Radiused edges on holes in sheet

Could always make a one-tooth cutter ala unibit, turn it with the proper radius and you're done. In fact, it seems to me you could do it all with one cut on a piece of drill rod if your toolbit has the right radius on the corner.

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

Just out of interest, how would the Byzantines have smoothed the holes?

Leon

Take a look at the "hand deburring cutters" at

How about a HS steel round over bit for a wood router. Use it in a drill press or a hand drill. It most likely will have a 1/4" pilot. Spin belt sand the pilot on the flexible part of a sanding belt to slip fit into the holes. Follow up with Cratex or such on the holes for further smoothness.

RJ

Hey Carl,

Looking over some of the other suggestions, I think you will find 18 gauge is so thin it is tough to get ONE side radiused smooth, let alone both. Trying to do both will almost certainly leave a convex "V".

There are de-burring tools from Vargus and others that are designed to do just what you ask. For instance, KBCTools shows Vargus blades "B30" and "E300".

Also, some clean-up required for finish afterwards, but have you considered sand-blasting? Or even a chemical etch.

Assuming that you wish to have a historically correct appearance, my next suggestion may be out of line, but have you considered using eyelets like in shoes?

My guess would be that the "originals" would have been deburred using a piece of string-gut with some sort of abrasive applied, and the apprentice armourer would have spent days and days just threading through and burnishing each hole.

Have fun. Where do you plan to use this anyway? We like those Canterbury Tales re-enactments.

Take care.

Brian Laws>I'd like to smooth, and I mean really _smooth_, the edges of a bunch of

On Fri, 11 Jun 2004 08:30:21 +0100, "Leon Heller" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

They got the slaves to lick em smooth! The slave was the CNC machone of those times.

Sometimes in a workplace you find snot on the wall of the toilet cubicles. You feel "What sort of twisted child would do this?"....the internet seems full of them. It's very sad

Laboriously. By hand. Exact tools? dunno.

I'm perfectly willing to apply modern technology to the problem. I'm looking at fixing a buddy's armor for pay and he's not the only one with this problem.

That's why I need a _really_ tiny radius.

Hmmm... I think I'd need something with a tighter radius, time to get making I guess.

I'm toying with the idea. Shoe eyelets tend to have split/rough edges on one side and that'll be too rough. I've done copper tubing eyelets in steel before and they're nice and smooth but it's pretty labor intensive, I figure it'd take me at least 24 man-hour to do the 1050 holes.

Or a rod/wire instead of a string, you could thread a bunch of plates on at once then work them each in turn.

The group is the Society for Creative Anachronism. If it's medieval and fun we do it. One of the things that's fun is tournament-style combat. The weapons are built of rattan.

Some pictures and an article:

You could use one of those Vargus tools with a slight modification. If you have a dremel tool it will be easy. Use a parting disc in the dremel and grind the radius you want in the blade of the vargus tool. Your best bet is a radius slightly larger than half the sheet metal thickness. The vargus blades already have a radius ground in them. What you will be doing is extending the flat sides into where the existing radius is and ending up with a smaller radius. Experiment with something esle before grinding on the vargus tool. Also, be sure to keep the grinding cool. So don't try to grind away too much at once. As long as the blade doesn't change color you will be all right. ERS

--Assuming the plates are small enough toss 'em in a tumbler for a few hours..

Probably the hole chamfering was done by a string of leather and some grit. Saw back and forth a lot and move around the hole as you go and quickly the hole gets a nice radiused edge to it.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

Can't tell from your post if this is new work or trying to fix something already made.

If new work, you should first try to minimize the burrs as much as possible. An accurate punch/die setup might be the answer. Then tumbling with appropriate media shoud give the holes a nice smooth edge.

If drilled (or ????) then remove all burrs possible so that the resulting edge is a sharp corner (might have some burrs pushed back into the hole). At this stage, tumbling should again do the trick.

Lacking a tumbler, might try a sanding disc on a small mandrel and do them manually. Rather labor intensive, but can give good results. Just plunge the mandrel into the hole, allowing the sanding disk to form into a cone as it enters the hole. This does wear out the disks very quickly.

Another option is to run an abrasive slurry through the hole. This is requires some pretty intricate engineering/fixturing etc. and probably not suitable, but who knows.

If you'll deburr the holes well enough to sit flat and pass a pin, you could use a boring head with a tool that has the exact radius you desire to cut the edges. It's easy enough to hand grind the tool, all it takes is a little patience and the corner of a smooth running grinding wheel. Make a base plate that will accommodate the parts, drill and ream a hole the same size as the holes in your parts. Use a pin that is an easy slip fit in the base plate and part to locate the part over the hole. Hold the plate with a couple toggle clamps, then remove the pin and drop the cutter on the hole in the plate. By setting a spindle stop you can easily machine the exact radius to the depth you desire. If the tool has a little positive rake and you lubricate it a little, the finish might even come out pretty nicely. You can do this in a drill press or a mill, but a mill would make it a lot easier. Remember, you want the spindle concentric with the hole in the plate. I can't imagine anything that would work as well, nor as fast.

Good luck! Tell us what works for you.

Harold

I was going to suggest sandblasting also. Harbor Freight have a spot sand blaster that is inexpensive. You will need to make a rubber mask or tip so you only abrade the edge of the hole.

Cheers,

Kelley

There are a couple products made for this sort of operation that work better than a plain disc. Have a look at the cross pads and the overlapped slotted discs in the Specialties .pdf on this page...

Sorry, wrong file. Here's the right one.

Ned Simmons

Cratex rubberized abrasives are probably the fastest solution.

You could do it the traditional way with abrasive coated string, just "shoeshine" it around each hole until you have the desired radiused edge.

Gary