I don't think that you answered his question

(You would get 0/10 if this was an english O level question)

The only tapered holes I have come across are for the pin at the top of the tool clapper on a shaper which lets the clapper swing

Some of the bigger shapers will have quite big holes

So you have a nice tight fit on a moving part which moves a lot, and as it wears from use you can tap it in a bit more, or tap it out and re-ream the hole for a slightly bigger pin

It seems to be a cheap way of producing an efficient reliable hinge which has some room for manoeuvre for wear and where the pin won't drop out

Edited By Ady1 on 06/07/2012 00:42:45

Hi Charlie, don't quite know what you mean by Core drills with flutes. Core drills are normally cylindrical and very often have diamond or tungsten cutters on the edge, they are used to cut lage holes in concrete and brick ect. Multi-fluted drills (which is what I think you are talking about) are used for enlaging holes that are already in place. These help keep the drill central in the hole and stop them wobbling and producing a mishaped hole, they normally have a rather large point and are not any good for drilling a new hole.

Regards Nick.,

Edited By Nicholas Farr on 06/07/2012 06:45:44

I think the core drills your talking about are designed to produce a true round and size hole. Normal two fluted drills especialy larger diameter ones will pounce and chatter when enlarging a smaller pilot hole. A multi fluted core drill won't and so will produce a clean and size hole.

@Charlie and all:

As someone else has remarked in another thread, issue 192 (August 2012) of MEW is another cracking issue.

Re Core drills I quote from part 11 of Mick Knight's excellent series "Engineering for Beginners"; which appears in MEW 192, page 15, 2nd column, mid way down, under the heading ""The drilled hole". (AES info: he's just finished talking about the reaming of holes). QUOTE: There is another method (i.e. apart from reaming as discussed in the arrticle immediately prior to this – AES info) of drilling a clean and size bore and that's by using a multi-flute core drill. I suspect it is highly unlikely ……. UNQUOTE: (this portion of general info deleted to save my poor copying typing skills as it's general comment only. But of interest here, the article continues as follows. QUOTE: Core drills, depending on diameter, are usually three or four fluted drills and are used to follow up a previously drilled hole. The core drill isn't ground to a point in the same way as a twin fluted drill but has cutting edges angled away from a flat bottom face. Core drills will cut a size while producing a clean finish in most materials. UNQUOTE:

Unfortunately, while the articles are rich in photos generally, there is no picture of a core drill.

Hope this helps (and thanks to Mr. Knights for an excellent series of extremely informative and well-written articles – to me they alone are worth the price of the MEW sub).

Cheers

AES

Edited By AES on 06/07/2012 21:13:15

Hi There

Photo of a core drill. They are useful for opening a predrilled or cored hole but not a lot of use for finishing a hole.

regards David

Edited By David Clark 1 on 06/07/2012 21:49:02

I have one bought from Tracy Tools just under 3/4″ diameter. It needs a 3/8 hole to start and is very useful to remove lots of metal quickly and without chatter when you want to bore a big hole in the lathe. Looks just like David’s photo.

Could they be bridge reamers? **LINK** I have used them to align holes for riveting, but we are talking full size locomotives here.

These might be bridge reamers as stated above. If that is the case they are used to put a "sized" hole through two (or more) separate, smaller holes in components that require bolting or rivetting together. The idea is to "bridge" any misalignment.

They might also be taper pin drills; these are used, as the name suggests, for opening out a parallel hole to accept a taper pin. They will have a constant taper (1:48 or 1:50 depending on imperial or metric) whereas, as far as I know, a bridge reamer is tapered for a certain length and then becomes parallel.

John.

Edited By JDEng on 09/07/2012 17:30:30