Cutting neat holes in sheet metal

[Dr.Al]

For my impending heat treatment oven build, I'm going to be making the control cabinet from scratch (rather than being sensible and buying a project box).

That's going to involve cutting lots of holes in the sheet metal (probably steel, but could be aluminium as I think I have some of each) for the various things to poke through. There will be quite a few push buttons requiring 22 mm diameter circular holes and quite a few other things requiring square/rectangular holes of various sizes (the smallest being for a mains toggle switch, the largest being for a PID controller).

I've been experimenting today with ways of cutting the holes (mostly in 0.8 mm steel, but I also tried some aluminium of a couple of different thicknesses and also some 3 mm steel). I'm struggling a bit so I'm after some advice!

My initial attempt was with a Bosch holesaw in a cordless drill, but that produced a hole that was a long way off round (I won't be able to do it in the pillar drill as the sheet will be too large).

My next attempt was with a plasma cutter, which I suspect is quite a good option, but I've never got to the point that I can get a neat cut when doing anything other than a straight line. I made some simple templates, starting with a plywood one with a 28 mm hole drilled in it (the tip offset seems to be 3 mm, so a 28 mm template should give a 22 mm hole). I kept finding the tip catching (preventing me moving it smoothly) and I also find it really hard to judge how fast to move the torch. Moving it smoothly in a circle seems to be rather challenging regardless of whether the tip catches. I also tried a 3D-printed template out of curiosity - I expected it to turn into a blobby mess, but it coped remarkably well. It didn't help me produce a neat circle though!

Cutting with the plasma cutter along a simple straight edge seems okay.

I'm not sure whether the problems are down to the sheer number of variables (current, air pressure, speed of movement, whether the tip is touching the metal or raised slightly above it, ....) preventing me from figuring out how to get a good cut or whether it's just that I'm completely inept when it comes to plasma cutting.

I'd appreciate any advice on how I can get a better cut of holes for things like push buttons, mains toggle switches etc, either with the plasma cutter or with something else (that I own!)

 

[Fintray]

Q-max punches may help.

 

[Wallace]

Q-Max cutters or similar brands.

 

[TEO]

Have you tried the TCT hole saws like this: -

20mm TCT Holesaw | CK (T3203 020)

I bought a set on AliExpress, thought I'd try them out then replace with decent branded ones once they wore out......years later they're still going strong

 

[Dr.Al]

Thanks both, those Q-Max things definitely look like they'll be a good option for the 22 mm round holes, but I still need to cut the other non-round holes, e.g. for these:

 

[Robotstar5]

I built panels for many years and always used a 22mm Starrett hole saw for push buttons.

 

[julianf]

I would, of course, cnc cut them all out of alloy, but, if i didnt have that option -

Id do the CAD. Id then add circles at the corners, and center mark them.
Id then print out the design 1:1 scale, and stick the paper to the job (eg spray photomount)
Id mark the centers, and drill
Id join up the drill holes with "whatever"
And file the corners as needed.

I cant cnc ferrous here, so, realistically, id just send the whole thing for lasering rather than mess about, but if i had to do it "same day" on ferrous, that is what id do.

 

[Wallace]

Thanks both, those Q-Max things definitely look like they'll be a good option for the 22 mm round holes, but I still need to cut the other non-round holes, e.g. for these:

View attachment 476448

You can get punches to do those switches but can be expensive. How many are you planning on fitting? If only a couple tgen hole punch and file would be my choice.

 

[cheb]

You can get non round Q max cutters, I've a d shaped one in a box somewhere. You might baulk at the price though, they were never cheap.

 

[Dr.Al]

You can get punches to do those switches but can be expensive. How many are you planning on fitting? If only a couple tgen hole punch and file would be my choice.

Only a couple. There are quite a few holes to make, but they'll all be different sizes, varying from 92 mm square at the upper end (for the PID controller) down to something like a 20 mm × 7 mm rectangle at the smaller end.

You can get non round Q max cutters, I've a d shaped one in a box somewhere. You might baulk at the price though, they were never cheap.

Given there will be a lot of different sizes and I'll be making one hole of each size, it really won't be worth paying for a cutter for each hole unfortunately. The 22 mm round one will be useful as I have a lot of push buttons, it won't make sense for the others.

