I think if you have a large machine it won't spin fast enough and it will be to easy to break the tiny drill point. If you have a tiny lathe the chuck might be too small for large diameter center drill.
John Figie On Sat, May 11, 2024, 8:19 AM Stuart Stevenson <stus...@gmail.com> wrote: > Hi, > Sounds like you guys are talking about the tool known as a combination > center drill and countersink. > Most CNC operations use a spot drill as a precision starting guide for the > drill point entry. > I don't know about the precision differences between the two styles but if > you really require a close tolerance hole position you should use a more > involved process than just a spot (or center) drill and drill. Drills walk. > The main reason to use a spot drill is time. A spot drill is faster. > > regards > Stuart > > On Sat, May 11, 2024 at 1:50 AM <marcus.bow...@visible.eclipse.co.uk> > wrote: > > > On 2024-05-11 03:32, andy pugh wrote: > > > That's it. really. Why? A large-diameter one with a small drill point > > > could > > > make all the sizes. as far as I am aware the drilled hole is > > > irrelevant. I > > > suppose it might have mattered as a reservoir for the white lead in the > > > days of solid centres. > > > > Interesting question! > > The pilot (parallel) drill creates a hole for the very tip of the mating > > centre. If the drill had to cut the exact shape of the conical tip of > > the female hole, it would struggle to have proper cutting edges and > > still make the true cone. > > You are right that the conical end on the body of a large centre drill > > (ignoring the parallel tip) could cut all sizes of cone. But there might > > be some reasons for the different sizes: > > > > 1. very small centres would enter the parallel drilled hole, but miss > > the conical part. I have just been trying to clean some small center > > holes in a clockmaking tool designed to support the ends of small > > diameter clock shaft pivots which run between two female centres. Those > > pivots would completely miss the conical part of the female hole which > > had anything but the smallest parallel section at the end. > > > > 2. for male centres which will take a decent load, the end needs to bear > > inside a large (deep) female hole, so a large drill can be used here, > > especially when pushing drilling feeds and speeds. The flip-side of > > that is that allowing the body of the centre drill to set the final > > diameter provides a small amount of parallel recess at the outer end of > > the centre, which will foul a centre and hold it off the female cone. > > Centre drills do exist to create 'protected' centres with a larger > > parallel recess just at the entry to the female cone. Those drills have > > a short stepped-out section of cutting edge of larger diameter than the > > largest end of the female cone. > > > > 3. In pre-CNC days, the best way to set the size of a hole would be to > > have a drill of the correct diameter(s) mounted in a turret with stops. > > The operator then would not need to think, but could just pull the > > lever. Aside from the problem in (1), you could, of course, set the stop > > to make a large drill create a small diameter centre. Which makes CNC > > an obvious advantage, of course. > > > > Marcus > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > -- > Addressee is the intended audience. > If you are not the addressee then my consent is not given for you to read > this email furthermore it is my wish you would close this without saving or > reading, and cease and desist from saving or opening my private > correspondence. > Thank you for honoring my wish. > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
