Punchin' holes in METAL!

I know some of you folks work with metal a lot so I figured I'd ask here.

I recently purchased a vintage hi-fi amplifier. It needs a little bit of restoration, but at least its complete- except for the bottom cover. Chassis parts for vintage hi-fi are hard to find on their own. Since the bottom plate looks like a mostly flat bit of metal with a 90° lip on one or two edges and some mounting holes and vents it should be simple to make one. However, the problem may be with making the vent slots. What would be the best way to make those? A fellow GRMer suggested some kind of die punch attachment for his hydraulic press, but so far I haven't found one (am I using the wrong search terms?).

The below picture is of a similar amp's bottom plate. Also, those two big holes at the lower right corner aren't part of the original design and I don't know why those are there.

How pretty do they need to be? That size slit looks perfect for gentle application of an angle grinder.

I'd say drill holes for ends of slots, connect dots with a dremel, and file by hand to perfection. Go slow.

i think the project binky guys did the die punch thing, though they did mention something about making the dies with a CNC machine, so it might be a bit out of reach.

milling machine or edm

I would drill two anchor holes to mark the ends of the slot.

Then I would use a piece of flat bar on either side clamped to the tin to mark the edges.

Then I would drill a bunch of holes along the length using the flat bars to keep methe drill bit in line.

Then I would finish with a file using the flatbar as a guide.

Or just look up your local waterjet or laser cutter and pay $200

Plasma CAD cutter or water jet.

I don't think it's critical they are slots, a few rows of holes in the same places of equal or greater area should be fine.

Thin metal I'd clamp a couple boards on each side for guides and use a router with a carbide bit.

Shotgun

Rotozip bit in a drill press?

Plunge cut with a router bit?

Cut a square (Drill holes + jigsaw?) and use 1/4" "hardware cloth" to cover the opening?

KyAllroad wrote: Shotgun

Maybe .308 :)

Bend the ends in a brake and then cut holes with a jig saw after drilling a hole in each corner (big square hole). Cover the hole with this or expanded metal. Metal shops carry t, could be found at hardware stores and some craft stores.

NOHOME wrote: I would drill two anchor holes to mark the ends of the slot. Then I would use a piece of flat bar on either side clamped to the tin to mark the edges. Then I would drill a bunch of holes along the length using the flat bars to keep methe drill bit in line. Then I would finish with a file using the flatbar as a guide.

That's how I was taught to do it in metal shop and in the sheetmetal part of the airframe portion of my A&P. Smaller drill bit just inside the lines connecting the end holes, file or hacksaw blade through the holes then file to the lines. Take your time.

codrus wrote:

KyAllroad wrote: Shotgun

Maybe .308 :)

Or my new favorite toy, a 6mm Remington.....

NOHOME wrote: I would drill two anchor holes to mark the ends of the slot. Then I would use a piece of flat bar on either side clamped to the tin to mark the edges. Then I would drill a bunch of holes along the length using the flat bars to keep methe drill bit in line. Then I would finish with a file using the flatbar as a guide.

914Driver wrote: Bend the ends in a brake and then cut holes with a jig saw after drilling a hole in each corner (big square hole). Cover the hole with this or expanded metal. Metal shops carry t, could be found at hardware stores and some craft stores.

I like these two ideas the best. This plate doesn't need to be factory-exact but I don't want it to look slapdash either. I even have a couple of pieces of that mesh that would work with 914Driver's idea. Thanks all!

Steel or aluminum? A little manual nibbler might work pretty well if it's light gauge steel or aluminum. Heavier stuff you could use an air nibbler.

https://www.amazon.com/Cables-Go-29524-Discontinued-Manufacturer/dp/B0001QNM7G

Those are formed with dedicated tooling on a sheet metal turret punch. Like so many things, it takes seconds to make each of thousands, but is infinitely harder to make a single one. That's why prototyping is so damned expensive, and why I do a lot of prototype work. Specialized skills=specialized money.

If you want obrounds like the part in the picture - ovals with radiused ends - the easiest way it to find someone with a vertical milling machine to chew them out for you. The pain in the ass is if it's larger than the work envelope, the part will have to re-fixtured one or more times, and big flat things are hard to hold down - they try to climb up the endmill and chips get underneath. It's harder than you'd think.

If it doesn't have to match, get a Uni-bit and make lots of holes.

All this and no one has said "laser"

Seriously draw it up in CAD, make a DXF file, call around to a few local fab shops. Should be able to get it done all in for around $100, less if you know a guy.

My first thought was to use a louver punch or stop by the local hot rod shop and have them punch it. Louvers would either protrude above or below then panel though and you may not want that.

93gsxturbo wrote: All this and no one has said "laser" Seriously draw it up in CAD, make a DXF file, call around to a few local fab shops. Should be able to get it done all in for around $100, less if you know a guy.

This is the easy option, not the cheapest but the easiest and it will look best.

Look into waterjet cutting services, you can usually ship them a file with specs and mail order, even if its a one off.

Can't speak to any companies, but 3 seconds of google

https://www.bigbluesaw.com/

http://www.emachineshop.com/machine-shop/Waterjet-Cutting-Service/page92.html

http://www.fedtech.com/services/waterjet.html

We used to have brake rotors made for our FSAE car via waterjet as well as tons of tabs and other parts. Works a treat.

There are also services who could do the same with laser or plasma.