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Cutting a large round hole

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petro1head21/11/2018 18:29:53
640 forum posts
116 photos

I need to cut a hole in some 2mm alloy sheets. Its for a computer as I want to add an extra 120mm fan.

I was just going to but a hole saw from screwfix **LINK**

Any advice ie should I sandwich between 2 pieces of wood

JasonB21/11/2018 18:37:28
16530 forum posts
1759 photos
1 articles

Have you got a boring head, could do it with that.

Neil Wyatt21/11/2018 18:41:34
16740 forum posts
689 photos
76 articles
Posted by petro1head on 21/11/2018 18:29:53:
should I sandwich between 2 pieces of wood

I would, then it should be easy.

Make sure it is well clamped, if it can move, it will.


petro1head21/11/2018 18:49:42
640 forum posts
116 photos

I have Jason but it not big enough

Cheers Neil

Andrew Johnston21/11/2018 19:08:04
4936 forum posts
560 photos

Mark the centre, scribe the circle with dividers, drill, saw, chisel the centre away, file to the scribed line. Shouldn't take more than 10 minutes or so in aluminium.


Edited By Andrew Johnston on 21/11/2018 19:08:23

petro1head21/11/2018 19:19:03
640 forum posts
116 photos

Jason, I think the hole saw option will be quicker and neater

Carl Wilson 421/11/2018 19:41:33
667 forum posts
53 photos
The hole saw option will be a complete dogs breakfast. Hole saws tend not to be especially round and you will end up with an oversize/oval hole.

The way to do this is to use an abrafile in a fret or coping saw. Mark it out with dividers then drill a small hole to get the abrafile in. Then saw out your hole.

Minimum amount of filing then required to achieve the final dimension.

Abrafiles are now sold labeled up as 'rod saw blades' I believe.
Michael Gilligan21/11/2018 19:48:21
14244 forum posts
627 photos
Posted by Carl Wilson 4 on 21/11/2018 19:41:33:

Abrafiles are now sold labeled up as 'rod saw blades' I believe.


Do you have a link to a reputable supplier, please, Carl ?

I have yet to find a decent modern equivalent to the original Abrafile.


Ian Hewson21/11/2018 20:02:23
259 forum posts
24 photos

The hole saw will cut a decent hole if used in a drill press and the plate clamped to a wood backing piece, I have done thousands over the years, usually freehand in a pistol drill.

The saw you link to will need an arbore to mount it though, a cost effective method would be the drill and file method.

Not a long job in aluminium.

alan ord 221/11/2018 20:09:19
71 forum posts

When I was making the splashers for my Pansy loco I made steel mig welded "cans / tubes" from 1.6mm thick steel sheet. The diameter from memory was around 5". I used a cheap treppaning tool in the drill press, clamped onto a sacrificial piece of wood on the table. Cutting half way through and turnoing over to complete the cut. Filed away the burs before going on to weld it to the rolled centre piece worked out well.

Should be a dodle with aluminium.


martin perman21/11/2018 20:10:09
1687 forum posts
70 photos

I smear tap/die lubrication which helps the hole saw work.

Martin P

Carl Wilson 421/11/2018 20:14:35
667 forum posts
53 photos
I've also yet to find an equal to the original abrafile. I have a small stock of originals that I use carefully.

I think the nearest equivalent now is a tungsten carbide tile cutting saw blade. Not as good as an original abrafile but should do a good job on the above.

A 120 mm hole saw is going to make a right mess.
JasonB21/11/2018 20:28:29
16530 forum posts
1759 photos
1 articles

You don't need a big head, just a tool out the side, this quick video was done for Ron in his boring head thread but I just used scraps of 2.5mm ali as an example.

Not a bad finish


Edited By JasonB on 21/11/2018 20:31:52

Edited By JasonB on 21/11/2018 20:46:06

John Rudd21/11/2018 20:29:20
1366 forum posts
58 photos

How about a tank cutter, treppaning tool?

JasonB21/11/2018 20:35:50
16530 forum posts
1759 photos
1 articles

If you don't know what a treppaning tool looks like it's the one bottom left. That would do the job too.

photo 49.jpg

Emgee21/11/2018 21:06:14
1267 forum posts
210 photos

The tool Jason refers to as a trepanning tool is probably what John and I call a tank cutter, originally used in an old fashioned brace, or very low speed power drill.


vintage engineer21/11/2018 21:17:02
199 forum posts
1 photos

You need a longer tool.

Posted by petro1head on 21/11/2018 18:49:42:

I have Jason but it not big enough

Cheers Neil

petro1head21/11/2018 22:44:57
640 forum posts
116 photos

Just had a look at the photos in the boring thread and now see what you mean. Will check my boring tool to see it the bit will fit the way. At the mo the tool bit points down

Edit:  yes it has  the tool it is triangular like this


Edited By petro1head on 21/11/2018 23:07:30

Marcus Bowman21/11/2018 23:02:22
162 forum posts

Bosch make hole saws with fine pitch teeth, specially for cutting holes in thin sheet metal. Not cheap, though.


Mike Poole21/11/2018 23:50:29
2187 forum posts
52 photos

The tank cutter type tool works well until you break through, i find attacking from both sides is helpful but you will probably still need to tidy up with a file. Hole saws seem to make a hole but holding to a size is not their strong point. If you don’t mind a bit of filing then jig saw most of the waste and file to size.


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