Cutting square holes in sheet metal (small run)

[fireberd]

Years ago, when I was building homebrew ham radio equipment, I used to use Greenlee "chassis punch" to make holes. I don't know what they have now but they used to have various types including square punches.

[jrides]

Seems like my part would be thicker than what I remember for Ham radio cases, but I might be wrong. I will start digging around to see what might be available. I didn't even consider DIY to be honest, since I'm looking tor decent precision. There might be a homebrew way that doesn't take too long, I suppose.

Thanks

[Lotus 7]

Greenlee and others like Simplex make square and rectangular punches in various sizes from about 1/2 inch to as much as 3 inches. If you need a hole that happens to be one of the standard sizes, that may be a possibility. However, those are high-quality production punches and are not cheap these days. A single Greenlee can cost between $100 and $ 300 with a nice set costing $900. Simplex punches are even more. Those punches require that a pilot hole is first drilled and the punch is then assembled onto the piece of sheetmetal. I have round Greenlee punches in (10) different diameters, but could never justify the cost of the square ones for their limited use. For the occasional time I need to make a rectangular or square hole, I use a round punch and then a "nibbler" tool to make the "corners".

That sort of DYI construction is great for a "one-off" job, but would be very time consuming for a run of 48 or 100 pieces.

Custom sizes can be specified for the chassis punches (also called "knock-out" or "panel-punches") but for a very small run of 48 pieces would be extremely expensive.

A alternative to using a mechanical punch would be to find a local waterjet cutting shop. There are shops that do this everywhere - just do a search for "custom waterjet cutting", or use an on-line service. Waterjet cutting is very fast, precise and its possible to cut many layers of sheet metal at the same time. There is a up-front, one-time programming cost, but the cost per part would be low. Waterjet cutting would probably be less expensive and faster than having the work done on a CNC machine, but you would have to get quotes to be sure.

[ritelec]

Yes greenlee makes a "square punch" plus the tool will set you back a bit ($$$).

Thinner than a dime? Two or four drilled pilot holes. Tin snips or sawzall..

To wrap the cut edge (if the design could go that way) something like this slides over and squeezes over the cut metal.....


It's the stuff you see on exposes edges on car doors and trunks...


Auto Moldings - Trim-Gard

[jrides]

I think I misrepresented the piece with the sheet metal description. Its a small metal paet about the size of a ruler, with top and bottom bends to fit on the designated area. Still metal though. Mentally, I had come to terms with spending 1k on the cuts already. If I do it on a part that is already painted, which (if any) method would damage the existing finish the least? Touching up the edges only would be ideal, rather than having to repaint.

Depending on the cost, it might be worthwhile to find someone with the punches, and hire them trouble do it. Might be worthwhile for both. I'm really interested in the waterjet solution though, as I would like it to be precise and look as fprofessional as possible.

Thanks guys. Some good basic info here. I have some research to do.

[BJosephs]

Assuming you are not going to go with a DIY option, here is some of what you would need to consider if you are going to approach a fabricator.

If this is a pre-made piece (I'm picturing a small flat plate with mounting holes like a the end cap for an enclosure) then most laser/CNC punch options are out already because they typically load up a full sheet of stock and cut every edge at one time, they have no built in system for mounting and cutting a smaller piece with any accuracy. We have a laser that we use to cut option ports into PCI brackets but you need good fixturing if the the relationship between the new cutout and the old has to be accurate and/or consistent from piece to piece. If you go with a pre made blank and want cutouts added (Typically we refer to rectangular holes as "windows" ) then a CNC mill is a good option. However, no CNC mill can make perfectly sharp corners (Because end mill cutters are round) so you would need to specify a minimum corner radius - typically the larger the radius the shorter the cycle time so look at what needs to go through the window and find out what allowances can be given. If the object coming through is truly square consider the option of making the cutout oversize with small radii or maybe a dog-bone readies... I don't know because I don't know what is being installed. Even if I was sure I knew it's still hard to explain without pictures.

If you can have a fabricator do them from scratch you should think about the following things:

Do you need a specific material? Lasers are less effective in aluminum and copper alloys because of reflectivity so, if this part needs to be aluminum, you may want to find a shop with a Turret Punch.

Do you really need a specific thickness? Thick steels are tough on punches but a good laser (2 to 4 Kw) can cut through them like butter. A thinner steel (less than 1/16" ) would be doable on a weaker laser like a 500 watt machine.

What are your tolerances? Loose tolerances always lead to cheaper parts but there are diminishing returns in some cases. Almost always on a Turret, laser, or CNC if you are cutting all the features at once the hole-to-hole precision is excellent - meaning larger allowances will be less attractive as the tighter ones are no challenge) but; a Turret punched cutout with a larger allowance would be smart as it might allow them to use a stock punch for you your project instead of buying one just for you (Our rectangular punches cost about $200). If you are adding features on a CNC the final position of your cutout is most challenging (not necessarily very challenging but likely the cost driving factor) so a ledger tolerance would be better. If you're soldering wires by hand you should be liberal here, if you need to line up a PCB your may need +-.005".

Like I said, lot's to consider.

Based on your quantity I would avoid any process that requires tooling or fixturing. You may find that a good laser house could make 50 pieces like this from scratch cheaper than a CNC mill shop would add your cutout to a prefabbed piece. The laser option will allow close tolerances on size and location (+-.005" would be standard, allowing +-.010" might save you some money). If you tell the shop you are flexible on the alloy and exact thickness they may have something in stock that will save you money.


Sorry, if that creates more questions than answers but you got me going.

-Brian

[jrides]

No need for apology Bjosephs. Any info is good at this point, as I know very little about the process. You brought up some good points. It is a USB plug on a plate that will be mounted behind the hole, not through it. A couple of holes will have to be drilled to mount the plate / bracket. Thought about having a new part made to my specs. Thickness is not a huge issue I don't think. Needs to be close enough to the original to make it fit. Laser may be an option. Tolerance will need to reasonably low not perfect.

Lots of things to consider.

[BJosephs]

Another thought: Do you have a finish in mind? If you had something in mind (like needing to match surrounding material) then it might narrow down your material selection... Or likewise, if you picked carbon steel for ease of laser cutting, you would have trouble matching to an anodized aluminum surrounding and you'd want something that prevents corrosion like powder paint.

Assuming your still considering a a custom part, do you want help with coming up with a drawing package? It would help in getting quotes if you had a fully dimensioned detail drawing and a 3D model. I have access to good software at work and this would be a small task, pm if you like.

Sent from my ADR6350 using Gearslutz App

[jrides]

Originally Posted by BJosephs

Another thought: Do you have a finish in mind? If you had something in mind (like needing to match surrounding material) then it might narrow down your material selection... Or likewise, if you picked carbon steel for ease of laser cutting, you would have trouble matching to an anodized aluminum surrounding and you'd want something that prevents corrosion like powder paint.

Assuming your still considering a a custom part, do you want help with coming up with a drawing package? It would help in getting quotes if you had a fully dimensioned detail drawing and a 3D model. I have access to good software at work and this would be a small task, pm if you like.

Sent from my ADR6350 using Gearslutz App

Definately will have to match existing paint. You have put forth a very generous offer sir. I may take you up on it. Its a bit early right now though. Still need to work out the placement of the cuts.

Thanks again for your help.
Thanks to all you guys for your ideas!