bending joints in metal

[medusa]

I've been pondering how to do this for ages and was going to wait until I had more time to work it out but a commission enquiry has prompted me to at least look into it in more detail, even if I end up not taking it.

Someone has asked me if I can make a bangle which locks around the wrist with a screw. They intend for it to be worn 24/7 so I don't think there would be an issue with screw threads in silver. They want it to be as simple and discreet as possible. But I don't think that at that length it could just be bent around like I do my collars, especially because the need for a screw would mean that there needs to be a significant bit of metal for it to bite into.

The most obvious way to do this would be to have two lapping joints, both of which close with a screw. If I cut the joints first then they will be straight but bending will deform them and if I bend first then I'm not sure I will be able to create a good enough fit of the joints.

I did wonder about forming two rings with one sitting snuggly inside the other then soldering them together but leaving solder away from two sections (using tippex?) and cutting through the top one and then the bottom one but a staggered cut and then finishing off the soldering up to the lapped ends with the two pieces separately. But then I thought that might be a really stupid way of doing it and there must be a better way!

So, any suggestions on making a seamless but opening circle of silver?

and if anyone actually fancies this commission, let me know because I honestly don't think I have time.

[Exsecratio]

Can I ask what material a screw would be made of?

best wishes

Dave

[Dennis]

I can't follow all of your description Liz, but if the bangle is oval so it cant rotate and overlaps on the underside of the arm it should be no trouble to make a hole through both layers and secure with a stainless steel screw from a glasses repair kit.

1. You need to provide a slightly larger hole, possibly counter sunk, in the outer metal and a slightly undersized hole for the screw to tap into on the inner part.
2. You need to provide the screw cut to length (and possibly a matching screwdriver).
3. The inner part can be thickened with a small smooth edged patch behind to give a more durable result.

A soldered on jump ring looks good to surround the screw head. Dennis.

[medusa]

Can I ask what material a screw would be made of?

best wishes

Dave

I'd tap it (or is that die it?) out hard sterling rod. It's a one time fix, so I figure that it should be ok.

I can't follow all of your description Liz, but if the bangle is oval so it cant rotate and overlaps on the underside of the arm it should be no trouble to make a hole through both layers and secure with a stainless steel screw from a glasses repair kit.

1. You need to provide a slightly larger hole, possibly counter sunk, in the outer metal and a slightly undersized hole for the screw to tap into on the inner part.
2. You need to provide the screw cut to length (and possibly a matching screwdriver).
3. The inner part can be thickened with a small smooth edged patch behind to give a more durable result.

A soldered on jump ring looks good to surround the screw head. Dennis.

oh good hint about the jump ring!

I suppose if the lapped connection is on the slightly straighter part, it wouldn't be so difficult in terms of it deforming. Any suggestions on doing it on a perfect circle though? I'd love to get a collar design using tube or rod. I get so many requests for them and I'm sick of turning them down.

[Dennis]

Quote: I'd tap it (or is that die it?) out hard sterling rod. It's a one time fix, so I figure that it should be ok.

Good luck, but unless you are very experienced you will end up with a slack fit. There's nothing easier than using a stainless steel screw as a self tapper.



Quote: I suppose if the lapped connection is on the slightly straighter part, it wouldn't be so difficult in terms of it deforming. Any suggestions on doing it on a perfect circle though? I'd love to get a collar design using tube or rod. I get so many requests for them and I'm sick of turning them down.

As you said somewhere above, end with two overlapping washers and screw them together. Dennis

[Exsecratio]

If Stainless is an acceptable material for the screw then a S1.4 x 0.6 pitch frame screw from a pair of glasses would do it. If so then drill for a final hole size as if you are using a roll tap (the thread will be formed not cut) and will be a LOT stronger.
On a pitch like that to achieve strength you need 60% x diameter of thread for depth (so 0.84mm thickness of material threaded). Meaning a drilled size finished of 1.1 MM to cold form the thread by inserting the screw. Copperslip makes a great lube for threading stainless using a form method.

Use two screws, the first to "form" the thread then remove and discard, the second to do the actual fixing job.

Die cutting a thread that fine onto stainless rod ,as Dennis said , usually doesn't end well unless you have had a lot of experience doing it, screws that small are usually roll formed. Stainless likes to be cut hard and slow with a good depth of cut or it tends to rip and tear behind the cut (STS303F and STS416FS) both cut well but have the additional issues of sulphur and phosphorus content (303 on occasion can also contain lead) that can cause issues due to an electrolytic action between dissimilar metals causing them to "grow" together.

best wishes

Dave

edit: Tapping the thread can be a problem, it takes 380 Grams of force to snap a 1.4mm tap and removing hardened steel tap stubs from silver isn't going to be fun, the taps themselves (good ones) are also surprisingly expensive

[josef1]

I got asked about something similar and how I would make it in cad last week, I have done a video on my version of it, I know its not everyone's cup of tea but may be worth a look, The screws wouldn't be made the same way as in the video, I would also use a tap and die, If you have a small pillar drill you can use a sensitive tapping attachment and this would help get things straight. I recon if everything fitted snug the screws would be fine in silver. But saying that I have not made the bangle so cant say for sure.

[Goldsmith]

I have made hundreds of items with sterling silver threads in my time without any problems. For small threads of 1mm. and less I use Bergeon watch makers taps and dies. for large diameter threads I use a standard BA tap and die set. For what you are suggesting Liz I would probably use a 10BA size thread which is 1.7mm diameter and for the threaded screw hole you drill with a number 54 drill or 1.4mm. diam. A 10BA thread has approx 72 threads per inch, which equates to 5.75 threads on a 2mm. thickness.

You may find thsi BA thread size chart useful. If you want to buy single taps and dies rather than sets try here; https://ekpsupplies.com they also sell readymade screws in brass or Stainless steel.
James