, feed so that there is a slight positive resistance to feed. I do not bottom out the reamer and I stop the machine when I finish the infeed before withdrawing the reamer; I do not retract the reamer with the machine running. I have reamers that are nearly 30 years old and are still sharp and accurate so this works for me.
The level of the lathe can have an impact on boring but it will be minimal. Most of your results are so oversized that I suspect the quality of your tools and the way you're using them is having more of an impact. The good thing is that this is easy to fix ... buy good tools and learn to use them well. Please know that I'm not criticizing you or dissing your stuff. I'm simply pointing out that you are trying to do precision work and that requires a realistic approach.
Okay, tired of typing.
