In Praise of the Centre Bit.

[Andy Kev.]

I agree with Jacob and phil.p in practical terms. It's pretty obvious from the results that I've been getting that I'm using this bit at the limit of its sensible applications. I also agree with Cheshire Chappie in that I bet there would be far less difficulty with the older style with its simple spike which as far as I can see (correct me if I'm wrong) has the function of simply holding the bit in place whiile the two cutting elements get to work.

I did start wondering yesterday why it had been thought necessary to introduce the threaded element.

All that said, it's fun experimenting and trying to identify what the limits of those sensible applications are. It's not as if I haven't got enough scraps of wood.

As an aside, all this fiddling about led me to a table of information which could be very useful (although it is not strictly related to hand tools; more to pillar drills). If you google Drill Press Speed Chart you should get to it.

 

[Jacob]

...
I did start wondering yesterday why it had been thought necessary to introduce the threaded element........

It's just a simple improvement - it pulls the bit more positively into the work and makes it easier/faster. Earlier versions wouldn't have it as it would be too technically difficult to manufacture by a small workshop or blacksmith.

 

[Andy Kev.]

...
I did start wondering yesterday why it had been thought necessary to introduce the threaded element........

It's just a simple improvement - it pulls the bit more positively into the work and makes it easier/faster. Earlier versions wouldn't have it as it would be too technically difficult to manufacture by a small workshop or blacksmith.

That makes sense. Once I've got the scoring blade fully sharpened I should get the benefit of the thread being better able to do its job properly.

 

[Andy Kev.]

The bit went through 3/4" walnut like a hot knife through butter and with no pilot hole. So maybe the thickness of the wood is the limiting factor.

 

[Cheshirechappie]

The bit went through 3/4" walnut like a hot knife through butter and with no pilot hole. So maybe the thickness of the wood is the limiting factor.

I think that's the case. The 'new type' centre bits are more than adequate performers in thicker stock where the pilot's wedging action won't split the wood, and the 'old type' cope with thinner stock better.

One question that does still hang a bit is how the 'new type' and 'old type' compare when hole size gets bigger. My Jennings pattern augers become hard work above about 3/4" in hardwoods, but the 'old type' centre bits perform quite well in larger sizes. It would be interesting to know if the same applies to the two types of centre bit, if anybody has both types in a range of sizes and would be kind enough to experiment a bit.

 

[Jacob]

My 32mm ridgeway type is like a hot knife etc. Fast and easy even in hardwood. Commonly used for Yale locks in doors 44 to 56mm.
The big advantage of a ratchet brace is not only in cramped corners but also allows you to get max leverage - a to and fro push/pull with the brace at 90º to the arm, rather than having to go round the full circle. Could this be your prob - 3/4 bit and a brace without ratchet?

 

[Andy Kev.]

My 32mm ridgeway type is like a hot knife etc. Fast and easy even in hardwood. Commonly used for Yale locks in doors 44 to 56mm.
The big advantage of a ratchet brace is not only in cramped corners but also allows you to get max leverage - a to and fro push/pull with the brace at 90º to the arm, rather than having to go round the full circle. Could this be your prob - 3/4 bit and a brace without ratchet?

No, it was a 1 1/2" bit and the brace has a ratchet. I think I'm content that too thin wood was doomed to split.

 

[Andy Kev.]

The bit went through 3/4" walnut like a hot knife through butter and with no pilot hole. So maybe the thickness of the wood is the limiting factor.

I think that's the case. The 'new type' centre bits are more than adequate performers in thicker stock where the pilot's wedging action won't split the wood, and the 'old type' cope with thinner stock better.

One question that does still hang a bit is how the 'new type' and 'old type' compare when hole size gets bigger. My Jennings pattern augers become hard work above about 3/4" in hardwoods, but the 'old type' centre bits perform quite well in larger sizes. It would be interesting to know if the same applies to the two types of centre bit, if anybody has both types in a range of sizes and would be kind enough to experiment a bit.

Experiments would be interesting. It could possibly lead to the ideal set of bits - by type and according to whether one is working with hard or soft wood - from 1/4" right up to say 3" plus.

