Box Clasp Step-by-Step2 March, 2006
Tube box clasp with double tongue.
This project is a slight variation on the standard box clasp, the clasp outlined here uses two tongues rather than one. This means that the clasp is much more secure, so there's no need for the 'figure of 8' safety mechanism which can sometimes spoil the clean lines of a piece. I learnt to make this clasp whilst at North Bennet Street School in Boston.
The project shown here uses round tube with an inside diameter of 5mm to house the clasp mechanism. Of course the shape of the clasp's housing can be changed to suit the bracelet or necklace design. However using tubing with an inside diameter anything smaller than 5mm would prove to be tricky, since there may not be room for a double tongue.
I used Argentium™ Sterling Silver for this project. You can of course use standard sterling, or whatever metal your design calls for. Argentium™ Sterling Silver was invented by Peter Johns, silversmith and tutor at Middlesex University, England. What makes it different is the addition of the element Germanium, which replaces a little of the copper content.
This results in a number of advantages over standard sterling. Those that I've found particularly useful are as follows: Firstly Argentium™ doesn't develop firescale when heated, so those hours of sanding away that pesky purple stain is thankfully a thing of the past.
Secondly, it is tarnish resistant so that beautiful hand-made sterling clasp you spent hours over will keep it's mirror finish for longer.
Thirdly it can be heat hardened using your kitchen oven. In it's annealed state Argentium™ has about the same hardness as standard sterling, heating it for 40 mins at 300°C makes it nearly twice as hard. My kitchen oven only goes up to 250°C and some have a top temperature of 220C. In this case, Peter Johns advises that the heating time be extended to approximately 2 hours. You need to make sure your Argentium™ is annealed beforehand. It's best to preheat your oven and also the firebrick or whatever the Argentium™ is to sit on. I use a glass Pyrex® dish without the lid.
Finally, Argentium™ sterling has a lower heat conductivity than that of standard sterling, so there's no need to heat the whole piece to get your solder to flow. This doesn't make too much difference when making a small clasp, but I've found it invaluable when making larger pieces. When soldering a hinge to a heavy gauge silver bracelet for example, there's no longer any need to get the whole bracelet up to temperature in order that the solder will flow, you can just direct your torch around the area you need to solder. It performs much more like gold in that respect.
There are a number of ways working with Argentium™ is a little different from working with standard sterling. The three differences I've found to be the most important to remember concern it's lower melting point, the annealing temperature of Argentium™ , and the effect that it's lower conductivity has on how it should be quenched.
The germanium in Argentium™ lowers the melting point of the alloy by 59°F (15°C) to 1410°F compared to standard sterling 1475°F. This means that using the standard hard silver solder isn't a good idea, because it's flow point is too high and you risk melting your piece. There are now Argentium™ silver solders on the market which contain germanium. They have lower flow points and don't tarnish. Alternatively you can use standard medium silver solder instead, but this will of course tarnish over time.
The annealing temperature of Argentium™ is also lower, and the red glow that you get when annealing Argentium™ is much much paler. Bringing Argentium™ up to standard sterling annealing colour would be too high. I tend to anneal in a dark corner, so that I can see the colour change more easily.
Care also needs to be taken when quenching Argentium™. Argentium's™ lower conductivity means that heat takes longer to dissipate from it. As a result, quenching the alloy too soon after annealing can cause stress cracks. I leave Argentium™ to rest for a good 20-30 seconds or so before I quench it.
There is much more to read about working with Argentium™, there's some really useful documentation available on the internet:
What you need:
Step by step:
1. First we need two lengths of tube for the clasp housing, one 4mm long and the other 9mm long. It's good practice to make sure all your stock is in a fully annealed state before you start working with it, particularly if you are using Argentium™. I and others have found that there is slightly more 'expansion' after annealing work hardened Argentium™ than there is in standard sterling. This difference is tiny, but I've found it can have an effect if you're working with very precise measurements as we are here. File the end of your tubing flat and square. Then scribe guide lines using your dividers, one at 4mm, one at 5mm and one at 14mm. I mark my metal with a Sharpie™ first so that the scribe lines are easy to see.
2. Saw between your 4mm & 5mm marks and on the outside of your 15mm mark. 4/0 and 5/0 saw blades are good for 22ga metal. File to your scribe lines, make sure that the ends of your tubing are filed flat and square.
3. Place your tubing on the 20ga sterling sheet and check that there aren't any gaps between the sheet and the tubing where light shows through. It's also important that the tubes are both perpendicular to the sheet and are not leaning like the Tower of Pisa. Mark out enough sheet for ends caps for each tube.
4. Solder the end caps on to your tube using Hard solder. If you are using Argentium™ silver, don't coat the whole piece in flux and anti-firescale coating, you just need flux on your joint to help your solder to flow.
