Don't worry too much what it looks like. Is it actually rough when you drag a fingernail along it or it is just an optical effect?

Either way, unless it has been hardened, it'll eventually wear smooth.

Probably would have been better with lubricant, assuming tool geometry and all other variables were OK. It's often helpful to bore with the tool 'upside down', working on the 'back' of the bore – the surface furthest from you (perhaps you did…). That reduces the risk of chips getting dragged between tool and work and spoiling the finish. Also, the feed is applied by conventional and familiar use of the dials, rather than having to subtract. But if it works OK, why bother?

Question might be: What difference would it make if you simply improved the finish with a fine abrasive? Likelihood is that there would be a good deal more collet contact with very little change in diameter or taper.

A test with engineer’s blue might be enlightening, just to check the contact between collet and holder.

I'm sure I'm not the only one that has trouble getting the best finish when hand turning the top slide on a blind taper. I made an ER32 holder and used emery wrapped round a collet to improve things.

pgk

The smoother the mating surfaces the better the grip, which – in theory – is a 'good thing'. Whether Robin's taper need improving is a much harder question. Depends how rough it is. I've often found feel to be better than a visual inspection. Running a finger or finger nail lightly over an object can detect invisible defects.

So I'd compare the feel of the new taper to that of another. If the new taper feels markedly rough in comparison, I'd polish it gently with a fine paper. (With care – overdoing metal removal could spoil the taper.)

There's a difference in my mind between the miniature screw-thread type of rough finish with pronounced peaks and troughs due to severe tearing, or wrong feed-rate, and the spoilt look you get when swarf is caught by the cutter and smeared over an otherwise flat surface. Ideally tapers should be polished, but I suspect smears matter less than ridges.

If the taper slips due to poor contact there's a high risk of damaging both male and female tapers, making them even more likely to slip in future. I suspect it would take a lot of time for such damage to become bad enough to matter in a home workshop. But it depends on how hard the taper is worked.

Some much for theory. In practice, I wonder if dirt getting into the tapers might be more serious than a mildly poor finish? Despite wiping off before each insertion, I've still found swarf crushed on the male. As well as reducing the grip, presumably dirt must also tilt the taper slightly. But I've not noticed dirt in the taper causing a real-world problem with a cut.

On balance, if the taper works and doesn't feel awful, I'd leave it alone.

Dave

Let sleeping dogs lie !!

Time to blue up and twist collet in the taper to see how good the fit really is. The look at and finger it test is remarkably sensitive and often something that doesn't seem to be as wonderful as you wanted is actually pretty good.

Which seems to be the case here.

However there is considerable potential friction involved in finally snugging down a collet so things generally go better with smooth polished contact surfaces. The contact area on ER systems is relatively large leading to potentially more friction. Which is why the published tightening torque figures are so high. My guess is that a less than smooth but still accurately shaped, surface will limit the maximum grip of the collet at sensible tightening torques. We Home Shop and ME types generally don't tighten the things up to full rated torque anyway and, usually, do just fine even tho' the grip in practice is less than book.

So long as the blue test shows 50% or more coverage and no shape errors, as in sorta like crappy thread, just surface finish I'd say you are good to go. If blue coverage is bit low then best to make a matching plug and lap these surfaces to improve the contact area.

Sounds like you re doing just fine but if you do do a blue test you will know.

Clive