Using expansive bits

[Eric The Viking]

Seeing Geoff's unusual one in the other thread prompted this:

I have tried, but I don't really get on well with expansive bits. I have a set made in the 1970s to Clarke's pattern, and find that when set up for narrow holes it clogs quite easily (there's a lot of metal in the way of the chips), and when doing a wide hole it wanders horribly. And on several occasions the adjustable part has slipped in the middle of something - horrible!

I know it's probably down to technique, and they are a lot easier to hone than ordinary Jennings-pattern, etc. augers, but I've wondered what I'm missing. I've always tried to start by scribing the circumference carefully with the spur tip before getting the cut started, but even that doesn't seem to help enormously.

Yet they were popular, for getting on for 100 years. So, if there is a trick to them, what is it, please?

E.

PS: never had the nerve to try them in hardwoods - do they work better then?
PPS: I learned to set them up with the spur directly under the brace handle, to get max downforce and thus slicing action. It seemed to give better results than a random position, but is that wrong?

 

[bugbear]

I always drill a pilot with a twist bit when using an expansive, just big enough to guide the lead screw, but still small enough for the lead screw to grip.

A bit so shallow is always going to wander if used for a deep hole, just like a centre bit (old or new pattern both).

BugBear

 

[Eric The Viking]

Thanks BB. I've got a suspicion the leadscrew on mine is pretty blunt, which doesn't help, but I can't think of an easy way to sharpen it. Advice welcome.

 

[AndyT]

Well, this sounds like a request for a few experiments, so I postponed all my other tasks for the day and popped down to the workshop...

Inspired by an enthusiastic blog post by Richard Maguire (http://www.theenglishwoodworker.com/expansive-bits/) I bought these two a while ago on eBay for not very much. They're both the very common Clarke's pattern, made in Sheffield by Ridgeway, probably early C20th, and look as if they have mostly stayed safely in their boxes.

The larger one is a big, chunky thing - here it is set at 2"

and here's the smaller one for comparison.

They each come with a large and a small cutter - worth checking for when buying one as they are presumably easily lost.

I tried borng a 2" hole first. The first problem with the large bit was that the square taper is too big to go in my favourite 10" Stanley brace - and most braces have a chuck this size:

It does go into this Toga brace, which is only an 8"

so I tried that.

I find the most comfortable position is to have the work vertical and go in at belly height:

With the first revolution the inner scriber scores around, and the outer one starts. There is no choice about this - the lead screw draws the tool in at a set rate. (I didn't drill a pilot hole in this softwood.)

One more revolution and the outer line is scored

cutting starts

and continues. The ratchet is useful, letting me just use the most efficient part of the stroke.

Problem! Since the chuck on this brace only has crocodile jaws, and they are working at the limit of their opening, with the level of torque I was applying, the taper worked out of position and the bit went crooked:

I fiddled about a bit and decided the best option was a different brace. I don't have anything really big enough, but this Spofford style is simple, sturdy and just about big enough.

Even without the benefit of a ratchet I could continue to bore the hole

stopping when the tip of the leadscrew came through the other side

But this led to the second problem. Going in from the other side, I soon got to the point where the lead screw had nothing to bite into. Shortly afterwards, the inner cylinder was no longer there to do any guiding. The result was a bit, narrower than the diameter of the hole, flopping about with nothing to guide it, making this mess:

So, another lesson learned - use a backing board and bore right through from one side.

With all the recent interest in making big chunky wine racks, I thought I had better try the 3" setting next.

Here it is, working quite well, with only my own puny arms to power it

but it started to feel as if it was trying to take too much wood off at once. I didn't want to break the bit or the brace, so I stopped.

That chip is about 3/32" thick! Note that the leadscrews both look quite fine - I would not want them any coarser.

In contrast, the smaller size breezed through very easily:

feeling like a very practical answer to problems such as making dog holes with just the right amount of clearance.

I pushed right through, and unsurprisingly got this amount of tear-out at the back

which I could have avoided - but if I wanted a bolt hole in two flooring joists it would not have mattered at all.

So, to sum up:

Yes they work, reasonably easily but can be a bit worrying at the extreme setting. You do need a good brace for the larger sizes. But every home should have one! (Or two. Or maybe one of each sort... :wink: )

 

[Cheshirechappie]

I bought mine (second hand Ridgway 3/4" to 3") donkey's years ago in the hope that it would save me from having to buy lots of fixed size bits. However, I've never had much luck with it, my experience being very much the same as Andy's. Holes above about 1" even in softwood need quite a bit of torque, and always end up quite ragged on the diameter.

Now that I have a selection of old-type centre bits (the sort with a spike rather than a taper lead screw), I'd always use them in preference to the adjustable. The absence of the screw pulling it into the work at a fixed rate means you can control the feed rate, and thus the torque required to turn them. They seem to give a much cleaner finish to the diameter, for some reason, too.

For really large holes - say 1 1/2" and above - I think I'd be inclined to chain-drill and chisel out the waste, cleaning up by paring gouge or rasp and sandpaper as appropriate. That said, such larger holes don't seem to be needed much in thicker stock. In thinner stock, I think I'd rather saw (coping, keyhole or bow as appropriate) and clean up with rasps, spokeshaves or whatever.

