Drilling big/long holes

[Richard Findley]

Hi all,

As you know I often make stuff that is too long for my lathe and so have to join them up. This I do by turning a round tennon and drilling a suitable mortice with a Forstner bit on the lathe.

This works ok but I recently read that Forstner bits can wonder a bit due to them only being the diam of the cut for say 1/2 - 3/4" at the cutting tip.

This kind of made sense to me so I was looking for big diam more normal twist type drill bits (at a reasonable price) I found Wealdon do 38mm Auger bits. These I know are not ideal as they have a threaded lead tip which pulls them into the work but they are made of carbon steel and I wodered about the possiblility of turning the threaded tip to a point with a normal HSS tool to make it into essentially a lip and spur drill.

Would this work?
Would I be wasting my time and money?

Thoughts please!!

Thanks,

Richard

 

[CHJ]

Yes Richard with care, slow speed, HSS stout scraper or similar.

Main problem would be that it is unlikely you have a chuck or spindle that will allow you to position drill bit deep enough in jaw to get support needed. (same problem with a Metal turning lathe, most home workshop machines will not have big enough hollow spindle)

Have hand ground threads off in the passed, just needs care to keep resultant spike true and central.

 

[jpt]

HI Richard

I have removed the thread on a number of augers to use on the lathe. I am lazy so do most of the work on the grinder then finish of with a hand file.

john

 

[Harlequin]

I tend to pre-drill a pilot hole usually 2-3 mm dia to the desired depth which the forstner bit follows quite well

 

[duncanh]

It depends how deep you want to drill, but it's possible to get drill bits with a morse taper. The one I have is 2nd hand but at about 1" diameter all the way down it's unlikely to wander. I don't often do deep drilling with it but tend to use it first before using a wide sawtooth bit.
You could always fit these into a morse extension (although that would prob. introduce some error). If you get a bit that's as wide as your quill then it would work well. The problem is that new large ones are very expensive.

My deep drilled blanks are pepper grinders and I drill them with a sawtooth, accept that the drill might wander and then mount them between home-made wooden cone centres to true up the ends parallel to the drill hole.

Hope that all make sense

Duncan