For instance, what is the best point to stop with one type of bit and switch to another? 3/4" for hardwoods might well be a sensible point. I've got the 1/4" centre bit on the laptop as I type and I'm wondering what the justification for its existence is and then there's the matter of how fiddly it's going to be to sharpen it.

 

[bugbear]

Experiments would be interesting. It could possibly lead to the ideal set of bits - by type and according to whether one is working with hard or soft wood - from 1/4" right up to say 3" plus.

For instance, what is the best point to stop with one type of bit and switch to another? 3/4" for hardwoods might well be a sensible point.

Returning, sort of, to the beginners tool kit thread, Hayward recommends (in the Junior Woodworker, 1953)

3/8" auger (for dowelling, I think)
snail counter sink
3/4 centre (the old style without leadscrew)
medium spoon or shell

His "The Complete book of Woodwork", 1955 has a slightly larger list; (*) means essential.

*1/4, *3/8, 1/2, 3/4 auger
*1/8 - *1/4 shell or twists bits for screw holes
Countersink *snail, rose
1/2, *3/4, 1" Centre bit
Turnscrew bit
Expansion bit

It looks like Hayward is very conscious of the importance of bit design w.r.t. hole size.

BugBear

 

[Cheshirechappie]

I only have one 'new-type' centre bit, a 5/8", so I've done a (rather limited!) comparison between a 5/8"Jennings twist auger and the two types of centre bit, both 5/8". All three bits were sharpened up and cleaned before trying them, the test piece was beech, and two braces were used, a 10" Stanley ratchet brace, and a 6" Skinner ratchet brace (I didn't use the old sixpenny brace for this one - the Skinner has a smaller sweep).

The Jennings auger was tried first, in the 6" brace. This proved too hard to turn comfortably, so a change was made to the 10" brace. This worked quickly, but needed a fair bit of turning power, though very little down-force. The bit was quite hot to the touch immediately after drilling.

The 'new-type' centre bit was tried, and needed a bit less force to turn using the 10" brace. A little down-force was needed, and a stop had to be made to clear clogging before resuming. Speed of cutting was marginally less than the Jennings auger. Again, the bit was hot to the touch on finishing.

The 'old-type' centre bit was very easy to turn in comparison with either of the others; it was even easy with the 6" brace. However, it needed significantly more down-force to keep it cutting, and was slower to complete the hole - about twice the time of the other two. The bit was warm on completion, but not as hot as the other two.

All three holes were clean and untorn on the diameter when finished, and all three measured accurately 5/8".

Conclusion - the newer centre bits and Jennings augers work faster, with less downforce, but need far more turning force than the older centre bits. All are capable of giving clean holes across grain in hardwood (beech).

Has anybody got any selections of larger bits, so as to add more data as it were?

 

[bugbear]

Conclusion - the newer centre bits and Jennings augers work faster, with less downforce, but need far more turning force than the older centre bits. All are capable of giving clean holes across grain in hardwood (beech).

Interesting; those properties might fit very well with the small sweep braces that were
dominant before the widespread introduction of "American" (i.e. steel, not wood)
braces.

BugBear

 

[nanscombe]

Of course, if the lead screw were longer than the stock in question was thick, it might be possible to drill a pilot hole larger than the lead screw and allow it to bite into a piece of scrap wood beneath the stock and pull the drill through.

 

[Billy Flitch]

I don't know whether this will add to the groups knowledge on center bit or not but I`LL add it any way.
I`ve never heard of the leading screw I`m not saying the term is wrong just I`v never heard of it I`v always known this part of the bit as the worm and it is the worms job to pull the bit through the piece.
Things to note about a center bit it only has one spur and only cuts on one side of the bit the opposite side to the spur, its easy to see if you are drilling square on to the piece as when the spur comes into contact it should form a complete circle if it does not the you are not drilling square on.
I do confirm what Jacob said that most Carpenters carried a 1 1/4" center bit for boring for a yale lock in a front door. The yale locks are usually fitted at chest height on a door and this does not lend its self to a good purchase on the bit but no problem as the worm is there to pull the bit through the door, wait for the worm to show then come at it from the other side.

