Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.
This will obviously depend on what your current collet runout is. It also depends on the tooling you are using. In general for multi-flute tooling you will at a minimum get more tool life for any reduction in runout.
A simplistic way of thinking of this is that the runout is adding to your chipload (and therefore feed). So lets make a simple example of a 2 flute cutter running a 0.002" chipload, running 10KRPM and TIR of 0.001". That chipload and RPM would result in a feed of 40IPM (1,016mm/m).
The worst case is where the edge of a flute is at the maximum runout position. What will happen in that case is that flute will actually take a 0.003" chipload or a functional 60IPM (1,524mm/m) cut. Then the as the next flute comes into the cut it is actually missing that material the first flute took from runout resulting in only taking a 0.001" chipload or a functional cut of 20IPM (508mm/m). In this example you can actually get to a point where you are simultaneous cutting too fast and too slow. Once the runout exceeds the chipload you are now only cutting with a single flute of the cutter but at functionally twice your programed feed.
Again, this is a simplified explanation and doesn’t account for tool helix, cutting depth, chip form, single flute cutters, etc. However, it gives a decent understand of one of the reasons why runout is important to tool life and cut quality.
So basically that means with a reduction in runout you can use the runout difference for chipload, get a more consistent cut between flutes, with more tool life.
Can you believe those bias people…
Hopefully this doesn’t get me in trouble.
From our experience with nomad customers the runout in the provided collets varies a lot. They have never been as bad as the random ones we see from a Amazon/ebay seller though. Of the people that contacted us, that actually measured with proper indicators, the range we have seen is 0.0002" to 0.0008" at the face with an outlier of 0.0015". Additionally, I can’t say how much of this is due to wear or abuse.
Also, keep in mind that collets are a consumable. So the just buy the shiny new collet method will turn into a habit if you cut enough.
In most cases they are additive (or should at least be assumed to be). However, if you have enough and the right type of runout in both, you can “clock” the collet and spindle to reduce the runout. The problem with this is that usually you can only clock out runout at a single position as angular runout increases the further you get from the collet face.
As mentioned before collets are a consumable. With their clamping range, assuming you are using proper shanks to collets, you are probably introducing more wear from cycling it or wear from cutting forces than over tightening.
That doesn’t follow for the collet nut though. The ground surface in the bottom of the nut will start to get a groove ground into it, or if not properly cleaned you will “smear” metal trapped in taper. That will offset the collet as the angle on the end of the collet can’t correctly seat. Over tightening makes this happen far faster.
We recommend this as well. Both to see where you currently are and to monitor the wear of the collets and spindle over time. It’s a decent investment for measurement equipment though.
This could help to try and prevent the worst case. However, the problem that you have with it is that you are trying to balance these across the helix and flute depth. The runout at the tip of the tool on a flute will not be same half way up the cut length on that same flute, unless it’s a 0 helix cutter and you only have radial runout.
If you keep in mind your intended cutting depth I guess you could clock it for the minimum increases across that tool for that cutting depth. But that’s more work than I’m willing to do for every cut. It might also be a minimal difference depending on the base runout, helix angle, and length of cut used. There’s also the risk of damage to a flute, especially with micro cutters.
This, plus clean the nut.
This also brings up a point not addressed previously. Make sure when you are measuring either the spindle runout or the total runout that your spindle is warmed up. The bearing in the spindle expand as they get warm and any measurements should be taken in that state. Runout is usually better at temp than cold as this is accounted for and relied on by spindle manufacturers. This is also why you shouldn’t do any cutting with a cold spindle (slop from unexpanded bearings).
I always liked the idea of that design. Still haven’t gotten a chance to test it. My concern was always with the flats replacing the taper.
The counter bore issue is variable though. Example: Source for good quality ER11 collets - #8 by jwr
Hopefully that’s useful. Let me know if there’s something I can help with or expand on.