I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

--
Chris Green

wrote in message ...
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

Toolstation do a blacksmiths drill of 14mm dia that is close for about
£3.50.

On 09/04/2012 18:43, dennis@home wrote:


wrote in message ...
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

Toolstation do a blacksmiths drill of 14mm dia that is close for about
£3.50.

I had a similar situation when abroad and limited tools at hand, it was
for a ceramic basin and I needed to enlarge the hole for a new tap. I
carefully marked the outline for the `new` diameter and used a conical
shaped stone in the elec drill, I took it as close as I dared to the
outline and then finished off with a round file. The conical shape sort
of self centers itself and it took care of the bulk of the enlargement.

In article ,
wrote:
Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I'd say a step drill would do it just fine if you keep the speed down and
don't let it overheat. You might have to do it from both sides due to the
distance between the steps, though.

--
*I wished the buck stopped here, as I could use a few*

Dave Plowman London SW
To e-mail, change noise into sound.

I've read that a tapered five-sided tool will enlarge a hole accurately, but
I'm afraid I've no idea if one is available in the sort of size you need.
I've seen truly conical file-type bits which would possibly be OK.

Bert

On 09/04/2012 19:12, Bert Coules wrote:
I've read that a tapered five-sided tool will enlarge a hole accurately,
but I'm afraid I've no idea if one is available in the sort of size you
need. I've seen truly conical file-type bits which would possibly be OK.

A reamer is the tool for enlarging holes to accurate sizes - although in
this case one would need to drill closer to final size first.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 09/04/2012 18:25, wrote:
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

As an aside, in case its of use...

My holesaws thread onto the arbour, and once in place there is enough
arbour still poking through into the saw to thread a second holesaw on.
Hence if you want to go up a hole saw size, you fit both to the same
arbour - with the smaller one "inside" the larger. That then acts as a
centre guide in the existing hole.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

You could probably just drill with the right size drill...


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 09/04/2012 19:31, John Rumm wrote:
On 09/04/2012 19:12, Bert Coules wrote:
I've read that a tapered five-sided tool will enlarge a hole accurately,
but I'm afraid I've no idea if one is available in the sort of size you
need. I've seen truly conical file-type bits which would possibly be OK.

A reamer is the tool for enlarging holes to accurate sizes - although in
this case one would need to drill closer to final size first.


critcher said.......................
you need a 15/16 inch tapered reamer, just make sure you use plenty of
lubricant and go easy on the pressure

In article , John
Rumm writes
On 09/04/2012 18:25, wrote:
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

As an aside, in case its of use...

My holesaws thread onto the arbour, and once in place there is enough
arbour still poking through into the saw to thread a second holesaw on.
Hence if you want to go up a hole saw size, you fit both to the same
arbour - with the smaller one "inside" the larger. That then acts as a
centre guide in the existing hole.

As 15mm seems to be the smallest, perhaps a dowel or a steel tube over
the centre drill would do the same job. Given it's only the outer
surface of the guide that needs to be hard, any gap between the drill
and tube could be made up with a build up of tape.

Proper 15mm one here for just over a tenner + vat but I'm sure there
will be cheaper if you just want it for a one off:

http://www.starrett.co.uk/shop/holes...teel_hole_saw/

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

Before John's suggestion I would probably have given it a go with a well
lubed step drill from both sides but I do have an expendable one here to
try.
--
fred
it's a ba-na-na . . . .

On Mon, 09 Apr 2012 19:31:18 +0100, John Rumm wrote:

A reamer is the tool for enlarging holes to accurate sizes - although in
this case one would need to drill closer to final size first.

A hand reamer would be damn hard work in 5mm thick steel... It would
also leave a slighly tapered hole if that is a problem.

A step drill generally has maximum thickness between steps of less
than 5mm as well so that would leave a stepped hole. Unless the final
step was the desired finished diameter.

Think I'd be tempted to just use a couple of sharp larger twist
drills but not sure how easy that would be with a hand held drill.

