Radiused edges on holes in sheet

Hmm ... how mild is the steel? If mild enough, you might try starting with a smaller hole (e.g. about 1/8"), and swaging it with a punch into a die to make the 1/4" hole with a tubular projection on the other side, and then use another punch from that side to roll it into a one-sided eyelet. It would wear better than the copper tubing eyelets, I think, and give you a larger radius.

And to polish it, you might consider burnishing it once formed, with a rotating hardened tool of the proper shape.

Good Luck, DoN.

I just got hold of a few of the plates, I mis-remembered them slightly. They are roughly 18ga but there are 8 holes per plate and they're 1/8".

Sort of blows the grommet idea out of the water. Oh well.

I think the plates were tumbled originally, the edges are not 'sharp' per se, but neither are they rounded.

Also, they are bent slightly but not uniformly ( >>>>>>> change the 'DOT' to '.' to email me

If you want to radius the edges on each side, a corner rounding end mill is the tool to use, if the pilot fits the holes. The smallest that I know of has a radius of 1/32. 18 gauge steel is what, about .0478"? You'd probably need a

For something that thin, deburring by hand followed by a quick pass with a wire brush or flap wheel should be adequate.

If you do want to use a powered cutter, you might think of something along the lines of an aircraft countersink. The stops are adjustable to thousandths.

John Martin

By all means a vibratory tumbler de-burring setup is the way to go with this.

Jim

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This is reproduction medieval armor we're talking about, Harold, not an aerospace project. This is basic sheetmetal work. The holes don't have to be precisely round, they don't each have to have a perfectly uniform radius, they just have to not saw the lacings in two. A couple of quick twists of the wrist with a die grinder fitted with an abrasive cylinder about 2/3 the diameter of the hole will do what's needed quickly and easily. Frankly, your idea of using a boring head, a form tool, and a fixture on a mill is so over the top for this job as to be ludicrous.

Gary

craytex bullets?

So what's your point?

A couple of quick twists of the wrist with a die grinder fitted with an

Said the guy that thinks he knows everything, but has little experience in moving metal. This isn't about making it perfect, it's about making it fast and easy. One need not work in a primitive manner because the work at hand is related to times of old. The sharp edges of drilled holes will be harder on the Cratex than the Cratex will be hard on the hole. Lest you forget, Cratex is rubber, which is easily abraded.

Frankly, your idea of using a boring head, a form tool, and a fixture

What is it, you didn't read this?

"A stick-it-in-and-spin-it-around de-burring tool is a start, but it leaves a chamfered edge. I'd like to get a smooth-radiused edge* and relatively quickly. there are around 150 plates and each has seven holes in it. 1050 or so ~1/4"holes."

For someone of low skill levels, I would image you'd see it that way. For someone that has worked on machines for a living, I can't agree. You'd change your tune quickly if you saw it done. While you're dicking around with each hole, trying to get past the sharp edge, I'd have a half dozen of the holes done on each side. You may know a great deal about running your buisness, but you're way the hell out of the loop where it comes to machining. Ludicrous? That would be your lame suggestion, which would be all the worse if the parts didn't already have the burrs removed. Sorry, Gary, you have to know when to hold 'em, and know when to fold 'em. You should have folded on this one.

Harold

I'm with Harold on this, as my original reply indicated... you could easily cut a form tool out of drill rod, harden it and go. Or if you have some HSS rod around, toolpost-grind that to shape.

A countersink in a cordless drill is *so* much more fun than a larger drill held in the fingers or such. ;-) (Except when it's like three holes in aluminum, but aluminum doesn't protect against swords very well anyway.)

Tim

Well, this is for rattan combat, guys hitting each other with sticks. In this case, aluminum works, sometimes quite well. --Glenn Lyford

Pretty worthless where it comes to putting a nice radius desired on the holes.

Harold

I don't know about that. We used to get steel threaded inserts at my former job, just formed, threaded, and cut off. They had terrific burrs and would cut your hands up rapidly when installing them.

Then they switched to a supplier who did vibratory tumbler de-burring - those things came out sweet. And even the edges of the holes had a nice smooth radius on them. The media was strange ceramic prisms, all different angles. I think if the size of the media were chosen correctly it would work just fine.

Jim

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Considering the relatively large flat surfaces on the items in question, and the small hole ( he changed the size to 1/8"), I'm inclined to think it would not work well, especially when he suggested he'd like a nice radius on the hole, alluding to the idea that a full radius might be desirable. I was thinking along those lines. It would be most difficult to get much more than a broken edge under these circumstances.

I have the utmost respect for tumbling. I used to use it myself, and still have my small vibratory tumbler. With the proper media, as you suggested, it can and usually does do one hell of a job, and almost labor free. The other thing that is a good advantage is the uniformity of the parts after tumbling. For parts that lend themselves to tumbling, and get handled a lot in the shop, it tends to yield much nicer looking finished parts. That, of course, is probably much more important for those of us that worked the hard way, no CNC, where you often handle complex parts a dozen or more times. Even careful workers tend to give parts a shop worn look.

The wrong media choice can be a nightmare when holes are involved. I've seen holes come out perfectly sharp, and also holes plugged endlessly with media, thanks to someone being asleep at the switch when media was selected. I'm sure you've seen it too!

Harold

I seems as if every one has come up with solutions that are more appropriate for making a precision part.

