Thread: Ways to Make Slots in Sheet Metal or Plastic

Originally Posted by kibble

Having a variable speed rotary tool doesn't compare to a fixed speed one. Get yourself one, you'll be glad you did!

The Ryobi seemed like a great compromise when I found it. I've had excellent service from all my Ryobi tools. But this rotary tool is struggling to find its place. I think you've highlighted a major weakness in its lack of variable speed, and it may force me to get a Dremel-branded tool.

There are a couple of other reason to get the Dremel brand. At Home Depot, I saw the #220-01 WorkStation mount for Dremel tools that looks really slick. There's also the Dremel #231 Shaper/Router Table, which might be a nifty slotting device.

There may be a Dremel in my future.

Originally Posted by kibble

Post some pics after you try it out! I'm curious to know how it works out for you.

Punch Testing

I've been playing with the Deep Throat Metal Hand Punch from Harbor Freight. It appears to be a knockoff of the Roper Whitney No. XX seen on this page. If the tooling for the Roper Whitney model fits this tool -- and pictures suggest that it might, then this tool may be able to punch slots. So far, though, I've only punched round holes.

I'm glad I bought the base; it makes it easier to use, but it needs to be mounted to a board; without it, the tool just tips over onto its nose. I attached the tool to the base, and the base to a piece of 5/8" plywood 5" x 8" with some 1" screws and fender washers. I didn't do any finishing to the base board other than file the edges to knock off the splinters. Here's how it looks mounted:

Click images to enlarge.

For size reference, the slot on the depth gauge is 3" long.

The manual assures us that everything we need is included, but there's a 2.5mm Allen wrench needed to tighten the set screws; it's not in the box, nor is it on the parts list. If you go to Harbor Freight to get this, buy a set of metric Allen wrenches at the same time.

I installed the 3/16" die set. I tried the punch on scraps of the types of steel I've been using for parts -- some .022" galvanized steel, an old computer case (.028" steel powder-coated on both sides), and some .031" stainless steel. The punch went through all of them. The force required depended on the material. The painted steel was easiest, probably because of the paint acting as a lubricant. The galvanized was almost as easy. The stainless steel was tougher, and I don't think I'll want to use this punch on that material. The stainless steel may have dulled the punch in a single use, because holes were just a little tougher after that. I confess that the instructions say "mild steel", and stainless isn't mild steel. Any damage done to the die set is clearly my fault for pushing it beyond its specified use. But that's just what research does.

There's a locator point on the tip of the punch, so I can locate holes precisely; once the punch is positioned, I just a push on the lever arm, and I have a hole. "Push" means "apply some pretty healthy pressure".

Here's a picture of the resulting holes in the test pieces:


The material on the left is .031" stainless steel; in the center is .028" powder-coated steel; on the right is .022" galvanized steel

I also tried punching 1/8" polyethylene, and it did just fine. The hole was smooth and very clean.

The dies come grease-coated and packed in clear wrap, which makes me suspect they need corrosion protection in the humidity of south Florida. I made a small container for them in my tool chest and I'll keep a grease rag over them so the atmosphere in the box is oily air.

The punch takes more initial setup than just slipping a drill bit into the drill press. But if I'm using a standard size hole -- I generally use 3/16" -- then I can just leave the punch set up with the 3/16" die set in it. It can sit on a lower shelf, ready to pull into action whenever I need holes.

I like the cleanup; there isn't any. I guess when I've punched enough holes, the slugs will start to fall out of the bottom of the die, but that's still almost no mess. I'll brush a little dab of grease on the punch and the die when I'm finished each time to keep them lubricated and rust-free.

If I just use it to make the holes at the end of slots, it's an improvement over drilling. The resulting holes are very clean and smooth-edged, and don't need any filing until final cleanup of the parts.

I made a quickie bracket for a temporary system I was building, and needed holes in a piece of bent sheet metal. I marked the holes with a center punch, stuck the metal in the punch a couple times, and BAM!, BAM!, there were holes, perfect holes, right where I needed them, with no finishing required. I've never made holes so quickly and easily in my life. Oh, I like this tool.

The verdict so far? While this is a handy tool for surprisingly low cost -- especially on sale -- it isn't the total answer to making slots. With the standard tooling, I'll still have to use the cutoff tool to complete the slots. The punch makes the process easier, but it doesn't produce instant slots, so I'm not ready to call it the "solution".

If it can accept the Roper Whitney tooling and punch slots, it could be the answer I wanted. I'll research that this week.

Even without that capability, it's a keeper.

Originally Posted by kibble

Hmmm I like the fact that it's not messy like drilling stuff. I may get one myself! Another thing I don't like about drilling is that the holes are sometimes not really 100% round because of the way the drill bit bites into the material.

I've punched enough holes with it that the slugs are falling out of the bottom, now. They just drop onto the workbench. When I'm done with the punch, I put it away and sweep the slugs into the metal scraps bin. I wish all my tools were as neat and easy to clean up after.