I've rather come to the conclusion that adjustable bits are a nice idea that don't really work particularly well in practice, especially if other options are available.

 

[bugbear]

I've rather come to the conclusion that adjustable bits are a nice idea that don't really work particularly well in practice, especially if other options are available.

I've certainly seen a lot of expansive bits in very good condition, condition that would be hard to explain if they'd seen much use.

BugBear

 

[AndyT]

Re use of expansive bits in hardwood - I spotted these instructions on an old sales listing, from a Ridgeway bit (probably 1960s from the look of the packaging).

1 - They say not on hardwoods - but Richard (using them commercially, with a real-world need to make big holes) found that they were ok.
2 - Does anyone really want to bore a 6" hole with one? :roll:

 

[bugbear]

.
2 - Does anyone really want to bore a 6" hole with one? :roll:

I've used a washer cutter to mark/knife a large hole, prior to waste removal with chisel and (hand)router.

BugBear

 

[Eric The Viking]

Re use of expansive bits in hardwood - I spotted these instructions on an old sales listing, from a Ridgeway bit (probably 1960s from the look of the packaging).

1 - They say not on hardwoods - but Richard (using them commercially, with a real-world need to make big holes) found that they were ok.
2 - Does anyone really want to bore a 6" hole with one? :roll:

It actually says, "Never attempt to bore large-dimeter holes in hard wood."

I take that as very sound advice, and I wouldn't use an expansive bit to try it, either. :wink:

 

[ED65]

've got a suspicion the leadscrew on mine is pretty blunt, which doesn't help, but I can't think of an easy way to sharpen it. Advice welcome.

It's not easy but: suitable needle file, your best reading glasses and a strong cup of coffee immediately before to help focus the mind!

There's an old trick of smearing the lead screw with abrasive paste and then working it into and out of wood a few times, but I don't think that really sharpens, just cleans up or polishes what's there.

 

[Racers]

I have done a 2" hole in oak and a 32mm in maple, the 2" one was in a table for an umbrella, I had two people holding the table while I turned the brace.
You can see the shaft twisting!

Pete

 

[Eric The Viking]

I have done a 2" hole in oak and a 32mm in maple, the 2" one was in a table for an umbrella, I had two people holding the table while I turned the brace.
You can see the shaft twisting!

Pete

Yebbut I'd trust you to have the thing pretty sharp!

For us mere mortals... ?

 

[Sheffield Tony]

I'm surprised the bigger one took such a thick shaving, much thicker than the thread pitch of the leadscrew. Presumably there is a sort of positive feedback going on here, lifting a bigger shaving forces the leadscrew in faster than the thread would naturally feed. I'm used to the reverse effect where a worn out auger causes the leadscrew to pull out rather than taking a shaving at all !

For holes say 1" - 1.5", it is worth finding some old scotch eye augers. They seem to come up at a reasonable price quite often, and can be rescued from a fairly rusty state. I picked some up for boring holes for chair legs - much easier to control the angle of drilling than a brace.

 

[AndyT]

I'm surprised the bigger one took such a thick shaving, much thicker than the thread pitch of the leadscrew. Presumably there is a sort of positive feedback going on here, lifting a bigger shaving forces the leadscrew in faster than the thread would naturally feed. I'm used to the reverse effect where a worn out auger causes the leadscrew to pull out rather than taking a shaving at all !

You can see from the photo that the lead screw is not worn, and the hole it made was not pulled apart by the forces. I reckon it must be to do with the way that the grain runs. There's an automatic problem when rotating a cutting edge into side grain. Unlike a plane or chisel edge, it is going to have to cut into grain going the wrong way, at least half the time. I think I could feel it diving down into the grain as the cutting edge lined up vertically.

In contrast, with an old-fashioned centre bit with a spike, you can control the feed rate with your own muscles/fat and take a much thinner shaving. I have just done a comparison using my biggest centre bit (2") and it was much easier - I made slower progress but could spin a lightweight sixpenny brace round as fast as I wanted. (As CheshireChappie reminded us here. )

 

[Eric The Viking]

You can see from the photo that the lead screw is not worn, and the hole it made was not pulled apart by the forces. I reckon it must be to do with the way that the grain runs. There's an automatic problem when rotating a cutting edge into side grain. Unlike a plane or chisel edge, it is going to have to cut into grain going the wrong way, at least half the time. I think I could feel it diving down into the grain as the cutting edge lined up vertically.

In contrast, with an old-fashioned centre bit with a spike, you can control the feed rate with your own muscles/fat and take a much thinner shaving. I have just done a comparison using my biggest centre bit (2") and it was much easier - I made slower progress but could spin a lightweight sixpenny brace round as fast as I wanted. (As CheshireChappie reminded us here. )

They do dive - it's at least partly the asymmetry and having the spur and the auger chisel-edge on the same side. As you say there's a riving/splitting action, and once that happens, all hope of a clean straight hole is lost!

Jennings-pattern are well balanced WRT the centre in that regard. It's another reason I don't get on with expansive bits really, except when I need a smaller hole at some odd, exact size.

 

[NazNomad]

I've had one for 35+ years and I've probably used it three times.