Advenntures in Experimental Metal Spinning

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dgoddard
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Advenntures in Experimental Metal Spinning

Post by dgoddard »

I came up against a new challenge but the results were quite satisfactory.
Problem: Close the end of a small tube with a smooth bullet nose closure made by reforming the existing tube.

Material: Argentium Sterling Silver See at: https://en.wikipedia.org/wiki/Argentium_sterling_silver
Tube dimensions
Length 12 inches
OD 0.180 inches
ID 0.140 inches
Tube Wall 0.020 Ref.
Argentium silver has a reduced copper content with the removed copper replaced with Germanium

Relevant to Machining the material has an increased ductility and is precipitation hardening
To accomplish the modification of the tubing end. I made a tool of O1 tool steel. A 1 inch length 1/2 diameter was chucked in the lathe and given a shallow center drilling at just over .180 diameter and just deep enough to produce about 0.010 depth of full diameter. Then a series of smaller diameter wire size drills in decreasing increments were used to deepen the center drill dimple in increments of about 0.010 down to about 0.005. Resulting in a somewhat rounded dimple.
The tube was placed in the chuck and spun at about 1500 rpm and the tool was placed in a chuck and run up against the end of the spinning tube.
As Silver is a slightly costly precious metal; the end of a 360 brass rod was turned to the Id and OD of the tube to make a test piece.
Results of spinning  a closure of the the tube end
Results of spinning a closure of the the tube end
The results of the test were very positive as a satisfactory result was achieved on the first attempt. In the case of the brass test piece a tiny hole can be seen at the very end but this is not objectionable for the intended use. The above image shows the argentium tubing, the brass test piece and the argentium with the desired tip form.

The Argentium silver tube also tended to form a small hole at the end, but additional pressure was used and the heating of the tube and pressure completed the closure.

The reason for the silver tubing is to produce an experimental device in which the tube will be used as a catheter to drain fluid in a biological application. Near the tip of the tube ports will be drilled through the tube wall and a fitting will yet have to be made for the other end of the tube. Silver has long been used in such applications because it has antibacterial characteristics. In the project at hand the smooth silver exterior of the tube will aid in preventing the introduction of in infection is subsequent re insertions of the catheter and it is an extra precaution in case it is not perfectly sterilized or should it pick up bacteria during insertion. The effectiveness of silver in such applications has long been know and it is for its antibacterial capabilites that it is, for instance, used on the international space station in the water purification system which recycles the astronauts urine. While there are other precautions used to remove pathogens the use of the sliver prevents bacteria from finding a place to multiply within the plumbing of the purification system.

As a historical note, in his later years Benjamin Franklin used a urinary catheter made of silver to prevent infection from his necessary use of the device., (I guess even a Wiz like old Ben had to whiz :roll: )
I never met anybody that I couldn't learn something from.
pete
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Re: Advenntures in Experimental Metal Spinning

Post by pete »

I'm more than impressed. And most of what you posted was all new to me. Pretty much all I know about metal spinning is what I've read. It's apparently not as easy as it looks.
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dgoddard
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Re: Advenntures in Experimental Metal Spinning

Post by dgoddard »

Awww, come on Pete. I have only ever seen it done before and doing this is a first time even trying it for me...... How hard can it be if it worked the first time.

The basics are you just set the piece of metal up on a lathe some how, get it spinning and push the metal around to where you want it.

Obviously the workpiece it has to be soft and ductile enough to move and then stay where you pushed it. Some tools I have seen for this have a roller nose and have some sort of backing or form that the metal is pushed against. And in this case to get the silver to seal up that hole on the end, I had to push hard enough so that the friction heated the metal enough to make it weld closed. Because the metal tool I was pushing with was a lot harder with a higher melting point than the metal I was pushing I was hoping that it would not weld the tool to the work piece, and it did not. (I have accidently welded a dead center to a work piece when the lubricant failed, but those were both steel).

Of course you will note that I did make a "throw-away" practice piece out of brass for a test of the principle. I had wished I had a 3/16 ball end mill to make the dent in the forming tool, but lacking that I resorted to an expedient that made an approximation, then I lathe filed the tip with a smooth file to clean it up and then emery polished out the tool marks and scratches.

This was just an experiment that I thought should work, and that tiny silver tube worked out to a bit over two bucks an inch. Not to mention that the preferred length for the product was 14 inches and the only suppliers I could find only stocked it in 12 inch pieces. With no losses, that would be enough but barely so.

I made my best guesses and tried it and it worked. Of course when you wrote, "I am more than impressed" if you meant I was very lucky I did not screw up $28 worth of silver tube,..... Well I could agree to that. :lol: :roll:
I never met anybody that I couldn't learn something from.
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dgoddard
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Re: Advenntures in Experimental Metal Spinning

Post by dgoddard »

OOPS
I forgot to mention one particular trick I had to resort to when making that silver catheter tube.

When chucking up that .180 diameter tube in the chuck, there is about 10 inches of it unsupported back inside the spindle where it is a 1.5 inch bore. That much cantilevered slender work piece can get to whirling and the centrifugal action can bend the tube and ruin it especially in a not so stiff metal like silver. To prevent this from happening I took some Styrofoam blocking material that something had once been packed with and cut a chunk large enough that I could get an inch and a half diameter piece. I shoved this through the spindle bore from the far end until it was close enough that the silver tube when inserted into the chuck would hit it.

Then I removed the tube and use a 12 inch long 3/16 twist drill slipped through the chuck to drill a hole in the Styrofoam. By adjusting the chuck jaws for a slip fit on the drill shank I got the support and guidance to get the drill to stay on center. This provided a support to the silver tube so it would not get off center and start whirling and bend itself. To get the metal spinning fast enough to heat and deform and weld the end closed I needed to run the lathe about 1500 rpm The Styrofoam plug in the spindle bore kept the tubing on center so that the centrifugal action could not pull the tube off center enough to create enough whirling action and force to bend the tube.
I never met anybody that I couldn't learn something from.
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Harold_V
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Re: Advenntures in Experimental Metal Spinning

Post by Harold_V »

dgoddard wrote:OOPS
I forgot to mention one particular trick I had to resort to when making that silver catheter tube.
Dandy!
It takes virtually no effort to keep an object on center, so that's one of the slickest ways I can think of to get 'er done!

H
Wise people talk because they have something to say. Fools talk because they have to say something.
pete
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Re: Advenntures in Experimental Metal Spinning

Post by pete »

LOL, nope I meant I was impressed with the whole post. I'm not impressed with thinking about haveing that instrument used on me though. :-) What I have read about metal spinning is the tools and forms idealy should be hardened and very highly polished. Might be something to consider if you've got a lot to do and the polishing you did takes a lot of time? Yes I've seen pictures of those backer bars as well. It's tough to find information since it's so scattered. But the guys swageing there own copper bullet jackets and lead cores have figured out some pretty clever methods if that would help. The benchrest shooters will accept nothing less than perfect bullets so the bench rest forums might be worth a check. Silver from the little I recall reading about it can get pretty fussy about playing nice and doing what's expected. So you did real well figuring out something that worked so well.
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