center drill bits

[adrian]

In an old Popular Woodworking, Adam Cherubini indicated that the "center drill bits" are (in his opinion) the best period bits, especially for hard woods. I acquired a few of these bits and tried out a 3/4" specimen. I sharpened the cutting edge and filed the inside of the outer spur and tried to make a hole in oak. The bit makes a hole, but it is excruciatingly slow. It seems that the problem is the center spur, which doesn't cut. It limits how fast the cutting edge can work. Bearing down as I drill doesn't seem to help. I found that when i drilled a pilot hole for the center spur then the bit cut much faster (like maybe 10 times faster). But the wrong sized pilot hole leads to problems with centering, and a ragged hole. And in any case, surely the best period bits shouldn't require a pilot hole. I tried sharpening the center spur but that didn't seem to make any difference.

So I'm wondering if anybody knows how to make these bits work.

Here's a picture of the type of bit I'm talking about to make sure there's no confusion. (Not my picture.)

 

[Phil Pascoe]

There is a reason why they are "period" bits - other methods are miles better. I suppose if you're recreating or forging something there's a reason, but otherwise why persist?

 

[adrian]

I personally just care about finding bits that work well in my brace. As far as I can tell, all of the available bits are "period" bits of one sort or another. Are you saying that auger bits are miles better? Auger bits can be annoying if the screw clogs, and at least all the ones I have are very long, which has occasionally been a problem in small spaces. Cherubini seems to think the center bits are better than augers. Modern bits like Forstners are presumably designed for faster speeds than I can produce with my brace, so there's no reason to believe they will be miles better than period bits, assuming my brace is willing to hold their round shanks. (I noticed, for example, that one of my forstners said the minimum rpm was 750, and indeed when I adjusted my drill press faster to achieve this, the bit cut better.)

 

[bugbear]

Since the lead of a center bit looks like a bird cage awl, it probably needs to be sharpened in the same way.

BugBear

 

[AndyT]

I think BB is right - the central point needs to be sharp enough on its arrisses to bore its own hole.
There is a very detailed section on the care and use of these bits in Cassel's 'Woodwork' edited by Paul Hasluck and published in 1912 which may help:

If you can't get anywhere with the bits you have, do try some more. They are not rare or expensive and in my experience work well.

 

[Sheffield Tony]

Gosh that loolks a great book Andy !

 

[JimB]

Thanks BB, makes sense and may give my aging arms a bit of a rest.

 

[AndyT]

Gosh that loolks a great book Andy !

Yes, it's one of my favourite books on old woodworking tools and projects - "Cassell's Woodworking" edited by Paul Hasluck and published in 1912 - which was where I got the design for my chair that converts to a set of steps. The original old book is not that common but there is a good cheap paperback reprint of it around, published by Bracken Books in 1995 under the title "The Handyman's Book" which is somewhat easier to find. The scope is huge - everything from a chicken coop to a mahogany whatnot, with lots of ideas and tips along the way.

 

[adrian]

Thanks for posting the pages from that book! I found it interesting that he doesn't seem to say anything about sharpening the centre point. (It also seems that there's an error on pg 110 where it says, "The nicker o (Fig 398) must be sharpened from the inside only" because on the figure, o is the centre spur.

I did try sharpening the centre point, and it didn't help. But I will follow BB's advice and work on it more and see where that gets me.