6. To fabricate the tongues, I find it best to use nickel white gold since it provides the 'spring' needed.
7.Using flat nose pliers to hold the tongue, fold the strip over at your scribe line using your fingers. Make sure your fold line is square and that you're not bending the strip at an angle. Ensuring your flat nose pliers are parallel with your scribe line will help with this.
8. Once you have bent the tongues back as far as you can with your fingers and the flat nose pliers, you will need to tap the bend gently with a hammer to complete the fold on each tongue. I find the ball end of my chasing hammer best for this. Hold the tongue with your flat nose pliers on a steel block and gently tap just slightly above the fold, rather than actually on it. Be careful not to hammer too much or you'll thin out the metal and weaken it.
9. You may find that this planishing has caused the metal to splay slightly at the fold, so you may need to file the tongue square again. Your tongues should also be springy now they have been work hardened.
10. Since I used 6mm tubing for my clasps' housing, it's necessary to bevel the edges of the upper part of the tongue, so that it has room to spring up into the tubing. Scribe a line on the upper part of the tongue 0.5mm in from the edge and file to this line at 45™. If your clasp housing is square or larger than mine, you won't need to do this step.
12. Solder the triggers onto the top centre edge of the tongues using hard solder. Make sure that they are dead centre and that they are pushed right up against the tongue. If you wedge something under your soldering block in order to tilt it slightly, it will help make sure your trigger stays butted up against the tongue whilst you solder. Try to use a small flame directed only at the trigger area and get in and out quickly so that you don't end up fully annealing your nicely work hardened tongue. You can also heat sink the tongue by holding the fold end with tweezers whilst you solder.
13. Prepare the short tube to receive the long ends of the tongue. Scribe two 4mm long, 0.5mm wide parallel lines, 0.5mm apart so that the midpoint between the two outside lines is the dead centre of the end cap.
15. Insert a 5/0 or 6/0 saw blade into your drill hole, tighten it in the frame and saw along your scribe lines.Be careful here not to saw over your line, the tongue needs to be a very tight fit. Using the saw blade gently as a file, ream away and smooth out the metal until the tongues fit tightly. You may find that using an 8/0 saw blade makes it easier to be more accurate. You can use micro files for this too, but if you don't have them, saw blades work just as well.
16. Position the long end of each tongue into the slots you have pierced. Make sure that the tongues are aligned straight with the tubing and that the back of the trigger butts up against the endplate when the trigger is compressed. Solder using hard solder.
17. Prepare the long tube to receive the folded ends of your tongue by following the procedure detailed in steps 12, 13 and 14. This time though your slots need to be 4mm long, very slightly more than 1mm wide, and again 0.5mm apart. Slowly saw and file away the metal, frequently checking your progress with the tongues. Be careful not to over file or your tongues will be loose within the clasp.
18. Insert the tongues into the large tube until the trigger butts up against the end plate. You can now scribe the position of the trigger where it hits the end plate,
19. Carefully saw and file away the unwanted metal. Again, it's important to be accurate so that there is no play in the clasp. Keep testing your progress with the clasp tongue, filing slowly until the two end caps butt up against each other and you hear the very satisfying 'click' of your well made box clasp. Make sure both tongues are clicking into place.
20. The final steps strengthen the 0.5mm wide cross-bar in the centre of the long tube's end plate. It can also help remedy a clasp that is loose due to over filing the two 4mm x 1mm slots in the end cap, so it's really worth doing. Saw and file a length of 24ga sterling the same width as the inside diameter of your tubing. Bevel the long edges of this strip very slightly so that it fits tightly into the tube. Make sure the end is flat and square so that it butts up against the end cap cross-bar with no gaps. I tend to leave the strip slightly long so that I can gentle tap it into place if need be. However if you need the keep the inside of your end cap clear, cut your strip shorter.
21. Solder your centre strip in place using medium solder, quench and pickle. File your centre strip flush if need be.
22. You can of course embellish your clasp trigger as you wish, small cabochon bezel set stones look good on the triggers and make the clasp comfortable on the fingers when opening and closing. If you do add a bezel, make sure your file down the triggers first - they should be about 5mm high in total.
You can heat harden your Argentium™ clasp in your oven as described. Make sure you've finished any soldering you need to do, since this will undo your oven hardening. You may find your Argentium™ comes out of the oven with a slight yellow tinge. This is easily pickled off.
When polishing Argentium™, it's a good practice to use separate polishing buffs than those you use for standard sterling. This prevents contaminating Argentium's™ tarnish resistant surface with standard sterling. Others also recommend using separate soldering bricks too, but I must admit that I don't do this and haven't noticed any ill effects so far.
My tongues have lost their spring.
Thanks to Rosemary Trainor and Jock Gifford at North Bennet Street School, Boston, MA and also to Peter Johns at Middlesex University, England.