Thread: Ways to Make Slots in Sheet Metal or Plastic

Originally Posted by kibble

I just do what you do but I make the openings a tiny bit smaller than actually needed. Then I get a smooth file and carefully remove material until I get it to the size/shape I want. Haven't come up with a better way to do it without the big tools, yet. :-(

I agree. My standard technique in metalworking is to go a bit oversize, and file to the dimension I want. On holes, I go undersize, like you, and file to the size I want. A set of miniature files makes the fine work a lot easier.

Originally Posted by Bazza_84

is there no way of getting a punch style tool put ur work in a vise, place the punch where you want it then either press it or the prefered meth of bang it with a hammer

not got to this stage yet, just an idea

The problem with most of those manual techniques is aligning the punch and the die well enough that we don't destroy one or the other when we tighten the vise or whack them with the hammer.

I did search for "sheet metal punch", and I ran into some light duty portable punches, like this $24 hand-held punch from JC Whitney. It looks very similar to this punch from BrandsOnSale.com. Neither company lists the source, but they appear to be like units from Roper Whitney, which has a webpage here showing punches and tooling, including slot-forming tooling, plus a low-cost bench-mounting base for the portable punch. This could be a pretty good alternative to hand-forming. Roper Whitney lists the price on the punch as $55, the kit with tooling and a case at $80, and the base at $28. I couldn't find a price on slot tooling, but their price for a 3/16" round punch and die set is $11.

**EDIT:

I modified the text to show that the punches from JC Whitney and BrandsOnSale.com are NOT from Roper Whitney, but are apparently copies. There's no way to know if Roper Whitney's slot tooling will work in the knockoff tools, so it's probably best to just buy the Roper Whitney tool if we buy this to make slots. The slot tools are available from Roper Whitney distributors.**

More on Punching Tools

The sheet metal punches seem like an interesting approach for making slots, especially if slotting dies are available. The Roper Whitney tool can definitely punch slots, but it's not a low-cost solution. I don't know if the tools from JC Whitney and BrandsOnSale.com can use the same die sets as the Roper Whitney tool. Until I discover otherwise, I'll have to assume they're just good for punching round holes.

But, even if the punch only produces round holes, it has advantages of over the drill for making the end holes; it's quieter, produces a cleaner hole, and leaves just a slug for waste. I could still use the cutoff wheel, or perhaps a series of overlapping holes could be filed down to make a slot.

I did some more research on the WWWeb, and we can add to the list of similar tools the larger 3-1/4" throat depth Deep Throat Metal Hand Punch from Harbor Freight, which costs $25. The base for it is $10. That looked like it could be a $35 solution, plus the cost of shipping.

It's interesting how things work out. I happened to be close to our local Harbor Freight this afternoon, and went in to see what they had in stock. Their Deep Throat Metal Hand Punch was on sale for $18, and the base for it was on sale for $5. I just couldn't pass it up.

I'll test it this weekend.

Originally Posted by Curiosity

For metal, I'd try another piece of metal with a straight edge as a guide and clamp it on, cut along the edge with a dremel. Thin aluminum might work as a guide for plastic that's curved, but molding a faceplate in might work better for small things like memory cards, and you can mess it up more.

Actually, I was referring to slots in sheet metal parts, where I think you're talking about slots in bezels and the like. But you bring up an interesting point: it may be possible to simply build a bezel without worrying about slots, and machine the slots and edges of the openings we need. I hadn't thought of that, and I think I'll try machining edges and slots in my bezel plastic to see if that's a possible production path.

I suspect the high speed of the Dremel-type tool might simply melt the material. A lower speed, as with a mill, might do well. Because the material is soft, a drill press could probably be used to mill plastic without tearing up the drill press bearings, but I think it would add a lot of side load on bearings not designed for side loads.

The "Dremel" that I have is actually a Ryobi 18V system. It works well, but isn't mountable like a true Dremel, and there's not a flat surface to run along a guide. An inverted Dremel in a work table might be a good idea. The way those little whizzers throw chips, though, I think I'd like to build a clear shield into the system somehow, or wear some really good goggles.

I've also wondered if I could run a milling tool in my router -- mounted upside down under a work table -- to make slots. My router operates at a single high rpm; I'd have to bring it down to the proper rpm for plastic or metal milling. Also, I don't know that its bearings -- which handle sawdust just fine -- are set up to handle hot metal fragments. When I was only thinking of sheet metal work, I couldn't easily resolve either issue, so I abandoned the idea. I might have to revive it for machining plastic, if I could control the speed.

I want a better way to form slots because I want to take less time and less effort, and I want better slot quality and consistency.

But one of the secondary reasons is that the current method involves lots of metal chips. I was wondering if there's a way to do "instant" slot forming -- like punching -- that only produces a slug, or a few slugs. I end up having to take off my shop shoes every time I walk into the house, because I don't have a housekeeper (except me), and I'd rather work in the shop than run the Roomba or a mop. If I can make less mess, I'll get more done because it'll be easier to clean up after myself.

Originally Posted by kibble

They actually have some wheels that are made to cut through plastic. They look like the big metal cut-off wheels. I use them myself and they work pretty well, but you have to make sure to not stay in one area too long or it will start melting the plastic.

I'd bought a kit of Dremel tools, and there's a mini-sawblade in there. But I was thinking of something more akin to a milling head, where we could simply machine a slot in the face of a plastic bezel. That would save a huge amount of finishing time. I believe the primary issue will be matching tool speed to the material; the softer the material, the slower we'll want to run the tool. Controlling the tool speed is probably easier in a 110V machine than a battery-powered one like mine, so I may have to invest in another Dremel-type tool (for research purposes, of course).

Unfortunately, I'm going to have to delay experimenting with plastic machining, because I'm leaving in the morning for an unexpected week or more on the road.

The good news is that today I got pictures of the punch and its results, and I'll get them posted as soon as I can write it up. I use GMail and Google Docs, so everything travels with me. Shouldn't be more than a day or so . . .