You are trying to duplicate a part that was made many centuries ago; how it was done had to have been simple. Tumbling seems like a method that might have been used back then. (put parts plus sand and water in a barrel and roll). Maybe use a 5 gallon plastic pail. Home depot sells pails for about

The best solution may be too not drill the holes but use a very small torch to melt a hole through the part. This could work out very well since after melting the hole you would end up with a little metal bead all around the hole almost like having a grommet put in the hole. The edge around the hole would probably be twice as thick as the metal and I suspect it would have a very nice radius. Many centuries ago the holes were probably made by heating the part and using a punch to make the hole.

Other possibilities: Sand blasting or maybe a wire brush in your grinder. A brush with fairly fine wire might work well. I have used wire brushes for de-burring but never on real small holes.

Scp

Actually not. The worse I've ever seen was a piece of prismatic ceramic stuck in one of the threaded inserts - and a tap with a pencil would pop it out. The threads were never buggered and the parts were *so* nice to work with after they were deburred that way.

Jim

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There's a tool made exactly for this purpose, I've got one with several sizes of cutters. You could use it in a drill or by hand. It's coarser than a rotary file, but has more teeth than a countersink. Mine was made by Severance. Very handy to deburr drilled holes in sheet metal. I'm not sure what it's called exactly, I got mine from MSC a few years back, ran about $12 per cutter. Something like a radius hole deburring tool, maybe.

Stan

I use those too - pretty handy. Keep one on an aluminum handle. No power - just a few half-twists and you're done.

What people are missing in this thread, I think, is that the steel sheet is only .045 or so thick. Hardly much more than a 32nd. The original poster seemed to want a true radius, which would have to be in the 1/64th range. Pretty tough to do with any precision, especially on pieces that are already curved.

Those Severance cutters are fine, but he won't find one with a 1/64th radius and a 1/8th pilot, I believe. Radius is likely to be in the 1/4" range. So he'll end up with a chamfer rather than a radius. Which, after running against a wire brush or a flap wheel or tumbling, will be closer to a radius and should be just fine.

Form cutters and boring heads don't seem to be the way to put a radius that small on a bent piece of sheet metal. To me, anyway. And a precise radius is not really what he needs.

I wouldn't worry particularly about getting tumbling media stuck in a .125" hole in .045" sheet metal.

Just my thoughts, though.

John Martin

Severance makes countersinks with six flutes, staggered a bit to try to minimize chatter.

The also have (IIRC) one mounted on a handle like a figure '7', with the countersink coming straight up from the free end of the crossbar of the '7', and a swivel handle on the angled upright. You grip it, put the countersink in the hole, and twist your hand causing the whole thing to rotate.

Did it look like what I have described?

What I use for deburing smaller holes (sometimes) is a tool by Vargus -- the people who make the hook-shaped blades in swivel handles (which might work well for this as well).

The one which I use for this is like a two-flute countersink in a ratchet in a handle similar to the others, You twist the handle clockwise, the countersink rotates with it. You twist it back, and the ratchet lets the handle rotate separate from the countersink, so you get a second (and third, if necessary) twist in without having to shift your grip.

I also sometimes pick up a plain countersink, depending on the size involved. 1" countersinks can be nice for this, and Severance makes their six staggered-flute one in this size too.

But the Vargus tool with the hook-shaped blades might actually be the best for this. There are several styles, most designed for deburing a straight edge of thick material, or the top edge of a deep hole. However, one is a sharper 'V', designed to debur both sides of thinner sheet metal, including holes in material of the thickness which you are considering. The inconvenience will be threading the deburing bits into holes as small as you have. But the radius of the 'V' might do well for your task.

If you want to do it under power, and are willing to do two passes (one for each side), you might consider the kind of countersinks made with a cone point and a diagonal hole through the body run parallel to one side of the cone. You could start by turning the contour you want into a cone on some drill rod, then cross drill it as above, and harden. (And perhaps you should apply a bit of a touch-up with a Dremel grinder.) There you have a custom radiusing countersink for the task. One might even last the whole job, if properly hardened and drawn, and if you keep the RPM within reason.

Also -- the other suggestion which I just read of burning the holes might produce something which is thicker than the plates, allowing a nicer radius.

Good Luck, DoN.

If you consider the original post, it would be an excellent way to radius the large number of holes involved, but the changes made with the second post certainly changed the complexion of the thing. By reducing the plate thickness and hole size, the amount of metal to be removed changed drastically. It would still work, even with the bent part, for it is bent in one plane, at least as he described it. All you'd have to do is use a narrow base plate on which you'd clamp the part. Toggle clamps would permit clamping, cutting, and unclamping in seconds with a full, uniform cut. It would still work for the thinner plate, but there is a lot less material that would be removed, if for no other reason, the radius would have been reduced considerably.

I agree, but a hole that small is likely to almost totally unaffected by tumbling aside from removing any burrs on the surface. To get a radius in such a small hole would require some pretty strange media. The idea was to establish a radius of sorts to prevent abrading lacing. I can't help but think the material would get no radius, and would be quite aggressive in cutting lacing on the corners of the holes. Without some means of cutting the metal away, the corners would likely remain relatively sharp, although burr free. Didn't he already mention that the plates have been tumbled?

Mine, too, John. I still think a boring head, or a small tool, custom made, would be the solution to the problem. A tiny rotary form tool, much like a corner rounding end mill, but with hole cross drilled to form a cutting edge, might be an excellent way to break the edge. That's really what he wants, a broken edge that is burr free. Tumbling isn't likely to do that, not in this case. I still maintain that the small size of the hole will almost guarantee that the media won't enter far enough to do any good.

Harold