As an apprentice I worked with Shipwright loftsmen and they would use the old style center bits for boring through 1/4" thick battens without splitting the piece the would refare to the center point of the bit as s brad or sprig bit point.

Shipwrights fitting wooden decks on boats would also use old style center bits but they would have the center point ground off and a short dowel about 3/8" dia and 1" long welded on to the center point, fist a 3/8" hole would be drilled in the plank and through a frame and then the center bit would be used to drill a counter sunk hole to allow the plank fitting to be sealed latter with a dowel.
I have often seen these bits included in sets over on e-bay and wondered if people knew what they where for, the brad point and the dowel where both being used for the same purpose to keep the bit centered in use.
I don't know whether this adds any thing to any ones knowledge on center bits but that's it.

 

[Andy Kev.]

Here's some wholly unscientific data from a bit of fiddling around I've just done (all bits newly sharpened and used in a 10" brace):

Bit Size 1/4 Wood Thickness 1/8 Distance centre of hole to edge of wood 1/4 Result: Split EC

Bit Size 1/4 Wood Thickness 1/8 Distance centre of hole to edge of wood 1/2 Result: OK EC

Bit Size 3/4 Wood Thickness 1/8 Distance centre of hole to edge of wood 1 1/2 Result: Split EC

Bit Size 3/4 Wood Thickness 1/8 Distance centre of hole to edge of wood 2 1/2 Result: OK EC

Bit Size 3/4 Wood Thickness 3/8 Distance centre of hole to edge of wood 1 3/8 Result: OK ABW

Bit Size 7/8 Wood Thickness 5/8 Distance centre of hole to edge of wood 1 Result: OK ABW

Bit Size 1 1/2 Wood Thickness 3/4 Distance centre of hole to edge of wood 1 5/8 Result: OK ABW

EC = European Cherry ABW = American Black Walnut

There are no conclusions which can be made from this but it would appear that you can get reasonably close to an edge with a largish bit provided that the wood is thick enough. That is hardly news. I was a bit surprised though at the 1/4" bit causing a split and needing to be relatively far from the edge of the 1/8" wood to deliver good results. I got identical results with a colt 6 mm HSS twist bit used in an eggbeater drill.

 

[Cheshirechappie]

I don't know whether this will add to the groups knowledge on center bit or not but I`LL add it any way.
I`ve never heard of the leading screw I`m not saying the term is wrong just I`v never heard of it I`v always known this part of the bit as the worm and it is the worms job to pull the bit through the piece.
Things to note about a center bit it only has one spur and only cuts on one side of the bit the opposite side to the spur, its easy to see if you are drilling square on to the piece as when the spur comes into contact it should form a complete circle if it does not the you are not drilling square on.
I do confirm what Jacob said that most Carpenters carried a 1 1/4" center bit for boring for a yale lock in a front door. The yale locks are usually fitted at chest height on a door and this does not lend its self to a good purchase on the bit but no problem as the worm is there to pull the bit through the door, wait for the worm to show then come at it from the other side.

As an apprentice I worked with Shipwright loftsmen and they would use the old style center bits for boring through 1/4" thick battens without splitting the piece the would refare to the center point of the bit as s brad or sprig bit point.

Shipwrights fitting wooden decks on boats would also use old style center bits but they would have the center point ground off and a short dowel about 3/8" dia and 1" long welded on to the center point, fist a 3/8" hole would be drilled in the plank and through a frame and then the center bit would be used to drill a counter sunk hole to allow the plank fitting to be sealed latter with a dowel.
I have often seen these bits included in sets over on e-bay and wondered if people knew what they where for, the brad point and the dowel where both being used for the same purpose to keep the bit centered in use.
I don't know whether this adds any thing to any ones knowledge on center bits but that's it.

I've seen the occasional 'pilotted' centre bit on Ebay, though they're fairly rare, I think. The 1938 Marples catalogue on Toolemera lists them in a range of sizes, but they could only be ordered by the dozen, and the purchaser had to specify the pilot diameter, which suggests they were only made to order. Nobody really needs a dozen of them, so it's understandable that people made up their own to the sizes they needed.