 

[Kram]

For thicker material a carbide burr in die grinder can work well, or a mounted stone, are good for finishing holes, along with some fine smooth files.

Nibbler drill attachements are great for removal, but then so is plasma. Both need a bit of practise and care to control.

I find for holesaws, its best to drill a pilot hole first and swap the pilot drill out for a 6mm or 1/4" HSS lathe bit to guide it.

Most insert switches and components will have a lip so that you wont see the cut edges.

If you use alu, anodising is a time consuming but worthwhile proccess.

 

[Dr.Al]

Thanks Kram

For thicker material a carbide burr in die grinder can work well, or a mounted stone, are good for finishing holes, along with some fine smooth files.

A die grinder is one of those things I mean to get one day but haven't quite summoned up the need!

Nibbler drill attachements are great for removal, but then so is plasma. Both need a bit of practise and care to control.

Any tips on how to improve my technique with plasma? It's hard to practise when you don't know what's wrong - is it the current setting, the air pressure, the speed I'm moving, the distance of the tip, something else???

I find for holesaws, its best to drill a pilot hole first and swap the pilot drill out for a 6mm or 1/4" HSS lathe bit to guide it.

Thanks

Most insert switches and components will have a lip so that you wont see the cut edges.

Believe me you will see the cut edge if it's cut as shonkily as I've been doing with the plasma cutter today

 

[E T]

Do you have a mill and would that panel fit on the table?
You could then mill the rectangular and square holes and do the round ones with a good holesaw or annular cutter.

 

[MattF]

kept finding the tip catching

Catching on what?

 

[Dr.Al]

Do you have a mill and would that panel fit on the table?
You could then mill the rectangular and square holes and do the round ones with a good holesaw or annular cutter.

I have a mill, but there's no way the panel would fit on the table.

 

[Agroshield]

Providing the diameter is correct, step drills are good in sheet metal:

https://www.screwfix.com/p/erbauer-step-drill-bit-6-36mm/5911v

As above, the carbide hole saws are better than the hacksaw-wrapped-into-a-circle type.

For the rectangular ones, drill a central hole and use a carbide endmill in a trim router. Use this style of jig to constrain the size:

Router Template Jig

The Router Template Jig is a woodworking tool used with a router to guide the cutting path of a workpiece. This high-quality jig is constructed from durable 8020 extrusions, providing a stable and rigid base for precise routing operations. The jig's base plate comes in 950x700mm, 700x500mm...

benchdogs.co.uk

I thought your woodworking these days was all hand tools, so what is wrong with that approach to metalwork? Scribe the lines, drill central hole, file to fit.

 

[Dr.Al]

Catching on what?

I think it's the molten steel from where the cut starts.

 

[Dr.Al]

Providing the diameter is correct, step drills are good in sheet metal:

https://www.screwfix.com/p/erbauer-step-drill-bit-6-36mm/5911v

As above, the carbide hole saws are better than the hacksaw-wrapped-into-a-circle type.

For the rectangular ones, drill a central hole and use a carbide endmill in a trim router. Use this style of jig to constrain the size:

That's an interesting idea; I don't think I ever would have thought to use a trim router on steel.

I thought your woodworking these days was all hand tools, so what is wrong with that approach to metalwork? Scribe the lines, drill central hole, file to fit.

Cutting a piece of wood with a chisel is a pleasant thing to do. Filing steel isn't! I've never aspired to hand-tool metalwork as it just feels like a chore. I don't mind the idea of a bit of filing to tidy up an edge, but filing to shape sounds horrible (especially on a relatively large piece of sheet that'll be very hard to clamp near the hole and hence will make a horrible sound when filing).

I know I can resort to that if I'm desperate, but having bought a plasma cutter I was hoping there would be an easier way

 

[MattF]

Are you holding the tip flat on the sheet, or at a slight angle? Drilling a start hole rather than plunge cutting(?) a start with the cutter?

 

[Brad93]

Are you holding the tip flat on the sheet, or at a slight angle? Drilling a start hole rather than plunge cutting(?) a start with the cutter?

This. All day long, always drill on the **** to begin with