Enlarging a hole

[penberth3]

would this work?

Armeg Wood Beaver 4-Flute Wood Drill Bit 165 x 32mm

No. That bit need a centre.

 

[Wing Mark]

would this work?

Armeg Wood Beaver 4-Flute Wood Drill Bit 165 x 32mm

My guess is that it would grab in the plastic quite forcibly, most wood drills are designed to kind of knife around the perimeter of the hole to cut the grain tidily.
Thet means pointy bits that will dig into plastic, however rigidly it's held.

I found the flat bit suitably ground so it cut on the tapered sides not on the end was reasonably well behaved, I used a hand held mains Bosch drill.
Obviously not all plastic is the same so your experience may vary.
I wouldn't be doing this to anything precious or not replaceable, unless desperate!
Milwaukee Flat Wood Drill Bit 32 x 152mm
Then you need something to grind it with, I used a bench grinder, but a grinding bit in a drill might be OK

I aimed to make something like an overgrown one of these: Tile & Glass Drill Bit 5 x 60mm at least as far as the cutting area I was actually using..
Taking care to feed slowly, it shaved off the plastic and didn't grab.

Take care though, bodging with power tools is never completely risk free.

A surform or other coarse rasp is another option.

 

[LadyInBed]

My link in #5 is to a 32mm max D bit with a hex shank.
I have two or three 6 inch hex shank extension shafts
This one is cheap from Toolstation Magnetic Bit Holder Set

 

[TiggerToo]

Thanks for everyone who responded to my query. The comments were very helpful. I am happy to relate that, for my purpose, the way that worked very well has been:

1) wedging in a piece of softwood (spruce?)
2) drilling a small pilot hole in the centre
3) using this (relatively cheap) drill bit

ARMEG WOOD BEAVER 4-FLUTE WOOD DRILL BIT 165 X 32MM (91676)

from Screwfix on a hand-held drill.

 

[KeelsonGraham]

The Starret Oops Arbor is what you need.

 

[superheat6k]

To enlarge a hole then two holes saws nested one inside the other works quite well, where one is the original diameter and centres the larger cutter, but 30 to 32 mm is likely not going to work as the wall thickness of the 32mm will likely not accommodate the 30mm. Perhaps a 28mm might work and provide sufficient centering on the original hole.

Or for just 1mm on the radius a new flap wheel would soon remove 1mm material, but would need to be careful to maintain sufficient roundness.

 

[Suffolk Explorer]

I have successfully enlarged a 50mm diameter hole in a glassfibre hull to 52mm by taking a length of dowel about 46mm diameter (actually an old rolling pin!) and wrapping sandpaper round it until it just fits in the hole. Then rotating the dowel enables you to grind away all round. Wrap additional sandpaper everytime it becomes easy to turn. It was surprisingly easy and took about 10 minutes to enlarge the hole in 15-20mm thick glassfibre. The OP's 130mm would be much more difficult, but something similar might work.

 

[Graham_Wright]

Surely you can find someone with a lathe?
If the object is round bar, it would be a five minutes doddle, and cheap, and near perfect.
Where are you?
What's your time scale?

 

[anoccasionalyachtsman]

STOP! He's already done it....

Thanks for everyone who responded to my query. The comments were very helpful. I am happy to relate that, for my purpose, the way that worked very well has been:

1) wedging in a piece of softwood (spruce?)
2) drilling a small pilot hole in the centre
3) using this (relatively cheap) drill bit

ARMEG WOOD BEAVER 4-FLUTE WOOD DRILL BIT 165 X 32MM (91676)

from Screwfix on a hand-held drill.

 

[forelle541]

Since I have a 32mm hole saw (yes, Starret) and my step drills don't go that big, I'd nick a trick I saw on AvE's channel.

Get a piece of scrap ply and use the holesaw to make a 32mm hole. Screw it/double-sided tape/just generally bodge it onto your workpiece and use it as a guide to make the new hole.

My favourite way too, mostly ignored.

 

[eddystone]

I need to re-purpose a circular hole in a GRP vertical cockpit bulkhead to take a new instrument but it needs to be enlarged from 1 & 3/4" to 2" so beyond filing. Obviously can't use a hole saw as nowhere to centre it. Thought of using a Dremel to grind it out or possible having a go with a power jigsaw. Think a multi-tool cutter only cuts in straight lines so not much use.

Any ideas?

 

[anoccasionalyachtsman]

I need to re-purpose a circular hole in a GRP vertical cockpit bulkhead to take a new instrument but it needs to be enlarged from 1 & 3/4" to 2" so beyond filing. Obviously can't use a hole saw as nowhere to centre it. Thought of using a Dremel to grind it out or possible having a go with a power jigsaw. Think a multi-tool cutter only cuts in straight lines so not much use.

Any ideas?

Post 14.

 

[Wing Mark]

I need to re-purpose a circular hole in a GRP vertical cockpit bulkhead to take a new instrument but it needs to be enlarged from 1 & 3/4" to 2" so beyond filing. Obviously can't use a hole saw as nowhere to centre it. Thought of using a Dremel to grind it out or possible having a go with a power jigsaw. Think a multi-tool cutter only cuts in straight lines so not much use.

Any ideas?

If the grp is not very thick, a drum sander is very effective. Because it sands along the edge, it doesn't flex the panel. It doesn't chip the gelcoat.

 

[eddystone]

If the grp is not very thick, a drum sander is very effective. Because it sands along the edge, it doesn't flex the panel. It doesn't chip the gelcoat.

I'll try that - the Dremel has attachments like a mini drum sander.

 

[penberth3]

I'll try that - the Dremel has attachments like a mini drum sander.

Remember you'll be making a lot of hazardous dust.

I'd use a coping saw with an abrasive blade, or a pad saw. Or as suggested refer back to Post #14 - fix a false centre behind the panel.

 

[Capt Popeye]

Might ask , is it a Blind Hole or an open ended hole ?

There are Hole Borers that are steped in incrimental sizes , they are sold with the Step Diameters stated ; they cut a better hole that a Drill becuse they are steped and tapered so cutting on more that two points = no juddering at all

 

[penberth3]

Might ask , is it a Blind Hole or an open ended hole ?

There are Hole Borers that are steped in incrimental sizes , they are sold with the Step Diameters stated ;......

I haven't seen one as big as 2 inches. Is there such a thing?

 

[Wing Mark]

I'll try that - the Dremel has attachments like a mini drum sander.

A drum sander set from screwfix or toadstation did it for me,
I was working on thin GRP, a single skin bit of a dinghy only 2mm or so thick.
Draw on it with felt pen, sand away material, job done.
If there were more to remove you could saw or chain drill most of it then finish with the sander.

But mostly, it's usually a game of using what tools are to hand within reason.
It's often quicker to do stuff the hard way than to go and buy more tools.

I do have one of those hole cutters with two hardened cutters adjustable along a bar;
Adjustable Hole Cutter 40 - 300mm
A great tool for certain jobs, but if things start going off-script, it quickly makes a big mess of things.

 

[anoccasionalyachtsman]

Remember you'll be making a lot of hazardous dust.

I'd use a coping saw with an abrasive blade, or a pad saw. Or as suggested refer back to Post #14 - fix a false centre behind the panel.

The piece of ply goes in front of the panel, and doesn't so much create a false centre as a false circumference into which the holesaw fits.

 

[eddystone]

Might ask , is it a Blind Hole or an open ended hole ?
It's an open ended hole but there is an air gap and then the thin GRP interior panel (also need to enlarge that to same dimensions) so can't really access the inner face. Coping saw wouldn't work and pad saw would probably make a mess of the edge.