Enlarging Holes in Thin Aluminium

All, The final thing I need to do on my 10V is enlarge the pilot holes on the aluminium cylinder cladding, to suit the drain cocks and exhaust stub.

I ordered a 4mm -12 mm step drill (1 mm increments) becasue I need 6 mm and 7 mm holes. I could only find a 1 mm increment step drill for a resonable price from Cutwel. They have now told me they cant get it until mid November, so I cancelled the order.

There must be an alternative way of enlarging these pilot holes. One hole is on a flat part of the cladding, the other two are on the curved part. I'm worried that sequentially drilling the pilots will cause grabbing and ruin the job.

Any suggestions?

Abrasive paper wrapped around a tapered stub and spun in a Dremel?

Thanks.

I don't know where you've been searching but I've looked on Arc's site and found one there and there's more than you can shake a stick at on another site. For around a fiver, if you want. Can't vouch for the quality, mind, nor give you a link, sorry.

John

A round needle file?

There are tapered reamers specifically for enlarging holes in electrical panels. You could try someone like RS Components.

It's a shame you can't give a link becasue I can't find any step drills on Arc to the specification I mentioned.

Bought a set of 3 step drills (3mm to 22mm ) from Lidl recently for £3.99 - even if they are carbon steel, whilst they claim to be HSS, as is often claimed by Chinese tool manufacturers (I think some of them think HSS means it's High Sulphur Steel! ) they will certainly cut aluminium - even L72 grade.

Yes, I guess so, but I'd like a very clean-edged hole, concentric with the pilot, and I'm not that good at filing.

1 mm increments?

You could use a cone drill bit.

This set is from Screwfix:

**LINK**

Seems to work ok on thin sheet.

Stuart

That sounds like an option - are they likely to grab the metal, or do you just turn them slowly by hand?

Thanks

You don't say how thin the aluminium is, but would a hole punch be a suitable method? I've made some in various sizes to punch bolt/stud holes in gasket material and found they work just fine on shim brass so maybe they would work on thin aluminium sheet too?

Thanks Stuart. That's an option, although I suppose like the reamer, it will leave a tapered hole.

It's a mm or two, so too thick for that really. Plus I'd have trouble getting the punch concentric with the pilot.

Comwell: 4mm - 12mm 9 Step- 4-12mm 9 Step

How thick is this cladding? I would sandwich it, for support, and cut with an end mill if the material is flat. If really thin, a hole punch would suffice - the way I cut holes in gasket material if unsuitable for cutting with a ball bearing or small ball-pein hammer.

edit to say I’ve since seen the last couple of posts🙂

Edited By not done it yet on 13/10/2020 12:18:59

Posted by Oily Rag on 13/10/2020 12:04:56:

Bought a set of 3 step drills (3mm to 22mm ) from Lidl recently for £3.99 - even if they are carbon steel, whilst they claim to be HSS, as is often claimed by Chinese tool manufacturers (I think some of them think HSS means it's High Sulphur Steel! ) they will certainly cut aluminium - even L72 grade.

1 mm increments?

3mm to 12mm in 1mm increments then 14, 15, 16, 18, 20 & 22mm

Thanks, but two of the holes are on a curved surface.

That would have been fine! Can't see it available now though.

Thanks - that looks like a good candidate. I'll give them a call - they're only 20 minutes away.

You can also just plunge cut with a milling cutter, 3-flute would be mu choice but 2 or 4 will be OK as you already have a pilot hole