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Embarrassingly stupid question!

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Allen Smithee:
You know how it is with those of us who never did this stuff for a living - we have knowledge and experience, but only of the limited range of things we've actually done. So as soon as we get to something basic, but previously not done, we have to ask embarrassingly basic questions. At least that's MY excuse, and I'm sticking to it!

The part I'm trying to make is very, very simple. It's a rotor adaptor for an electric ducted fan unit to go from a 4mm motor shaft into a 6mm bore in the fan. It is a very simple bit of turning that looks like this:



I'm making one because (for reasons too tedious to detail) I want to make a steel one rather than the stock dural one. The fits need to be quite good to preserve balance because the fan unit does around 140,000rpm (for example there are two grub screws simply because the vibration when only one is fitted is enough to wreck the motor bearings), but it's still a very simple thing to make.

So I made one and I reamed the 4mm hole. It's a superb fit on the shaft BUT it's a blind hole - a 6mm hole in a shaft that has an M6 thread has to stop well short of the thread for obvious reasons. I realise now that reaming a blind hole is something I've never done before - the reamer appears to have a taper over the first 6mm or so, because the shaft jams before the end of the hole. I've looked around and a I can't see anyone offering "bottoming reamers" so am I looking in the wrong place or is there some other technique for doing close-fitting blind holes?

I know it's a stupid question, but what am I doing wrong? :-[ :-[ :-[ :-[

AS

Ian S C:
You might even find it better to use 3 grub screws at 120* so that it is easier to centre the shaft. You could drill the full length of the shaft maybe 2 mm to get rid of some weight.
Ian S C

steamer:
The simplest solution would be to bore it to size.   Otherwise a a custom D bit would do the job.    I would make the bore first,  and then turn a 4mm mandrel and mount it on and turn the OD.

Vixen:
Hello Allen

A hand reamer has a long taper lead in to align the reamer with the hole.
A machine (chucking) reamer has almost no taper lead in, as it relies on the lathe to achieve the alignment.

A machine reamer may be the answer

Cheers

Mike

Jo:
Peter you need to effectively bore the hole... (cheap  ::) ) purchased boring bits don't go that size but D-bits do. So you need to make yourself a D-bit or alternatively find a smaller milling cutter and use that as the edge to bore the hole.

Jo

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