Need a perfect 8mm hole - to ream or bore?

[HankMcSpank]

Thank for you valuable input.

Here's my strategy for now...

1. Order up an MT2 Tailstock ER32 collet holder (on account I already own a full ER32 collet chuck & collets for the spindle....not essential I realise, but they're only £20 inc shipping from China & will be highly useful for some of the small intricate things I want to finally make)

2. Check tailstock alignment!!!

3. Order a full set of centre drills (the one I had was a bit piddly)

4. Order up some new 8mm drills (ie abort the concept of drilling a smaller hole & boring until I become more lathe savvy!)


thanks once again!

[HankMcSpank]

Just to give some closure here.

Last night I finally got around to mounting/using my ER32 collect chuck on my mini lathe.

I flipped the workpiece around since taking that photo above (it's 20mm diameter where I've turned it down...which just fits into my largest ER32 collect nicely).

Anyway, my larger centre drill arrived yesterday so I used that & then followed up with an 8mm drill......it's turned out just fine for my needs.

So it was all much ado about nothing rally ...no drilling undersize & then borring needed. (I still need to revisit why the boring tool seems woeful at erhm....boring - for another day though!)

Coming back to why the drill bits wandered - bit of a mystery ...I'd have to think it was something to do with the tailstock not being fully secures &/or centred (I made doubly sure the tailstock nut was tightened extremely well this time...possibly moved during the drilling process last attempt?) & then using the larger centre drill seems to have helped.

And wow...what a difference using an ER32 collet chuck is on my lathe - it's made the whole experience quick & accurate & enjoyable. I no longer have to think "B0ll0****...there's a turning job I need to do, but that *&$*ing 4 jaw....euugh"

[miopicman]

That's what engineering is. i.e. whatever is adequate for the purpose. There are pros and cons for all methods.

I have a similar engineering situation and I will be using an undersize drill followed by a reamer. The pros for this is that it is quick and can be used over and over again with consistant results. Like a twist drill the reamer can be used more than once. Also a reamer will make a consistantly parallel hole; this is something to be aware of when boring deep/long holes - is the lathe quality good enough? You don't want to end up with a hole that is ok at one end and tight or slack at the other.

This my part. It's a chopper disc for speed feedback on a spindle motor.