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barts
01-28-2010, 04:46 AM
I'd like to find/make a small cutter that will put a roughly hemispherical head on a Olympic rivet; the commercial tool is $200 which is a little steep. What I need is essentially the reverse of a 7/16" ball end mill. Only a portion of the sphere is needed, as the rivet head is only 5/16" in diameter.

Is such a thing made? I can see my way clear to making the blank for the cutter w/ my homemade up & over radius gadget, but I'm not sure how to get the teeth on there.... and just the bit for the commercial tool is $150 or so...:eek:

In case anyone is curious, we're working on a 1971 Airstream - lot of small
projects, and these rivets install like pop rivets but look like the original buck style - handy for repairs w/o removing all the interior skins.

Ideas appreciated - thanks!

- Bart

Black_Moons
01-28-2010, 05:09 AM
Iv seen radius cutters http://www.fignoggle.com/tooling/figNoggle_radiusCutter.jpg
Even got a set of cheapos for like $100 (like a 10 peice set)

You could use one of those while turning the rivet in your vice on a rotary table...

Iv seen concave cup 'grinding' stones, I believe are for gringing the ends of rods and pipes (deburing them anyway), and I know you can dress a concave into normal stones too.. but you probley want to cut not grind.

John Stevenson
01-28-2010, 05:16 AM
Rivet in lathe chuck and HSS tool freehand ground to shape?

Or if I'm missing something about how to apply said cutter then get a ball nose cutter of the right diameter, feed it into the end of a piece of drill rod / silver steel to form the shape you want.
Then mill a flat on it so 1/2 the shape from the side is removed and you have a 'D' bit.
Heat to cherry red and quench, don't bother tempering for alloy it will hold up better.
Light grind on the flat face of the D and fit to whatever is going to spin it.

WD40 or kerosene as lubricant.

.

form_change
01-28-2010, 06:03 AM
Once upon a time when I wanted a hole with a spherical bottom to it I got a drill bit (6mm) and ground that. It worked. If you are wanting the opposite can you find a grinding tip of the right size and use that to grind a cavity into the end of a drill bit the right size? You would then have to fiddle a bit with a die grinder/ dremel to provide some relief to the cutting edge bit if you are only shaping Al, you might not have to worry too much. The only issue may be that as you would not have a chisel point in the middle, the depth of cut is limited to the cavity radius - would that be a problem?

Circlip
01-28-2010, 06:47 AM
Same as Sir John but I'd remove two opposite quadrants so it's similar to a wood "plug" cutter.

Regards Ian.

Paul Alciatore
01-28-2010, 10:43 AM
I agree with Sir John, form tool in the lathe.

barts
01-28-2010, 12:52 PM
The lathe would be a great approach, but these blind rivets need to be installed before the rivet shaving operation forms the profile head.

I'll try making a cutter from drill rod. I'm a little dubious about how to get the center to trim the mandrel correctly.

Here's a youtube video of installation and shaving....

http://www.youtube.com/watch?v=g7EUXOA9d78

Thanks for all the ideas...

- Bart

Tony Ennis
01-28-2010, 01:42 PM
How many rivets do you intend to need? I'd buy the tool if thousands are needed. What material are the rivets made of?

Back in the day, I made nice round-headed rivets from steel rod using an air tool with a 'bit' that was little more than a hunk of steel with a semi-circle milled into it.

ptjw7uk
01-28-2010, 02:07 PM
Hi,
Had a look for the rivets and found this utube shows the tools in action, seems simple enough
http://www.youtube.com/watch?v=g7EUXOA9d78
although I think you will need more than the cutter, you will also need to limit the depth of cut.

Peter

Stuart Br
01-28-2010, 02:59 PM
I did my apprenticeship in the early 1980's and we used an air driven rivet mill to finish countersunk rivets in the aviation business. That was much simpler though as it was a flat cutter. I have never seen these rivets before, but they look a neat solution. I can't offer any advice on making the cutter though.

Stuart

barts
01-29-2010, 04:35 AM
How many rivets do you intend to need? I'd buy the tool if thousands are needed. What material are the rivets made of?


These rivets are used for repair jobs; the first job will require shaving of perhaps 25 aluminum rivets. Over time, as I fix other issues I'll be doing more. Buying the tool makes perfect sense for a commercial shop; that's not me.

Thanks -

- Bart

Ian B
01-29-2010, 08:28 AM
Bart,

This is the tool that you're trying to copy I guess:

http://www.vintagetrailersupply.com/PhotoDetails.asp?ShowDESC=N&ProductCode=VTS-177

(kind of them to show an exploded drawing)

The tool reminds me of an aircraft countersink tool with built-in depth stop - this kind of thing:

http://www.aircraftspruce.com/catalog/topages/microstopcountersink.php

Costs about $38, maybe available on ebay used. They take replaceable countersink cutters - make your own custom cutter out of drill rod, harden it and you're done. Depth settable to 0.001", better than the original!

Ian

ptjw7uk
01-29-2010, 10:49 AM
Try these
http://cgi.ebay.co.uk/2-Countersink-Cages-w-New-Bits-Aircraft-Tools_W0QQitemZ380201042830QQcmdZViewItemQQptZLH_D efaultDomain_0?hash=item5885bf838e
Nearer you than me!

Peter

Paul Alciatore
01-29-2010, 10:52 AM
The lathe would be a great approach, but these blind rivets need to be installed before the rivet shaving operation forms the profile head.

I'll try making a cutter from drill rod. I'm a little dubious about how to get the center to trim the mandrel correctly.