Hurry, if you're going to get one on sale -- it ends July 22, I believe. But, even at its full $37 price, this is a really good tool, terrific for quick holes. And, now that I'm used to it, changing the punch only takes about a minute.

I still have to check on getting the Roper Whitney slot punch and die to see if they fit.

If you can use plastic, a router would be the way to go. Simply clamp a straight edge to your piece and plunge a router bit in to make the slot. You might even be able to do it with metal if you found the right bit.

Originally Posted by golfguy

If you can use plastic, a router would be the way to go. Simply clamp a straight edge to your piece and plunge a router bit in to make the slot. You might even be able to do it with metal if you found the right bit.

For plastic, a router would be good, but mine is a single-speed router. I'd need to control the speed so the tool doesn't melt the plastic; just the friction between the spinning tool and the material would cause melting, so the tool couldn't stop until it got to the end of the cut. That makes a variable-speed Dremel-type tool seem pretty attractive.

I guess a mill could do both the plunge and the slotting in steel, but it would take some experimentation with material that thin. I'd also guess it would demand pretty low plunge and travel speeds to keep from bending the sheet metal.

What About The Nibbler?

I'd been wondering if there isn't a way to make my air nibbler function as a slotting device. Using it hand-held doesn't give me much more accuracy than the cutoff wheel. I thought maybe mounting it in a frame and providing a deck to slide the parts on -- similar to what we have with a drill press or a table-mounted router -- would be good. Since I have a universal table like that, I thought I'd see what it would take to make it work with the nibbler mounted to the bottom of it. But then I remembered two things:

Attack Chips
The downside to the nibbler -- in addition to the high noise level -- is the nasty little crescent-shaped chips. I can't use the nibbler unless I'm wearing boots in the shop, because those chips are like little curved double-ended daggers. They stick to everything like cockle burrs, and they're easy to track into the house on the bottom of my shoes. Despite brushing my clothes off and taking extra time to clean my boot-bottoms, I've found a few in the carpet with my bare feet, and it was definitely exciting. The nibbler is a tool that I almost think should be used out on the lawn, so the little chips will just sink down and add iron to the soil instead of adding daggers to the carpet. If I flip it upside down and mount it under a work table, I suspect it means I'd be getting a faceful of those chips. That would be a deal-breaker.

Big Hole
The other downside: the entry hole has to be large enough to get the tool through, and that entry hole is wider than the slot I want. That's another deal-breaker.

So never mind the nibbler . . . I'll focus on the punch.

Slot-Making Update

This was posted in my worklog, but pertains to slotting, so I've duplicated it in this thread.)

Originally Posted by monkeyracer

I really think that a slot punch would be the way to go, but I just can't find one online. I thought I saw one on Harbor Freight, but it's not where I thought, and searching brought up 1000 results.

I found a terrific punch at Harbor Freight, but it's only for round holes. The punch -- at list price -- is $35 with the stand.

(I reviewed that punch in post #13 of this thread. Pictures, links to it, and results are there.)

I really thought it was going to be the answer to this slotting thing, once I got a slotting punch and die set for it. Then I called Roper Whitney to ask about prices. Hoo, boy! The only stock slotting punch and die set is 1/4" x 7/16", and it's $140.40. They custom make anything else for a few dollars more; the slotting punch and die set I'd want, 3/16" x 1/2", is $147.80. I just wouldn't use it enough to justify that expense for the low-volume stuff I do.

I'll keep on using the punch for round holes. It makes sheet metal work soooo much easier. But when it comes to slots, I'll use the punch to form the end holes and keep on using the cutoff tool to cut out the metal between them. As much as I like the idea of instant slots, I'm just not willing to pay that price for them.

Originally Posted by monkeyracer

I think if it's a low run project, you might search for waterjet cutters nearby and see how much they would charge.

A search on google maps using keywords: "waterjet loc: Palm Beach Gardens, FL" came up with 73 results.

The place near me charges a minimum $60 per job, but if you're buying milling attachments and hand press punches for a little less, you might as well just cough it up and have it come out exactly perfect. Your cutter might have a lower minimum. Usual tolerances are as low as .01 inches. I'd say have them slot it and cut it, then you can bend it (some shops will bend for a couple extra bucks.)

I'm totally into DIY, but there are some things that are just not worth the effort.

I'm into DIY, too. I like to do the tinkering. For most of what I do, I'm experimenting with sizes and shapes right up to the last part I produce, and my car is a drivable prototype; every modification is a one-of-a-kind or two-of-a-kind thing.

Once I've solved the problem, I want to move on to the next challenge, not make a bunch more of what I just did. Taking the time to get the designs into a CAD program and get them produced on a waterjet is simply too production-oriented for me. I'd just as soon turn it over to a production shop and go on tinkering. I've had some requests for duplicates of my parts, so I'll keep that waterjet process in mind.

ah... I just wish I had a shop. I end up in a lawn chair working on top of my dogs kennel on the apartment balcony. saving for a garage with a house attached!