Working phosphor bronze sheet.

The sheet is 0.2mm thick.

I want to make a short strip of finger springs, similar to those which are used to ensure good conductivity between a metal case and its lid - although these are not for that purpose.

I'll explain. I have a small digital camera to which I would like to attach a filter, and, of course there is no thread round the lens on these small ones.

The outer-most section of the lens barrel, which is extended when the camera is switched on, is around 28mm in diameter, the depth of this section being 9mm.

The filter I wish to mount is a 28mm one, the ouside diamter of which is a mm or so greater the barrel.

I want to take a strip of phosphor bronze sheet, 10 to 15mm wide by 90-odd mm long, cut it so that it has a few fingers around it and bend it into a circular band.

It would be permanently fixed to the filter with one of today's magic adhesives, so that the fingers now extending from it would grasp the lens barrel.

I am quite dexterous but have no experience of working with this material, so any suggestions/advice could well save me a few quid which might otherwise go into the swear-box.

I have two suggestions:

1. Use a jewellers piercing saw with a fine blade to cut out your outline. Fix a flat piece of plywood horizontally to the bench top with 2 - 3 inches of overlap, and saw out a V on the outer edge. Hold the metal down onto the plywood with your left hand, and use the saw vertically with your right, cutting downwards, with the sides around the V keeping it all flat. It may help if you sit - tradition requires a three legged stool. Be prepared to break a few blades (and try not to stick a blade into your left fingers if you do break one ...)

2. A sharp pair of tin snips will cut the material instead - or even a good pair of scissors. Not so easy to follow complex curves, but for your job you may find it OK.

Then run a fine file around the edges to take of burrs, and the job is nearly done.

cheers, Tim

Hi David,
It used to be possible to buy what you want ready made. It is called "finger stock" It is used for making connections to forced air cooled valves in high power UHF transmitters.

This is what it looks like.

Les.

Edited By Les Jones 1 on 09/04/2014 18:46:06

David

I had a similar problem when I had a plate camera and none of the lenses had a filter thread. I machined up a short tube of aluminium, threaded one end for the filter. Other end was bored a couple of mm larger than the lens barrel and a strip of baize glued around the inside so its a close, but easy fit on the lens barrel.

Regards Barry

I have seen aluminium filters with the inner partly separated with two slots around the tube. Two short cuts at 90-degrees to the uncut sections leave four 'fingers' that wrap around the lens. the fingers can be slightly bent to get an appropriate level of grip.

Neil

Neils idea is the best, most of our add on attachment lenses use that method. Its just a simple alu. tube slit around and then cut to allow springing to hold in place. Quickly attached or removed.

Clive

Thank you all for the information.

I like the three suggested methods. Not sure yet which route I will follow. A variation of the aluminium tube might be the easiest - if I can acquire a short length of suitable diameter.

Yes, Les, I have found one or two suppliers of ready made finger stock. I first became aware of it donkey's years ago in various electronics equipment with which I worked.

If I remember to do so, I might take photographs of what I do and post them here.

Edited By jason udall on 09/04/2014 23:39:23

Had never heard of tolerance rings until now. RS Components search facility coughs up zero items, but a Google search gave me some pictures.

Not suitable I'm afraid, but I'm glad that I now know of them.

I think over time those metal fingers could scratch the lens casing. How about something like a neoprene sleeve?

David, I'v seen a magnetic system, a ring(like a large washer) is stuck to the camera with a self adhesive backing, the lens/filter has a ring shaped magnet that holds it in place. Seen in a camera shop in Christchurch NZ.

Ian S C

That is interesting. I wonder what it would be like, machining a magnet down on the lathe? Something to do in a quiet moment.

graham.

David I would personally fear putting a magnet anywhere near a camera either digital or mechanical can I refer you to SRB photographic at www.srb-photographic.com

Roy

Here in NZ I can get a wide range of magnets of the shelf, or to order from Magnets New Zealand LTD.

Web site: www.magnets.co.nz Its an over night service Auckland to Darfield (near Christchurch), and the prices are reasonable.

The commercial fittings in the camera shop were specially for use on digital cameras. Ian S C

There's a good supplier of magnets here in the U.K. too,at **LINK**. There are probably others.

Despite the misgivings of placing magnets near a camera I think the field from a tiny neodymium one would be weak enough not to be a problem.

Nevertheless, of all the good ideas presented, since I have the necessary material to hand, I shall try, at least initially, to fabricate one from the phosphor bronze sheet.

On the subject of small magnets, I used a pair of them 2mm dia by 3mm long, with opposing poles instead of a spring on a miniature Morse key to keep the contacts normally open.

What about a turned ring with a small O ring groove in the inside... or outside if that works better? The O ring will grip.

O rings are easy to source.

Or a small rubber lip seal fitted in a turned ring. Just take the camera to your local supplier to get one that fits

**LINK**

Most bearing suppliers carry O rings and seals

Regards
John

Nice idea John but I haven't got a lathe. Got plenty of o-rings though!

I've started cutting to make spring fingers with the phospjhor bronze sheet. It'something I already had to hand so didn't have to search for other bits and pieces.

If it isn't to my liking I will pursue one of the other methods mentioned on the various posts.

David, remember you can anneal Phos.Bronze to work it easier, no hardening except time/age hardening though.

Clive

I am leaving it as it is Clive. Don't want to sacrifice its spring.