Failing that a half round file.

--
Cheers
Dave.

On 09/04/2012 21:26, Dave Liquorice wrote:
On Mon, 09 Apr 2012 19:31:18 +0100, John Rumm wrote:

A reamer is the tool for enlarging holes to accurate sizes - although in
this case one would need to drill closer to final size first.

A hand reamer would be damn hard work in 5mm thick steel... It would
also leave a slighly tapered hole if that is a problem.

You can get parallel reamers... but then you need a target hole not far
from finished size.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 09/04/2012 18:25, wrote:
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

Plenty of 15mm hole saws turn up when I do a Google search.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

You could tack weld a plate over the other side of the hole.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

A taper drill would be the better option, as few step drill have 5mm steps.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

If you need a parallel hole, that is the way to finish off, after using
the taper drill from both sides to minimise the amount you need to remove.

Colin Bignell

In article o.uk,
Dave Liquorice wrote:
A step drill generally has maximum thickness between steps of less
than 5mm as well so that would leave a stepped hole. Unless the final
step was the desired finished diameter.

I've just measured one of mine and it's exactly 5mm. So you would have to
take care not to put a chamfer on the hole. Or do it from both sides.

--
*What hair colour do they put on the driver's license of a bald man? *

Dave Plowman London SW
To e-mail, change noise into sound.

wrote in message ...
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

--
Chris Green

Possibly a mag drill with broach cutter. Would certainly do the job if you
could adequately seat the drill and centre the cutter. This is presuming
it's above water line.
HTH,
Nick.

Nick wrote:
wrote in message ...
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

--
Chris Green

Possibly a mag drill with broach cutter. Would certainly do the job if you
could adequately seat the drill and centre the cutter. This is presuming
it's above water line.
HTH,
Nick.




Why all the complications, just do as Rumm says, drill it with a 15mm
drill. (you can get them with step down shanks and probable manage it
with a big battery drill on low speed.)

On Mon, 9 Apr 2012 18:25:08 +0100, wrote:

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Air-driven die grinder and use a conical carbide cutting bit.

"Dave Plowman (News)" wrote:
In article o.uk,
Dave Liquorice wrote:
A step drill generally has maximum thickness between steps of less
than 5mm as well so that would leave a stepped hole. Unless the final
step was the desired finished diameter.

I've just measured one of mine and it's exactly 5mm. So you would have to
take care not to put a chamfer on the hole. Or do it from both sides.

OK, thanks for this and for all the other replies. It looks as if a
step drill (or a taper drill) should be able to do the job.

--
Chris Green

Nightjar wrote:
On 09/04/2012 18:25, wrote:
I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

Plenty of 15mm hole saws turn up when I do a Google search.

Yes, there are some down to 14/15mm, but not so many.


There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

You could tack weld a plate over the other side of the hole.

A bit difficult since the hull is lined with expanded polystyrene
there and it's just by the bed in the aft cabin! :-)

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

A taper drill would be the better option, as few step drill have 5mm steps.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)

If you need a parallel hole, that is the way to finish off, after using
the taper drill from both sides to minimise the amount you need to remove.

It's not that critical, it's to mount a bulkhead fitting to feed a
10mm pipe through the hull so a bit of taper won't matter.

--
Chris Green

I need to enlarge a hole in the hull of our boat which is 5mm thick
mild steel. I've previously cut quite big holes (like two 40mm ones
recently) using a hole cutter but there are two problems in this case:-

I only need around 15mm diameter, hole cutters (the round saw type)
seem to start at 16mm or so.

There's a hole there already, of about 10mm so I'd need to do
something clever to locate the arbor of the hole cutter.

Would a taper drill or a step drill manage this for me? It's probably
only a one-off so if I wear it out on one hole I won't be too sad.
Because of the one-off requirement I really want a cheap solution.

I suppose I could just take a round file to it but that sounds a bit
like hard work! :-)


One of these.

http://www.ukdrills.com/productdetai...=126&catid=240

Mike