Here's a youtube video of installation and shaving....

http://www.youtube.com/watch?v=g7EUXOA9d78

Thanks for all the ideas...

- Bart

Well, with a big four jaw and a really big lathe, just mount the whole job and center on the installed rivets, one by one.

Seriously, you didn't say after installation. That does make a wee bit of difference. If you are trying to imitate the first tool Ian showed, it looks to me like the outer bushing forms a guide for the inner cutter. It appears to fit on the outer edge of the rivet head to effect the centering. The inner cutter will have little centering action by itself. The whole thing has bearings and a spring to provide pressure on the cutter. Looks like a nice weekend project.

As for the inner cutter, I would look into getting a replacement cutter from the guys who make the tool. This is not a simple drill shaped tool. Study the geometry of an end cutting end mill. To grind one you would probably need a T&C grinder and even then, the concave cutter would be an unusual shape that would be challenging. They are probably made with a special CNC grinder. Since it probably has a special shank for mouting, I would get the cutter itself first and then make the tool around it.

An E-Bay search sounds like a really good idea if you have the time to wait until one turns up.

Timewarp
01-29-2010, 12:34 PM
Hi, I saw a diamond sharpening bit with a hemishperical bottom yesterday, used for sharpening button bits on rock drills. like this:
http://www.pora-agentti.fi/images/teroituskupit.jpg
It might give you some ideas.

bborr01
01-29-2010, 12:46 PM
What Sir John said. It's called a coining punch. Used for coining rivets.

Drill rod in a lathe or a mill with a v-block and a ball nose end mill of the right radius. Polish and then harden.

Brian

Circlip
01-29-2010, 01:22 PM
No, you're confusing a coining punch with a rivet snap

Regards Ian.

Oldbrock
01-29-2010, 06:10 PM
http://picasaweb.google.com/oldbrock15/20100129# I rough these out on a pedistal grinder then finish the radii with an appropriate dia dremel. I carefully grind the top rake to keep the cutting edge on center height then hone the top to give a sharp edge. The one on the right is ground to blend a bore and a face. I threw the two concave ones in to show how to grind the top rake to keep the profile horizontal so the whole cutting edge is at center height. Like Sir John said. Peter

dewat
01-29-2010, 08:41 PM
I made this quick and dirty, I didn't give it any rake but it cuts anyway. I cross drilled a piece of " CRS 7/16" and cut the flutes in a collet block, when I got close to center I just kept flipping the block till I got to the center. I made one BIG mistake, can you see it ?

http://i81.photobucket.com/albums/j218/dewat/cutter003.jpg

http://i81.photobucket.com/albums/j218/dewat/cutter002.jpg

The flutes are on the wrong side , I had to run it in reverse. :D

wierdscience
01-29-2010, 09:18 PM
x's2 for Dewat's cutter.

BadDog
01-29-2010, 09:54 PM
When I got my first lathe, a machinist friend of mine told me how to form a "perfect" radius form tool. Choose your material (in my case, HSS) and rough to shape. Of course, closer saves time. Then cover the lathe bed and chuck a piece of material ("mild" steel or aluminum) turned to the right size. Load it with appropriate abrasive grit, and press the bit onto the rotating stock. Laps a very nice and uniform edge in fairly short order. Of course, staged grits might be useful, particularly for larger form tools. In your case, might be nice for sharpening your new tool.

Paul Alciatore
01-30-2010, 12:34 AM
I made this quick and dirty, I didn't give it any rake but it cuts anyway. I cross drilled a piece of " CRS 7/16" and cut the flutes in a collet block, when I got close to center I just kept flipping the block till I got to the center. I made one BIG mistake, can you see it ?

http://i81.photobucket.com/albums/j218/dewat/cutter003.jpg

http://i81.photobucket.com/albums/j218/dewat/cutter002.jpg

The flutes are on the wrong side , I had to run it in reverse. :D

Rake can be positive, zero, or negative. Yours is simply zero. No problem.

What may not be obvious at first glance is the clearance angle. You MUST have clearance in order for a cutting edge to penetrate into the work. Your cutter does have clearance since it is measured relative to the surface being cut. You are cutting a round surface and the face of your cutter is straight in the direction perpendicular to the edge. But that straight is at an angle to the circle and produces the required clearance. A cross section view at each point being cut would show this.

But I have to wonder if a tool like this would work with the hemispherical shape the OP wanted. It would have a greater tendency to wander off center.

dewat
01-30-2010, 01:18 AM
Rake can be positive, zero, or negative. Yours is simply zero. No problem.

What may not be obvious at first glance is the clearance angle. You MUST have clearance in order for a cutting edge to penetrate into the work. Your cutter does have clearance since it is measured relative to the surface being cut. You are cutting a round surface and the face of your cutter is straight in the direction perpendicular to the edge. But that straight is at an angle to the circle and produces the required clearance. A cross section view at each point being cut would show this.

But I have to wonder if a tool like this would work with the hemispherical shape the OP wanted. It would have a greater tendency to wander off center.

Paul, thanks for the feedback, I was thinking if this basic cutter design will work it should be used with a guide bushing of some type and maybe the shank should be threaded for depth adjusting nuts, maybe 7/16-20 then reduce the shank to 3/8 or just a collar. With my limited knowledge in the machining field, I have to do a lot of trial and error.

barts
01-30-2010, 01:56 AM
That looks like a good place to start; I'll start on this tomorrow.

Thanks for all the ideas!

- Bart